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Differential functioning of deep and superficial lumbar multifidus fibres during vertebral indentation.. Apperley, Scott 2008

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DifferentialfunctioningofdeepandsuperficiallumbarmultifidusfibresduringvertebralindentationperturbationsbyScottApperleyB.H.K.,UniversityofBritishColumbia,2005ATHESISSUBMITTEDINPARTIALFULFILLMENTOFTHEREQUIREMENTSFORTHEDEGREEOFMASTEROFSCIENCEinTheFacultyofGraduateStudies(HumanKinetics)THEUNIVERSITYOFBRITISHCOLUMBIA(Vancouver)June2008?ScottApperley,2008AbstractIntroduction:Lumbarspinestabilityprogramshavebeenadvocatedtopreventandrehabilitatelowbackinjury.Specifically,abdominal?drawingin?hasbeenusedtotrainmotorcontroldeficitsinindividualswithlowbackpain.Thistechniquerequiresdifferentialactivitywithindeepandsuperficiallumbarmultifidusfibres,yettheabilityofthesefibrestoactdifferentiallyhasnotbeenextensivelyexamined.Deepfibresarehypothesizedtoactasspinalstabilizerswhilesuperficialfibresarehypothesizedtoactasglobalmoversofthetrunk.Objective:Toinvestigatedifferentialexcitationofdeepandsuperficiallumbarmultifidusfibresduringsegmentalindentationloadstothelumbarspine.Methods:Posterior-anteriorindentationloadswereappliedtoindividuallumbarspinousprocessesofproneparticipantsatthreedifferentvelocitiesandthreedifferentindentationdisplacements.Indentationsconsistedofaninitialdownwarddisplacementthatwassubsequentlyheldfor500milliseconds.Intramuscularelectromyography(EMG)ofdeepandsuperficiallumbarmultifidusfibresatL3,L4andL5wasrecorded.EMGwasquantifiedby?average?rootmeansquare(RMS),peakRMSofaslidingRMSwindowandtime-to-peakRMSovertheindentationphaseand500millisecondholdphase.Results:Increasedindentationdisplacementattheslowestvelocityresultedinincreased?average?RMSofonlytheL5superficialmultifidusfibres.Increasedindentationvelocityproduceddifferentialeffectsindeepandsuperficialmultifidusfibres.?Average?RMSandpeakRIVISsignificantlyincreasedwithincreasingindentationvelocityinmostdeepfibrerecordingsites,yetsuperficialfibreexcitationdidnotsignificantlyincrease.InmostEMGrecordingsites,thetime-to-peakRMSincreasedwithincreasingindentationdisplacementanddecreasedwithincreasingindentationvelocity.Conclusion:Differentialexcitationofsuperficialanddeepmultifidusfibreswasfoundwithincreasingindentationvelocity;however,theresultwasoppositetothathypothesized.Thisresultisclinicallyrelevantbecauseitsuggestsdeepmultifidusfibreexcitationmayincreaseinresponsetoincreasedperturbationmagnitude,possiblytorestorevertebralbodyposition.Differentialexcitationeffectsmayalsoberelatedtodifferentmechanicalstimuliexperiencedbydeepandsuperficialfibresduetovertebralbodymovementduringindentationloads.11TableofContentsAbstract.iiTableofContentsiiiListofTablesvListofFiguresviAcknowledgementsViii1.Introduction12.Reviewofliterature52.1.Lumbarspinestability52.1.1.Thepassivesubsystem52.1.2.Theactivesubsystem82.1.3.Trunkstiffness122.1.4.Theneuralsubsystem142.2.Thelumbarmultifidus162.2.1.Anatomy162.2.2.Lumbarmultifidusreflexes182.2.3.Lumbarmultifidusactivityduringvoluntarytrunkmovements232.3.Theroleoflumbarmultifidusinlumbarspinestability262.3.1.?Drawingin?andthe?abdominalbrace?272.3.2Differentialfunctioningoflumbarmultifidus353.Statementoftheproblem384.Hypotheses395.Operationaldefinitions406.Methodsandprocedures416.1Studyparticipants416.2Electromyographyandmultifidusimaging426.3Motordisplacementandforce466.4Respiration481116.5Experimentalprotocol.496.5.1Vertebralmotionandparticipantexperimentalposition496.5.2Indentationperturbations506.6.Dataanalysis547.Results577.1Experimentalconditionsvalidation597.1.1Trialexclusion597.1.2Perturbationvelocityanddisplacement597.2Electromyography667.2.1PartA:Theeffectofperturbationdisplacement687.2.1PartB:Theeffectoflowandhighperturbationvelocities708.Discussion758.1Perturbationdisplacement778.2Perturbationvelocity818.3Perturbationlevel868.4Limitationsandtrialexclusions888.5Clinicalimplications909.Conclusion9210.References93Appendices109AppendixA:Fine-wireelectrodefabrication109AppendixB:Lumbarmultifidusimagingandfine-wireelectrodeinsertion118B.1Lumbarmultifidusimaging118B.2Fine-wireelectrodeinsertion120AppendixC:Ethicalapprovalandparticipantconsentform128AppendixD:Statisticaltests130AppendixE:Individualsubjectdata135ivListofTablesTable6.1Listofparticipantagesandanthropometry41Table6.2ExperimentalDesignemployedforanalysisofeachEMGchannel(Note:Thethirddimension(perturbationlevel)ofthis3x3x3experimentaldesignisnotshownhere)55Table7.1Meanperturbationvelocities(mis)acrosssubjectsforeachperturbationdisplacementandvelocitycombinationateachperturbationlevel60Table7.2Meanperturbationdisplacements(mm)acrosssubjectsforeachperturbationdisplacementandvelocitycombinationateachperturbationlevel61Table7.3SummaryofstatisticalpvaluesforPartAandBstatisticaltests.Statisticallysignificanteffectsaredenotedwith**67vListofFiguresFigure6.1TransverseplaneultrasoundimageattheL4vertebrallevelshowingthefascialborderofthelumbarmultifidus43Figure6.2Examplefine-wireelectrodeinsertionlocations.(A)L5superficialneedleusedtoinsertthefine-wireelectrodeinSubject06,(B)L3superficialwireinSubject08,(C)L5deepneedleusedtoinsertelectrodeinSubject10and(D)L4deepneedleandL4superficialwireinSubject1045Figure6.3Theservo-motorusedtodelivertheindentationloadsbymanipulatingthepositionoftheindentationrod.Theforcetransducerbetweentheindentationrodandthecuppedfeltcontactsurfacerecordedforcebetweentherodandskin46Figure6.4Schematicofdigitalservo-motorcontrolduringexperimentalposterior-anteriorindentations47Figure6.5Experimentalsetuptodeliverindentationperturbationswhilerecordingdisplacement,forceandintramuscularelectromyography51Figure7.1Displacement,forceandelectromyographyofa(a)slowvelocity,shallowdisplacementperturbation(Vi-Di)anda(b)mediumvelocity,intermediatedisplacementperturbation(V2-D2)inSubject03.Forcomparisonpurposes,bothperturbationsareplottedonthesamescaleofaxis58Figure7.2Idealizedperturbationvelocityprofilesforslow,mediumandfastperturbationvelocities(Notethexandyscalesforeachvelocityprofilearedifferent)63Figure7.3Velocityprofilestime-normalizedtothelengthoftheactiveindentationphaseandexpressedasapercentageoftheirtargetvelocity.Perturbationstodifferentdisplacementsareexpressedindifferentcolours(Dl=blue,D2?red,D3=black).NotethatonlyVelocity1(Vi)perturbationsachieved100%oftheirtargetvelocity.64Figure7.4TherevisedexperimentaldesignexcludingV3andD3perturbations66Figure7.5?Average?rms(toppanel),peakrms(middlepanel)andtime-to-peakrms(bottompanel)foreachEMGchannelatDlandD2displacements.Forcomparisonpurposes,the?average?rms,peakrmsandtime-to-peakrmsaxesareconsistentacrossFigures7.5,7.6,7.7and7.869viFigure7.6PartB:?Average?rmsforDi(toppanel)andD2(bottompanel)perturbationdisplacements.Forcomparisonpurposes,the?average?rms,peakrmsandtime-to-peakrmsaxesareconsistentacrossFigures7.5,7.6,7.7and7.871Figure7.7PartB:PeakrmsforDl(toppanel)andD2(bottompanel)perturbationdisplacements.Forcomparisonpurposes,the?average?rms,peakrmsandtime-to-peakrmsaxesareconsistentacrossFigures7.5,7.6,7.7and7.872Figure7.8PartB:TimetopeakrmsforDi(toppanel)andD2(bottompanel)perturbationdisplacements.Forcomparisonpurposes,the?average?rms,peakrmsandtime-to-peakrmsaxesareconsistentacrossFigures7.5,7.6,7.7and7.874Figure8.1IndentationdisplacementduringVi-Dl(orangedashedline)andVi-D2(solidbrownline)perturbationdisplacementsacrosstime.Thedottedbluelineatthetopofthefigurerepresentsthelengthofthetimeintervalbetweentheonsetoftheactiveindentationphaseandtheendoftheindentationholdphase80Figure8.2Conceptualizedthreevertebraemodeloftherelativestretchwithintheshorterdeeplumbarmultifidusfibresandlongersuperficialmultifidusfibres.Astheindentationloaddisplacesthevertebralbody,superficialanddeepfibreattachmentsexperiencethesameorthogonaldisplacement.Deepfibresexperienceagreaterrelativestretchandlargerangulardeviationthansuperficialfibres83viiAcknow1edementsIwasveryfortunatetoworkwithmanyterrificresearcherswhoseknowledgeanddedicationtotheirresearchwastrulyinspiring.Mygraduatesupervisor,Dr.DavidSanderson,providedinvaluableguidancethroughoutmygraduatedegreeandwithouthissupportmypersonalandacademicgoalswouldnothavebeenachieved.Iamalsogratefultomycommitteemembersfortheirinsightandinvestmentoftimeinthisproject.Drs.Jean-SebastienBlouin,TimothyInglisandDavidSanderson,wereinfluentialtomyacademicdevelopmentasaresearcherandwithouttheircommitmentandleadershipthisprojectwouldnothavebeenpossible.Iwouldliketothankmyfellowgraduatestudents,particularlymybiomechanicslabmembersEllexis,Ryan,KarineandJuliafortheirencouragementandfriendship.IwouldalsoliketoacknowledgeChrisandDanoftheSpineNeurophysiologylabfortheirhelpduringdatacollection.ThankstoDr.BillSheelforprovidingandassistingwiththepneumotachometerandDr.DonnaFordintheDepartmentofAnatomyforfurtheringmyunderstandingoflumbarspineanatomy.Iwouldliketothankmyfamilyandfriendsfortheirsupport,reliabilityandhonestypriortoandthroughoutmydegree.SpecialthankstoKristaforlookingoutformetheentireway,providingemotionalsupportandunderstanding.Agraduatedegreeisanacademicventure,yetthecontributionsoftheseindividualsallowedthisacademicexperiencetobecomeoneofpersonaldevelopment.vii?1.IntroductionLowbackpain(LBP)isawidespreadandcostlyhealthcareproblemintoday?ssociety.LBPhasbeencitedasthesecondmostcommonreasonforgoingtothedoctor(Andersson1999;Mengiardietal.2006).ThelifetimeprevalenceofdevelopingmoderateorsevereLBPinwesternpopulationshasbeenestimatedtobebetween70%and85%(Andersson1999;Frymoyeretal.1983).ThemajorityofindividualswhodevelopLBParestillexperiencingsymptomsoneyearaftertheinitialepisode(Croftetal.1998).Inareviewofeighteenstudiesfromeightdifferentcountries,thepointprevalenceofLBPwasbetween4.4%and33%(LoneyandStratford1999).InCanadiansovertheageoftwelve,?backproblems?werethesecondmostprevalentchronicconditionin1996/1997andaffectedmoreCanadiansthanasthma,highbloodpressureorarthritis(SchultzandKopec2003).BasedonStatisticsCanadasurveysin1994/95and1996/97,Perez(2001)examinedthetwoyearprevalenceofbackproblemsinCanada.Ofover6,000Canadianworkerswhoreportedtheirhealthas?verygood?,?good?or?excellent,?9%haddeveloped?backproblems?withinthenexttwoyears(Perez2000).LBPhasspecialimplicationsforindividualsintheworkforceandtheelderly.Duringthe2003calendaryear,lowbackinjurieswerethesecond(16%)mostcommonlyinjuredbodypartinCanadiansaged18-85(WilkinsandMackenzie2007).Additionally,inCanadiansovertheageof55,almost20%ofchronicconditionswereattributedto?non-arthriticbackproblems?(WilkinsandPark1996).ThecostsofLBPtoboththeindividualandsocietycanbeconsiderable.ThedirectannualcostsofspineandbackdisordersintheUnitedKingdomwere1.6billionpoundsin1998(ManiadakisandGray2000),whileinCanadathesedisorderscostapproximately670milliondollarsannually(Coyteetal.1998).Thesedirectcostsaredwarfedbytheindirectcostssuchaslostworktimeandproductivity(Limetal.2006).TheyearlycostoflostworktimeduetoLBPwasestimatedtobeover7.5billiondollarsinCanada(Coyteetal.1998)and28billiondollarsintheUnitedStates(MaetzelandLi2002).AcuteLBPoftendisappearsspontaneously(Hidesetal.2001);however,insomeindividualsLBPcanbecomechronic.ChronicLBPhasthehighesteconomicalcostasfewerthan10%ofLBPclaimsmakeup64.9-84.7%ofLBPcosts(Hashemieta!.1998).LBPinterventionprogramshavehadsomesuccess,althoughmanyhavebeenconsideredtobeineffective(Ebenbichleretal.2001).InacomparisonofnationalclinicalguidelinesforthemanagementofLBPinelevencountries,Koeseta!(2001)revealeddiscrepanciesinmanagement,particularlyastheyrelatetotheefficacyofexercise,whenexercisesarewarrantedandwhetherspecificexercises(eg.McKenzieBackExercises)shouldbeprescribed(Koesetal.2001).Theratesofbacksurgeryinelevendifferentcountriesvariedconsiderablyandappearedtobelinearlyassociatedwiththenumberofavailablesurgeonsaswellasthenationalratesofdiscretional(eg.tonsillectomy)surgeries(Cherkinetal.1994).IndividualswithLBPformaheterogeneousgroup(Kangetal.2007)makingdiagnosisofaspecificcauseproblematic.LumbarsegmentalinstabilityhasbeenimplicatedassignificantcauseofLBP(Panjabi2003)andasacausativefactorin20-30%ofchronicLBPcases(TaylorandO?sullivan2000).SegmentalinstabilitythatresultsinrecurrentLBPinresponsetosmall,unpredictableorrapiddisturbancestothelumbarspineisoftenreferredtoasclinicalinstability(TaylorandO?sullivan2000),howeverexactdefinitionsdiffer(Criscoeta!.1992).Clinicalinstabilitydescribestheinabilityofthevertebralcolumntopreservenormalmovementofindividualvertebraewhenexposedtocommonphysiologicalloads(White1990).Thelinkbetweensegmentalinstabilityandbackpainiswellestablished,however,theassociationisnotunidirectional.Injurytoanatomicalstructuresinthelowbackcanresultinlumbarsegmentalinstability;however,instabilitycanalsobethecauseofbackinjury(McGilletal.2003).RegardlessofwhethersegmentalinstabilityisthecauseoreffectofLBP,manyclinicalresearchershaveinvestigatedthecontributingfactors,deficitsandmechanismsoflumbarspinestability(CholewickiandMcGill1996;CholewickiandVanVliet2002;GranataandEngland2006;HodgesandRichardson1996;McGill2001;McGill2007;MoorhouseandGranata2007;Richardsonetal.1999;Richardsonetal.2004).Bergmark(1989)wasoneofthefirstresearcherstomathematicallymodelspinalstabilitybydividingthetrunkmusclesintotwoprimarygroups:localmuscleswithdirect2attachmentstothevertebralcolumnandglobalmusclesthatactasprimemoversofthetrunk(Bergmark1989).Untilrecently,electromyography(EMG)ofthelocalmuscleswaschallengingduetothedepthofthesemusclesandlackofanobjectivemethodofensuringneedleelectrodeinsertionaccuracy(DonischandBasmajian1972;FloydandSilver1951;FloydandSilver1955;Morrisetal.1962).Fine-wireelectrodesinsertedusingultrasoundguidance(Anderssonetal.1996;Anderssonetal.2002)haveovercomethesechallengesandsignificantlyincreasedourknowledgeofintersegmentalanddeeptrunkmusclefunction.AgroupofresearchersfromtheUniversityofQueenslandinAustraliahaveextensivelyexaminedthefunctionofthesemusclesinpeoplewithhealthybacksandthosewithLBP(Hideseta!.1995;Hideseta!.2001;HodgesandRichardson1996;HodgesandRichardson1997a;HodgesandRichardson1997b;HodgesandRichardson1999a;RichardsonandJull1995;Richardsonetal.1999;Richardsonetal.2002).Basedonobservationsoflumbarmultifidus(Hidesetal.1994;Hidesetal.1996)andtransversusabdominusimpairments(HodgesandRichardson1998;HodgesandRichardson1999b)inindividualswithLBP,theseresearchersdevelopedaspecific?drawingin?techniquedesignedtotrainandrehabilitatedlumbarsegmentalinstability(RichardsonandJull1995;Richardsonetal.1999;Richardsonetal.2004).This?drawingin?techniqueconsistedofco-contractionbetweentransversusabdominusandthedeepfibresoflumbarmultifidus(Richardsonetal.1999;Richardsonetal.2004).Randomizedclinicaltrialshavesupportedtheuseofspecificsegmentalstabilizationexercisestoteachthe?drawingin?techniqueoverconventionalLBPtreatmentprograms(Hidesetal.1996;O?Sullivanetal.1997).ChronicLBPpatientshadreducedpainanddisabilityafteratenweekprogramofspecificstabilizingexercisestotrain?drawingin?(O T Sullivanetal.1997),whileacuteLBPsufferershadareducedrecurrencerateoffutureLBPafterthesespecificstabilizingexercises(Hidesetal.2001).The?drawingin?techniquerequirescontractionofthedeepfibresoflumbarmultifiduswhilethesuperficialfibresaretoremainelectricallyinactive(Richardsonetal.1999).Thesuperficialfibresoflumbarmultifidusarehypothesizedtofunctionwiththeglobalmusclesandactasprimemoversofthetrunk(MacDonaldetal.2006).Thiswouldimplydifferentialfunctionofthesuperficialanddeeplayersoflumbarmultifidusinsituations3requiringspinalstability.Differentialfunctioningwithinasinglemusclehasbeenobservedbetweenthelongandshortheadofbicepsbrachii(Brownetal.1993),whilethefelinespleniusmuscleisanatomicallycompartmentalized(Richmondetal.1985).Rapidarmmovementandtrunkperturbationstudieshavesupportedthehypothesisofafunctionaldifferentiationbetweenthesuperficialanddeeplayersoflumbarmultifidus(Moseleyetal.2002;Moseleyetal.2003),however,controversyremainsastowhetherthisdifferentiationexists(MacDonaldetal.2006).Thisstudywillexaminedeepandsuperficiallumbarmultifidusfibreexcitationduringsegmentalchallengestospinalstability.EMGfromthedeepandsuperficiallumbarmultifidusfibresduringperturbationsofvaryingdisplacementandvelocitywillbeexaminedtosupportoropposethehypothesisthatdeepandsuperficiallumbarmultifidusfibreshavetheabilitytofunctiondifferentially.42.Reviewofliterature2.1.LumbarspinestabilityLumbarspinestabilityhasbeenproposedtobecontrolledbythreesubsystems:thepassive,activeandneuralsubsystems(Panjabi1992a).Lumbarspinestabilityistask-specific(Reevesetal.2007)andrequirestheintegratedfunctionofthesesubsystemstodynamicallymeetstabilityrequirements.ManoharPanjabi(PanjabiI992b)proposedthatthegoalofthesesystemswastomaintainintervertebraljointmotionwithinthenon-elasticorneutralregionofthetotalrangeofvertebralmotion(Panjabi1992b).2.1.1.ThepassivesubsystemThepassivesubsystemiscompromisedofthelumbarvertebrae,ligamentsofthelumbarspine,theintervertebraldiscs,thefacetjointsandcapsulesandthenon-contractile,elasticcomponentsofmuscle(Panjabi1992a).Thevertebralbodiesinthelumbarspinearethelargerandstrongerthaninthethoracicandcervicalvertebralcolumns(Tortora2000).Thelumbarfacetjointarticularsurfacesareorientedverticallyatanobliqueangletothesagittalandcoronalplanes(Tortora2000).Thefacetjointsaresurroundedbyzygapophysialjointcapsulesthatpreventthearticularsurfacesfromseparating(McGill2007)andlimitaxialrotation(Panjabi2003).Thesecapsulesareinnervatedbythesuperiorandinferiormedialbranchesofthelumbardorsalramus(Bogduk2000a).Severalligamentsinthelumbarspinerestrictvertebralmotion,particularlyattheendofthejointrangeofmotion(ROM).Theanteriorandposteriorlongitudinalligamentsrunanteriorandposteriortothevertebralbodiesandareinnervatedbynerveplexuses(Bogduk2000a).Theanteriorlongitudinalligamentassistsinpreventingexcessvertebralcolumnextension,whiletheposteriorlongitudinalligamentassistsinpreventingsagittalplaneflexion(McGill2007).Thesupraspinousligamentextendsalongthespinousprocessesandalsoresistsexcessivevertebralcolumnflexion(McGill2007).Theinterspinousligamentislocatedjustanteriortothesupraspinousligamentandconnectsspinousprocessesofsuccessivevertebrae(McGill2007).Boththesupraspinousand5interspinousligamentsareinnervatedbythelumbardorsalramus(Bogduk2000a)andareformedinpartbytheposteriorthoracolumbarfascia,lumbarmultifidusanderectorspinaetendons(JohnsonandZhang2002).Shortintertransversariiligamentsconnectadjacenttransverseprocesses,althoughtheirexactmorphologyisuncertain(McGill2002).roleofthesepassivestructuresandtheintervertebraldiscinsagittalplanemotionhasbeeninvestigatedinporcinelumbarspines(Kaigleetal.1995).Kaigleetal.(1995)introducedeightdifferentsurgicalinjuriestoporcinespinesincludingtransverseprocessinjury,interspinousligamentremoval,intervertebraldiscincisionandfacetjointinjury.Facetjointinjuriesresultedinsignificantlygreatersagittalrotation,whileanteriorintervertebraldiscinjurieswereassociatedwithgreatervertebralmovementalongthelongitudinalaxis(ie.axialtranslation)(Kaigleetal.1995).Thecombinationofanteriorintervertebraldiscinjuryandinterspinousligamentremovalresultedinsignificantlygreatersagittalrotationandanterior-posteriortranslationduringflexionandextension(Kaigleetal.1995).Theyconcludedthattheroleoftheintervertebraldiscwastopreventexcessiveaxialtranslation,whiletheinterspinousligamentlimitedsagittalrotation(Kaigleetal.1995).Inaddition,totheirroleinlimitingaxialrotation,thefacetjointslimitedvertebralsagittalrotationandsheartranslation(Kaigleetal.1995).Despitetheactionsofthesepassivestructures,theligamentousvertebralcolumnisquitesusceptibletobucklingwithoutmuscularforces.Whenamassisplacedatthetopofavertebralcolumnwithoutmuscles,themagnitudeoftheloadcausingthecolumntobendisreferredtoasthe?bucklingload?(CriscoandPanjabi1992).Thethoracolumbar(Tisacrum)bucklingloadinthecoronalplanehasbeenreportedtobe20N(LucasandBresler1961),whilelumbarbucklingloadshavebeenmeasuredtobe88N(Li-Si)and98N(L2-S1)(Criscoetal.1992).Surgicalintervertebraldiscinjurydecreasedthebucklingloadby17-50%andfacetjointinjuryby40-80%inthelumbarspinespecimens(Criscoetal.1992).Thesebucklingloadsaresignificantlylessthanthevertebralcolumnexperiencesinvivo(CriscoandPanjabi1992)whichhighlightstheimportantroleofmusclesinspinalstability.ThepassivesubsystemappearstoexertitsgreatesteffectinrestrictingspinalmotionneartheendofthenormalROM(Panjabi1992a).Inthesagittal6plane,thishypothesiswasreinforcedbyLeeandEvans(2000)whoappliedposterior-anteriorforcestospinalunitsconsistingoftwovertebrae.Dissectionoftheligamentumflava,supraspinousligament,interspinousligamentorzygapophysialcapsulejointsdidnotleadtosignificantlygreatermovementpatterns(LeeandEvans2000).TheseauthorsreasonedthatthiswasbecausetheydidnotfullyloadthevertebralunitstotheirphysiologicalROM(LeeandEvans2000).Itshouldbenotedthatmanyofthesestudies(Criscoetal.1992;Kaigleetal.1995;LeeandEvans2000;LucasandBresler1961)didnotincludethepassivepropertiesofmuscleandthethoracolumbarfascia.Thethoracolumbarfasciaiscomposedofthreelayers(anterior,middleandposterior)thatoriginateatthevertebraeandblendtogethertoinsertatthelateralraphe(BogdukandMacintosh1984).Theanteriorandmiddlelayersencirclequadratuslumborumbyoriginatingatthelumbartransverseprocessesandpassinganteriorandposteriortoquadratuslumborum,respectively(Bogduk2000b;Hansenetal.2006).Theposteriorlayerattachestothelumbarspinousprocessesandpassesposteriortothedorsalbackmusclestomergewiththeotherlayersatthelateralraphe(Bogduk2000b).Theposteriorlayeriscomposedofadeeplaminawithfibrespassinginacaudolateraldirectionandsuperficiallaminawithfibrespassingcaudomedially(BogdukandMacintosh1984).Theposteriorlayerofthethoracolumbarfasciahasbeenhypothesizedtoproduceatrunkextensormomentthroughahydraulicamplifiermechanism(Gracovetskyetal.1977)orthroughlateraltensionatthelateralraphe(Teshetal.1987).Thehydraulicamplifiermechanismreferstoparaspinalmusclesexpandingdorsallywithactivecontractionwhichtensionstheposteriorthoracolumbarfasciaandcausestrunkextension(BogdukandMacintosh1984).Thevalidityofthismechanismanditscontributiontotrunkextensionremainsinquestion(Bogduk2000b).Duetothedifferingorientationofthedeepandsuperficiallaminaoftheposteriorthoracolumbarfascia,ithasbeenhypothesizedthatlateraltensiontoallthreelayersatthelateralraphecouldproducealumbarextensormoment(BogdukandMacintosh1984).Lateraltensionwouldproduceacaudolateralforceonthedeeplaminaandrostrolateralforceonthesuperficiallamina.Ifthetension7wasappliedbilaterallytheresultantforceswouldcausethelowerlumbarvertebraetomoverostrallyandtheupperlumbarvertebraetomovecaudallyresultingintrunkextensionduetothenaturallordosisofthelumbarspine(BogdukandMacintosh1984).Barkeretal.(2006)applied20Noflateraltensiontothetransversusabdominusaponeurosis(whichoriginatesatthelateralraphe)ofcadaversandobservedincreasedtrunkresistanceandsegmentalstiffnesstotrunkflexionanddecreasedresistanceandsegmentalstiffnesstotrunkextension.Theauthorsconcludedthatlateraltensionthroughthemiddleandposteriorthoracolumbarlayershasastabilizingeffectonthelumbarspine(Barkeretal.2006).2.1.2.TheactivesubsystemMusclesandtendonsspanningthevertebralcolumnmakeuptheactivespinalstabilitysubsystem(Panjabi1992a).Manyshortmusclesconnectvariouspartsofadjacentvertebrae.Eachlumbarspinousprocesshasbilateralinterspinalesmusclesthatattachthespinousprocessesofadjacentvertebrae(Bogduk2000b;Richardsonetal.1999).Therearethreeintertransversariimusclesthatconnectadjacenttransverseprocesses(Bogduk2000b).Theintertransversariimedialesattachesattheaccessoryprocessofthesuperiorvertebraeandatthemamillaryprocessoftheinferiorvertebra(Hansenetal.2006).Boththeintertransversariilateralesdorsalesandventralesattachcaudallyatthetransverseprocess,butdorsalesattachesrostrallyattheaccessoryprocess,whileventralesattachesrostrallyatthesuperiortransverseprocess(Bogduk2000b).Theexactfunctionofthesemusclesisunknown(Bogduk2000b);however,theyhavebeenproposedtohaveaproprioceptivefunction(McGill2007).Thethoracicerectorspinaemuscleswereoriginallythoughttobecontinuouswiththelumbarfibres;however,detailedanatomicalstudieshaveshownthisisnotthecase(Bogduk1980).Thethoracicerectorspinaeconsistsofthelongissimusthoracisparsthoracisandiliocostalislumborumparsthoracis.Bothofthesemusclesformtendonsthatmergetoformtheerectorspinaeaponeurosis,insertingatthesacrumandposteriorsuperioriliacspine(Bogduk2000b).Thethoracicerectorspinaemusclesextendthe8trunk(Tortora2000),whilelongissimusthoracisparsthoracisalsohasaroleinlateralflexion(Bogduk2000b).Thelumbarerectorspinaemusclesconsistofthelongissimusthoracisparslumborumandiliocostalislumborumparslumborum.LongissimusthoracisparslumborumfasciclesarisefromtheL1-L5transverseprocessesandattachtotheposteriorsuperioriliacspinewiththeL5fascicleattachingmostmedialandeachsuccessivefasciclemorelaterally(Bogduk2000b;Richardsonetal.1999).Iliocostalislumborumparslumborumfibresalsoarisefromthetransverseprocessesandinsertattheilium(Richardsonetal.1999),withbothsuperiorandinferiorattachmentslateraltothelongissimusthoracisparslumborumattachments(Bogduk2000b).Lumbarmultifidusconsistsofsuperficialanddeepfasciclesthatspanbetweentwoandfivevertebrallevels(Macintoshetal.1986).Deepfibresbeginatthevertebrallaminaandruntwoorfewervertebrallevelscaudaltoattachatthemamillaryprocesses(Macintoshetal.1986).Superficialfibresarisefromthespinousprocessesandspangreaterthanthreevertebrallevelsattachingtocaudalvertebrae,thesacrumandilium(Macintoshetal.1986).Amoreextensivediscussionoflumbarmultifidusanatomywillbepresentedinsection2.2.1.Psoasmajoralsohasdirectattachmentstolumbarvertebraeandconsistsofvertebralfibresanddiscalfibres(Hansenetal.2006).VertebralfibresattachtothevertebralbodiesofT12toL5andbecometendinousastheyattachtothelessertrochanterofthefemur(Bogduk2000b;Jemmettetal.2004).DiscalfibresrunfromtheT12toL5medialtransverseprocessesandintervertebraldiscstoalsoattachatthefemorallessertrochanter(Bogduk2000b;Jemmettetal.2004).Psoasmajorfunctionstoflexthehip(Hansenetal.2006)whileconcurrentlygeneratessignificantlumbarspinecompressionforce(McGill2007).Thelateralfibresofquadratuslumborumarebelievedtoweaklylaterallyflexthetrunk(Bogduk2000b;Richardsonetal.1999),whilethemedialfibresprovidesegmentalstability(Richardsonetal.1999).McGilletal.(1996)recordedquadratuslumborumactivityduringuprightstandingasweightwasprogressivelyaddedbilaterallytotheindividual?shands.Eventhoughtheindividualdidnotmovefromtheiruprightposture,increasesintheloadheldbilaterallycausedincreasedquadratuslumborumactivityandthisleadtheauthorstohypothesizeastabilizingrole(McGilletal.1996).9Theabdominalmusclesalsoplayaroleinspinalstability.Transversusabdominushasreceivedsignificantattentionasaspinalstabilizerduetoitsabilitytogenerateintraabdominalpressure(Hodgesetal.2003),itsattachmenttothethoracolumbarfascia(BogdukandMacintosh1984)anditsimpairmentinindividualswithLBPduringrapidarm(HodgesandRichardson1996;HodgesandRichardson1999a)andlegmovements(HodgesandRichardson1997a;HodgesandRichardson1998).Transversusabdominusbilaterallyoriginatesattheiliaccrests,lateralraphesandl2ribsandwrapsaroundthetrunkblendingwithinternalobliquefibresandthelineaalbaatthemidline(Richardsonetal.1999).Muscularonlythroughtheanteriorone-thirdofitscourse(Jemrnettetal.2004),thistendinousmusclecanbilaterallycontracttocompresstheabdomen(Tortora2000).anatomyofbiomechanicalmodelshascommonlybeenbasedoncadaverdissections(Bogduketal.1992),othermodels(Gardner-Morseetal.1995)anddatafromTheVisibleHumanProject?(DaggfeldtandThorstensson2003).Thesemodelshaveattemptedtodistinguishthestabilityrolesandmuscularmomentcontributionsduringtrunkextensorefforts.CholewickiandMcGill(1996)usedvariousimagingtechniques,cadaverdissectionsandapreviousmodel(Bogduketal.1992)toexaminemechanicalinvivolumbarspinestabilityduringavarietyoftasks.Tocalculateastabilityindex,theseauthorsdevelopedamathematicalmodelthatincludedtheanatomyof90musclefascicles,thepelvis,ribcageandlumbarvertebrae(CholewickiandMcGill1996).Reevesetal.(2007)viewedone-dimensionalstabilityasaballsittinginabowlwherethesteepnessofthebowlwallsdeterminedhowrobusttheballwastoinstability.Ifarelativelysmallforceactedontheball,thesteepnessofthewallswouldpreventitfromleavingthebowl(McGill2002).CholewickiandMcGill(1996)extendasimilaranalogytoeachlumbarvertebraforsixdegreesoffreedom(animaginarysix-dimensionalbowl)andlookedforlocalpotentialenergyminimaoftheresultingenergysurface.IntheanalogyofReevesetal.(2007),theselocalpotentialenergyminimarepresenttheballbeinginastablepositionatthebottomofthebowl.EMGwasrecordedfromsubjectsperformingvarioustasksandtheresultingexcitationprofileswereinputintotheir10stabilitymodel(CholewickiandMcGill1996).Theseresearchersfoundthatthelumbarspinewasmorerobusttoinstability(meaningalesserriskofinstability)intaskswithgreatermuscleexcitationprofilesthantaskswithlittleactivemuscularinput(CholewickiandMcGill1996).Cholewickietal.(1996)justifiedthesefindingsonthebasisthatbackinjuriescanoccurinlowmuscularefforttaskssuchasbendingovertoretrieveaninanimateobjectfromthefloor.Todeterminehowmucheachindividualmusclecontributestolumbarspinestability,EMGwasrecordedfromsubjectsperformingavarietyofisometrictrunkmovements(CholewickiandVanVliet2002).Theresultingmuscleexcitationprofileswereinputintothestabilitymodelandindividualmusclesweresequentiallyremovedfromthecalculation(CholewickiandVanVliet2002).Theseauthorsfoundthatremovalofanindividualmuscleresultedinastabilityindexreductionbetween0-30%;however,nosinglemusclecausedagreaterreductionthan30%(CholewickiandVanVliet2002).Itshouldbenotedhowever,thatthismodel(CholewickiandMcGill1996)didnotincludetransversusabdominus,nordiditconsiderintra-abdominalpressureasanextensormomentgeneratingfactor.Andersonetal.(1985)firstacknowledgedthat?betterapproximationsoftheattachmentstothevertebrae,andmorerealisticvaluesofrestinglength?(Andersonetal.1985,p.S?7?7)areneededtoimprovespinalbiomechanicalmodels.Morethantwentyyearslater,thisviewwasechoedbyHansenetal.(2006)whoreviewedquantitativedataonmusclelengths,momentarms,crosssectionalareas(CSA)andjointrangesofmotion.Duetothedetailedanatomyofthelumbarspine,severalresearchershaveexaminedtheinvitrokinematiccharacteristicsofcadaverlumbarspineswithsimulatedmuscleattachments(Kaigleetal.1995;Panjabietal.1989;Quintetal.1998;Wilkeetal.1995).Physiologicallymomentswereappliedtointactandinjuredlumbartwo-vertebraunitstoexaminetheeffectsofintersegmentalmusclesonkinematicmotion(Panjabietal.1989).Intersegmentalmuscleswereartificiallymodeledassymmetricalvectorsthatpulledthesuperiorvertebralbodyanterolaterallyandinacaudaldirection(Panjabietal.1989).Theapplicationofa60Nforcethroughthesimulatedintersegmentalmusclesreducedintervertebraljointmotionwithinthenon-elasticregion(orneutralzone)duringflexion,extensionandaxialrotationmoments(Panjabietal.1989).Theauthorsconcludedthat11reducingmotionwithinthisnon-elasticregionwasthefunctionalroleofintersegmentalmuscles.Wilkeeta!.(1995)carriedoutamoredetailedinvitrostudy,attachingsymmetricalcablestoL4tosimulatethemuscularactionoflumbarmultifidus,thelumbarerectorspinaemusclesandboththevertebralanddiscalfibresofpsoasmajor.Intervertebraljointmotionwasexaminedduringflexion,extension,lateralflexionandaxialrotationmomentswithandwithouttensioninoneorallofthecablesattachedtoL4(Wilkeetal.1995).SimulatedmusculartensioninallmusclesincreasedjointstiffnesswhichdecreasedtheROMinalldirections(Wilkeetal.1995).Lumbarmultifiduswasfoundtoprovidemorethantwo-thirdsofthesegmentalstiffnessthatcausedthisreductioninROM(Wilkeeta!.1995).2.1.3.TrunkstiffnessPassivelumbarstiffnesshasbeenmeasuredaboutsagittal,coronalandtransverseplanes(BrownandMcGill2008;McGilletal.1994);however,thisreviewoftrunkstiffhesswillbelimitedtostiffnessinresponsetoposterior-anteriorforces.Passivetrunkstiffnesstostaticorslowlyappliedposterior-anteriorindentationforceshasgenerallybeencalculatedastheslopeofaforce-displacementgraphoveraspecificforcerange.Posterior-anteriortrunkstiffnessinresponsetoposterior-anteriorforcesappliedtotheskinoverlyingspinousprocesseshasrangedfrom12N/mmto30N/mm(Collocaeta!.2004;Kelleretal.2003;Latimereta!.1996a;Latimeretal.1996b;Latimereta!.1998;Shirleyeta!.2002;Shirleyeta!.2003).Manypossiblevariablescouldaccountforthiswidevariationinstiffnessmeasures.Cyclicposterior-anteriorforces(30-90N)appliedtotheskinoverlyingtheL4spinousprocessresultedinanaveragestiffnessof13.2N/mm;however,stiffnessduringthefirstcyclicalloadwassignificantlylessthansubsequentloads(Shirleyetal.2002).Additionally,Latimeretal.(1996b)measuredposterior-anteriorstiffnesstoforcesupto1OONinLBPpatientsandobservedasignificantdecreaseinstiffnessfollowingresolutionofpainsymptoms.Leeetal.(1994)investigatedtherelationshipbetweenposterior-anteriorstiffnessandlumbarvertebrallevelinhealthybackindividualsandconcludedthatduringbothquasi-staticandcyclicalloadingthestiffnessatL5wasgreaterthanatL4andstiffnessatL4greaterthanatL3(LeeandLiversidge1994).Theinverserelationshipwasfoundinpatientswithnon12specificLBPwhereaveragestiffnesscoefficientswere17.46N/mmatL3,15.94N/mmatL4and15.14N/mmatL5(Latimeretal.1996a).Bothofthesestudiescalculatedstiffnesscoefficientsoversimilarlinearforceregions:30-105N(Latimeretal.1996a)and20-1OON(LeeandLiversidge1994).Averagestiffnesstoposterior-anteriorforcesinLBPpatientswasalsogreaterwhenappliedtovertebralspinousprocessesthanvertebraltransverseprocesses(CollocaandKeller2001b).Themajorityofthestudiesinvestigatingposterior-anteriorlumbarspinestiffhesshavedonesoattheendofnormalexpiration(functionalresidualcapacity)tostandardizelungvolume(CollocaandKeller2004;Latimeretal.1996a;Latimeretal.1998;LeeandLiversidge1994;Leeetal.1993;Shirleyetal.2002).Shirleyetal.(2003)measuredposterior-anteriorstiffnesstocyclicindentationloads(1Hz,150N)appliedtotheL2andL4spinousprocessesduringdifferentphasesofrespiration.Inspirationandexpirationsignificantlyalteredtrunkstiffness;however,agreaterincreaseinposterior-anteriorstiffnesswasrecordedduringexpiration(Shirleyetal.2003).ForbothL2andL4,thelargestaveragestiffnesswasrecordedatresidualvolumeandtheloweststiffnessrecordedatfunctionalresidualcapacity(Shirleyetal.2003).Atalllungvolumes,therelationshipbetweenappliedforceandindentationdisplacementwaslinearovertheforcerange50-lOON(Shirleyetal.2003).Theactivespinalstabilitysubsystemalsoinfluencesposterior-anteriorstiffness.Isometrictrunkextensioneffortsduringtheapplicationoflowfrequencyposterior-anteriorindentationforcesincreasedL3stiffnessbyanaverageof350%comparedtorestingvalues(Leeetal.1993).Trunkextensionalsosignificantlyincreaseddynamicstiffnesstoshortduration(5ms)indentationimpulsesappliedtotheL3spinousprocesscomparedtotherestingcondition(CollocaandKeller2004).Kelleretal.(2007)appliedmechanicalstimulationdirectlytotheanaesthetizedovineL3spinousprocessesatvariablefrequencies(0.46-19.7Hz)withandwithoutmuscularstimulation.Theseauthorsfoundthattrunkstiffnesswasmodulatedbythefrequencyofmechanicalstimulationandthefrequencyofartificialmultifidusmusclestimulation(Kelleretal.2007).13Respiration(Shirleyetal.2003),vertebrallevel(LeeandLiversidge1994),muscularactivity(Kelleretal.2007)andLBP(Latimeretal.1996b)allappeartoinfluenceposterior-anteriortrunkstiffness.Recentstudieshavealsoidentifiedseveralothervariablesinthecalculationofstiffnessincludingsubjectposition,thegenerationofintraabdominalpressureandtherangeofforcesoverwhichstiffnessiscalculated(KawchukandFauvel2001;Latimeretal.1998).Thesestudieshighlighttheimportanceofastandardizedexperimentalprotocoltocontrolforthesevariableswhenapplyingposterior-anteriorindentationloadstothelumbarspine.2.1.4.TheneuralsubsystemDynamicspinalstabilityinvolvesthecoordinationofthepassive,activeandneuralsubsystemstofollowa?movingtarget?(McGilletal.2003;Reevesetal.2007).Activemusclecontractioncanincreaselumbarspinalstabilitybyincreasingjointstiffness;however,thisactivecontractioniscontextdependentandmustoccurinthecorrectmuscleswithappropriateexcitationlevelstoachievestability(McGill2002;McGill2007).Thiscontextdependencywasdemonstratedinanunstablesittingtaskwitheitherminimalmuscleactivityormuscularco-contraction(increasedactivesubsysteminput)(Reevesetal.2006).Increasingactivestiffnessthroughmuscleco-contractiondecreasedtheprecisionoftheneuralfeedbacksystemaslargerforcesmeantgreaterforcevariabilityandgreater?over-corrections?(Reevesetal.2006).Additionally,greatermuscleco-contractionmayproducegreatercompressivespinalloadsthatmayleadtospinalinjury(McGill2002).Feedbacktotheneuralsubsystemcouldstemfrommultiplestructuresinboththepassiveandactivesubsystems(Panjabi1992a).Vertebraereceiveinnervationfromlongnervesthatspreadthroughthevertebralbody(Bogduk2000a)andmanyofthelongitudinalandintersegmentalspinalligamentsarealsoinnervated(Bogduk1983;Kangetal.2001).Theouterlayersofintervertebraldiscsareinnervated,especiallyinthelateralregion(Indahletal.1995);however,thenucleuspulposusdoesnotreceiveinnervation(Kangetal.2001).Paraspinalmusclescontainsensoryreceptorsthatprovidedirectfeedbacktothe14neuralsubsystemandhavebeenshowntoevokereflexesinresponsetospinalmanipulative-likeperturbationsinafelinemodel(Kangetal.2003;Pickar2002;PickarandKang2006;Pickaretal.2007).Theshortintersegmentalmusclesinparticularhavereceivedattentionasfunctioningprimarilyaslengthproprioceptors(McGill2007).Thesefibreshavesmallforceproducingcapabilitiesandareconsequentlyunabletoproducesignificanttrunkmoments(McGill2007);however,theyappeartohavelargerconcentrationsofmusclespindlesrelativetootherparaspinalmuscles(NitzandPeck1986).Shortmedialmusclesspanningonlyafewintervertebraljointscontainmuchgreatermusclespindledensitiesthanmorelaterallongermuscles(Pecketal.1984).Theseshortintersegmentalmusclesmayprovidevaluablefeedbacktotheneuralcontrollersubsystem.TheimportanceoftheneuralsubsysteminlumbarspinestabilitywasevidentinthemotorcontroldeficitsseeninmanyindividualswithLBP.PaulHodgesandcolleagues(HodgesandRichardson1996;HodgesandRichardson1997a;HodgesandRichardson1998;HodgesandRichardson1999a)haveuncoveredtransversusabdominusmotorcontroldifferencesbetweenLBPpatientsandhealthycontrols.Duringrapidupperandlowerlimbmovements,transversusabdominusonsetappeareddelayedinLBPpatientsandthisdeficitmayhavebeenacontributingfactortopaininthesepatients(HodgesandRichardson1996;HodgesandRichardson1998;HodgesandRichardson1999a).LBPpatientsalsodonotnormallydisplaythetypical?flexion-relaxationphenomenon?observedinindividualswithhealthybacks(Geisseretal.2005).ThisphenomenonischaracterizedbyanabsenceofsurfaceEMGatmaximumtrunkforwardflexionwhichisabsentinLBPpatients(Geisseretal.2005).TrunkrepositioningaccuracywasbelievedtobeabsentinLBPpatients(Brumagneetal.2000);however,arecentstudyshowedthatgivenadequatepracticetheseLBPpatientscouldaccuratelycompleterepositioningtasks,albeitbyusingadifferentmotorcontrolstrategy(Descarreauxetal.2005).DifferingmotorcontrolstrategiesinsomeLBPpatientswerealsoobservedduringisometrictrunkflexionandextensiontasks(Descarreauxetal.2004).Adoptingmaximallyflexedposturesforextendedperiodsoftimecanresultinbiomechanicalcreepofspinalviscoelasticstructures(McGillandBrown1992).Theseposturesareassociatedwith15diminishedparaspinalreflexesandthusmayalsoaffecttheneuralsubsystem?sabilitytomaintainlumbarspinalstability(RogersandGranata2006).2.2.Thelumbarmultifidus2.2.1.AnatomyThelumbarmultifidusiscomposedoffivefibregroupingsextendingfromeachlumbarvertebraecaudolaterallytocaudalvertebrae,theiliumandsacrum.Thesefivegroupingsformoverlappinglayerssuchthatmultifidusfibresoriginatingatsuperiorlumbarvertebraearesuperficial,lateralandrostraltomultifidusfibresoriginatingatinferiorvertebrae(Hanseneta!.2006;Kimetal.2005).Atlowervertebrallevels,lumbarmultifidusisthemostprominentbackmuscle(Bogduk2000b)andcontributesone-quarterofthetotaltrunkextensormomentduringmaximaltrunkextensionefforts(Bogduketa!.1992).Therearefivebilateralsetsofdeep(orlaminar)lumbarmultifidusfibresarisingfromeachofthelumbarvertebrallamina.(Bogduk2000b;Hansenetal.2006;MacDonaldetal.2006;Macintoshetal.1986).WiththeexceptionofthedeepfibresarisingfromL5,thesefibresinsertatthemamillaryprocessesandzygapophysialjointcapsulestwolevelscaudad(Bogduk2000b;Hansenetal.2006;Kimeta!.2005;Lewinetal.1962;Macintoshetal.1986).ThedeepfibresarisingfromtheL5vertebrallaminainsertatalocationsuperiortothesacralforaminabetweenSiandS2(Hanseneta!.2006).Additionally,acomprehensivelumbarmultifiduscadaverdissectionstudynoteddeeplumbarmultifidusfibresattachingadjacentlumbarvertebraeinapproximately25%ofcadaversstudied(Macintosheta!.1986).Arecentanatomicalstudyofasinglemalecadaverreporteddeepfibresoriginatingatthevertebral!aminaeandinsertingatthemamillaryprocesses,yettheauthorsdidnotspecifytheactualnumberofvertebrallevelsbetweentheseattachments(Jemmettetal.2004).Superficiallumbarmultifidusfibresoriginatebilaterallyfromeachlumbarspinousprocessandinsertattheiliumorsacrum(Bogduk2000b;Jemmettetal.2004;Macintoshetal.1986).Twosetsofsuperficiallumbarmu!tifidusfibresoriginatefromeachofthe16Li,L2andL3spinousprocesses:onesetoriginatingfromthelateralbaseofthespinousprocess(referredtoas?base?)andtheothersetfromthedorsolateraltipofthespinousprocess(referredtoas?tip?)(Bogduk2000b;Macintoshetal.i986).The?Li-tip?fibresformacommontendonwiththe?L2-base?fibresandinsertattheposteriorsuperioriliacspine(PSIS),L4/L5zygapophysialjointcapsule,andmamillaryprocessesofL5andSi(Bogduk2000b;Jemmettetal.2004).The?Li-tip?fibresmayalsoattachtotheerectorspinaeaponeurosis(Macintoshetal.1986),whilethe?Li-base?fibresinsertattheL4mamillaryprocess(Bogduk2000b;Macintoshetal.1986).InananalogousfashiontotheLi/L2commontendon,the?L2-tip?fibresand?L3-base?fibresformacommontendontoinsertatthePSIS,iliaccrestandmamillaryprocessesofL5andSi(Bogduk2000b;Jemmettetal.2004).Thetwocommontendonssharethesamecaudalattachment;however,theL2/L3commontendoninsertsmediocaudallytotheLi/L2commontendon(Macintoshetal.1986).The?L3-base?fibresinsertattheSimamillaryprocessesontheposteriorsacrum(Bogduk2000b;Macintoshetal.i986).OnesetofsuperficialfibresarisefromeachoftheL4andL5spinousprocesses?tips.TheL4andL5superficialfibresinsertatthesacrumlateralandmedialtothesacralforamina,respectively(Macintoshetal.1986).Thesacroiliacattachmentsofsuperficiallumbarmultifidusfibresfollowaconsistentdirectionalpatternwherebyfibresarisingfromsuccessivelyiowervertebrallevelsattachmedialtouppervertebrallevelfibres(Macintoshetal.1986).Thecaudolateralorientationofsuperficialmultifidusfibresendowsthesefibreswithverticalandhorizontalforcecomponents(MacintoshandBogduk1986).Thelateralobliquityofthesefibresinthefrontalplaneincreasesfrom13-15?attheLIspinousprocess,reachingamaximumatL3(20-23?)beforedecreasingtoapproximately6?atL5(MacintoshandBogduk1986).Inthesagittalplane,superficialfibresinsertingatinferiorlumbarvertebraeformanapproximaterightangle(84-89?)totheanterior-posteriorvertebralaxis(Hansenetal.2006;MacintoshandBogduk1986).Superficialfibresinsertingattheiliumandsacrumformslightlymoreobtuseangles(94-103?),however,arestillapproximatelyorthogonaltothevertebralfrontalaxis(MacintoshandBogduk1986).Theseorientationsimplythatlumbarmultifidusisideallyalignedtogeneratei7compressiveforcesfromeachlumbarvertebracaudally(McGill2007)andthatfibresattachingtotheiliumandsacrumaremoresuitedforposteriorsagittalrotation.Alllumbarmultifidusfibresarisingfromaspecificlumbarvertebraareinnervatedbythemedialbranchofthelumbardorsalramusimmediatelybelowthelumbarvertebra(Bogduk1983;Bogduk2000a).Thisinnervationmeansthatallmultifidusfibresarisingfromalumbarsegmentallevelareinnervatedbythedorsalramusofthesamesegmentalnumber(Bogduk2000a).ArecentanimalmodelreportedthatnociceptiveafferentsfromlumbarmultifidusatL5weresuppliedbyabellshapeddistributionofdifferentdorsalrootgangliacenteredatL3(Taguchieta!.2007).Theseauthorsconcludedthattheinnervationoflumbarmultifiduswasshiftedtwovertebrallevelscranial(Taguchietal.2007),however,itisimportanttonotethatmultifidusfibresfromalllumbarlevelscrosstheL5vertebralbody.Thus,acranialshiftwouldbeexpectedwhentracingafferentpathwaysfromfibresspanningtheL5vertebrallevelandthesefindingsdonotrefutethesegmentalinnervationoflumbarmultifidus.NitzandPeck(1986)reportedthattheconcentrationofmusclespindlesintherotatoresbrevisattheL4/L5levelwas4.58-6.23timesthespindleconcentrationinlumbarmultifidus(NitzandPeck1986).Anatomicalstudiesoflumbarmultifidusindicatethattherotatoresmusclesareabsentinthelumbarspine(Macintoshetal.1986)andthustheseauthorslikelymeasuredthisincreasedspindledensityinthedeeplaminarfibresoflumbarmultifidus.Additionally,theworkbyAmonoo-Kuofi(1983)hasbeencitedasevidenceofalowermusclespindleconcentrationinmultifidusrelativetoiliocostalisandlongissimus(McGill2007).Contrarytothisbelief,closeinspectionofthisreport(Amonoo-Kuofi1983)revealedthatinthelumbarspinespecifically,themusclespindleconcentrationactuallyappearedtobehigherthanthatoftheerectorspinaemusclecolumns(seefigure3intheoriginalmanuscript).LumbarmultifidusreflexesMultifidusreflexeshavebeenrecordedfollowingelectricalstimulationofthelateralintervertebraldisc(Indahletal.1995;Indahietal.1997),facetjointcapsulestimulation18(Indahietal.1995;Kangeta!.2002),supraspinousligamentstretch(Solomonowetal.1998)andduringspinalmanipulationtherapy(Herzogeta!.1999;Symonsetal.2000).Lumbarmultifidusreflexeshavealsobeenevokedbyposterior-anteriorforcestolumbarvertebrae(Collocaetal.2003)andtheskinoverlyinglumbarvertebrallandmarks(CollocaandKeller2001a;CollocaandKeller2001b).Reflexlatenciesduringtheseposterior-anteriorforceshaverangedfrom2msto18msusingbothintramuscularandsurfaceEMG(CollocaandKeller2001a;CollocaandKeller2001b;Collocaetal.2003).Theveryshortlatenciesmeasuredduringtheseindentationloadshavegenerallybeenmeasuredbetweenthetimeatpeakindentationforceandtheinitiationoflumbarmultifiduselectricalactivity.Paraspmalmusclestretchreflexlatencieshavebeenreportedtorangefrom8-16msusingtendontappulsedurationsof8-19ms(Dimitrijevicetal.1980;Tanietal.1997).Stretchreflexlatenciesadjustedforpulsedurationhavehypothesizedthata?zeropulse?tendontapwouldproduceanaveragereflexlatencyof6.5ms,whichisconsistentwiththeconductionvelocitiesandsynapticdelaysassociatedwithamonosynapticstretchreflex(Skotteetal.2005).AageIndahiandcolleagues(Indahietal.1995;Indahietal.1997)recordedlumbarmultifidusEMGduringelectricalstimulationoftheintervertebraldiscandfacetjointcapsule.ElectricalstimulationofthelateralLi/L2intervertebraldiscelicitedbilateralEMGatmultiplelevelsthatwaslargestipsilaterallyattheL4vertebrallevel(Indahietal.1995).Lidocaineinjectionintothefacetjointcapsulereducedthisactivity(Indahletal.1995)whiletheinjectionofphysiologicalsalineintothefacetjointcapsulealsoreducedEMGactivityinresponsetointervertebraldiscstimulations(Indahletal.1997).Theseauthorshypothesizedthatstretchingthejointcapsule(withsaline)mayhavecausedafferentsignalstofacilitateinhibitoryintemeuronsthatproducedmotoneuroninhibition(Indahletal.1997).Theyfurthersuggestedthatthisreflexpathwaymayberesponsibleforthe?flexionrelaxationphenomenon?commonlyobservedinhealthyindividualsusingsurface(KippersandParker1984)andintramuscularEMG(FloydandSilver1955).Indahletal.(1995)alsoobservedalocalizedEMGresponseduringelectricalstimulationoftheL1/L2facetjointcapsules(Indahletal.1995).Thisstimulationproduceda19responseconcentratedinthelumbarmultifidusfibresatL2andoccurredwithminimalcontralateralactivity(Indahietal.1995).ThislocalizedEMGresponsewasalsodiminishedafterlidocaineinjectionintothefacetjointandabolishedaftermuscledetachment(Indahietal.1995).Basedonthesefindings,Indahletal.(1995)concludedthattheobservedEMGresponseswerereflexive;however,thisconclusionhasrecentlybeenchallenged(Kangeta!.2002).Kangetal.(2002)stimulatedthemedialbranchofthelumbardorsalramusorthefacetjointcapsulewhilerecordingcompoundactionpotentialsfromlumbardorsalramiatmultiplelevels.Theseauthorsreportedthatfacetjointcapsulestimulationwasassociatedwithmultifidusexcitationthatdecreasedafterlidocaineinjectionintothefacetcapsule;yetpersistedaftercuttingthenerveinnervatingthefacetjoint(Kangetal.2002).TheyreasonedthatIndahietal.(1995)observedamultifidusreflexafterfacetjointstimulationbecausethestimulatingcurrentmayhavespreadtoadjacentspinalstructures(includingmuscles).Additionally,lidocaineinjectionintothefacetjointmayhavespreadtolumbarmultifidusresultinginadiminishedmuscleresponse(Kangetal.2002).Kangeta!.(2002)alsodocumentedintersegmentalreflexesbetweenlumbarsegments.ElectricalstimulationoftheL3,L4orL5mediallumbardorsalramusbranchevokedcompoundactionpotentialsatthemedialbranchesoflumbarsegmentsoneandtwovertebrallevelsrostralorcaudal(Kangetal.2002).Lumbarmultifidusisalsoexcitedwithelectricalstimulationofthesupraspinousligamentinhumanandfelinespines(Solomonowetal.1998;Stubbsetal.1998).StimulationofthefelinesupraspinousligamentfromL1toL6producedbilateralEMGactivitythatwaslargestinmultifidusfibresonelevelcaudaltothestimulationsite(Stubbseta!.1998).Whenthevertebralbodieswerefixatedwithmetalrods,lumbarmultifidusexcitationwaspresentduringsupraspinousligamentstimulationyetsubstantiallyreducedcomparedtotheunboundcondition(Solomonoweta!.1998).Bilateralreflexiveactivationoflumbarmultifidushasbeenhypothesizedasa?ligamento-muscularprotectivereflex?wherebysupraspinousligamentstretchfacilitateslumbarspineextensorstoreducethisstretch(Stubbseta!.1998).Inadditiontorecordingsinafelinepreparation,thisprotectivereflexhasbeendemonstratedinvivoinhumansundergoinglumbarspinesurgery(Solomonoweta!.1998).Compatiblewiththisproposedreflexpathway,supraspinous20ligamentdamagehasbeenimplicatedasapossiblereasonthatcertainLBPpatientspresentclinicallywithhyperlordoticpostures(Dankaertsetal.2006).Theamplitudeofthismultifidusreflexinducedbystretchofthefelinesupraspinousligamentcanbealteredwithprolongedligamentstretchataconstantload(Jacksonetal.2001;Solomonowetal.2003a;Solomonowetal.2003b).Reflexivelumbarmultifidusactivitydeclinesquicklyandsubsequentlyexhibitsburstsofexcitationwithprolongedsupraspinousligamentstretch(Jacksonetal.2001;Solomonowetal.2003a).Therelationshipbetweenstretchmagnitudeandreductionofinitialfelinemyoelectricactivityappearstobeanexponentialdeclinewithinitialincreasesinstretchsignificantlyreducingactivityandsubsequentstretchhavingasmallereffect(Solomonowetal.2003a).Thereflexpathwayalsodoesnotimmediatelyrecoverwithrestperiodsaslongassevenhoursnotbeingsufficienttorestoreinitialexcitationlevelsduetotwentyminutesofstaticflexion(Jacksonetal.2001;Solomonowetal.2003a).StudiesinhumanshaveshownfoursetsofseatedmaximaltrunkflexioneachfourminuteslongreducedparaspinalmusclereflexgainrecordedbysurfaceEMG(RogersandGranata2006).Reducedreflexgainwasmeasuredbypseudorandomperturbationstoachestharnesswornbysubjectsanddidnotreturntoinitialvaluesaftersixteenminutesofrecovery(RogersandGranata2006).Colloca,KellerandcolleagueshaveexaminedmultifidusreflexestovertebralindentationloadsinLBPpatientsundergoingbacksurgeryoperations(Collocaetal.2003;Collocaetal.2004).IndentationloadsappliedusingtheActivatorIIAdjustingInstrument(Kelleretal.1999)directlytovertebralprocessesandtheskinoverlyingtheseprocessesproducedpositiveEMGresponsesinlumbarmultifidus(Collocaetal.2003).Positiveresponsesweredefinedassignalswithpeak-to-peakamplitudesgreaterthan2.5timesthebaselinesignal(Collocaetal.2003;Collocaetal.2004).EMGresponseswereseeninmanytrials;however,theseresponseswereclassifiedaspositiveresponsesinonly0-37.5%ofindentationperturbationsdependingonindentationlocation(Collocaetal.2003).TheseresearchersalsorecordedcompoundactionpotentialsfromSinerveafferentsjustproximaltotheSidorsalrootganglion(Collocaetal.2003;Collocaetal.2004).Inall21butoneLBPpatient,whenbothpositiveEMGandcompoundactionpotentialresponseswerenoted,thelatencyofpositivecompoundactionpotentialswasshorterthantheEMGresponse.toinhumans,posterior-anteriorindentationforcesapplieddirectlytoexposedovineL3spinousprocessesproducedpositiveEMGresponses(Collocaeta!.2006;Collocaeta!.2007).Increasesinindentationforceataconstantduration(lOOms)orincreasesinimpulsedurationataconstantforce(80N)increasedthepeak-to-peakamplitudeofEMGresponsesintheseovinemodels(Collocaeta!.2006).CompoundactionpotentialsshoweddifferentpatternrelativetoEMGresponses.Instantaneousdischargefrequencyofspinalnerveafferentsincreasedwithdecreasingimpulsedurationandshowedaveryslightdecreasewithincreasedforce(althoughthiswasonlynotedbetweenlOOmsand200msimpulsedurations)(Collocaeta!.2007).Theinherentlimitationofinterpretingcompoundactionpotentialsfromafferentnervesenteringthespinalcordisthatthesepotentialsrepresentglobalafferentactivityfrommanysources(Collocaetal.2004).Thislimitationcloudsanyrelationshipthatmaybehypothesizedbetweenafferentactivityandlumbarmultifidusexcitation.JoelPickarandcolleagueshavedevelopedafelinemodelinwhichtheyareabletorecordandclassifyindividualnerveafferentdischargeduringposterior-anteriorspinalloadstotheL6spinousprocess(Geetal.2005;Kangeta!.2001;Pickar1999;PickarandGe2007;PickarandKang2006;PickarandWheeler2001;Pickaretal.2007;Sungeta!.2005).Thedevelopmentofthismodelmeansthatmusclespindleafferentresponsestoposterior-anteriorloadsofvaryingforce(Kangeta!.2001;PickarandKang2006;Sungetal.2005),displacement(Pickareta!.2007)andduration(PickarandKang2006;Pickareta!.2007;Sungeta!.2005)canbeinvestigated.Sungeta!.(2005)recordedchangesininstantaneousdischargefromsixafferentsarisingfromwithinmultifidusorlongissimus(allbutoneafferentwastypeIorII).Appliedloadsof33%,66%and100%felinebodyweightdidnotsystemicallyalterafferentinstantaneousdischarge(Sungetal.2005).Contrarytothisfinding,adifferenceinmeaninstantaneousdischargewasnotedbetweentheapplicationofa25%bodyweightpreloadforceanda100%bodyweightrapid22impulseforcetothefelineL6spinousprocess(PickarandWheeler2001).Thismaybeduetothedifferentdurationsofthepreloadforceandrapidimpulseforce.Theeffectofposterior-anteriorvertebraldisplacementwasalsorecentlyinvestigatedinafelinemodel(Pickaretal.2007).Musclespindleinstantaneousdischargewassignificantlyincreasedduringposterior-anteriorforcesproducingonemillimetreofanteriorvertebraltranslationcomparedtotwomillimetres(Pickaretal.2007).Theauthorsreasonedthismaybeduetothesignalrangepropertiesofmusclespindles(Pickaretal.2007).ThemajorityofworkpublishedbyJoelPickarandcolleagueshasfocusedonchangesinafferentinstantaneousfrequencyduringspinalmanipulative-likeposterior-anteriorimpulsesofvaryingdurations(PickarandKang2006;Pickaretal.2007;Sungetal.2005).Thesespinalmanipulative-likeimpulseshavebeenmodeledashalf-sinewavesandhavebeenappliedtotheseauthors?felinepreparation.Asimpulsedurationdecreasedfrom800msto200ms,meanafferentinstantaneousdischargeremainedfairlyconstantalthoughmayhaveexhibitedslightincreaseswithshorterimpulses(PickarandKang2006;Pickaretal.2007;Sungetal.2005).Betweenimpulsedurationsofl00-200ms,aninflectionpointwasfoundwherebyfurtherimpulsedurationdecreasesresultedinexponentialincreasesinafferentdischarge(PickarandKang2006;Pickaretal.2007;Sungetal.2005).Thisinflectionpointhasbeennotedforbothprimaryandsecondaryafferentfibres(Pickaretal.2007).Theexistenceofthisinflectionpointmayhaveclinicalrelevanceforhigh-velocity,low-amplitude(HVLA)chiropracticthrusts;however,mayalsoplayaroleinlumbarmultifidusreflexes.2.2.3.LumbarmultifidusactivityduringvoluntarytrunkmovementsAstabilityrolehasbeenattributedtotheentirelumbarmultifidusduringmanytrunkmovements(Ebenbichleretal.2001).Biomechanically,themechanicallineofactionoflumbarmultifidusforcesuggeststhatthismuscle?sprimaryroleisinposteriorrotationoflumbarvertebraeinthesagittalplane(MacintoshandBogduk1986)Manyresearchershaverecordedmultifidusexcitationduringanumberofgrosstrunkmovementsusingbothintramuscular(Anderssonetal.2002;DonischandBasmajian1972;Jonsson1970;23McCooketal.2007;Morriseta!.1962;Pauly1966;ValenciaandMunro1985)andsurfaceEMG(Arokoskietal.2001;Danneelsetal.2002;McCooketa!.2007;Ngetal.2001;Ngetal.2002;Ngetal.2003;O?Sullivaneta!.2002).Multifidusexcitationmeasuredusingsurfaceelectrodeshasrecentlybeenshowntobemorecloselyrelatedtolongissimusexcitationthanmultifidusexcitationrecordedusingintramuscularelectrodes(Stokesetal.2003).Theseauthorsconcludedthatsurfaceelectrodesdonotaccuratelyrecordfromlumbarmultifidus(Stokeseta!.2003)andthusinterpretationofsurfaceEMGrecordingsmustbemadewithcaution.IntramuscularEMGrecordingsoflumbarmultifidusduringuprightstandinghaveproducedinconsistentresults.IntramuscularEMGrecordedfromthelumbarspinejustadjacenttothemidlinehasfoundnoactivity(Anderssonetal.1996;Morrisetal.1962),intermittentactivity(ValenciaandMunro1985)orslightactivity(DonischandBasmajian1972;Jonsson1970)duringquietstance.Thediscrepancyinresultsisnotnecessarilysurprisingbecausenaturalswayduringquietstancemayproducedifferentreactiveforcesonthetrunktomaintainbalance.Morrisetal.(1962)reportedthat?apositionofrestforiliocostalisdorsiandlumborumandthemultifiduswaseasilyfound,althoughthesemusclesbecameactiveasthesubjectswayedslightlyforward?(Morrisetal.1962,p. 512).Increasedmultifidusexcitationwithforwardswayappearstofitwiththehypothesizedbiomechanicalfunctionoflumbarmultifidusasalumbarextensor(orposteriorlumbarvertebraesagittalrotator)(MacintoshandBogduk1986).Paraspinalmuscleactivityduringforwardtrunkswayactstoresistthegravitationalforceactingonthetrunktosustainuprightstanding(Gupta2001;KippersandParker1984).Multifidusexcitationhasalsobeenrecordedintramuscularlyduringcontrolledtrunkflexionfromuprightstanding(Anderssoneta!.1996;DonischandBasmajian1972;FloydandSilver1955;Morriseta!.1962;PaulyandSteele1966;ValenciaandMunro1985)toresisttrunkgravitationalforce.Inkeepingwithlumbarmultifidus?roleasalumbarextensor,intramuscularactivityhasbeenrecordedduringuprighttrunkextension(DonischandBasmajian1972;Morriseta!.1962),sittingtrunkextension(Jonsson1970;McCooketa!.2007)andpronehyperextension(ValenciaandMunro1985).Bilateral24lumbarmultifidusexcitationhasalsobeenrecordedduringpronebilaterallegextension(Jonsson1970;ValenciaandMunro1985).Anatomytextbooksoftendescribemultifidusashavingoneormorefunctionsconsistingoftrunkextension,lateralflexionandrotation(Drake2005;Martini2006;Seeley2003;Tortora2003).Thereisstrongevidencethatlumbarmultifidusproduceslumbarextension,however,itsroleinlateralflexionislessclear.Jonssonetal.(1970)onlynoticedaslightincreaseinlumbarmultifidusactivityduringuprightstandingwhileholdingaweightononesideofthebody.Macintoshetal.(1986)furtherconcludedthatthehorizontalvectorcomponentoflumbarmultifiduswastooshorttocontributesignificantlytolateralflexion.Lumbarmultifidusexcitationduringaxialrotationhasbeenextensivelystudyinsittingandstandingpostures(Anderssonetal.2002;DonischandBasmajian1972;Jonsson1970;Morrisetal.1962;Ngetal.2001;Ngetal.2002;Ngetal.2003;ValenciaandMunro1985).UnrestrainedaxialrotationduringsittingproducedgreaterlumbarmultifidusintramuscularEMGactivityonthesidecontralateraltothedirectionofrotation(ValenciaandMunro1985).Whenthesamesubjectsadoptedanuprightstandingposture,thisdirectionalpatternofactivityremained;however,multifidusexcitationlevelsweregreater(ValenciaandMunro1985).Donischetal(1972)reportedthat14of25subjectshadincreasedcontralateralintramuscularEMGduringaxialrotation,however,7of25didnotdisplayadirectionalbiasand3of25hadincreasedipsilateralactivity(DonischandBasmajian1972).Morrisetal.(1962)predominantlyfoundcontralateralintramuscularEMGactivitywithrotation,butdidnotethatoccasionallyipsilateralactivitywasfoundinsomesubjects(Morrisetal.1962).Ngandcolleagues(Ngetal.2001;Ngetal.2002;Ngetal.2003)recordedlumbarmultifidussurfaceEMGduringstandingisometricaxialrotationanddidnotfindexcitationdifferencesbetweenipsilateralandcontralateralsides,butdidreportincreasedexcitationwithincreasedaxialtorque(Ngeta!.2001;Ngeta!.2002;Ngetal.2003).Asdiscussedpreviously,surfacerecordingsofmultifidusmaybesusceptibletocrosstalkfromtheadjacentlumbarerectorspinaemuscles.25Anderssoneta!.(2002)attemptedtoresolvetheseliteraturecontradictionsbycomparingtrunkmuscleexcitationduringeasyunresisted,maximalunresistedandmaximalresistedaxialrotationwhilestandingandsitting(Anderssonetal.2002).IntramuscularEMGoflumbarmultifidusduringunresistedsittingandstandingrotationwasgreatestonthecontralateralsideandincreasedwithrotationintensity(Anderssoneta!.2002).Duringresistedrotations,thispatternswitchedwithgreateractivityrecordedonthesideipsilateraltorotationdirection(Anderssonetal.2002).Multifidusexcitationwasalsogreaterduringstandingrotationcomparedtosittingrotationforbothunresistedandresistedconditions(Anderssonetal.2002).Theabdominalobliquemusclesappeartobethemajortrunkrotators(Anderssonetal.2002);however,contractionofthesemusclesproducesatrunkflexormoment(Hansenetal.2006).Severalauthorshavesuggestedthattheroleoflumbarmultifidusduringrotationistocounteracttheflexormomentgeneratedbytheobliquemuscles(Hanseneta!.2006;MacintoshandBogduk1986;Ngetal.2002).Thus,changesinbilaterallumbarmultifidusexcitationandmaybeinresponsetochangesinthedirectionoftheforcegeneratedbytheobliquemusclesatdifferenttrunkrotationalpositions.2.3.TheroleoflumbarmultifidusinlumbarspinestabilityComparisonsbetweenhealthycontrolsubjectsandthosewithLBPrevealdifferencesintrunkmusclemorphologyandmotorcontrol.HistologicalstudiesandstudiesofmuscleCSAhavenotedlumbarmultifidusdifferencesinindividualswithLBP(Hideseta!.1994;Rantaneneta!.1993).Additionally,alteredmotorcontrolpatternswerenotedinthetransversusabdominusmuscleofLBPpatientsduringtasksrequiringspinalstability(HodgesandRichardson1996;HodgesandRichardson1998;HodgesandRichardson1999a).TheobserveddifferencesinLBPandhypothesizedfunctionoftransversusabdominusandlumbarmultifidusleadagroupofresearchersfromtheUniversityofQueenslandtodevelopthe?drawingin?techniquetostabilizethelumbarspine(RichardsonandJull1995;Richardsonetal.1999;Richardsoneta!.2004).Thedevelopmentofthisstabilizationtechniqueandchallengestoitsstabilizingpotentialwillbediscussedinthefollowingsection.The?drawingin?techniquerequiresdifferential26functionofthesuperficialanddeepfibresoflumbarmultifidus(MacDonaldeta!.2006).Evidencesupportingandrefutingthecapabilityofmultifidustofunctiondifferentiallyisdiscussedinsection2.3.2.2.3.1.?Drawingin?andthe?abdominalbrace?MuscleCSAhasbeenassociatedwithmuscularstrength(Tortora2000)andevaluationofCSAmaybeaclinicallyusefultoolindiagnosis.JulieHidesandcolleagueshaveevaluatedlumbarmultifidusCSAusingultrasoundimaginginnumerousstudies(Hidesetal.1994;Hidesetal.1995;Hideseta!.1996;Hidesetal.2001;Hidesetal.2006;Hidesetal.2007).OneoftheirmajorfindingsusingthistechnologywasthatlumbarmultifidusCSAwasasymmetricinunilateralacuteLBPpatients(Hidesetal.1994).ThisasymmetryinvolvedadecreasedCSAonthepainfulsideandin24of26subjectswasfoundtooccuradjacenttothevertebrallevelclinicallydiagnosedasresponsibleforLBPsymptoms(Hideseta!.1994).BilateralchronicLBPpatientswerefoundtohavedecreasedmultifidusCSAatL4andL5comparedtohealthycontrolsusingCTandultrasoundscanning(Hidesetal.2006;Kamazetal.2007).UnilateralchronicLBPpatientspresentedwithmultifidusasymmetryattheclinicallypainfullevelandthusdemonstratedthesamepatternasunilateralacuteLBPpatients(Hidesetal.2006).Multifidusasymmetrieswerealsofoundin79%ofunilaterallumbosacralradiculopathypatients;however,nodifferencesintheratioofpuremuscletototalmuscleareawasfoundbetweenpatientsandhealthycontrols(Hyunetal.2007).PuremusclewascalculatedasthetotalmuscleareawiththeCSAoffattydepositssubtracted(Hyunetal.2007).biopsiesoflumbarmultifidushavereportedmusclefibretypeconversions(Demoulinetal.2007),typeIandtypeIIfibreatrophy(Yoshiharaetal.2003),selectivetypeIIatrophy(Rantaneneta!.1993)ornodifferences(Demoulineta!.2007)betweenLBPpatientsandhealthycontrols.IncreasesinthepercentageoftypeImusclefibres(Yoshiharaeta!.2003)anda?moth-eaten?appearanceoftypeIfibreshasalsobeenobservedinLBPpatientswithintervertebraldischerniation(Rantanenetal.1993).27Rantaneneta!.(1993)comparedmusclebiopsysamplesfromLBPpatientsduringlaminotomysurgeryandfiveyearspost-surgery.TheseresearchersfoundthatLBPpatientswhorespondedpositivelytosurgeryhadtypeIandtypeIIhypertrophyandareductioninthe?moth-eaten?appearanceoftypeIfibres(Rantaneneta!.1993).Thisstudywasanimportantstepinestablishingacausalrelationshipbetweenmultifidushistologicalchangesandlowbackinjury.LumbarmultifidusCSAmeasuredusingultrasoundsignificantlydecreasedwithonlyfourteendaysofbed-rest,despitenosignificantdecreaseinerectorspinaeCSAafterfifty-sixdaysofbed-rest(Hidesetal.2007).Thismayindicateanincreasedsusceptibilityoflumbarmultifidustorapidatrophywithdisuse(Hidesetal.2007).Hodgesetal.(2006)introducedspecificlesionsinaporcinemodeltoevaluatethetimecourseoflumbarmultifiduschangeswithlowbackinjury.AsegmentalandunilateralreductioninlumbarmultifidusCSAwasdetectedwithinsixdaysofunilateralintervertebraldisclesionandoccurredipsilateraltothelesionatthesamesegmentallevel(Hodgeseta!.2006).Theauthorsarguedthatthecausalrelationshipbetweendiscinjuryandlocalizedsegmentalatrophymaybeduetospecificatrophyofthedeepfibresoflumbarmultifidus(Hodgesetal.2006).Superficialmultifidusfibresspanmultiplevertebrallevelsandatrophyofthesefibreswouldhavelikelyresultedinamoregeneralizedpatternofmultifidusatrophy(Hodgeseta!.2006).Deepmultifidusfibreshaveshortmomentarms(McGill1991)whichprimarilyproducelumbarspinecompression(Bogduketa!.1992).Hodgeseta!.(2006)hypothesizedthatdecreasedneuraldrivetothedeepmultifidusfibresmayreducelumbarspinecompressionandcauseselectivesegmentallumbarmultifidusatrophy.ThemotorcontroloftransversusabdominusinhumansubjectsperformingrapidlimbmovementsappearstobedifferentinhealthybackindividualsandthosewithLBP(HodgesandRichardson1996;HodgesandRichardson1997a;HodgesandRichardson1998;HodgesandRichardson1999a).Duringrapidandintermediatevelocityshoulderflexion,abductionandextension,theonsetoftransversusabdominusEMGactivityprecededthatofothertrunkmusclesinhealthycontrolsbutwasdelayedinLBPpatients(HodgesandRichardson1996;HodgesandRichardson1999a).TransversusabdorninusexcitationlatencywithrespecttodeltoidEMGonset(primemover)wasnotsignificantly28differentbetweenmovementdirectionsinhealthycontrols(HodgesandRichardson1996;HodgesandRichardson1997b).LBPpatientsdidhoweverexhibitdifferingtransversusabdominusonsetlatencieswithshoulderflexion,abductionandextensionmovements(HodgesandRichardson1996).Transversusabdominuswasthefirsttrunkmuscleexcitedduringhipflexion,abductionandextensioninhealthycontrolsanddisplayedthesamenon-directionspecificityaswitharmmovements;however,thisdidnotoccurinLBPpatients(HodgesandRichardsonl997a;HodgesandRichardson1998).DelayedonsetoftransversusabdominusanddirectionalonsetlatencydifferenceshavebeenfoundduringtheserapidlowerlimbmovementsinindividualswithLBP(HodgesandRichardson1997a;HodgesandRichardson1998).BasedontheirobserveddeficitsanddifferencesincomparisontopeoplewithoutLBP,thisgroupofresearchershascontendedthattransversusabdominusandlumbarmultifidushavespecializedrolesinlumbarspinestability(RichardsonandJull1995;Richardsonetal.1999;Richardsonetal.2004).Inadditiontoitsearlyonsetandnon-directionspecificity,transversusabdominusmaydirectlyorindirectlyproduceanextensormomentbyincreasingintra-abdominalpressure(Bartelink1957;DaggfeldtandThorstensson2003).Cresswellandcolleagues(Cresswelletal.1992;Cresswelletal.1994)recordedintramusculartransversusabdominusexcitationandintra-abdominalpressurewithanintra-gastricpressuretransducerduringdifferenttrunkmovements(Cresswelletal.1992).Transversusabdominuswasexcitedduringbothisometrictrunkflexionandextensionwithlessthana15%differenceinexcitationlevelbetweendirections.Transversusabdominuswasalsomostcloselyrelatedtochangesinintraabdominalpressurerelativetootherabdominalmuscles(Cresswelleta!.1992).Theseresearchersalsoexaminedself-initiatedandunexpectedventralloadingofthetrunkwhichconsistedofaweightdroppingontothefrontofaharnesswornbysubjects(Cresswelletal.1994).Earlytransversusabdominusonsetwithself-initiatedloadingwasexpectedasafeed-forwardresponse;however,transversusabdominuswasalsoparadoxicallyactivefirstwithunexpectedloading(Cresswelletal.1994).Unexpectedloadingofthetrunkwasanticipatedtoresultinearlyonsetofthedorsalmusclestocounteractthetrunkflexormomentintroducedbytheload(Cresswelletal.1994).29Transversusabdominusmaypressurizetheabdominalcavitytogenerateatrunkextensormomentormayprovidearigidcylinderbywhichdiaphragmorpelvicfloormusclecontractionincreasesintra-abdominalpressureandproducesanextensormoment(Hodgesetal.2001).Hodgesetal.(2001,2003)simulatedtransversusabdominustensionusingabdominalbeltsduringunilateralorbilateralphrenicnervestimulationtomeasuretrunkextensormoment(Hodgesetal.2001)andposterior-anteriortrunkstiffness(Hodgesetal.2005).Diaphragmevokedcontractionbyphrenicnervestimulationproducedanincreaseinintra-abdominalpressureandaside-lyingtrunkextensormomentintheabsenceofparaspinalmuscleactivity(Hodgesetal.2001).Phrenicnervestimulationalsoincreasedposterior-anteriorspinestiffnessby8-31%duringindentationperturbationsatL2andL4(Hodgesetal.2005).Anatomicalcadaverstudiesofthehumantrunkhavedeterminedthattransversusabdominusformsanattachmentwiththethoracolumbarfasciaviathelateralraphejustsuperiortotheilium(BogdukandMacintosh1984).Asdiscussedinsection2.1.1,lateraltensioninthethoracolumbarfasciaviatransversusabdominuscontractionmayalsoincreasetrunkstiffnessandgenerateatrunkextensormoment(Barkeretal.2006).Theevidencesupportingthespecializedroleoflumbarmultifidusinspinalstabilityislessclear.Thedeepfibresoflumbarmultifidusarehypothesizedtofunctionasspinalstabilizerswhilethesuperficialfibresactasprimemoversofthetrunk(Richardsonetal.1999;Richardsonetal.2004).Thishypothesishasbeenpartlybasedonanatomicalandbiomechanicalobservations(Bogduketal.1992;McGill1991;RichardsonandJull1995)andinvivorecordingsofthedeepandsuperficialfibresduringrapidlimbmovementsandtrunkperturbations(Moseleyetal.2002;Moseleyetal.2003).Thesmallsizeofdeepmultifidusfibressuggeststheydonotproduceenoughforcetosignificantlycontributetotrunkmovements(McGill2002).Moreover,theproximityofthesedeepfibrestothelongitudinalaxisofthetrunkandtheirbiomechanicallineofactionsuggeststheyproduceprimarilycompressivespinalforces(Bogduketal.1992).Theproximityofthesedeepfibrestothevertebralcolumnlikelymeansthattheyundergosmalllengthchangeswithtrunkmovements(McGill1991)andthusmaybeatanoptimalcontractile30lengthregardlessoftrunkposition.Invitrostudieshavesuggestedthatmultifidusincreasesspinestabilitythroughincreasedstiffness(Quintetal.1998;Wilkeetal.1995),reducedirregularvertebralmotion(Kaigleetal.1995)andthatthedeepfibresinparticularcontrolintersegmentalvertebralmotion(Panjabietal.1989).LorimerMoseleyandcolleagues(Moseleyetal.2002;Moseleyetal.2003)werethefirsttoshowinvivodifferencesindeepandsuperficiallumbarmultifidusfibresduringfunctionaltasks.DeeplumbarmultifidusfibreEMGonsetwasfoundtobeconsistentbetweenrapidshoulderflexionandextensionmovementswhilesuperficialfibreonsetvariedwithmovementdirection,occurringearlierinshoulderflexion(Moseleyetal.2002).ConsistentEMGonsetlatenciesinthedeepfibresdespitedifferentmovementdirectionsparalleledtransversusabdominusEMGonsetsduringarmmovementsandsuggestedastabilityrole(Moseleyetal.2002).RepetitiveandrapidalternatingshoulderflexionandextensionproducedtwodeepfibreEMGpeaksjustpriortoshoulderflexionandextension(Moseleyetal.2002).SuperficialmultifidusfibreEMGtracesprimarilydisplayedasinglepeakpriortoshoulderflexion(Moseleyetal.2002).Asubsequentstudyexaminedthedifferentialfunctioningofthesefibresduringpredictableandunpredictabletrunkperturbations(Moseleyetal.2003).Standingsubjectswereblindfoldedandworeheadphoneswhileholdingabucketinfrontoftheirbodieswithelbowsflexedtoninetydegrees(Moseleyetal.2003).Aweightdroppedintothebucketwhensubjectspressedatriggerbuttononthebucket(predictablecondition)oratarandomtime(unpredictablecondition)(Moseleyetal.2003).Insixofsevensubjects,theonsetofdeepmultifidusfibreexcitationwasearlierinthepredictableconditionrelativetotheunpredictablecondition;however,thisdifferencewasnotstatisticallysignificant(Moseleyetal.2003).Intheunpredictableconditionalllumbarmultifidusfibreswereexcitedconcurrently,yetinthepredictableconditionthedeeplumbarmultifidusfibreswereexcitedpriortothesuperficialfibres(Moseleyetal.2003).WhenthedeepfibreEMGamplitudeinthepredictableandunpredictableconditionswascomparedinthehalfsecondintervalpriortotheweighthittingthebucket,amplitudedifferenceswerenotedasearlyas400mspriortotheperturbation(Moseleyetal.2003).TheamplitudeofdeepfibreEMGactivityinthepredictableconditionwasgreaterthantheamplitudeinthe31unpredictablecondition(Moseleyetal.2003).Thesestudiesconcludedthatthedeepandsuperficialmultifidusfibresweredifferentiallyactiveduringthesetasksandthedeepfibreswereresponsibleforlumbarspinalstability(Moseleyetal.2002;Moseleyetal.2003).hypothesizedspecializedroleoftransversusabdominusandlumbarmultifidusformedthefoundationoftheabdominal?drawingin?technique(JullandRichardson2000;RichardsonandJull1995;Richardsonetal.1999;Richardsonetal.2004).TheQueenslandUniversitygrouphaveadvocatedteachingthistechniquetoretrainandcorrect?motorcontroldeficits?(JullandRichardson2000)inLBPpatients(Richardsonetal.1999;Richardsonetal.2004).Thistechniquehasbeendescribedasa?segmentalstabilizationexercise?andinvolvesgentlydrawingthelowerabdominalsdorsallythroughco-contractionofthetransversusabdominusanddeepfibresoflumbarmultifidus(MacDonaldetal.2006;Richardsonetal.1999;Richardsonetal.2004).BiofeedbacktechniquesinvolvingultrasoundandEMGhavebeenemployedtotraincontractionofthesemusclesandtolimitactivityinmoresuperficialabdominalandparaspinalmuscles(Richardsonetal.1999;Richardsoneta!.2004).RichardsonandJull(1995)havealsoadvisedclinicianstobeganteachingthistechniqueinsimpleposturessuchasfour-pointkneelingandpronelyingbeforeprogressingtoperformingfunctionaltaskswhile?drawingin.?Thistechniquehasbeenpurportedtoensurelumbarspinestabilitythroughincreasedcontrolofintersegmentalvertebralmotion(Richardsoneta!.1999;Richardsoneta!.2004).Recentclinicaltrialshaveexaminedtheefficacyofthis?segmentalstabilizationexercise?inindividualswithacuteLBP(Hidesetal.1994;Hidesetal.1996;Hidesetal.2001;O?Sullivanetal.1997).Hidesetal.(1994)observedasymmetricCSAoflumbarmultifidusattheclinicallypainfullevelinacuteunilateralLBPsubjects.TheseLBPsubjectswererandomlydividedintotwotenweekLBPinterventiongroups:a?medicalmanagement?groupandan?exercisetherapy?group(Hideseta!.1996).The?medicalmanagement?groupreceivedstandardmedicalcare,prescriptiondrugsandmedicaladvicewhereasthe?exercisetherapy?groupwasprescribedspecificsegmentalexercises32totrainthesesubjectsinthe?drawingin?technique(Hidesetal.1996;Hideseta!.2001).Bothinterventiongroupshaddecreasedpainanddisability;however,multifidusCSAasymmetriespersistedinthe?medicalmanagement?groupattenweekspostinjury(Hidesetal.1996).?Exercisetherapy?reducedmultifidusasymmetryfrom26%to0.2%attenweekfollow-up,whereas?medicalmanagement?reducedasymmetryfrom22%to14%(Hidesetal.1996).Moreover,subjectsinthe?exercisetherapy?grouphadareducedLBPrecurrencerateasdeterminedbyphonequestionnairesatoneyearandthreeyearsaftertheinitialinjury(Hidesetal.2001).O?Sullivanetal.(1997)randomlyassignedchronicLBPsubjectswithspondylolysisandspondylolisthesisintotwodifferentexercisesgroupsconsistingoftenweeklonginterventionprogramswhileassessingpain,disability,lumbarspineandhipROM(O?Sullivaneta!.1997).Oneexercisegroupconsistedofweeklyphysiotherapysessionstolearnthe?drawingin?techniqueinpreviouslypainfulpostureswhiletheothergroupreceivedgeneralaerobicandabdominalexercises(O?Sullivaneta!.1997).Followingthetenweekinterventionsthegrouplearningthe?drawingin?techniquereportedsignificantlyreducedpainanddisabilityscoresthatwerestillpresentthirtymonthsaftertheinitiationoftheintervention(O?Sullivanetal.1997).Thegeneralaerobicandabdominalexercisegroupdidnotreportanysignificantdecreasesinpainordisabilityattenweek,threemonth,sixmonthandthirtymonthfollow-ups(O?Sullivaneta!.1997).StuartMcGillhasopposedthepracticeoftrainingLBPsubjectstolearnthe?drawingin?techniqueasamethodofstabilizingthelumbarspine(McGill2002;McGill2007).McGillhasacknowledgedthatmotordeficits,particularlyintransversusabdominus,maybepresentinLBPsubjectswarrantingmotorre-educationprograms;however,hehasarguedthatthe?drawingin?techniquedoesnotstabilizethespine(GrenierandMcGill2007;McGill2002;McGill2007).McGillandcolleagues(CholewickiandMcGill1996;CholewickiandVanVliet2002;Cholewickietal.1997)havemodeledthelumbarspine(CholewickiandMcGill1996)anddeterminedthestabilityindexduringanumberofmovementtasks(Kavciceta!.2004a;Kavcicetal.2004b).Analysisofindividualmusclecontributionstothismodelhasshownthatnoonemuscleisresponsibleformorethan30%oftrunkstability(CholewickiandVanVliet2002).McGillcontendsthatspinal33stabilityisa?movingtarget?andthatacombinationofmanymusclesworktogethertoensurestabilityindifferenttasks(McGilletal.2003).Thisviewopposesthehypothesisthatlumbarmultifidusandtransversusabdominushavespecializedstabilityroles.Usingtheanalogyofthevertebralcolumnasanantennawithmusclesactingas?guywires,?McGillarguesthattensioningaspecificmusclewilloniyimprovespinalstabilityifthatparticular?guywire?isslack(McGilletal.2003).Basedontheirresearchintolumbarspinestabilityandstabilityindices,McGillandcolleagueshavedevelopedthe?abdominalbrace?tostabilizethelumbarspine(GrenierandMcGill2007;McGill2002;McGill2007).The?abdominalbrace?consistsofcocontractionofthetransversusabdominus,internalobliqueandexternalobliqueatanintensitybetween5-10%MVC(McGill2002;McGill2007).Thistechniqueismosteffectivelytaughtthroughself-palpationoftheanterolateralabdominalwallafteritisfirstdemonstratedtosubjects(McGill2002).Theuseofanabdominalco-contractiontechniquewithconsequentparaspinalmusclecontractionarisesfromtheprinciplethatincreasedjointstiffnessincreasesjointstability(McGilletal.2003).ComparativestudiesusingthemodeldevelopedbyCholewickietal.(1996)haveshownthatthestabilityindexofanelectromyographicallyrecorded?abdominalbrace?isfarsuperiortothe?drawingin?technique(GrenierandMcGill2007).Theseauthorsalsomodeledbothaperfect?drawingin?techniqueusingindependentcontractionofthetransversusabdominusandaperfect?abdominalbrace?(GrenierandMcGill2007).Theirfindingsindicatedthattransversusabdominusonlycontributed0.14%tothe32%increaseinstabilityindexassociatedwiththesimulated?abdominalbrace?(GrenierandMcGill2007).Asecondstudyalsodemonstratedthatduringrapidtrunkperturbationsthe?abdominalbrace?resultedinincreasedspinalstability;however,itwasalsoassociatedwithhigherspinalcompressiveforcesrelativetothe?drawingin?technique(Vera-Garciaetal.2007).TheQueenslandgrouphasalsocomparedthe?drawingin?techniqueand?abdominalbrace?toassesswhichtechniquebetterstabilizesthelumbarspine(Richardsonetal.2002).Richardsonetal.(2002)vibratedtheanteriorsuperioriliacspineofpronesubjects34at200Hzwhiletheyperformedeitherthe?abdominalbrace?or?drawingin?ofthelowerabdominalwall(Richardsonetal.2002).SacroiliacjointlaxitywasassessedbymeasuringthecouplingbetweentheiliumandsacrumusingDopplerultrasound(Richardsonetal.2002).Theseauthorsfoundthatbothstabilizationmethodsdecreasedjointlaxity(andhenceincreasedjointstiffhess),however;?drawingin?resultedinsignificantlylesssacroiliacjointlaxity(Richardsonetal.2002).2.3.2DifferentialfunctioningoflumbarmultifidusTherapidarmmovementandexternaltrunkperturbationstudiesperformedbyLorimerMoseleyandcolleagues(Moseleyetal.2002;Moseleyetal.2003)proposedthatthedeepandsuperficiallumbarmultifidusfibresfunctiondifferentially.Duringrapidarmmovements,deepfibreEMGonsetwasconsistentbetweenmovementdirections;however,thisonsetwasmeasuredrelativetotheonsetofsurfaceEMGelectrodesatdifferentpositionsoverthedeltoid(Moseleyetal.2002).Predictableexternaltrunkperturbationsresultedintheonsetofdeepfibreexcitationoccurringearlierthanduringunpredictedperturbations,however,thisdifferencewasonlyatrendanddidnotreachstatisticalsignificance(Moseleyetal.2003).TheratiobetweendeepfibreEMGamplitudeduringpredictedperturbationsandamplitudeduringunpredictedperturbationswassignificantlygreaterthanonepriortotheperturbation(Moseleyetal.2003).Inotherwords,priortopredictedperturbationstheamplitudeofdeepfibreexcitationamplitudewassignificantlygreaterthanexcitationamplitudeduringunpredictedperturbations.Itshouldbenotedthatunpredictedtrialsinwhichdeepfibreexcitationoccurredpriortotheperturbationwereexcludedfromanalysisandthusanysignificantdeepfibreexcitationduringsomeorallpredictedtrialsmayhaveproducedthisresult(Moseleyetal.2003).Moseleyetal.(2003)acknowledgethepossibilityofarecruitmentordereffectwherebydeepmultifidusfibresareexcitedfirstandasneuraldriveincreasessuperficialmultifidusfibresaresubsequentlyrecruited(Moseleyetal.2003).Theyconcludethispossibilityisunlikelybecauseifdeepfibrescontainedalargerrelativepercentageofslowtwitchfibrestheirburstdurationwouldbelongerthansuperficialmultifidusfibresandtheirdatadonotsupportthis(Moseleyetal.2003).35DifferentialdeepandsuperficiallumbarmultifidusEMGactivityhasbeeninvestigatedduringgaitusingdifferentlocomotormodes(walk,run)andatdifferentvelocities(1,2,3,4,5mIs)(Saundersetal.2004;Saundersetal.2005).Transversusabdominusexcitationisrelativelytonicthroughoutthegaitcycle,yetsuperficialanddeeplumbarmultifidusfibresarephasicallyexcited(Saundersetal.2004;Saundersetal.2005).Bothsuperficialanddeeplumbarmultifidusfibresweremodulatedbythefrequencyofmotion(Saundersetal.2004)andtheredidnotappeartobeaconsistentrelationshipbetweendeepandsuperficialfibreexcitationonsets(SeeFigure4inSaundersetal.2004).Thetotalpercentageofmuscleexcitationthroughthegaitcycleincreasedcomparablyinerectorspinae,deepandsuperficiallumbarmultifidusfibres(Saundersetal.2004).Theseinvestigationsconcludedthatduringgaittherewaslittleevidencetosupportdifferentialactivityofthesuperficialanddeeplumbarmultifidusfibres(Saundersetal.2004;Saundersetal.2005).Inarecentreview,proponentsofthe?drawingin?techniquealsoconcedethereisnoevidencetosupportdeeplumbarmultifidusfibreco-contractionwithtransversusabdominusduring?drawingin,?butthereisalsonoevidencetorefutethispossibility(MacDonaldetal.2006).Duringtrainingofthe?drawingin?technique,surfaceEMGhasprimarilybeenusedtoensuresuperficialmusclesarenotelectricallyactivewhiledeepfibremuscleexcitationhasbeenassumedorimagedwithultrasoundtoviewarchitecturalmusclechanges(Richardsonetal.1999).Thesearchitecturalchangesmayreflectactiveorpassivemusclepropertiesduetoactivecontractionormorphologicalchangesofsurroundingstructures.Thehypothesisthatdeepmusclefibresstabilizethespinewhilemoresuperficialmusclesactasprimemovershasalsobeenattributedtothecervicalandthoracicspines(Bexandereta!.2005;Leeeta!.2005).Inaninvestigationofdifferenteyepositionsduringheadrotation,multifidusandobliquuscapitisEMGactivitylevelswereindependentofdirection,suggestingastabilizingrole.Contrarytothisfinding,Blouinetal.(2007)observeddirectionspecificexcitationinmultifidusduringisometricsweepcontractions.Furthermore,coherenceanalysisrevealedacommonfrequencyofneuraldrivetomultifidusandotherneckmuscles,indicatingthatitwasunlikelythatseparateneural36signalsweresenttodeepandsuperficialmusclesfunctioningtostabilizeandmovethetrunk,respectively(Blouinetal.2007).Differentialfunctioningofthoraciclongissimusandmultifidushasalsobeensuggestedtooccurtomovethetrunkandstabilizethespine,respectively(Leeetal.2005).Inmostsubjects,thoracicmultifiduswasreportedtobedirectionallynon-specific(especiallyatT5)duringslowseatedaxialrotationsuchthatleftorrightrotationresultedinsimilarincreasesinmuscleexcitation(Leeetal.2005).Theseauthorsacknowledgedthattherewasconsiderablevariabilityinthemultifidusresponse(SeeFigure4inLeeetal.2005),yetsuggestthatthoracicmultifidusmayhavefunctionedasastabilizertocontrolintersegmentalmotion(Leeetal.2005).AsecondstudyinvestigatingfasteraxialrotationtasksdidnotsupporttheiroriginalstudyasthoracicmultifidusEMGwassignificantlygreaterduringcontralateralrotation(Leeetal.2007).Inthissecondstudytheauthorsreconcilethisapparentcontradictionbystatingthat?closeinspectionofthosedata[theoriginalstudy]suggestatrendformarginallygreateractivitywithcontralateralrotation?(Leeetal.2007,p.7).373.StatementoftheproblemTheabdominal?drawingin?techniquehasbeenproposedtodifferentialexcitethedeepfibresoflumbarmultifidus,whilethesuperficialfibresarenotelectricallyexcited.Thesedeepfibreshavebeenimplicatedasfunctionalstabilizersduringlumbarspinestabilitytasks.Thereispreliminaryevidencetosupportthisclaim;however,thedifferentialresponseofthesefibrestovaryingperturbationmagnitudeshasnotbeenquantified.Evidenceagainsttheproposeddifferentialactivityinthecervicalandthoracicspineshasfurtherconfoundedtheseproposals.Additionally,differentiallumbarmultifidusactivityhasprimarilybeeninvestigatedatL4anditisunknownifotherlumbarvertebrallevelsproducesimilarresults.Toaddresstheseissues,weintendtointroduceposterior-anteriorindentationperturbationsofvaryingamplitudeandvelocitytoindividualvertebraeandrecordtheresponsesofsuperficialanddeeplumbarmultifidusfibresatmultiplelumbarvertebrallevels.384.HypothesesPosterior-anteriorindentationperturbationstothespinousprocessesoflumbarvertebraearehypothesizedtocausedifferentialEMGresponsesinsuperficialanddeeplumbarmultifidusfibres.Morespecifically,thethreeprimaryhypothesesareasfollows.1.DeeperindentationdisplacementswillcauselargerEMGresponsesinsuperficialfibreswhereastheresponseofdeepfibreswillnotbeaffectedbyperturbationdepth.2.HighervelocityperturbationsareexpectedtoresultinincreasedsuperficialanddeepfibreEMGactivity;however,therateofsuperficialfibreactivityincreasewillbegreaterthantherateofincreaseindeepfibres.Theincreaseindeeplumbarmultifidusfibreexcitationwithincreasedvelocitywillbeintheformofincreasedstretchreflexamplitudewhichwilloccurveryshortlyaftertheinitiationoftheperturbation.3.Lastly,itishypothesizedthatindentationperturbationswillresultinsimilarbutdiminishedEMGresponsesatadjacentvertebrallevelsduetothemulti-levelinnervationoffacetjointcapsules.395.OperationaldefinitionsDeeplumbarmultifidusfibres:Multifidusfibresarisingfromthevertebrallaminae,insertingatthemamillaryprocessesandspanningnomorethantwovertebrallevels.Superficiallumbarmultifidusfibres:Multifidusfibresoriginatingatthebaseortipofalumbarspinousprocessandinsertingtothelumbarvertebrae,iliumorsacrumgreaterthantwolevelscaudaltothefibres?origin.Indentationstartposition:Theindentationstartpositionoftheperturbationrodwasdefinedasthedisplacementatwhichtheindentationrodproducestherequiredpreload(20N).indentationphase:Thisphaseoftheindentationperturbationbeganwhentheperturbationrodwasintheindentationstartpositionattheinitiationoftheperturbation.Thisphaseendedwhentheperturbationrodreacheditsmaximumdownwarddisplacement.holdphase:Thisphaseoftheindentationperturbationfollowedtheactiveindentationphaseandcommencedatthemomentfullindentationdisplacementwasreached.Thisphaselastedfor500millisecondsandendedatthebeginningoftheindentationresolutionphase.Indentationresolutionphase:Thisphasefollowedtheindentationholdphaseandbeganwhentheindentationrodinitiatedupwardmovementawayfromthespinousprocessesandendedwhenthemotorhadreacheditsmaximumupwarddisplacement.406.Methodsandprocedures6.1StudyparticipantsTenhealthyparticipants(8male,2female)withoutahistoryofneck,back,lowerlimbpainorneuromuscularpathologywererecruitedforthisstudy.Theseparticipantshadamean(standarddeviation)ageof28.6(7.4)yearsold,heightof1.77(0.10)metresandabodymassof74.6(9.9)kilograms.IndividualparticipantanthropometricdataarepresentedinTable6.1.Theexperimentalprotocolincludingintramuscularelectrodeinsertiontechniqueandpossibleexperimentalrisksandcomplicationswereexplainedtoallparticipantspriortothestartoftheexperiment.ThisstudywasapprovedbytheUBCClinicalResearchEthicsBoardandallparticipantssignedinformedconsentformspriortoparticipating.Table6.1Listofparticipantagesandanthropometry.GenderAge(yrsold)Height(metres)Mass(kg)BMI(kglm2 )Subject01M471.737826.14Subject02M261.838224.37Subject03M221.767524.30Subject04F231.555824.12Subject05F251.686121.70Subject06M351.767123.12Subject07M261.758126.37Subject08M301.888624.37Subject09M251.838525.52Subject10M261.826720.34Mean(SD)28.5(7.5)1.76(0.09)74(10)24.03(1.90)416.2ElectromyographyandmultifidusimagingFine-wireelectrodeswerecustomfabricatedfrominsulatedstainlesssteelwirewitha0.05mmdiameter(StainlessSteel304,CaliforniaFineWireCompany,California,USA).Twostrandsofbipolarstainlesssteelfine-wirewereinterwovenandguidedthroughhypodermicneedles.Fine-wireelectrodesthatwereinsertedintodeeplumbarmultifidusfibreswereinsertedusinga2?Monojectneedle(Kendall,Massachusetts,USA),whileelectrodesinsertedintosuperficialfibreswereinsertedusinga1.5?PrecisionGlideneedle(BectonDickson,NewJersey,USA).Bothneedleswereregularbevel25-gaugehollowhypodermicneedleswiththeonlyfunctionaldifferencebetweenthembeingtheircannulalength.Theexposedendsofthewirewerehookedbackontotheneedleandeachstrandwastransverselycut.Onestrandwascuttoleave4mmofwirehookedoutsidethecannulawhiletheotherwirewascuttoleave0.5mmoutsidethecannula.Theoppositeendsofthewireweresolderedtonickelplatedtipplugconnectors(EmersonCanada,Ontario,Canada).Allfine-wireelectrodesweremedicallysterilizedpriortoinsertion.Foradetaileddescriptionoffine-wireelectrodefabricationrefertoAppendixA.Participantswereaskedtolieproneonacomfortableandadjustablebed(Accessmodel,Athlegen,Lewisham,Australia).TheleveloftheL4spinousprocesswasdeterminedbypalpationeitherfromthesacrumcraniallyorbymovingcaudallyafteridentifyingtheLispinousprocess.Thelumbarparaspinalmusculaturewasimagedwithanultrasoundtransducer(SonositeMicromaxx,13-6MHzHFL38Transducer)tolocatethesuperficialanddeeplumbarmultifidusfibres.TheultrasoundtransducerprobewasinitiallyplacedattheleveloftheL4spinousprocessinthetransverseplane(Figure6.1).Personalobservationsofcadaverparaspinalanatomy,anatomicalfigures(Hidesetal.2007;Kamazetal.2007;Kangetal.2007;Moseleyetal.2003)andaxialimagesofthemaleVisibleHuman?showthemultifidusasthemostsuperficialandmedialmuscleatthislevel.TheultrasoundtransducerprobewastranslatedsuperiorlyandinferiorlytoidentifylumbarmultifidusattheL3,L4andL5vertebrallevels.42Figure6.1TransverseplaneultrasoundimageattheL4vertebrallevelshowingthefascialborderofthelumbarmultifidus.43Oncetheexperimenterwassatisfiedthatlumbarmultifiduscouldbeimagedaccurately,thenon-sterileultrasoundgel(Aquasonic100,ParkerLaboratoriesmc,NewJersey,USA)wasremovedfromtheparticipant?slowerbackandtheintendedelectrodeinsertionssitesandsurroundingskinwascleanedwithIsopropylalcohol.Sterileultrasoundtransmissiongel(Aquasonic100sterile,ParkerLaboratoriesmc,NewJersey,USA)wasplacedonthelowerbackandtheultrasoundtransducerprobewasplacedinasterileprobecover(CIV-flex,8.9x91.5cmtelescopicfold,ConeInstruments,Ohio,USA).Atotalofsixfine-wireelectrodeswereinsertedunilaterallyandunderultrasoundguidanceintotherightsuperficialanddeepfibresattheL3,L4andL5vertebrallevels.Figure6.2displaysultrasoundimagesofexamplefine-wireelectrodeinsertionplacementswithinlumbarmultifidus.Oncetheneedlereacheditsdesiredlocation,itwaswithdrawnandplacedinaneedleshieldtapedtotheparticipant?sskin.Foradetaileddescriptionofmultifidusimagingtechniquesandfine-wireelectrodeinsertionrefertoAppendixB.Theelectrodeconnectorswerepluggedintoahighimpedancedifferentialpre-amplifier(DigitimerNeurologNL844,Hertfordshire,England,Inputimpedance:100M,Commonmoderejectionratio:>90dbat1kHz)thatgainedtheEMGsignalsbetweenlOOxandl000x(dependingonthesubjectandrecordingelectrode).Thepre-amplifierwasconnectedtoalargeramplifier(DigitimerNeurologNL820housedinaNL820Isolator,Hertfordshire,England,Inputimpedance:1OOk2)whichfurthergainedthesignals1-5x.AMicro1401analog-to-digitalconverter(CambridgeElectronicsDesign,Cambridge,UK)sampledeachEMGchannelat20,000HzandthesesignalswererecordedbyaPCcomputerusingSpike2software(CambridgeElectronicsDesign,Cambridge,UK).44Figure6.2Examplefine-wireelectrodeinsertionlocations.(A)L5superficialneedleusedtoinsertthefine-wireelectrodeinSubject06,(B)L3superficialwireinSubject08,(C)L5deepneedleusedtoinsertelectrodeinSubject10and(D)L4deepneedleandL4superficialwireinSubject10.456.3MotordisplacementandforceAlinearbrushlessdigitalservo-motor(SimplIQBassoon,ElmoMotionControl,Westford,MA,USA)wasusedtoapplyposter-anteriorindentationperturbationstoindividuallumbarspinousprocesses.Theservo-motorhadapeakforceof902.5N,peakcurrentof15.OA,aresistanceof8.62andanelectricaltimeconstantof0.0007seconds.Theservo-motorwasaffixedtoasturdysteelframepositionedovertheAthiegentreatmentbed.Theservo-motordeliveredindentationperturbationsbymanipulatingthepositionofalongnarrowrodwithacuppedfeltcontactsurfaceontheend(Figure6.3).Thecuppedfeltcontactsurfacewasusedtocradleeachspinousprocessandincreasesubjectcomfort.Figure6.3Theservo-motorusedtodelivertheindentationloadsbymanipulatingthepositionoftheindentationrod.Theforcetransducerbetweentheindentationrodandthecuppedfeltcontactsurfacerecordedforcebetweentheindentationrodandskin46TwoPCcomputerswereusedtocontrolthedigitalservo-motoranddeliverindentationperturbations.AcustomcomputerprogramwaswritteninElmoMotionStudiosoftware(ElmoMotionControl,Westford,MA,USA)anduploadedtotheSimpllQBassooncontrollerusingthefirstPCcomputer.Thisprogramcontainedperturbationsubroutineswithvaryingperturbationvelocityanddisplacementandeachvelocity-displacementcombinationwastriggeredwithaspecificbinaryinputtothecontroller.AsecondPCcomputerrunningSpike2deliveredthebinaryinputstothecontrollerthroughthedigitaloutputoftheMicro1401.ThisexperimentalsetupallowedtheexperimentertotriggerperturbationsbypressingaspecifickeyonthesecondPCcomputerfromwithinSpike2.AschematicofhowthemotorwascontrolledispresentedinFigure6.4.PCComputer:PCComputerElmoMotionStudioSpIke2connected(Peiturbatlonsubroutines)toMIcro1401_________________DateulsitionUnit=DblneiyInputsc0oIrto...SImpIIQBassoonDacementquadratureMotorConfroller_____________________RCAInput+toensureforcelsproduclr,gbelOW100Indentetlon?MForceTansduceimeaeudn9forcebetweenskinandblOUIJ)UtIndentationfromUnearForceTw,sducerFigure6.4Schematicofdigitalservo-motorcontrolduringexperimentalposterior-anteriorindentations.47IndentationroddisplacementwasmeasuredbysamplingthefourquadraturechannelsfromtheSimpllQBassooncontrollerauxiliaryfeedback.Quadraturechannelsweresampledat100,000HzaseventchannelsusingSpike2softwareandtheMicro1401analog-to-digitalconverter.DisplacementwascalculatedofflineusingacustomprogramwritteninMATLAB7.4(TheMathworks,Inc.,Massachusetts,USA)thatcreatedadisplacementchannelsampledat1000Hz.Forcebetweentheindentationrodandskinoverlyingthespinousprocesswasmeasuredwithasmallone-dimensionaltwenty-fivepoundloadcell(Honeywell,Ohio,USA).Theloadcellhadaforcerangeof11iNandwasfittedbetweentheindentationrodandthecuppedfeltcontactsurface.ForcewassampledbytheMicro1401analog-to-digitalcontrollerat1000HzandrecordedbySpike2software.6.4RespirationRespiratoryflowwasmonitoredduringtheexperimentalprotocoltodeterminethetime-pointattheendofnormalexpirationcorrespondingtofunctionalresidualcapacity.Asdiscussedinsection2.1.3,trunkstiffnesstoposterior-anteriorindentationforcesdirectedatlumbarspinousprocessesissignificantlymodulatedbylungvolume(Shirleyetal.2003).Respiratoryflowwasbemeasuredbyapneumotachometer(HansRudolphmc,Series1110,KansasCity,KS,USA)andsampledbyananalog-to-digitalconverter(Micro1401)at1000Hz.Pronestudyparticipantsbreathedintoamouthpiecemountedinthefaceholeoftheadjustablebedthatwasdirectlyattachedtothepneumotachometer.Respiratorygascollectionwasnotrequiredandthusexpiratorygaseswerere-directedfromthe?outvalve?backintothepneumotachometertorecordbothinspiratoryandexpiratoryflow.Studiesemployingposterior-anteriorindentationloadshaveprimarilyappliedtheseloadsattheendofnormalexpiration(CollocaandKeller2004;Collocaetal.2003;Hodgesetal.2005;KawchukandFauvel2001;Kelleretal.2003;McGilletal.1994;Moseleyetal.2002).Inthecurrentstudy,pneuomotachometrywasdisplayedonlineduringindentationperturbationsandtheexperimentertriggeredeachperturbationattheendofnormal48expiration.Trialsinwhichtheperturbationwasnotdeliveredattheendofnormalexpirationwereexcludedfromanalysis(SeeResultssection7.1.1).6.5ExperimentalprotocolTheexperimentalprotocolwasdividedintotwoparts.Thefirstpartconsistedofevaluatingvertebralmotionduringslowvelocityperturbationsanddeterminingtheproperexperimentalpositionforeachparticipant.Thesecondpartconsistedofthreeexperimentalblocksofposterior-anteriorindentationperturbations.Theexperimentalprotocolisdescribedinthefollowingsections.6.5.1VertebralmotionandparticipantexperimentalpositionParticipantslayproneontheAthlegentreatmenttablewhilethreeorfourindentationperturbationsof7.5mmatO.Olm!swereappliedtotheskinoverlyinganindividuallumbarspinousprocess.Duringtheseperturbations,theposterolateralaspectofthelumbarvertebraebeingperturbedandtheadjacentinferiorvertebraewereimagedusingultrasound.UltrasoundvideofilesofvertebralmovementduringtheseindentationperturbationswerecapturedbytheSonositeultrasoundunit.Theperturbationrodwasplaceddirectlyoverthespinousprocessbeingperturbedandthustheultrasoundprobewasplacedlateraltotheperturbationrodandatanangledirectedmediallytowardthevertebralbody.Thistransducerprobeorientationgenerallyallowedthevertebrallaminaeand/orsuperiorarticularprocessestobeimagedclearlyduringtheseperturbations.Theselandmarksallowedsagittalplanemovementtobeassessedduringperturbations.Allvideoswereviewedrealtimeandstoredofflineforlateranalysis.Followingtheseindentationperturbationsduringpronelying,bothendsofthetreatmenttablewereinclinedtoextendthetorsoandhips,positioningstudyparticipantsinhyperextension.Thetreatmenttablewasinclinedslowlyandincrementallywhileaskingparticipantshoweachincrementfeltandwhethertheywouldbecomfortableinthatpositionduringthethreeexperimentalperturbationblocks.Thetreatmenttablewas49inclineduntilparticipantswereneartheirlimitof?comfortable?hyperextension.Onceapositionof?comfortable?hyperextensionwasreached,ultrasoundvideosofthesamethreetofourposterior-anteriorindentationperturbationsof7.5mmat0.01mIswereviewedinreal-time.Theseultrasoundvideoswerestoredonthecompactflashdriveoftheultrasoundunitforadditionaloff-lineanalysis.Vertebralmovementduringperturbationsinthepronepositionandhyperextendedpositionwerecompared.Pilottestingrevealedthatposterior-anteriorperturbationsinthepronepositionprimarilyproducedvertebralrotationinthesagittalplanewhileperturbationsinthehyperextendedpositionresultedinanteriorvertebraltranslation.Ifvertebralmotionduringtheperturbationsinthehyperextendedpositiondidnotproducevertebraltranslation,thetreatmentbedwasre-adjustedandvertebralmovementduringindentationperturbationswasre-evaluateduntiltheperturbationproducedvertebraltranslation.Thetreatmentbedpositionwasrecordedandthebedwasloweredbacktoproneafterfindingapositionof?comfortable?hyperextensionthatproducedvertebraltranslationduringperturbations.Fine-wireelectrodeswereinsertedunderultrasoundguidanceasdescribedinsection6.2andthenparticipantswerereturnedtothesamehyperextendedpositionbyreturningthetreatmentbedtotherecordedposition.6.5.2IndentationperturbationsAsingleblockofindentationperturbationswasdeliveredtoeachoftheL3,L4andL5spinousprocessesresultinginatotalofthreeperturbationblocks.Theorderofeachblockwasrandomlydeterminedforeachparticipant,however,allperturbationsineachblockwerecompletedbeforethenextblockcommenced.Atthestartofeachblockthelongnarrowindentationrodwaspositionedoverthespecifiedspinousprocess,orientedperpendicularlytotheskinsurface.Previousexperimentalprotocolshaveorientedindentationperturbationsperpendiculartothevertebralbodyanterior-posterioraxis.ThishasresultedinperturbationsbeingdeliveredtoL2andL3atcephaladanglesof5.5-11.5?,toL4atacaudadangleof4.5?andtoL5atacaudadangleof16?(Hodgesetal.2005;Latimeretal.l996a;Leeetal.1993;Shirleyetal.2003).Wechosetoorientthe50indentationperturbationrodperpendiculartotheskinsurfaceofeachproneparticipanttominimizeanylateraldistensionoftheskinsurfaceduringindentationperturbations.TheexperimentalsetupisshowninFigure6.5.F.4Figure6.5Experimentalsetuptodeliverindentationperturbationswhilerecordingdisplacement,forceandintramuscularelectromyography.51Initially,a5Npreloadwasappliedtothespinousprocessthroughtheindentationrodpriortoeachindentationperturbation.Whenanindentationperturbationwastriggeredbytheexperimenter,theindentationroddisplaceddownwardtowardthespinousprocessat0.0002mIsuntiltheforcebetweentherodandskinreached20N.Theindentationrodheldthispositionfor200millisecondsbeforedeliveringtheindentationperturbation.ApplyingapreloadtothespecifiedtargetisthefirstphaseofaHVLAthrust(Herzogeta!.1993;Pickar2002)andhasbeenroutinelyemployedwhenapplyingindentationperturbations(CollocaandKeller2001b;Collocaeta!.2004;Collocaetal.2006;Collocaeta!.2007;Kelleretal.2006;Kellereta!.2007;PickarandWheeler2001).Clinically,preloadforcestothethoracic,lumbarspinesandsacroiliacjointshaverangedbetween20Nandl8ON(Conwayetal.1993;Galetal.1997;Herzogetal.1993;Herzogeta!.2001;Pickar2002;TrianoandSchultz1997).Thepurposeofthepreloadwastoreducetheeffectofskinandsofttissuecompliancebylimitingthe?toeoff?componentofthestiffnesscurve(Kellereta!.2007)aswellasmovingtheintervertebraljointbeingmanipulatedtotheendofitsRUM(PickarandGe2007).The20Npreloademployedinthisstudywassmallrelativetothoseusedinspinalmanipulationtherapy,yetstillwithintherangeofpreloadvaluesreportedforspinalmanipulationtherapy.Perturbationdisplacementsof5.00mm(Dl),6.25mm(D2)and7.50mm(D3)fromtheindentationstartpositionwereeachpairedwithperturbationvelocitiesof0.01m?s(V!),0.1SmJs(V2)and0.40m!s(V3).Thisresultedinatotalofninedifferentperturbationdisplacement-velocitycombinations.Indentationperturbationsconsistedofthreephases:theactiveindentationphase,indentationholdphaseandindentationresolutionphase(definedinsection5).Duringtheactiveindentationphase,theindentationrodmoveddownwardatthespecifiedvelocityandstoppedatthespecifieddisplacement.Theindentationrodheldthispositionfor500milliseconds(indentationholdphase)beforedisplacingupward(indentationresolutionphase)atthespecifiedvelocitytoapositiontwomillimetresabovetheindentationstartposition.Perturbationorderwithinanexperimentalblockwasrandomized;however,twoperturbationsofthesamedisplacementandvelocitydidnotoccurinsuccession.Ninety52totalperturbationsoftheninedisplacement-velocitycombinationsweredeliveredtoeachvertebralspinousprocesswhichresultedinanaverageoftenperturbationsateachdisplacement-velocitycombination.Theseninetyperturbationsweredeliveredintwosub-blocksofforty-fivetrialsandaftereachsub-block,participantswereallowedtoremovethepneumotachometermouthpieceandtheindentationrodwasremovedfromtheirlumbarspine.Eachperturbationsub-blocktypicallylastedbetweeneightandtwelveminuteswithrestintervalsbetweensub-blockslastingtwotothreeminutes.Attheendofeachperturbationsub-block,theparticipantwasaskedtobilaterallylifttheirlegstoextendthehipsandexcitethelumbarmultifidus.PilottestingrevealedthatthismovementelicitedEMGactivityatallmultifidusEMGrecordingsitesandwasperformedtoensurethattheintegrityofeachEMGchannelwasmaintainedthroughouttheperturbationsub-block.Theuseofaforce-controlordisplacement-controlexperimentalprotocolhasbeendebatedforbothinvitroandinvivospinalbiomechanicaltesting(Goeletal.1995).Bothforce-control(PickarandKang2006)anddisplacement-controlprotocols(Pickaretal.2007)havebeenemployedduringposterior-anteriorindentations.Ithasbeenarguedthatdisplacement-controlprotocolsproducequicklyrisingforcesduringmotionintheelasticzoneanddonotrepresenttheintrinsicpropertiesofincreasedstiffnesswithincreasedstretch(McGill2007).Ontheotherhand,displacement-controlledexperimentalprotocolsarebetterabletoreproduceinvivovertebralmotionsespeciallyduringlowjointstiffnessranges(Goeletal.1995).Thecurrentstudyemployeddisplacement-controlfortwoprimaryreasons.Firstly,posterior-anteriorindentationloadstotheskinoverlyinglumbarspinousprocesseshavebeenshowntoproducealinearrelationshipbetweenforceanddisplacementovertheforcerange50-lOON(Shirleyetal.2003).Secondly,themotorcontrollercanbepre-programmedtodeliverspecificdisplacementswhileforce-controlwouldnecessitatefeedbackresponsesfromtheforcetransducerpossiblyresultinginincreasedprocessingtimedelays.Duringcyclicindentationloads,trunkstiffnessduringthefirstcyclewasreportedtobesignificantlylessthanduringfoursubsequentcycles(Shirleyetal.2002).Toprevent53changesintrunkstiffnesswhichmayaffectEMGresponses,?habituationtrials?wereperformedateachvertebrallevelpriortoexperimentalperturbationsatthatlevel.Tenperturbationsatthehighestvelocity(V3)anddeepestdisplacement(D3)weredeliveredtothevertebralspinousprocessbeingperturbedinthecurrentexperimentalblock.Duringeachexperimentalblockofninetyindentationperturbations,indentationdisplacementandvelocitycombinationswererandomized(asdescribedabove)tofurtherguardagainstexperimentalordereffects.Theservo-motorwasequippedwithanumberofsoftwareandhardwareprecautionstoensureparticipantsafety.Themotorwasprogrammedtolimitthemaximalforceofeachindentationto100N,ahardrubberstopwasplacedat10mmtopreventindentationroddisplacementbeyondthispointandtheexperimentercouldimmediatelycutpowertothemotoratanytimeusingamanualkillswitch.6.6.DataanalysisBreathing,force,displacementandEMGchannelswererecordedusingSpike2softwareanddataanalysisprocedureswereperformedinMATLAB7.4.Posterior-anteriortrunkstiffnesswascomputedusingthemethodofcentraldifferencesasthechangeinforceoverthechangeindisplacement.Asdescribedinsection6.3,perturbationvelocityanddisplacementwerecontrolledbytheninedifferentperturbationsubroutines;however,theseindependentvariableswerealsocomputedfromthedisplacementquadraturechannels.Perturbationvelocitywascomputedbythemethodofcentraldifferencesbydifferentiatingperturbationdisplacement.Breathingduringeachperturbationwasexaminedonlineandofflineandtrialsinwhichbreathingdidnotoccurattheendofnormalexpirationwereeliminated.EMGchannelswerebandpassfilteredat100-2000Hzusingdigitalzero-phasefourthorderButterworthlowandhighpassfilters.EMGchannelswerequantifiedbycomputingthe?average?rootmeansquare(RMS)ofeachchanneloverthecombinedactiveindentationandindentationholdphasesforeachperturbation.Despiteexperimental54precautionsandbandpassfiltering,EMGchannelsinsometrialscontainedasmallamountofelectrical?noise?duetothedigitalservo-motor.Toeliminatethis?noise?fromaffectingexperimentaldependentmeasures,baselineelectricalactivitywassubtractedfromeach?average?RIvISvalue.BaselineactivitywascomputedbytakingtheRMSvalueoftheleastvariable200millisecondwindowwithinthetwosecondwindowpriortotheperturbation.This200millisecondintervalwasfoundbytakingaslidingwindowofthestandarddeviationineachEMGchannelduringthetwosecondintervalpriortotheperturbationandcalculatingtheactivityoverthewindowwiththeloweststandarddeviation.Themotorwasstationaryoverthisintervalandthus,thismethodwasreasonedtobethemostaccurateindeterminingbaselinemotor?noise.?EachEMGchannelfromeachperturbationwasindividuallyexaminedandtrialsinwhichmotorartifactsornon-random?noise?contaminatedEMGrecordingswereexcludedfromanalysis.The?average?RIVISofeachEMGchannelwasaveragedforeachperturbationofthesamevelocityanddisplacementateachperturbationlevel.Thisproduceda3x3x3matrix(perturbationvelocity,displacementandlevel)foreachEMGchannelwithasinglevalueforeachsubjectineachcell.TheinitialexperimentaldesignispresentedinTable6.2.Duetothenatureofmultifidusintramuscularrecordings,itwasnotpossibletoaccuratelynormalizeEMGchannelstoaspecificactivity(i.e.maximalvoluntarycontraction).Consequently,eachEMGchannelwasseparatelystatisticallytestedusinga3x3x3repeatedmeasuresANOVAdesignwithperturbationvelocity,displacementandlevelasindependentvariables.Table6.2ExperimentalDesignemployedforanalysisofeachEMGchannel(Note:Thethirddimension(perturbationlevel)ofthis3x3x3experimentaldesignisnotshownhere).PeriuibatioiiDisplaceiiientPeiturl,ationVelocity131=5.00mm[12=6.25mm03=7.50mmVi=0.01msVi-OlV1-132V1-D3V2=0.15insV2-D1V2-02V2-03V3=0.40insV3-D1V2-D2V3-0355Twodependentmeasureswereaddedtothedataanalysisprotocolaposteriori:peakRIVISandtime-to-peakRMS.A20.05millisecondslidingRMSwindowwascomputedforeachEMGchannelcorrespondingto401data-pointsattheEMGsamplingfrequencyof20,000Hz.TheRMSovereach401data-pointwindowwascomputedandenteredintheslidingRMSvectoratthetimevaluecorrespondingtothe201stdata-point.ThepeakvalueofeachslidingRMSvectorandtime-to-peakRMSwerecomputedforeachEMGchannelduringthetimeintervalfromthestartoftheactiveindentationphasetotheendoftheindentationholdphase.ThesedependentmeasureshavebeenpreviouslyusedtoquantifytheEMGresponsemagnitudeduringhorizontalsimulatedwhiplashperturbations(Blouinetal.2006).ThepeakRMSandtime-to-peakRMSofeachEMGchannelwasaveragedforeachperturbationofthesamevelocityanddisplacementateachperturbationlevel.Inananalogousfashiontothe?average?RMSdependentmeasure,averagingacrosstrialsproduceda3x3x3matrix(perturbationvelocity,displacementandlevel)forpeakRMSandtime-to-peakRMSwithasinglevalueforeachsubjectineachcell.StatisticaltestswerecarriedoutusingSPSS14.0forWindows(SPSSmc,Illinois,USA).Mauchly?stestofsphericitywastestedpriortoperformingeachANOVAandthestatisticalsignificancelevelwassetaprioriatct?0.05.Greenhouse-geissercorrectionswereemployedinstatisticaltestswhichviolatedtheassumptionofsphericity.567.ResultsRepresentativedisplacement,forceandEMGresponsesforaslowvelocity,shallowdisplacement(Vi-Dl)andmediumvelocity,intermediatedisplacement(V2-D2)perturbationaredisplayedinFigure7.1onthefollowingpage.57(a) Slow Velocity, shallow displacement (Vi-Di)Displacement (mm)???--??---??----.Force (N)_?L3 deepL3 supL4deepL4sup1- I??if f I 4! ! I II 1 -d I Ii. 1I I. If I I(b) Medium Velocity, medium displacement (V2-D2)mm150N[.$;I 44 #1 + 4 I I I I IIHr 1.I i4I ftI?tI IIhll1f H I Ii 4?I15001500 iiV1500 iVI 500pVI 500 iiV1500 livFigure 7. 1 Displacement, force and electromyography of a (a) slow velocity, shallow displacement perturbation (VI-DI)and a (b) medium velocity, intermediate displacement perturbation (V2-D2) in Subject 03. For comparison purposes, bothperturbations are plotted on the same scale of axis.L5 deepL5 supTime (seconds) 200 ms Time (seconds) 200 mstJ,007.1Experimentalconditionsvalidation7.1.1TrialexclusionAsinglesubjectwasexcludedfromdataanalysisduetothepresenceofelectricalartifactsintheEMGchannelsofmanytrials.TheseartifactswereinitiallyobservedduringdatacollectionandEMGelectrodes,wiresandconnectionsweremanipulatedduringcollectioninanattempttoreducetheseartifacts.Despitetheseattempts,anexperimentalsetupcouldnotbefoundthatcompletelyeliminatedallartifacts.Thisparticipantwasmaleofaverageheightandweight(1.75m,81kg)andhadtheseartifactsbeeneliminated,thereisnoreasontobelievethatthisparticipantwouldhaveproducedadifferentpatternofEMGresponses.Atotalof2473perturbationsweredeliveredtothenineremainingsubjects.Allbreathing,forceandperturbationdisplacementchannelsoftheseperturbationswereindividuallyinspectedforexperimentalprotocolandequipmenterrors.Forty-eighttrialswereexcludedduetotheperturbationoccurringatthewrongstageofbreathing(1.98%),whilethirteentrials(0.52%)wereexcludedtoduetheforcetransducerexceedingthemaximumvoltageoutputandfivetrials(0.20%)duetomotordisplacementcommanderrors.Additionally,eachEMGchannelwasinspectedfornon-randommotor?noise?orelectricalartifactsandaconservativeapproachwastakensuchthatanyelectricalactivitythatmaynothavebeenofphysiologicaloriginwasexcludedfromanalysis.Thisapproachresultedinatotalof833individualchannels(5.61%)beingexcludedfromanalysis.Agrandtotalof8.28%ofallchannelswereexcludedfromdataanalysis.Amaximumof13.85%oftrialswereexcludedfromanysinglesubject.7.1.2PerturbationvelocityanddisplacementPerturbationvelocityduringtheactiveindentationphaseandmaximumperturbationdisplacementforeachsubjectwerecollapsedacrosstrialsbyaveragingalltrialswithinasingleperturbationvelocity,displacementandlevelcombination.PerturbationvelocityanddisplacementforeachconditionateachperturbationlevelarepresentedinTable7.1and7.2.Two3x3x3matricescorrespondingtoperturbationvelocityandperturbationdisplacementwerestatisticallytestedwithrepeatedmeasuresANOVAs.Table7.1Meanperturbationvelocities(mis)acrosssubjectsforeachperturbationdisplacementandvelocitycombinationateachperturbationlevel.(A)PerturbationLevel=L3PenurbationVelocityPertenbationDisplacementDlD21)3Vi(mi)0.011(0.0008)0.011(0.0008)0.011(0.0007V2(in?s)0.107(0.003)0.129(0.002)0.145(0.002)V3(in/si0.108(0.004)0.134(0.004)0.159(0.001)(B)PerturbationLevel=L4PerinibationVelocityPertiitbaiionDisplacementDl02D3Vi(m?s0.01140.0004)0.011(0.0003)0.01140.0003)V2(m?s)0.108(0.002)0.12940.002)0.145(0.003)V3(in:s)0.109(0.003)0.135(0.003)0.160(0.003)(C)PerturbationLevel=L5PertiiibationVelocityPerturbationDisplacementDl0203Vi(ins)0.011(0.0005)0.011(0.0005)0.011(0.0004)V2(ins)0.106(0.003)0.12840.003)0.143(0.003)V34m:s)0.109(0.003)0.134(0.004)0.158(0.004)60Table7.2Meanperturbationdisplacements(mm)acrosssubjectsforeachperturbationdisplacementandvelocitycombinationateachperturbationlevel.(A)PerturbationLevel=L3PerturbatiopiVelocityPertuibationDisplacementDi(inni)D2(nun)D3(nun)Vi4.96(0.004)6.20(0.01)j7.13(0.66)V25.02(0.04)6.24(0.05)j7.46(0.08)V35.01(0.08)6.23(0.04)j7.49(0.041(B)PerturbationLevel=L4PertulbationVelocityPertuibationDisplacementDl(mm)D2(nun)D3(miii)Vi4.9510.004)6.20(0.005)6.9940.63)V25.0340.06)6.2640.08)7.48(0.05)V35.01(0.06)6.29(0.0917.53(0.06)(C)PerturbationLevel=L5PerturbationVelocityPeittirbationDisplacementDi(innflD2(nini)D3(mm)Vi4.9540.01)6.21(0.004)6.7840.61)V24.9940.05)6.2940.05)7.5040.08)V35.0140.06)6.2840.07)7.48(0.05)61TheperturbationvelocityANOVAproducedsignificantmaineffectsofperturbationvelocity(F(2,l=14632.41,p<O.OOl,MSe0.00003,9 2 >0.99),perturbationdisplacement(F(2 ,l6)=33768.12,p<O.OOl,MSe0.0000005,2 >0.99)andsignificantinteractionsbetweenvelocityanddisplacement(F( 4 , 32 )10639.78,p<O.OOl,MSeO.000O004,aswellasdisplacementandlevel(F( 4 , 32 )3.42,p=O.O2,MSe=0.0000007,?q 2 =0.30).Thesignificantinteractionsindicatethatthemagnitudeoftheperturbationvelocitydependedontheperturbationdisplacementandlevel.Theperturbationvelocitiesforeachconditionwerequalitativelyanalyzedanditwasobservedthatnotallperturbationvelocitiesreachedtheirtargetvelocity.TheV2(0.15m!s)andV3(0.4OmJs)perturbationvelocitiesdidnotachievetheirtargetvelocitiesduetotheshortdisplacementsrequiredbytheexperimentalprotocol.Theexperimentalprotocolconstrainedperturbationaccelerationanddisplacementandthusitwasknownthatthetime-to-targetvelocitywouldbedifferentbetweenperturbationvelocities.Aschematicoftheidealizedperturbationvelocityprofilesfortheslow,mediumandfastvelocitiesaredisplayedinFigure7.2.Perturbationvelocitiesdidnotachievetheirtargetvaluesbecausethemotor?smaximumaccelerationwasnotsufficienttoacceleratetheindentationrodtotargetvelocityovertheshortdisplacementsemployedbythisstudy.6224-?04-??34-?a)0???DlD3Figure7.2Idealizedperturbationvelocityprofilesforslow,mediumandfastperturbationvelocities(Notethexandyscalesforeachvelocityprofilearedifferent).StowVelocity(Vi)I???15mm/s250msMediumVelocity(V2)I?,?100mm/slOmsFastVelocity(V3)1100mm/slOmsTime(milliseconds)63TheperturbationvelocityprofilesforeachconditionwereamplitudenormalizedtotargetvelocityandtimenormalizedtoactiveindentationtimeanddisplayedinFigure7.3..1000PercentageofActiveIndentationPhase(%)100Figure7.3Velocityprofilestime-normalizedtothelengthoftheactiveindentationphaseandexpressedasapercentageoftheirtargetvelocity.Perturbationstodifferentdisplacementsareexpressedindifferentcolours(D1=blue,D2red,D3black).NotethatonlyVelocityI(VI)perturbationsachieved100%oftheirtargetvelocity.TheperturbationdisplacementANOVAproducedsignificantmaineffectsofperturbationvelocity(F(2 ,l6)=9.13,p=O.OO2,MSe=O.0000001,i=O.53),perturbationdisplacement(F(2 , 16 )=832.53,p<O.OO1,MSe=O.0000001,=O.99)andsignificantinteractionsbetweenvelocityanddisplacement(F(4 , 32 )=5.99,p=O.04,MSe=O.000000l,ri 2 =O.43),displacementandlevel(F(4 , 32 )=3.42,p=O.O2,MSe=O.0000000l,ii 2 =O.3O)andvelocityandlevel(F(4 , 32 )=3.96,p=O.Ol,MSe=O.00000001,ri 2 =O.33).ThesignificantinteractionsVelocity1(Vi)050Dl???-D2D364suggestthatthemagnitudeofperturbationdisplacementdependedontheperturbationvelocityandlevel.Closeexaminationofperturbationdisplacementandforceprofilesrevealedthatindentationperturbationsattheslowestvelocityanddeepestdisplacement(V1-D3)didnotreachtheirtargetdisplacement.TargetdisplacementswerenotreachedbecausetheforceexceededthelOONsafetylimitoutlinedintheexperimentalprotocol(refertosection6.5.2)andthustheperturbationdisplacementceasedwhenthissafetylimitwassurpassed.TheforcesafetylimitwasexceededinthreeofninesubjectsatL3,fourofninesubjectsatL4andsevenofninesubjectsatL5.Duetothemotorlimitationsandsafetyprecautionsofthisstudy,perturbationsattheV3targetvelocity(O.4OmJs)andD3displacement(7.5mm)wereexcludedfromanalysisandthedesignwasmodified.Additionally,perturbationvelocitiesatV2(0.15mJs)werenotconsistentacrossperturbationdisplacementsbecauselargerdisplacementspermittedalongerperiodofpositiveandnegativeaccelerationallowingtheindentationrodtoreachahigherpeakvelocity.Consequently,theeffectofperturbationdisplacementcouldonlybestatisticallytestedatViandtheeffectofvelocitycouldonlybestatisticallytestedatdiscreteperturbationdisplacements.Toaccommodatetheseconstraints,dataanalysiswasdividedintopartAandpartBtotestperturbationdisplacementandperturbationvelocity,respectively.Aconsistedofa2x3repeatedmeasuresANOVAdesignwithtwoperturbationdisplacements(Dl,D2)andthreeperturbationlevels(L3,L4,L5)atvelocityVi(0.01mIs).PerturbationvelocitieswereonlyconsistentacrossperturbationdisplacementsatViandthustheeffectofperturbationdisplacementcouldonlybetestedatthisvelocity.?Average?RMS,peakRMSandtime-to-peakRMSwerestatisticallytestedusingthe2x3ANOVAdesignforeachEMGchannel.TheeffectofperturbationvelocitycouldonlybetestedatdiscretedisplacementsandthuspartBwasdividedintotwoseparateanalysesattheDlandD2perturbationdisplacements.TheV2velocityateachdisplacementwasnotconsistent,however,V2wasconsistentlylargerthanViateachdisplacementandthusperturbationvelocitiescouldbelabeledas?low?or?high?ateachdisplacement.The?average?RMS,peakRMSandtime-to-peakRMSateach65displacementwerestatisticallytestedwitha2x3repeatedmeasuresANOVAwithindependentvariablesperturbationvelocityandperturbationlevel.TheexclusionofallconditionsutilizingeithertheV3velocityorD3perturbationdisplacementdidnotsignificantlyaffectthenumberoftrialsexcludedfromanalysis(8.28%vs.8.26%).Limitingthenumberofconditionsalsodidnotaffecttheproportionoftrialsexcludedforanyspecificreason(breathing1.71%,motordisplacementerrors0.20%,EMGartifacts6.28%).Themaximumnumberoftrialsexcludedfromasinglesubjectinthenewdesignwas13.42%.ThefollowingresultsaredividedintopartAandBtoreflectthemodificationsmadetotheexperimentaldesign.ThemodifiedexperimentaldesignissummarizedinFigure7.4.PartAPanBPernubationVelocityVIPernubationPerturbationlO.Olrns)[)ispiacenientDl(5.OOinmIDisplacementD216.25mm1Dl15.OOmmiD216.25ninilVI(low)V2thigh)VI(low)?12(highlL313_________________________PerniihaiionPeituibationLevelL4LevelIA_______________________L5L5_______________________Figure7.4TherevisedexperimentaldesignexcludingV3andD3perturbations7.2ElectromyographyAsummaryofstatisticalprobabilityvalues(pvalues)foreachanalysisispresentedinTable7.3.Statisticallysignificanteffectsaredenotedinthistablebyadoubleasterisk.Theeffectsize,degreesoffreedom,meansquareerrorandstatisticforeachanalysisarepresentedinAppendixD.Thefollowingsectionsdescribeonlythesignificantmaineffectsandinteractionsofeachstatisticaltest.Allotherstatisticaltestswerenotsignificant.66Table7.3SummaryofstatisticalpvaluesforPartAandBstatisticaltests.Statisticallysignificanteffectsaredenotedwith**?PartA(Velocity=VI)DependentMeasuieAveraie?RMSPeakRMSTime-to-peakRMSIndependentVailableDispLevelDispLevelDispLevel13deep0.280.320.170.290.110.1113superficial0.150.380.10.160.01?0.9814deep0.30.160.170.710.01?0.18LIsuperficial0.940220.88026<0.001?0.6315(Jeep0.580.360.10.460.003?0.0715superficial0.045?0.330230.340.10.38PailB(Displacement=Dl)DependentMeasuie?Averae?RMSPeakRMSTinie4o-peakRMSIndependentVariableVelLevelVelLevelVelILevel13deep0.006?0.690.01?0.83Interaction=0.04?13superficial0.630.390250.43<0.001?0.7714deep0.080.560.047?0.95<0.001?0.3114superficial0.30.390.150.34<0.001?0.315deep0.470.370.120.48<0.001?0.048?15superficial0.180.210.160.26<0.001?0.18PartB(Displacement=D2iDependentMeasureAveraeRMSPeakRMSTime-to-eakRMSIndependentVariableVelLevelVelLevelVelLevel13deep0.01?0.350.01?0.33<0.001?0.8913superficial0.060.36020.42<0.001?0.8714deep0.04?0.580.01?0.92<0.001?0.4414superficial0.180.360.140.38<0.001?0.8215deep0.02?0.530.03?0.81<0.001?0.1715superficial0.120.270.090.38<0.001?0.18677.2.1PartA:TheeffectofperturbationdisplacementThe?average?RMS2x3repeatedmeasuresANOVAwithindependentvariablesdisplacement(Dl,D2)andperturbationlevel(L3,L4,L5)producedastatisticallysignificanteffectof?average?RMSfortheL5superficialEMGrecordingelectrode(p=O.O45 ).Thismaineffectindicatedthat?average?RMSincreasedwithperturbationdisplacementintheL5superficialfibres.Thetime-to-peakRMS2x3repeatedmeasuresANOVAyieldedsignificantmaineffectsofperturbationdisplacementfortheL3superficial(pO.Ol),L4deep(p=O.Ol),L4superficial(p<O.OO1)andL5deep(pO.OO3)electrodes.Thesemaineffectsindicatedthatthetime-to-peakRMSincreasedwithincreasingperturbationdisplacement.Themeantime-to-peakRMSofallsubjectswasgreateratD2foreveryperturbationlevelineveryEMGrecordingelectrode.The?average?RMS,peakRIVISandtime-to-peakRMScollapsedacrossperturbationlevelarepresentedforeachEMGrecordingsiteinFigure7.5.684-,0Lf)a)4-,0?Average?RMSwithperturbationdisplacementatVi35oD2Dlc;)c;)cc-oPeakRMSwithperturbationdisplacementatVi2801D2Dlcc-OTime-to-peakRMSacrossperturbationdisplacementsatVi:;:TTFigure7.5?Average?rms(toppanel),peakmis(middlepanel)andtime-to-peakrms(bottompanel)foreachEMGchannelatDlandD2displacements.Forcomparisonpurposes,the?average?rms,peakrmsandtime-to-peakrmsaxesareconsistentacrossFigures7.5,7.6,7.7and7.8.697.2.1PartB:TheeffectoflowandhighperturbationvelocitiesThe?average?RMSvaluesofeachEMGchannelforlowandhighperturbationvelocitiesduringDlandD2perturbationdisplacementsaredisplayedinFigure7.6.The?average?RMS2x3repeatedmeasuresANOVAattheDldisplacementproducedasignificantmaineffectofperturbationvelocityintheL3deeprecording(p=O.OO6).ThismaineffectindicatedthatintheL3deeprecordingthe?average?RMSincreasedwithperturbationvelocity.The?average?RMS2x3repeatedmeasuresANOVAattheD2displacementproducedsignificantmaineffectsofperturbationvelocityintheL3deep(p=O.O1),L4deep(pO.O4 )andL5deep(pO.O2 )EMGrecordingelectrodes.Thesemaineffectsindicatedthatindeepmultifidusrecordingsthe?average?RMSincreasedwithperturbationvelocity.Figure7.7displaysthepeakRMSofeachEMGchannelforlowandhighperturbationvelocitiesduringDlandD2perturbationdisplacements.ThepeakRMS2x3repeatedmeasuresANOVAattheDldisplacementproducedsignificantmaineffectsintheL3deep(pO.Ol)andL4deepFMGrecordings(pO.O47).ThesemaineffectsindicatedthatintheL3andL4deeprecordingsthepeakRMSincreasedwithperturbationvelocity.ThepeakRMS2x3repeatedmeasuresANOVAattheD2displacementproducedsignificantmaineffectsofperturbationvelocityintheL3deep(pO.Ol),L4deep(pO.O4)andL5deep(p=O.O3)EMGrecordings.ThesemaineffectsindicatedthatindeepmultifidusrecordingelectrodesthepeakRMSincreasedwithperturbationvelocity.700cc)ci)4-,0cc)a)?Average?RMSwithperturbationdisplacementatDl70350vic;)0-ccc3-o?Average?RMSwithperturbationdisplacementatD270TTTT(occ-0Figure7.6PartB:?Average?rmsforDl(toppanel)andD2(bottompanel)perturbationdisplacements.Forcomparisonpurposes,the?average?mis,peakrmsandtime-to-peakmisaxesareconsistentacrossFigures7.5,7.6,7.7and7.8.714-?0V.)cij-S0V.)a)0280PeakRMSwithperturbationdisplacementatDl00-)280PeakRMSwithperturbationdisplacementatD2107.7PartB:PeakmisforDl(toppanel)andD2(bottompanel)perturbationdisplacements.Forcomparisonpurposes,the?average?mis,peakmisandtime-to-peakrmsaxesareconsistentacrossFigures7.5,7.6,7.7and7.8.72Themeantimes-to-peakRMSatlowandhighperturbationvelocitiesaredisplayedinFigure7.8.Thetime-to-peakRMS2x3repeatedmeasuresANOVAyieldedsignificantmaineffectsofperturbationvelocityinallEMGrecordingsattheDlandD2displacements.TherewasasignificantinteractionbetweenperturbationlevelandvelocityattheDldisplacementintheL3deeprecording(p=O.04).Post-hocTukeytestrevealedthatateachperturbationleveltherewasasignificanteffectofperturbationvelocity;however,therewasonlyastatisticallysignificantperturbationleveldifferencebetweenL3andL4atthelowvelocity(p=O.02).Thetime-to-peakRMSwassignificantlyshorterattheL4perturbationlevelrelativetotheL3perturbationlevelatthelowvelocity.ThemaineffectsofperturbationvelocityinallEMGrecordingsitesindicatedthatthetime-to-peakRMSdecreasedasperturbationvelocityincreasedatbothDlandD2displacements.TherewasastatisticallysignificantmaineffectofperturbationlevelattheDldisplacementintheL5deeprecording(p=O.O48).Post-hocTukeytestindicatedthatthetime-to-peakRMSwassignificantlyshorterattheL5perturbationlevelthanattheL3perturbationlevelatthelowvelocity(p=O.O4).73Time-to-peakRMSacross-CI?CI?perturbationdisplacementsatDlTime-to-peakRMSacrossperturbationdisplacementsatD2Figure7.8PartB:TimetopeakrmsforDl(toppanel)and02(bottompanel)perturbationdisplacements.Forcomparisonpurposes,the?average?rms,peakrmsandtime-to-peakrmsaxesareconsistentacrossFigures7.5,7.6,7.7and7.8.T0ViV2-occ-O-O748.DiscussionTheoverallfindingswere:1.Perturbationdisplacementattheslowestvelocity(Vi)didnotproducedifferent?average?orpeakRMSvaluesforeachEMGrecordingsite.Theexceptiontothistrendwasthe?average?RMSoftheL5superficialEMGrecordingelectrodewhichsignificantlyincreasedwithperturbationdisplacement.Thetime-to-peakRIvISsignificantlydecreasedwithincreasedperturbationdisplacementatallEMGrecordingsitesexceptL3deepandL5superficial.2.?Average?andpeakRMSincreasedwithperturbationvelocityintheL3deeprecordingelectrodeatDiandalldeepmuitifidusrecordingsitesatD2.PeakRv1SalsoincreasedwithperturbationvelocityintheL4deeprecordingelectrodeatDl.Time-to-peakRMSsignificantlydecreasedwithperturbationvelocityinallEMGrecordingelectrodesatbothperturbationdisplacements(DlandD2).3.Perturbationleveldidnotproducedifferent?average?orpeakRMSvaluesforallanalyses;however,perturbationleveldidproducestatisticallysignificantdifferencesinthetime-to-peakRMSattheDldisplacement.Time-to-peakRMSintheL5deepelectrodewasshorterduringDlindentationstotheL5spinousprocesscomparedtotheL3spinousprocess.Additionally,time-to-peakRMSintheL3deepelectrodewasshorterwhenVi-DiindentationswereappliedtotheL4spinousprocesscomparedtotheL3spinousprocess.ThiswasthefirststudytorecordlumbarmultifidusintramuscularEMGduringposterior-anteriorindentationstotheskinoverlyingthelumbarspineofconscioushumans.IntramuscularEMGresponsestoindentationloadshavebeenpreviouslyreportedinlumbarradiculopathypatientsundergoingsurgery(Collocaetal.2003).Additionally,surfaceEMGhasbeenrecordedduringposterior-anteriorindentationstotheskinoverlyingvertebrallandmarks(CollocaandKeller2001a;CollocaandKeller2004)andduringspinalmanipulativetherapy(Herzogetal.1999;Symonsetal.2000).Thesestudiesallowedgeneralcomparisonstobemadetotheresultsofourstudy;however,75mostpreviousstudiesappliedindentationloadswhileparticipantswerelyingprone.Thefollowingparagraphprovidesanoverviewofthestatisticallysignificantresults.Thisstudyappliedposterior-anteriorindentationforcestoparticipantsinhyperextensiontoensureanteriorvertebralbodytranslation(refertosection6.5.1).Duringmaximumtrunkextensionfromuprightstanding,lumbarintervertebraljointsextended(posteriorsagittalrotation)approximatelyequalamounts(Leeeta!.2002;Wongetal.2004).MaximaltrunkextensionalsoyieldedhorizontalintervertebraltranslationsbetweenadjacentvertebralbodiesatL3,L4andL5(Kanayamaeta!.1996).Thesevertebralmovementsduringtrunkextensionmaybesimilartothoseexperiencedduringposterior-anteriorindentationforces.Theapplicationofatensecondposterior-anteriorforce(90-liON)totheskinoverlyingtheL3,L4orL5spinousprocessproducedconcurrentlumbarvertebralextensionatL3,L4andL5asmeasuredbyMRI(Powersetal.2003).LeeandEvans(1997)applieda150Nposterior-anteriorforcetoL4producinganaverageof10.2mmofskinsurfacemovement,intervertebralextensionsbetween1.2-2.4degreesandintervertebraltranslationsof2mmorless(LeeandEvans1997).Theapparentkinematicsimilaritybetweentrunkextensionandvertebralmovementduringposterior-anteriorindentationsuggeststhattheexperimentalpositionemployedmayhaveincreasedintervertebraltranslationalpriortotheperturbation.Anexperimentalpositionwithincreasedintervertebraltranslationsmayhaveresultedinspecificperturbationdisplacementsproducinggreateractiveorpassivetissuestretchthanthesamedepthofdisplacementwouldhaveproducedinpronelying.Thispossibilitynecessitatescautionwhencomparingspecificposterior-anteriordisplacementsinthehyperextendedandpronelyingpositions.768.1PerturbationdisplacementInthemodifieddesign(describedinsection7.1.2),theeffectofperturbationdisplacementonlumbarmultifidusEMGwascomparedbetweentheDiandD2displacementsattheconstantperturbationvelocityofO.Olm!s(Vi).WehypothesizedthatperturbationdisplacementwouldresultinincreasedsuperficialfibreEMGactivityandourresultdidnotconsistentlysupportthishypothesis.?Average?RMSincreasedwithperturbationdisplacementintheL5superficialrecordingelectrode,butnootherperturbationdisplacementeffectswerenoted.ThismayhavebeenbecausetheDlandD2displacements(separatedby1.25mm)werenotsufficientlydifferentenoughtoproducedifferentEMGresponses.Pickaretal.(2007)acknowledgedthatindentationloadsstretchparaspinalmusculatureonlyafractionoftheamountoftheverticalindentationdisplacement.Theseauthorsmodeledthestretchproducedbyoneandtwomillimetreorthogonaldisplacementsapplieddirectlytofelinelumbarvertebraeandconcludedthatthesedisplacementsonlyrepresented0.17%and0.35%stretchofa50mmlongparaspinalmuscle(Pickaretal.2007).Estimationoftheamountofstretchappliedtolumbarmultifidusinthecurrentstudydependedontheamountofdisplacementtransferredthroughtheskintothespinousprocessaswellasthelengthandorientationoflumbarmultifidusfibres.Asdiscussedabove,a1SONindentationtotheskinoverlyingtheL4spinousprocessproducedanabsoluteskindisplacementof10.2mm,absolutevertebraldisplacementsof8.8-11.5mmandintervertebraltranslationsoflessthan2mm.Theabsolutedisplacementofthespinousprocessinthecurrentstudywasdifficulttoestimatebecausedisplacementduringthepreloadphasewasnotrecordedandthenatureoftherelationshipbetweenintervertebraltranslationsandperturbationforcewasnotknown.Regardless,perturbationforcedidnotexceedlOONandthusitwasassumedthatevenatthe6.25mm(D2)displacementintervertebraltranslationswerelikelylessthan2millimetresbasedonLeeandEvans?(1997)estimates.Theseintervertebraltranslationswouldhaveoccurredorthogonaltotheplaneinwhichthemuscleslieandusingthecosinelawa2mmintervertebraltranslationwouldonlyproducea16micrometrestretchina119mmlong77muscle(thelengthoftheL3superficialmusclefibregroupasreportedby(Hansenetal.2006)).Additionally,thestretchproducedbythisintervertebraltranslationwouldhaveoccurredwithinthemuscle-tendonunitandthedegreeofstretchwithintheactivemultifidusfibreswasunknown.Ifthedifferencebetweenperturbationdisplacementswassufficienttoproducesignificantlydifferentmusclestretches,increasedperturbationdisplacementonlyincreasedthe?average?RMSofL5superficialmultifidusfibres.Thiswastheoppositeresultexpectedifmuscletensionincreasedsimilarlyinallsuperficialfibres.SuperficialfibregroupingsarisingfromthetipandshaftoftheL4spinousprocessandtraversingtheL5vertebratoattachatthesacrumhavebeenreportedtohavethelargestphysiologicalcross-sectionalarea(Hansenetal.2006)).SuperficialfibrerecordingsattheL5vertebrallevelwerelikelywithinthesefibresinmostsubjectsbecausetheymakeupthebulkofthesuperficialfibresatL5.Duetotheirlargercross-sectionalarea,thesefibresproducegreatertensionthanothersuperficialfibreswiththesameincreaseinmuscleexcitation.Consequently,L3andL4superficialfibresmustreceiveagreaterexcitationincreasetoproducethesametensionasamodestandpossiblyundetectableexcitationincreaseinL5superficialfibres.AsignificantincreaseinonlythelargerL5superficialfibresimpliedthattensionwithinthesemusclefibresincreasedsubstantiallyrelativetoothermultifidusfibres.ThismayhaveindicatedthatL5superficialfibresbehavedinadifferentmannerthanothersuperficialfibres,possiblyrelatedtotheirforceproducingcapabilities.ItmustbenotedthatalargermusclemassresultedinanEMGrecordingsitethatrepresentedasmallerpercentageofthemusclemasswithintheL5superficialfibres.Nevertheless,withninestudyparticipantsitwasassumedthatEMGrecordingsitesweredifferentacrossparticipantsandrepresentedarandomsampleofmuscleexcitation.Itwaspossiblethatdeepandsuperficiallumbarmultifidusexcitationatothervertebrallevelsdidnotincreasewithperturbationdisplacementbecauseotherspinalstructuresresistedindentationloads.Passivespinalstructuressuchastheanteriorlongitudinalligamentwhichresistslumbarextension(McGill2007)andthoracolumbarfasciamayhaveproducedenoughtensiontomakemultifidusexcitationunnecessary.Lumbarerectorspinaemusclefibresalsoattachtolumbarvertebraetransverseprocessesandtheilium(MacintoshandBogduk1987)and78producebiomechanicalextensionmomentsaboutalllumbarvertebrallevels(Bogduketal.1992).Theeffectofposterior-anteriorindentationdisplacementandforcehaveproducedmixedresultsinanimalmodels(Collocaetal.2006;Collocaetal.2007;PickarandKang2006;Pickaretal.2007;Sungetal.2005).Meaninstantaneousfrequencyoffelineparaspinalspindleafferentsincreasedtoagreaterdegreewithonemillimetredisplacementscomparedtotwomillimetredisplacements(Pickaretal.2007).Sungetal.(2005)reportedthathalf-sinewaveloadingprofilesofincreasingforcemagnitudeatconstantindentationdurationdidnotproducesignificantlydifferentmeaninstantaneousspindlefrequenciesinfelinepreparations.Ifindentationforceanddisplacementwererelatedinthesepreparations,largerposterior-anteriorforceswouldproducelargerdisplacementswhichdidnotappeartoeffectspindledischargefrequency.Inanovinepreparation,forcesof20N,40Nand60Natimpulsedurationsof100millisecondsapplieddirectlytospinousprocessesresultedinincreasedEMGresponseswithincreasedimpulseforce(Collocaetal.2006;Collocaetal.2007).Collocaetal.(2006)reportedthatgreaterforcesresultedinincreasedEMGamplitudesasmeasuredbythenumberofresponsesthatexceededpeak-to-peakamplitudesof1.5,2.0and2.5timesbaselineactivity.Collectively,animalmodelstudiesindicatethatspindleafferentdischargemaydecreaseorremainconstantwithperturbationdisplacementwhilemuscularexcitationincreases.Detailedinvestigationsofvertebralkinematicsandmodelsoflumbarmultifidusmusclestretchduringposterior-anteriorindentationsmayclarifytheeffectofperturbationdisplacementondeepandsuperficialmultifidusfibreexcitation.Fortunately,theadventofultrasonicindentationtechniques(KawchukandElliott1998;Kawchuketal.2000;Kawchuketal.2001;Kawchuketal.2001;Kawchuketal.2006)torelateskinandspinousprocessmovementduringposterior-anteriorindentationsaffordsamethodbywhichthesevertebralmovementscanbeassessed.Thetime-to-peakRMSsignificantlyincreasedwithperturbationdisplacementinallbuttwomultifidusrecordings(L3deep,L5superficial).Withperturbationvelocity79constrained,displacementandvelocityprofilesfortheDlandD2perturbationdisplacementsweresimilaruntiltheDlperturbationdisplacementof5.00mmwasreached(Figure8.1).Consequently,itwasexpectedthattheEMGresponseswouldbesimilaruntiltheDldisplacementwasreached.TheonlykinematiceventthatwouldoccurataconsistentlylongerlatencybetweenDlandD2perturbationswouldbetheonsetoftheindentationholdphase.Longertimes-to-peakRMSduringD2perturbationsmayindicatethatpeakRMSduringDlandD2perturbationsoccurredattheonsetoftheindentationholdphase.Thisresultsuggeststhatevenattheslowperturbationvelocitypeakmuscleexcitationoccurredwhentherewasachangeinthevelocityofmusclestretch.Eb004-,0DlTime(seconds)500ms625msFigure8.1IndentationdisplacementduringVI-DI(orangedashedline)andV1-D2(solidbrownline)perturbationdisplacementsacrosstime.Thedottedbluelineatthetopofthefigurerepresentsthelengthofthetimeintervalbetweentheonsetoftheactiveindentationphaseandtheendoftheindentationholdphase.Dl2.5mm500ms80Inoppositiontothisview,thetimeintervalbetweentheonsetoftheactiveindentationphaseandtheendoftheindentationholdphasewaslongerduringD2perturbations(625ms)relativetoDlperturbations(500ms).ThisisvisuallydisplayedbythedottedbluelinesatthetopofFigure8.1.EMGresponseswerenotalwaysobservedduringViperturbationswhichmayhaveresultedinpeakRMSbeingchosenasthesummationofdifferentnon-physiologicalelectricalsignalsduringsomeVi-DlandVi-D2indentations.IfpeakRMSwaschoseninthismanner,thelocationofpeakRMSwouldbeessentiallyrandomwithinthetimeintervaloverwhichpeakRMSwascalculated.Overmanytrials,themeanlocationofpeakRMSwouldhavetendedtowardthemiddleofthetimeintervalbetweentheonsetofactiveindentationandtheendoftheindentationholdphase.ThistrendwouldhaveoccurredforbothVi-DIandV1-D2perturbations;however,becausethetimeintervalwaslongerforVi-D2perturbationsthiswouldhaveresultedinlongertimes-to-peakRMSinthelongerVi-D2perturbations.FurtheranalysisoftheamplitudeofthepeakRMSvaluesrelativetobaselineactivitytodetermineifaresponseoccurredwouldberequiredtosubstantiateorrefutethispossibility.Time-to-peakRMSwasnotstatisticallysignificantlydifferentbetweenperturbationdisplacementsattheL3deepandL5superficialrecordingsites.Lackofstatisticallysignificantdifferencesdidnotmeanthatthetimes-to-peakRMSwerethesame;however,itsuggestedthatifadifferenceexisted,itwasnotasrobustasinothermultifidusfibres.Asdiscussedabove,L5superficiallumbarmultifidusfibresmayhaverespondedinadifferentmannertoothersuperficiallumbarmultifidusfibres.8.2PerturbationvelocityHigherperturbationvelocitiesweregenerallyobservedtoelicitgreaterEMGresponsesinmostEMGchannelsasshowninFigures7.6and7.7.IncreaseddeepfibreEMGwithperturbationvelocitysupportedourdeepfibreperturbationvelocityhypothesis;however,theabsenceofastatisticallysignificantincreaseinsuperficialfibreEMGactivitydidnotsupportoursuperficialfibrevelocityhypothesis.Differentialvelocityeffectsondeepandsuperficialfibresmayhavebeenduetodifferencesinthemagnitudeandvelocityof81stretchappliedtodeepandsuperficialfibres.Deepfibresspantwoorfewervertebralsegmentswhilesuperficialfibresspanthreetofivevertebralsegments(Macintoshetal.1986).Ifsarcomerelengthsindeepandsuperficialfibresaresimilar,orthogonaldisplacementsofdeepandsuperficialfibreattachmentsmayhaveproducedgreaterrelativemusculotendinousstretchindeepmultifidusfibregroupings.Greaterrelativestretchwouldhaveoccurredbecausedeepfibregroupingshaveshortertotaldistancesbetweenoriginandinsertionandexperiencegreaterangulardeviationsinresponsetoindentations.Increasedrelativestretchofdeepfibremuscleandtendoninthesametimeintervalaslesserstretchesinsuperficialfibremuscleandtendonwouldhaveresultedingreaterdeepfibrelengtheningvelocities.AnabstractmodelofthedifferentstretchesproducedinsuperficialanddeepfibresispresentedinFigure8.2.Theorthogonaldisplacementoftheperturbedvertebrawitheachindentationroddisplacementwasunknown.Despitetheorthogonaldisplacementbeingunknown,deepandsuperficialfibresattachtothevertebraatspecificlandmarksandthustheirmuscularattachmentsexperiencedthesameorthogonaldisplacement.82SuperficialFibreDeepFibreDeepfibreangulardeviationIndentationjLoad/?angulardeviationFigure8.2Conceptualizedthreevertebraemodeloftherelativestretchwithintheshorterdeeplumbarmultifidusfibresandlongersuperficialmultifidusfibres.Astheindentationloaddisplacesthevertebralbody,superficialanddeepfibreattachmentsexperiencethesameorthogonaldisplacement.Deepfibresexperienceagreaterrelativestretchandlargerangulardeviationthansuperficialfibres.VertebralBodiesSuperficialfibre83Half-sinewaveimpulsestofelinelumbarvertebraeappeartohaveathresholdimpulsedurationatwhichspindleafferentdischargeincreasessignificantlyandexponentiallywithdecreasingimpulseduration(PickarandKang2006).TheexistenceofasimilarthresholdinhumansmayhaveexplainedthedifferentialEMGresponseofsuperficialanddeepfibrestoidenticalorthogonalindentations.Thisthresholdmayhavebeenreachedearlierindeepfibresthansuperficialfibresduringposterior-anteriorindentationsandatlessertotalorthogonalindentationvelocities.Withonlytwoperturbationvelocitylevels,thisdesignwasnotabletodeterminetheperturbationvelocityatthishypothetical?responsethreshold?ortherelationshipbetweenEMGresponsesandvelocityafterthis?threshold?.WecannotexcludethepossibilitythatsensoryreceptorsotherthanmusclespindleafferentsaremodulatingorcontributingtotheEMGresponsesobserved.Attheshallowperturbationdisplacement(Dl),L5deepmultifidusfibresdidnotproducestatisticallysignificantdifferencesin?average?RMSorpeakRMSbetweenlowandhighperturbationvelocities.Asdiscussedinsection2.1.3,posterior-anteriortrunkstiffnessofindividualvertebraetostaticandcyclicindentationloadsincreaseswithdecreasingvertebrallevel(LeeandLiversidge1994).Posterior-anteriortrunkstiffnessinresponsetoindentationloadsattheL5spinousprocessisgreaterthaninresponsetoindentationloadsatL3andL4spinousprocesses(LeeandLiversidge1994).Increasedstiffnessmayhaveresultedinlessvertebraldisplacementatthisvertebralleveldespiteaconstantindentationdisplacementattheskinsurface.ThiswasbecauseifindentationstiffnessatL5wasgreaterthanothervertebrallevelsthengreatercompressionoftissuebetweentheL5spinousprocessandskinmayhaveoccurred.DuringDlperturbations,L5deepfibresspanningtheL5/S1jointandattachingtothesacrummaynothavebeenstretchedenoughtogenerateEMGresponsesduringperturbationstoL3,L4orL5spinousprocesses.ItisalsoimportanttorememberthatpeakvelocitiesduringV2-D2perturbationswerelargerthanVi-DlperturbationsduetolongertimeintervalsoverwhichthemotorcouldaccelerateattheD2displacement.Thetime-to-peakRN/ISdecreasedsignificantlywithincreasingperturbationvelocityatbothDiandD2perturbationdisplacements(Figure7.8).Thisoccurredforboth84superficialanddeepfibresdespitethelackofastatisticallysignificantincreaseinsuperficialfibre?average?orpeakRIvISwithperturbationvelocity.Higherperturbationvelocitiesresultedingreaterindentationdisplacementsbeingreachedearlierrelativetoperturbationonset.Theremayalsohavebeenalagbetweentheinitiationofindentationandtheonsetofvertebraldisplacementduetocompressionofsofttissuebetweentheindentationrodandvertebralspinousprocess.Highervelocityindentationsmayhavedecreasedthelatencyofthis?softtissuecompression?lagandresultedinearliervertebraldisplacementrelativetolowervelocityindentations.Thetotallengthofthecombinedactiveindentationandindentationholdphaseoverwhichthisvariablewascalculatedwasalsoshorterduringhighervelocityperturbationsduetothedecreasedlengthoftheactiveindentationphase.Therefore,ifperturbationsdidnotelicitEMGresponsesindeeporsuperficialfibres,peakRMSwouldhavebeenasummationofnon-physiologicalelectricalactivity.Overmanytrials,thelocationofpeakRMSwouldhavetendedtowardthemiddleoftimeintervalwhichwouldhavebeenearlierinhighervelocityperturbations.PeakRMSofdeepfibressignificantlyincreasedwithperturbationvelocityandthuswecanassumethatatminimum,EMGresponsestoindentationsconsistentlyoccurredindeepfibresathigherperturbationvelocities.Time-to-peakRMSchangesmayhavealsobeenafunctionofposterior-anteriorstiffnesschangeswithincreasedperturbationvelocity.Cyclicposterior-anteriorindentationloadsofhigherfrequency(1-2Hz)havebeenreportedtoresultinhigherposterior-anteriortrunkstiffnessthanlowerfrequencyandquasi-staticloads(loadsappliedoveratwentysecondinterval)(LeeandSvensson1993;Squireseta!.2001).Theseauthorsreasonedthatthiswasduetotheviscousbehaviourofskin,ligaments,tendons,musclesandintervertebraldiscs(LeeandSvensson1993;Squiresetal.2001).Higherperturbationvelocitiesmayhaveresultedinstiffnesschangesduetotheviscosityofthesetissueswhichchangedthetemporalrelationshipofkinematiceventsresultinginashortertimeto-peakRMS.Inthecontextofthehypothetical?responsethreshold?paradigm,deepfibrepeakRMSmayhaveoccurredearlierathigherindentationvelocitiesbecausethe?response85threshold?wasnotreachedduringlowvelocityperturbations.The?responsethreshold?mayhavealsooccurredearlierduringhighvelocityperturbationsduetodecreasedlatenciesbetweenindentationinitiationandvertebraldisplacement.Deepfibretime-to-peakRMSmayhavealsodecreasedbecauseofgreaterperturbationdisplacementsbeingreachedearlieratlowvelocityperturbations.FurtheranalysisoftherelationshipbetweenindentationinitiationandvertebraldisplacementaswellastheprevalenceofEMGresponsesateachperturbationvelocitywouldhavebeenrequiredtoclarifyinterpretationofthedecreasedtime-to-peakRMS.8.3PerturbationlevelTheresultsofthecurrentstudydidnotsupporttheexistenceofsegmentalmultifidusresponsestoposterior-anteriorindentations.The?average?RMSandpeakRMSwerenotstatisticallydifferentbetweenperturbationlevelsinallEMGchannelsforallanalyses.Inlinewithourresults,intersegmentalreflexesuptotwovertebrallevelsrostralandcaudalhavebeenreportedwithelectricalstimulationofmedialdorsalramusafferentpathways(Kangetal.2002).Thisfindingimpliesthatregardlessoftheindentationlocationusedinthisstudy,theEMGresponseasmeasuredby?average?RMSandpeakRMSwasthesameineachofthedeepandsuperficialfibresatL3,L4andL5.ThisresultmayhavebeenexpectedifnoEMGresponsewasproducedbytheindentation;however,itoccurredforallanalysesatallperturbationdisplacementsandvelocities.Thisresultmayhavealsobeenanticipatedindeeplumbarmultifidusfibresiftheyfunctionasstabilizers,yetoccurredinbothsuperficialanddeepfibresatallvertebrallevelsrecorded.TheseresultssupportedourhypothesisthatsimilarEMGresponseswouldbeobservedatadjacentvertebralsegments.Alimitationofnotmeasuringvertebralkinematicsisthatwewereunabletoquantifytheamountofadjacentintersegmentalmotionduringthesesegmentalperturbations.Kelleretal.(2003)appliedposterior-anteriorloadstotheL2spinousprocessoflowbacksurgicalpatientsatforcesbetween30-150N.Theseauthorsobservedposterior-anteriorandaxialaccelerationresponsesintheadjacentL3/L4intervertebraljointasmeasuredbybone86pins(Kellereta!.2003).Inthecurrentstudy,EMGactivityatadjacentvertebralsegmentsmayhaveoccurredinresponsetoadjacentintersegmentalmotionratherthanintersegmentalspinalreflexes.Thetime-to-peakRMSacrossperturbationlevelsmayhaveprovideinsightintothelikelihoodofadjacentintersegmentalmotionasthismotionwouldhavelikelyoccurredatadelayedlatencywithrespecttotheperturbedvertebra.Ifintersegmentalmotionoccurred,thelatencyofEMGresponsesatadjacentsegmentswouldhavelikelybeenlongerthanattheperturbedsegment.Time-to-peakRMSwassignificantlyshorterintheL5deeprecordingwhenDlperturbationsweredeliveredtotheL5spinousprocesscomparedtotheL3spinousprocess.ThisresultwasconsistentwiththeexpectationthatperturbationstotheL5spinousprocesscausedL3/L4intersegmentalmotionatadelayedlatency.L3/L4intersegmentalmotionmayhaveoccurredifpassiveoractivestructuresexertedforcesontheL4vertebraeduetotheL5indentationperturbation.Despitethispossibility,theoveralllackofdifferencesinthetime-to-peakRMSacrossperturbationvelocitiesanddisplacementsindicatedthatthismeasuremaynothavebeensensitiveenoughtoexposelatencydifferences.ItwasalsonotpossibletodeterminewhetherEMGelectrodesinsuperficialfibreswerelocatedinthesamemusclefascicles.SuperficialfibresfromL3,L4andL5spanthelowerlumbarspineandattachtothesacrumandilium(Macintosheta!.1986),thusEMGelectrodesinsertedintothesesuperficialfibresmayhavebeenlocatedinthesamefibregroupings.Thispossibilitymayexplainthelackofasignificantperturbationleveleffectinsuperficialfibres,yetperturbationleveleffectswerealsonotconsistentlyobservedindeeplumbarmultifidusfibres.Additionally,differenceswerenotedbetweensuperficialfibregroupingswithperturbationdisplacement(describedinsection8.1)whichopposedthispossibility.878.4LimitationsandtrialexclusionsRevisingtheexperimentaldesignwasnecessaryafterexaminationofindentationrodkinematics.Thisstudyhighlightstheneedofposterior-anteriortrunkindentationstudiestovalidatetheirperturbationparameters.Ourattemptedvalidationoftheseparametersrevealedthatslowvelocity,deepdisplacementindentations(Vi-D3)didnotreachtheirmaximumdisplacementinallsubjects.MaximumdisplacementwasnotreachedinthreesubjectsatL3,foursubjectsatL4andsevensubjectsatL5duetoperturbationforceexceeding1OON.Stiffnesstoposterior-anteriorindentationsincreaseswithdecreasingvertebrallevel(LeeandLiversidge1994)andhencefewersubjectsreachedmaximumdisplacementatlowerperturbationlevels.Thiswasonlyobservedattheslowestmovementvelocity(Vi)becausethelatencybetweenfullindentationdisplacementandthefeedbackresponsefromlowbacktissuetothemotorcontrollermayhavebeentoolongforonlinecorrectivemotiontooccurbeforefulldisplacementatV2andV3.Perturbationvelocityprofilesofthelow(Vi)andhigh(V2)velocities(displayedinFigure7.3)wereappreciablydifferentbecauseaccelerationateachvelocitywasthesame.Whethervelocityoraccelerationshouldbeconstrainedduringposterior-anteriorperturbationsisdebatableastheprecisebiomechanicalandneurophysiologicalmechanismsgoverningmuscleresponsestotheseperturbationsarenotknown.Pickarandcolleagues(Pickar1999;PickarandKang2006;PickarandWheeler2001;Pickaretal.2007)haveemployedhalf-sinewavedisplacementprofilesduringperturbationstofelinelumbarvertebrae.Displacement,velocityandaccelerationprofilesaresimilarwitheachdisplacement-timeperturbationcombination,yetperturbationvelocitiesandaccelerationswouldhavebeendifferentforeachcombinationandwouldhavechangedthroughouttheperturbation.TheforcelimitoflOONwassignificantlylessthantypicallyexperiencedduringposterior-anteriorindentationloads.TheActivatorAdjustingInstrumentusedbyColloca,Kellerandcolleagues(Kellereta!.1999)producesmaximumforcesof150NwhilePickarandcolleagueshaveappliedindentationloadsupto100%bodyweightintheir88felinepreparation(Kangeta!.2002;PickarandKang2006;Sungeta!.2005).TheresultsofthisstudyareonlyapplicableatindentationforcesuptolOONasstiffnessresponsesmayincreaseexponentiallyasintervertebraljointmotioncontinuesintothe?elasticzone?(Panjabi1992b).IncreasedjointstiffnessmayalterEMGresponsesmakingextrapolationoftheseresultstolargerforcesinvalid.Theseresultsarealsonotdirectlyapplicabletospinalmanipulationtherapytechniquesemployedinchiropractictherapy.DuringchiropracticHVLAthruststothelumbarspineandsacroiliacjoint,peakimpulseforcesexceeded500N(TrianoandSchultz1997).Thispeakimpulseforcerepresentedaresultantforce;however,theposterior-anteriorcomponentofthisforcewasestimatedtobeapproximately300N(TrianoandSchultz1997)andwassignificantlylargerthanthemaximumforcedeliveredtoparticipantsinthisstudy.Thecontactareaoftypicalspinalmanipulationimpulsesappliedbyafull-timeclinicianincreasedwithimpulseforcewhilethepointofpeakpressuremovedanaverageof9.8mm(SD=9.4mm)(Herzogeta!.2001).Theexperimentalprotocolofthecurrentstudyensuredthatforcewasconsistentlyappliedthroughthecontactsurface;however,centerofpressuremovementwithinthiscontactsurfacemayhaveoccurred.Forceprofileswerealsodifferentbetweenperturbationsofdifferingvelocity.Thiswasnotsurprisingbecausedifferingratesofdisplacementwouldlikelyhaveresultedindifferentratesofforcedevelopment.Themostnotableforceprofiledifferenceotherthanrateofloadingappearedtobethedoublepeakgenerallyobservedinhighervelocityperturbationsnearthecessationoftheactiveindentationphase(seeFigure7.ib).Astheindentationroddisplacedanteriorly,activeandpassivespinaltissuesweredisplacedinananteriordirection.Atthecessationofindentationroddisplacement,themomentumofthespinalstructuresbeingperturbedmayhavecausedfurtheranteriordisplacementbeforeactivecontractionorpassivestretchacceleratedthesetissuesposteriorly.Theanteriormomentumofthelumbarspinegeneratedbytheindentationmayhaveresultedinalocalforceminimumjustaftertheactiveindentationphaseduetothelumbarspinecontinuingtomoveanteriorwhiletheindentationrodstopped.Thislocalforceminimumwouldhavecausedtheobserveddoublepeakintheforceprofileattheendoftheactiveindentationphase.CloseexaminationofthelatencybetweenEMGonsetandtheinitial89upwarddeflectionofthesecondforcepeakmayhavedeterminedifactivemultifiduscontractionprovidedallorpartoftherestorativeforceneededtoacceleratethelumbarspineposteriorly.Perturbationsatlungvolumesotherthantheendofnormalexpirationnormallyresultedinthe1OONforcelimitbeingexceeded.Thisobservationsupportedthecontentionthattrunkstiffnesstoposterior-anteriorforcesincreasedaslungvolumeincreasedordecreasedfromfunctionalresidualcapacity(Shirleyetal.2003).Consequently,theresultsofthisstudyareonlyvalidduringperturbationsattheendofnormalexpiration.8.5ClinicalimplicationsThepossibilityofamechanical?responsethreshold?afterwhichafferentandefferentpathwaysincreaseneuralactivitymaybeofclinicalinteresttothecontroversysurroundinglumbarstability.Ifthedeepandsuperficiallumbarmultifidusfibresareexciteddifferentiallyduetodifferentialtimingofbiomechanicalthresholds,time-basedEMGonsetcomparisonsmaynotbeoptimaltodeterminedifferencesinthefunctionalroleofthesefibres.Frequency-basedcoherenceanalysismaybemoreusefultodeterminewhetherneuralsignalsexcitingdeepandsuperficialfibresarisefromthesameordifferentneuralstructures.ThisisnottosaythatreportsofdifferentialmultifidusexcitationbasedonEMGonsetlatenciesareinvalid(Moseleyetal.2002;Moseleyetal.2003)astheexperimentaltaskanddescendingmotorcontrolinthecurrentstudywasquitedifferent.Moseleyandcolleagues(Moseleyetal.2002;Moseleyetal.2003)studieddifferentialcontrolduringwholebodymovementsrequiringposturalstabilitywhichmostlikelyinvolvedneuralsignalsfromsupraspinalstructures.Thecurrentstudyinvestigatedmultifidusexcitationtosegmentalperturbationswhichmayhavebeengeneratedbyneuralcircuitrywithinthespinalcord.Theresultsofthecurrentstudyattesttotheneedtounderstandvertebralkinematicsandexcitationmechanismsduringsegmentalandgrosswholebodymovements.Thisneedcanbeemphasizedifweassumeforthemomentthatamechanical?responsethreshold?existedwherebymultifidusexcitationincreasedthroughsupraspinalpathways.Inthe90unpredictableandpredictablebucketexperimentperformedbyMoseleyetal.(2003)(describedinsection2.3.2),subjectsmayhavemadeslightposturaladjustmentspriortotheweightdroppinginthebucketduringpredictableperturbations.Theimpulsedeliveredtoparticipantsduringpredictableandunpredictableperturbationswasthesame;however,theseadjustmentsmayhavebeenmadetoreducethepeakforceoftheexternaltrunkperturbationwhileincreasingtheimpulseduration.Increasingimpulsedurationmayhaveresultedinalongerlatencybetween?responsethresholds?beingreachedinthedeepandsuperficialfibresbyincreasingthetimebetweenvertebralkinematicevents.Thishypotheticalexampleispurelyspeculative,yetmaywarrantfurtheranalysisoftheexistenceandpossibleneuralpathwaysofdifferential?responsethresholds?indeepandsuperficialfibres.Ifthedifferentialmultifidusfibreresponseswereduetodifferentmotorcontrolstrategies,thenthecurrentstudysuggeststheoppositerelationshipbetweendeepandsuperficialfibrestothatcontendedbyproponentsofthe?drawingin?technique.DeepmultifidusfibreEMGactivityincreasedwithperturbationvelocitywhilesuperficialfibreEMGactivityrespondedinasimilarmanneracrossperturbationdisplacementsandvelocities.Thisresultopposestheviewthatdeepmultifidusfibresstabilizethespinewhilesuperficialfibresactasprimemoversandrespondtothedifferentreactiveforcesimposedonthetrunk.Thisisclinicallysignificantbecauseifdeepfibresactaslumbarspineprimemoversandrestorevertebralpositionthentheywouldbeexpectedtoincreasetheirexcitationresponsewithincreasedperturbationmagnitude.Thismayrequireclinicallumbarstabilityprogramstofocusoncontext-dependentexcitationofthesedeepfibresratherthantonicco-contractionwithtransversusabdominus,asismandatedbythe?drawingin?technique.919.ConclusionClinicianshaveusedlumbarstabilitytechniquesinLBPrehabilitationprogramsasamethodofrelievingLBPandpreventinginitialorfurtherinjury.Aspecificlumbarstabilitytechnique,abdominal?drawingin?,requirestoniccontractionofthedeepmultifidusfibreswhilesuperficialfibresaretoremaininactive.Evidenceofdifferentialexcitationtodeepandsuperficialfibreshasbeenreported,however,recentstudiesofthedeepandsuperficialactivityinthecervicalandthoracicspinehavedisputedthisevidence.Theresultsofthisstudysupportedthehypothesisthatdeepandsuperficialfibresaredifferentiallyexcited;however,theoppositepatternofdifferentialactivitywasfound.Deepmultifidusfibresincreasedmuscleexcitationwithincreasingperturbationmagnitude,whilethesameperturbationsdidnotresultinincreasedsuperficialfibreexcitation.Thisdifferentialeffectmayhavebeenrelatedtodifferentmechanicalthresholdsbeingachievedindeepandsuperficialfibresbecauseoftheirdifferinganatomyandgeometricorientations.Thesegmentalperturbationsemployedbythisstudyarenotdirectlyapplicabletowholebodystabilitytasks,yetcallattentiontotheneedtounderstandvertebralkinematicsandtheirresultingeffectsonlumbarmultifidusfibres.Agreaterunderstandingofthebiomechanicaleffectsofdifferenttrunkmovementsonmusclearchitectureisimportanttomaximizethepotentialoflumbarstabilitytrainingprogramstorehabilitatelumbarsegmentalinstabilityorlowbackinjury.Futureresearchinvestigatingconcurrentsuperficialanddeepmultifiduselectromyographyandintervertebralmovementisrequiredtodeterminewhetherdeepandsuperficialfibreshavethecapabilitytofunctiondifferentiallyduringlumbarstabilitytasks.9210.ReferencesAmonoo-KuofiHS.Thedensityofmusclespindlesinthemedial,intermediateandlateralcolumnsofhumanintrinsicpostvertebralmuscles.JAnat136:Pt3:509-519,1983.AndersonCK,ChaffinDB,HerrinGDandMatthewsLS.Abiomechanicalmodelofthelumbosacraljointduringliftingactivities.JBiomech18:8:571-584,1985.AnderssonEA,GrundstromHandThorstenssonA.Divergingintramuscularactivitypatternsinbackandabdominalmusclesduringtrunkrotation.Spine27:6:E152-60,2002.EA,OddssonLI,GrundstromH,NilssonJandThorstenssonA.EMGactivitiesofthequadratuslumborumanderectorspinaemusclesduringflexion-relaxationandothermotortasks.ClinBiomech(Bristol,Avon)11:7:392-400,1996.AnderssonGB.Epidemiologicalfeaturesofchroniclow-backpain.Lancet354:9178:581-585,1999.ArokoskiJP,ValtaT,Airaksinen0andKankaanpaaM.Backandabdominalmusclefunctionduringstabilizationexercises.ArchPhysMedRehabil82:8:1089-1098,2001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ntramuscularelectrodes.Thespecificationsofthematerialsusedandwherethesematerialswerecommerciallyavailableisincludedineachstep.1.Approximatelythreefeetofafine-wirewasmeasuredfromthespoolandthetwolooseendswereheldtogethertoformaloop.Asinglestrandofannealedstainlesssteelwirecoatedwithliquidenamelinsulationwasused.Furtherspecificationsofthewirewere:?Stainlesssteel304?MaterialNo:cfw-100192?Diameter:0.002?Temper:annealed?Insulation:H-MLliquidenamel?Color:NaturalThiswirewaspurchasedfromCaliforniaFineWireCompanyintheUnitedStates.?CaliforniaFineWireCompany?P.O.Box446Beach,CA93483-0446?Phone:805-489-5144?Fax:805-489-5352?website:www.calfinewire.com1092.Thewirewasloopedthroughapaperclipthatwasfittedintoadrill(FigureA.1).Thelooseendsofthewirewereheldfirmlyusingtweezerswhilethedrillwasspuntocoilthetwostrandsoffine-wirearoundeachother.Whilethewirewasheldtightly,thetwocoiledstrandswereintermittentlysmoothedbyrunningone?sfingersoverthecoiledwiremovinginadirectionfromthedrilltowardsthetweezers.Thedrillwasusedtocoilthetwostrandsoffine-wireuntiltheywerealmostindistinguishablefromasinglestrand.FigureA.1Thetoppaneldisplaysthefine-wireloopedaroundthepaperclipwiththelooseendsbeingheldbytweezers.Thebottomleftpanelisaclose-upviewofthewirebeingheldwithtweezerswhilethebottomrightpanelisaclose-upviewofthewireloopedaroundthepaperclipdrillbit.1103.Thecoiledwirewasremovedfromthepaperclip(FigureA.2)andfedthroughahollowhypodermicneedlebyguidingthelooseendsofthewirethroughthetipofthecannula(FigureA.3).I..........Figure.A.2.Thecoiledfine-wirewasremovedfromthepapercliponcethetwostrandsofwirearetightlyintertwined.Notethattheloopthatwaswrappedaroundthepaperclipwasstillintact.Figure.A.3.Thecoiledfine-wirewasfedthroughthecannulaofthehollowhypodermicneedle(Becton-DicksonPrecisionGlide1.5?needleshownhere).1114.Twotypesofsterilesingle-use25-gaugehypodermicneedlewereusedinthecurrentstudy.KendallMonoject2?(25-gauge)hypodermicneedles(FigureA.4leftpanels)wereusedtoinsertfine-wireelectrodesintodeeplumbarmultifidusfibres.Theseneedles(Productnumber:537-200441)werepurchasedfrom:?TheStevensCompany?8188SwensonWayDelta,B.C.V4G1J6?Phone:604-634-3088?Fax:604-585-0193?website:www.stevens.caBectonDickson(FranklinLakes,NJUSA)PrecisionGlide1.5?regularbevelneedles(FigureA.4rightpanels)wereusedtoinsertfine-wireelectrodesintosuperficialmusclelocations.Theseneedleswerepurchasedfrom:?KerrisdalePharmacy?5591WestBoulevardVancouverBC,V6M3W6?Phone:604-261-0333?Fax:604-261-0311FigureA.4Thetwotypesofhypodermicneedlesusedinthisstudy.AKendall25gaugeMonoject2?hollowhypodermicneedleisshownintheleftpanelwhileaBectonDickson25gauge1.5?PrecisionGlidehollowhypodermicneedleisshownintherightpanel.-?.112FigureA.6.Thetwocutendsareseparated(toppanel).Thewireisthensliddowntheneedleandthetwolooseendsarebentbackwardsaroundthetipoftheneedle(bottompanel).5.Thewirehookedendswerecutto4mmand0.5mmtomaximizetheelectroderecordingareawhileensuringthatbothhookendscouldreliablybeinsertedintothesamegroupofmusclefibres.(FigureA.7).Thehookedendswerecuttodifferentlengthstopreventthetwocutendsfromtouchingandformingaclosedcircuitwhileinthemuscle./7/VFigureA.7Thetwowire?hooks?beingcutto4.0mmand0.5mmwithasharpblade.4.Thewireloopthatwaspreviouslyhookedontothepaperclipwascutatitsmidpoint,perpendiculartothewire,withasharpblade(FigureA.5).Thewirewasthenbentbackwardsaroundthetipofthehypodermicneedletoformtwohooksprotrudingfromtheneedletip(FigureA.6).FigureA.5.Thewireloopbeingcutwithsharpblade.1136.Thetwolooseendsofwireextendingoutofthehypodermicneedlehubwerescrapedwithasharpbladetoremovetheliquidenamelinsulation(FigureA.8).Approximately10mmofwirewasexposedbygentlyandrepeatedlydraggingthebladeoverthewire,thenremovinganyadditionalinsulationwithone?sfingernails.IFigureA.8Removingtheliquidenamelinsulationfromthelooseendsofeachfine-wirestrand.7.Aftertheinsulationwasremoved,thetwolooseendsofexposedwireweresolderedtonickelplatedconnectors(FigureA.9).Theseconnectorswerefilledwith60/40Rosincoresolderandheateduntilthesoldermelted(FigureA.10).Theexposedwirewasinsertedintotheliquidsolder(FigureA.11).Thespecificsoftheconnectorswere:?NickelplatedinsulatedsmalltipplugsJohnsoncomponents#105-0772-001?10Amp,0.08Dmaletipjack?ohmscontactresistanceTheseconnectorswerepurchasedfromElectrosonicInc.(productnumber229-105-0772-001):?ElectrosonicInc(e-sonic.com)?1100GordonBakerRoadToronto,OntarioM2H3B3?Phone:800-56-SONICFigureA.9.Nickelplated?Fax:416-496-3030tipplugconnector.114FigureA.11.Bothwireendssolderedintothenickelplatedconnectors.FigureA.10.Theexposedlooseendsofthefine-wirebeingsolderedtotheconnector.1158.Theclosedendoftheplasticneedleshieldwasdrilledthroughandtheneedleelectrodewasinsertedintotheshield(FigureA.12).Theendoftheshieldwasopenedtoallowsterilizationgastoaccesstheneedletipduringmedicalsterilization.FigureA.12.Oncetheconnectorsweresolderedtothewire,theneedleshieldnearthetipwasdrilledthroughandtheneedlewasplacedintotheneedleshield.9.Theconnectorsweretapedtotheneedleshield(FigureA.13)andtheentirefine-wireelectrodewasplacedinaself-sealsterilizationbag(FigureA.14).Thesterilizationbagspecificationswere:?HenryScheinSelfSealSterilizationbag?Productnumber:100-2973?Bagdimensions:3.5?x9?Thesterilizationbagswerepurchasedfrom:?HenryScheinAshArcona?1619FostersWayDelta,B.C.V3M6S7Phone:800-668-5558?Fax:800-263-3962FigureA.13.Theconnectorsweretapedtotheshieldto?website:www.henryschein.capreventthewirefrombeingtangledduringsterilization.11610.TheneedlesweremedicallysterilizedattheUBCHospitalSterileProcessingDepartment.FigureA.14.Theentireelectrodeandshieldwereplacedinaselfsealsterilizationbag.117AppendixB:Lumbarmultifidusimainandfme-wireelectrodeinsertionB.1LumbarmultifidusimagingAvarietyoftechniqueswereusedtoimagethelumbarparaspinalmusculatureusingultrasound(SonositeMicromaxx,13-6MHzHFL38Transducer).UltrasoundimagingbeganattheleveloftheL4spinousprocessbecauseatthislevellumbarmultifiduswasthemostsuperficialmuscleatthemidline(FigureB.i).TheL4spinousprocesswaslandmarkedbyidentifyingtheLispinousprocessandcountingspinousprocessescaudallyoridentifyingthesacrumandcountingspinousprocessescranially.Theexperimenteridentifiedthelumbarmuitifidusmuscleandthenaskedthestudyparticipanttoperformlowintensitybackextensioneffortsorraisetheipsilaterallegtoevokeamultifiduscontraction.Tensioninthemultifidusandlumbarerectorspinaemusclesproducedifferentpatternsoffibremovementinthetransverseplane(Stokesetal.2005).Themultifidusmusclefibresmoveinacircularfashionthathasbeendescribedasa?lavalampeffect?(Stokesetal.2005,p.124).Thefascialbordersofmultifidusareroughlyperpendiculartothecutaneoussurfaceandthusareslightlymorechallengingtoobserveusingultrasound;however,thesecontractionsassistedwithfascialborderidentification.FigureB.1.TransverseplaneultrasoundimageattheL4vertebrallevelshowingthefascialborderofthelumbarmultifidus.118Asecondtechniqueusedtoidentifythelumbarmultifidusfibreswastorotatetheultrasoundtransducerheadandimagethelumbarparaspinalmusculatureintheapproximatelongitudinalplane.Thetransducerheadwasrotatedpastninetydegreestoobtainaslightlyobliqueangletothelongitudinalplane(10l50caudolateraldirectionoftheinferioredgeofthetransducerprobe)andtoaligntheultrasoundimagewiththeapproximateorientationoflumbarmultifidusfibres.Atthisslightlyobliqueanglethetransducerheadwasplacedapproximately5-10cmlateraltotheL4spinousprocessoverthebulkofthelumbarerectorspinaemusculature.Thelumbarerectorspinaemuscleshaveadorsocaudalorientationduetomorecranialfibresattachingprogressivelymoredorsallyontheilium(MacintoshandBogduk1987).Atthislateralultrasoundtransducerprobelocationtheorientationofthesefibreswasvisibleontheultrasoundimage(FigureB.2a).Thetransducerheadwasthentranslatedmediallymaintainingthe10-15caudolateralangletothelongitudinalplane.Asthetransducerprobeapproachedthemidline,musclefibreswithaventrocaudalorientationappearedatalocationvisceraltotheerectorspinemusclefibres(FigureB.2b).Theseventrocaudallumbarmultifidusfibresbecameincreasinglysuperficialastheprobecontinuedtotranslatemedially.FigureB.2showsultrasoundimagesofparaspinalmusculatureintheapproximatelongitudinalplaneat5cmand1cmlateraltotheL4spinousprocess.FigureB.2.Ultrasoundimagesofthelumbarparaspinalmuscleswithatransducerprobeorientationof10-15?caudolateraltothelongitudinalplane.Theleftimagewastaken5cmlateraltothemidlineandshowsthedorsocaudalorientationoftheerectorspinaemuscles.Therightimagewastaken1cmlateraltothemidlineandshowstheventrocaudalorientationoflumbarmultifidusbeneaththeerectorspinaemuscles.119Usingeitherimagingtechnique,thesuperficialanddeepfibresofmultifidusweredifferentiatedtodeterminethepreciselocationofneedleinsertion.Oncethelumbarmultifiduswascapturedintheultrasoundimage,?microadjustments?weremadetothetransducertosimultaneouslyimagethevertebrallaminae.Duetothelackofrotatoresmusclesinthelumbarspine(Macintoshetal.1986),deepmultifidusfibreswerethedeepestmusclefibresvisibleinthelumbarspine.Imaginglumbarmultifidusanatomypriortofine-wireelectrodeinsertionassistedindeterminingthemosteffectivewaytoinsertfine-wireelectrodesintothedeepandsuperficialmultifidusfibresattheL3,L4andL5vertebrallevels.B.2Fine-wireelectrodeinsertionTheexperimenterperformingfine-wireelectrodeinsertionsworesterileSensicarenon-latexpowderfreegloves(Productnumber:053-484402)duringallneedleinsertions.Thesegloveswerepurchasedfrom:?TheStevensCompany?8188SwensonWayDelta,B.C.V4G1J6?Phone:604-634-3088?Fax:604-585-0193?website:www.stevens.caTheelectrodeinsertionsitesandsurroundingskinwerethoroughlycleanedwithgauzesoakedin70%Isopropylalcohol.Aquasonic100ultrasoundtransmissiongel(ParkerLaboratoriesmc,NewJersey,USA)wassqueezedintoasterileultrasoundtransducerprobecover(CIV-flex,latex-free,8.9x91.5cmtelescopicfold)(FigureB.3).Theprobecoversweresecuredtotheultrasoundtransducerusingsterileelasticbands(FigureB.4)andtheelectrodeinsertionsitewascoveredwithAquasonic100sterileultrasoundgel.120FigureB.3UltrasoundtransmissiongelwasdepositedintothesterileultrasoundtransducerprobecoverFigureB.4.Thesterileultrasoundtransducerprobecoverwassecuredontotheultrasoundtransducerprobewithsterileelasticbands.121Aquasonic100ultrasoundtransmissiongelwaspurchasedfrom:?Macdonald?sPrescriptionsandMedicalSupplies?746WestBroadwayVancouver,B.C.V5Z1G8?Phone:(604)872-2662?Fax:(604)876-0242?website:www.macdonaldsrx.comThesterileprobecovers,sterileelasticbandsandsterileultrasoundgelwerepurchasedasapackagefromConeInstruments(Item#914679).?ConeInstruments,Inc?POBox73065Ohio44193?Phone:800-321-6964?Fax:800-987-2663?website:www.coneinstruments.comTheelectrodeinsertionsitewascoveredwithsterileAquasonic100ultrasoundtransmissiongel(ParkerLaboratoriesInc,NewJersey,USA)andtheultrasoundtransducerprobewasplacedonthelowback(FigureB.5).Atotalofsixfine-wireelectrodeswereinsertedunilaterallyintotherightsuperficialanddeepfibresattheL3,L4andL5vertebrallaminarlevels.FigureB.5TheultrasoundJoelStein(Steinetal.1993)andAndrewtransducerprobeinsidethesterilecoverwasplacedonthelowbacktoHaig(Haigetal.1991)haveeachimagethelumbarspine.developedandtesteddifferenttechniquestoinsertneedleelectrodesintolumbarmultifidus.JoelSteindescribedtwoseparatetechniquesthatbothlimitneedleinsertiondepthto2.5cm:theSteinmidlinetechniqueandSteinparamediantechnique(Steinetal.1221993).TheSteinmidlinetechniqueconsistsofamidlineneedleinsertiondirectedcaudolaterallyincontrasttotheparamediantechniquewhichrequiresaneedleinsertion3mmlateraltothemidline(Steinetal.1993).TheHaigtechniqueemploysamediallydirectedinsertionat45?,1cmsuperiortotheinferiortipofthespinousprocessat2.5cmlateraltothemidline.TheHaigtechniqueappearstobemoreaccuratewithareportedaccuracyrateof81%incadaverswhichtheyreasonwouldhavebeen97%ifEMGwasavailabletoguideinsertiondepth(Haigetal.1991).Kimetal.(2005)comparedbothtechniquesandreportedcadaveraccuracyratesof73%and66%fortheHaigandSteintechniques,respectively(Kimeta!.2005).NoinjectionswerefoundtopenetratethespinalcanalusingtheHaigtechnique,however,2.5%ofinsertionsusingtheSteintechniqueswereinadvertentlyinsertedintothespinalcanal(Kimeta!.2005).Thesestudiesdidnotsimultaneouslyimagethelumbarmusculatureandtheseaccuracyrateswouldhavelikelyimprovedsignificantlywithreal-timeultrasoundimaging.PaulHodgesandcolleagueshaveinserteddeepandsuperficiallumbarmultifidusfibreelectrodesatL4(Moseleyetal.2002;Moseleyetal.2003;Moseleyeta!.2004;Saunderseta!.2004;Saundersetal.2005)usingatechniquesimilartothatdescribedbyAndrewHaig(Haigetal.1991).Needleelectrodeswereinsertedatadistanceof40mmlateraltothemidlinewithonesetadvancedmediallytotheL4lamina(deepfibres)andtheothersetadvanced10mmintotheskin(superficialfibres)(Moseleyetal.2002;Moseleyeta!.2003;Moseleyeta!.2004;Saundersetal.2004;Saundersetal.2005).Vasseijeneta!.(2006)insertedintramuscularelectrodes30-40mmlateraltothemidlinewithamedialdirectiontomakerecordingsfromlumbarmultifidusatL5.Torecordfromdeepfibrestheneedlewasadvanced30mmintotheskinwhilethesuperficialfibreelectrodeswereadvanced10mmintotheposterolateralmultifidusfascialborder(Vasse!jenetal.2006).Thesestudiesallemployedalateralinsertionsitewithamediallydirectedneedletorecordfromthedeepandsuperficiallumbarmultifidusfibres.Similartothesetechniques,thisstudyemployedamodifiedHaiginsertionwithsimultaneouslyultrasoundimagingduetoitsincreasedaccuracyandsafety(Kimeta!.2005).123Ateachvertebrallevel,fine-wireelectrodesrecordingfromsuperficialfibreswereinsertedpriortodeepfibreelectrodesandatinsertionsitesmarginallyclosertothemidline.Thefine-wireelectrodewasinsertedintotheskinbutnotthemuscleandtheparticipantwasaskediftheinsertionsitefeltuncomfortable.Generally,participantsdidnotfmdtheinsertionpainful;however,onafewoccasionstheparticipantfeltastingingsensationwhichquicklyfaded.Theexperimenterthenguidedtheneedlethroughthefirstmusclefasciallayerandintotheparaspinalmusculature(FigureB.6).FigureB.6.Theneedleelectrodebeinginsertedintotheskinunderultrasoundguidance(leftpanel)andtheneedlebeingadvancedintotheparaspinalmusculatureunderultrasoundguidance(rightpanel)Duringfine-wireelectrodefabricationitwasdeterminedthattherewasapproximately1.0-1.5mmbetweenthetipofthehypodermicneedleandthetrailingedgeofthebeveledcannulatip.Astheinsertionneedlepenetratedthroughskinandmuscle,thehookedwireendsprotrudingfromthecannulatipwerelikelypushedtowardthetrailingedgeofthebeveledcannulatip.Accountingforthehookedwirelengthsof4.0mmand0.5mm,itwasdeterminedthattheelectroderecodingsitewasbetween1.5and5.0mmsuperficialtotheneedletipvisibleunderultrasound.Toaccountforthisdistance,theneedletipwasinsertedpastitstargetlocationtoensurethatbothhookedendswerewithinthesamemusclefibregroupings.Superficialfibreelectrodeswereinsertedmediallytowardthespinousprocessandpastthelumbarmultifidusfasciallayer,whichwasusually(dependingontheparticipant)10-25mmbeneaththeskin(FigureB.7a).Deepfibreelectrodeswereinsertedlateraltosuperficialfibreelectrodesanddirectedmediallytowardsthevertebrallamina(FigureB.7b).124FigureB.7.Superficialanddeepfine-wireneedleelectrodeinsertions.ThesuperficialneedleelectrodeinsertionshownwasatL5ofSubject06(leftpanel).Notethatthesuperficialneedlewasmediallydirectedtowardthespinousprocessandinsertedpastthefascialayersurroundinglumbarmultifidus.ThedeepneedleelectrodewasinsertedtothevertebrallaminaatL5ofSubject10(rightpanel)andwasusuallytappedagainstthevertebrallaminatoensureitwaswithinthedeepestmultifidusfibres.125Inmostsubjects,thedeepfibreneedleelectrodetipgentlytappedthebonyvertebrallaminabeforebeingwithdrawn.Thisprocedurewasdelicatelyperformedtoensurethatthesefine-wireelectrodeswereinsertedintothedeepestmultifidusfascicles.Oncethedesiredmusclelocationwasreached,theneedlewasremovedfromtheskinleavingthewireinthemuscle(FigureB.8)./IIFigureB.8.Fine-wireelectrodesembeddedinthesuperficialanddeeplumbarmultifidusfibresatL3,L4andL5aftertheinsertionneedleshadbeenremoved.Thewirewastapedtotheskinwithsufficientslackinthewiretoallowthesubject?sskintomoveduringtheexperimentalactivity.Tosecuretheneedle,hypodermicneedleshieldswerecutalongtheirlengthtoallowtheneedletobeplacedintheshieldthroughthesideoftheshield(FigureB.9).(L1FigureB.9.Theneedleshieldwascutalongitslength(toppanels)toallowtheinsertionneedletobeplacedintheneedleshieldthroughthesideoftheshieldwhilethefine-wirewasstillwithintheneedle?scannula(bottompanels).TheleftpanelsshowaKendallMonojectneedleandshieldandtherightpanelsshowaBectonDickinsonneedleandshield.126Theseexposedneedleshieldsweretapedtotheparticipant?sskinlateraltotheelectrodeinsertionsites.Aftertheneedlewaswithdrawnthefine-wireelectrodecouldoftenbeimagedwiththeultrasoundtransducer(FigureB.10),althoughthiswasgenerallymoredifficultthanimagingthefine-wireinsertionneedle.FigureB.1O.Ultrasoundimageofafine-wireelectrodeinsertedintothesuperficialfibresoflumbarmultifidusatL3(justadjacenttotheL3spinousprocess).Thisimagewastakenaftertheneedlewaswithdrawnfromthemuscle.127AppendixC:EthicalapprovalandparticipantconsentformTheUniversityofBritishColumbiaOfficeofResearchServicesClinicalResearchEthicsBoard?Room210,828West10thAvenue,Vancouvet,BCV5Z1L8ETHICSCERTIFICATEOFFULLBOARDAPPROVAL:RENEWALWITHAMENDMENTSTOTHESTUDYPRINCIPALINVESTIGATOR:DEPARTMENT:UBCCREBNUMBER:?ean-S?bastienBlouinUBCH04-70633NSTITUTION(S)WHERERESEARCHWILLBECARRIEDOUT:InstitutionISiteUBCVancouver(excludesUBCHospital)Otherlocationswheretheresearchwillbeconducted:NotApplicable.CO-INVESTIGATOR(S):T.ApperleyJ.TimothyInglisRomeoChuaJean-S?bastienBlouinDavidJ.SandersonSPONSORINGAGENCIES:3ritishColumbiaKnowledgeDevelopmentFund-?Neurophysiologyofthecervicalspine;applicationofoboticsandelectroencephalographytoinjuryprevention,assessmentandrehabilitation?anadaFoundationforInnovationJBCDeanofEducationJBCDepartmentofHumanKinetics-?Neurophysiologyofthecervicalspine;applicationofroboticsandelectroencephalographytoinjuryprevention,assessmentandrehabilitation?JBCFacultyofEducationPROJECTTITLE:NeuralConsequencesofInnocuousandNoxiousVertebralStimulationsThecurrentUBCCREBapprovalforthisstudyexpires:December11,2008128DMENDMENTSBELOWREVIEWEDATREBFULLBOARDMEETINGDATE:December11,2007______________________MENDMENT(S):MENDMENTAPPROVAL___________________________________________)ATE:DocumentNamelVersionlDate)ecember20,2007Protocol:NovemberAmendmentstofullprotocol56,2007ConsentForms:NovemberSubjectconsentform6,2007Advertisements:NovemberAdvertisementtoRecruitSubjects1112007ERTIFICATION:Inrespectofclinicaltrials:1.ThemembershipofthisResearchEthicsBoardcomplieswiththemembershiprequirementsforesearchEthicsBoardsdefinedinDivision5oftheFoodandDrugRegulations.2.TheResearchEthicsBoardcarriesoutitsfunctionsinamannerconsistentwithGoodClinicalPractices.3.ThisResearchEthicsBoardhasreviewedandapprovedtheclinicaltrialprotocolandinformedconsentformforthetrialwhichistobeconductedbythequalifiedinvestigatornamedaboveatthespecifiedlinicaltrialsite.ThisapprovalandtheviewsofthisResearchEthicsBoardhavebeendocumentedinvriting.TheUBCClinicalResearchEthicsBoardhasreviewedthedocumentationfortheabovenamedproject.Theresearchstudy,aspresentedinthedocumentation,wasfoundtobeacceptableonthicalgroundsforresearchinvolvinghumansubjectsandwasapprovedforrenewalbytheUBCClinicalResearchEthicsBoard.ApprovaloftheClinicalResearchEthicsBoardbyoneofDr.GailBellward,Chair129AppendixU:Statisticaltests?Average?rms,peakrmsandtime-to-peakrmswerestatisticallytestedwith2x3repeatedmeasuresANOVAs.InpartA,theindependentvariableswereperturbationdisplacement(Dl,D2)andperturbationlevel(L3,L4,L5).InpartB,theindependentvariableswereperturbationvelocity(low,high)andperturbationlevel(L3,L4,L5).Table0.1StatisticalFvaluesofthestatisticalrepeatedmeasuresANOVAtestsforeachEMGchannel,independentanddependentvariable.--PailA(Velocity=ViiDependentMeasure?AveraeRMSPeakRMSTime-to.eakRMSIndependentVariableDispLevelDispLevelDispLevelL3deep1.371.132.231.33252.27L3superficial2.590.873.350.6110.890.0214deep1.250.652.270.1910.110.76LIsuperficial0.0071.640.021.4732.050.18L5deep0.340.943.360.6217.853.2315superficial5.651.091.71.043.551.02PanB(Displacement=Di)DependentMeasureAveraeRMSPeakRMSTime-to-eakRMSIndependentVariableVelLevelVelLevelVelLevel13deep13.460.3810.860.1975.631.1913superficial0240.850.110.7229.190.27LIdeep1.060.65.530.05221.791.27LIsuperficial1.241.012.561.0848.611.29L5deep0.580.932.940.6227.263.7L5superficial2.121.822.351.5173.91.91PailB(Displacement=D21DependentMeasureAveraeRMSPeakRMSTime-to-eakRMSIndependentVaiiableVelLevelVelLevelVelLevel13deep10.231.0110.481.12132.640.12L3superficial1.760.911.9302545.470.14LIdeep5.890.556.430.0959.360.71LIsuperficial2.11.082.731.0318.280.21L5deep8.170.436.590.07277.871.97L5superficial2.961.413.741.0296.630.76130Alldegreesoffreedomforperturbationdisplacementandvelocitywere(1,8)andalldegreesoffreedomforperturbationlevelwere(2,16).Mauchly?stestofsphericitywasevaluatedpriortoeachstatisticaltestandgreenhouse-geissercorrectionswereappliedwhenthisassumptionwasviolated.Thefollowingtablereportstheactualdegreesoffreedomaftergreenhouse-geissercorrections(whenapplicable).TableD.2DegreesoffreedomforeachstatisticalrepeatedmeasuresANOVAtestforeachEMGchannel,independentanddependentvariable.PartA(Velocilv=V1)DependentMeasure?Averaqe?RMSPeakRMSTime4o-eakRMSIndependentVariableDispLevelDispLevelDispLevel13deep1,81.09,8.751,81.18.9.401,82,1613superficial1,81.02.8.131,81.02,8.201.82,16L4deep1,81.19.9.501,81.20,9.601.8125,10.0014superficial1,82.161,82.161.82.1615deep1,81.01,8.051,81.06.8.501.82.1615superficial1.81.01,8.091,81.03.8.211,82,16PanBDisplacement=Dl)DependentMeasure?Aveiaqe?RMSPeakRMSTime-toeakRMSIndependentVariableVellevelVelLevelVelLevel13deep1.82.161.82.161.82.1613superficial1,81.08.8.631,81.07,8.591.82,1614deep1.82,161.82.161,82,1614superficial1,81.12.8.951.81.12,8.941.82,16ISdeep1,81.04.8.341,81.11.8.891,82,16L5superficial1,81.18,9.401,81.08,8.671,82,16PartBIDisplacemeni=D2)DependentMeasuie?Averaq&?RMSPeakRMSTime-to-)eakRMSIndependentVaiiableVetlevelVetlevelVetlevel13deep1,81.21.9.651.81.20,9.541.82.16L3superficial1.81.06.8.461.81.04.8.321.82.16L4deep1.82.161.82,161,81.12.8.9314superficial1.82,161.82,161.82.1615deep1.81.01.8.111.81.08,8.671,82.1615superficial1,82,161.82,161,82.16131TableD.3.SummaryofstatisticalpvaluesforPartAandBstatisticaltests.Statisticallysignificanteffectsaredenotedwith**PailA(Velocity=ViiDependentMeasure?Averae?RMSPeakRMSTinie4o-peakRMSIndependentVariableDispLevelDisplevelDispLevel13deep0.280.320.170.290.110.1413sul)ellicial0.150.380.10.460.01?0.98L4deep0.30.460.170.710.01?0.48LIsuperficial0.940.220.880.26<0.001?0.6315deep0.580.360.10.460.003?0.07L5superficial0.045?0.330.230.340.10.38PartBB(Displacement=Dl)DependentMeasureAverae?RMSPeakRMSTime-to-peakRMSIndependentVariableVelLevelVelLevelVelILevel13deep0.006?0.690.01?0.83Interaction=0.04?L3superficial0.630.390.750.43<0.001?0.7714deep0.080.560.047?0.95<0.001?0.3114superficial0.30.390.150.34<0.001?0.3L5deep0.470.370.120.48<0.001?0.048?L5superficial0.180.210.160.26<0.001?0.18PanB(Displacement=D2)DependentMeasure?Averae?RMSPeakRMSTime-to-eakRMSIndependentVaiiableVelLevelVelLevelVelLevel13deep0.01?0.350.01?0.33<0.001?0.89L3superficial0.060.360.20.42<0.001?0.8714deep0.04?0.580.04?0.92<0.001?0.44LIsuperficial0.180.360.110.38<0.001?0.82L5deep0.02?0.530.03?0.81<0.001?0.1715superficial0.120.270.090.38<0.001?0.18132TableD.4.MeansquareerrorvaluesforeachstatisticalANOVAtestforeachEMGchannel,independentanddependentvariable.PartAlVelocitv=V1)DependentMeasure?Averae?RMSPeakRIdSTime-to-peakRMSIndependentVaiiableDispLevelDispLevelDispLevelL3deep2.04210.6739.281702.40.0080.01413superficial1.661177.1118.9815208.530.010.0214deep0.29378.3890.3948840.020.05LIsuperficial31.78664.54629.488925.860.0070.0615deep17.262288.03599.8423702.890.0050.02L5superficial1.271067.11332.76198.220.0080.02PailBiDisplacement=Dl)DependentMeasureAverae?RIdSPeakRIdSTime-to-eakRMSIndependentVariableVelLevelVelLevelVelLevelL3deep9.9273.91208.09495.150.020.01L3superficial86.92771.71095.419558.270.030.01LIdeep122.4230.31191.18171.960.010.02LIsuperficial743.382682.193527.8620896.720.020.01L5deep112.971231.621230.9212958.190.0040.0115superficial421.02567.291627.8834860.020.01PailB(Displacement=D2jDependentMeasure?AverweRIdSPeakRMSTime-to-)eakRIdSIndependentVariableVelLevelVolLevelVelLevel13deep18.42208.22151.061617.80.010.0113superficial53.67815.05848.018551.70.030.02LIdeep313.12123.381265.76651.020.010.02LIsuperficial1291.271110.6512019.1314817.460.010.0215deep402.411906.88816.5822374.290.010.01L5superficial515.16355.774764.211848.740.020.01133TableD.5.Estimatesofeffectsizeasmeasuredbypartialetasquare(n2 )foreachEMGchannel,independentanddependentvariable.PartAlVelocitv=Vi)DependentMeasure?Averae?RMSPeakRMSTime-to-eakAMSIndependentVariableDispLevelDispLevelDispLevel13deep0.150.120.220.140.290.2213superficial0.250.10.30.070.58<0.01L4deep0.140.080.220.020.560.09L4superficial<0.010.17<0.010.160.80.0615deep0.040.10.30.070.690.2915superficial0.410.120.180.120.310.11PailB(Displacement=Di)DependentMeasureAverae?RMSPeakRMSTime-to-peakRMSIndependentVariableVelLevelVelLevelVelLevelL3deep0.630.040.580.020.90.1313superficial0.030.10.010.080.780.0314deep0.310.070.410.010.960.1414superficial0.140.110.210.120.860.1415deep0.070.10.270.070.970.3215superficial0.210.190.230.160.90.19PailB(Displacement=D2)DependentMeasure?AveraeRMSPeakRMSTime4o-eakRMSIndependentVariableVelLevelVelLevelVelLevelL3deep0.560.120.570.120.940.0113superficial0.370.110.190.080.850.0211deep0.420.060.150.010.880.08LIsuperficial0.210.120.250.110.860.0215deep0.50.050.450.010.970.2015superficial0.270.150.320.110.920.09134AppendixE:IndividualsubjectdataTheindividualsubjectdataarepresentedinAppendixE.Thefollowingeighteenpages(pages136-153)containtablesofthedependentmeasuresfortheninestudyparticipantsincludedindataanalysis.Theindividualparticipantmeansarealsodisplayedgraphicallyinfiguresattheendofthisappendix.Subject07wasremovedfromanalysisduetoreasonsdiscussedinsection7.1.1andthisparticipant?sdatawereremovedfromthetables.ParticipantMeansEMGresponsestoperturbationsofthesamevelocityanddisplacementwereaveragedforeachsubjecttocreateninemeansforeachofthenineperturbationvelocity-displacementcombinationsforeachperturbationlevel,EMGchannelandparticipant.Thesemeansaredisplayedinthefollowingtableswitheachrowadifferentparticipantandeachcolumnadifferentperturbationvelocity-displacementcombination.PerturbationsattheV3velocityortotheD3displacementwereexcludedfromanalysis;however,themeansfortheseperturbationsaredisplayedinthefollowingtables(refertosection7.1.2forthespecificvelocitiesanddisplacements).ThemeansforeachperturbationlevelaredisplayedinadifferenttablewithallperturbationlevelsforasingleEMGchanneldisplayedonthesamepage.The?average?RMSdependentmeasureisdisplayedfirstandisfollowedbypeakRMSwiththevaluesofbothofthesedependentmeasuresinmicrovolts(DV).Thelastdependentmeasuredisplayedistime-to-peakRIvISwithvaluesdisplayedinseconds.Thelasttworowsofeachtabledisplaythemeanofallindividualparticipantmeansandthestandarderroroftheparticipantmeans.ItmustbenotedthatEMGvalueswerenotnormalizedandthusthesemeansmaynotbeindicativeofthegeneraltrendwithineachparticipant.135ON-40eNCCDCDCD(NCD0)> OCI)Ci)Ci)CI)a <- 000 00000 -m 0 CD 0) 0) 01 . 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SN)k)C)--4 01IDCD- . 0 -4 010 N) CC) N)CD N) 01 N) - -C) 0CDC.)CDCD 0)CJ1 ID0- CD C) -4 0N)CO CD<COC) C.)cC?Ic?ICDU?Co>(N(NQc?c?CD00)0)(NCLO-?-(L.CDU)?COU)c?iCocoCDrcCNCoU)(N(N>?(Nr?CNtCoCDCD2Qqqc.1tCD>(N-oQ?or-I(N>--CD?Dlr-cocJr>-?-(N?CDiL?N>rCDoDCDCoU)rr-U)??.1)c>?(N??-00000000C1)(i)(O(OCI)C/)CoO)CDLoU)LOCiCoCDN-.>(NN-CoCDCo0)?iCoCD0)C?J0CDCo>-CDN-CDCD-LqN-aDCDdr0)0CDCo0)OCr-I(N>(NCDqo)r-N2i(NCNCCD-10)>-cOLON---CDCDOT-LOCCCU)c(Nco,U)0)0)(N(NL?CDI?-??CoCD0CDe?c-.i0CD>?-?--COa)>-Co-COCI)(O(I)0N-CDCoCD0)U)Q-CLICoCD(t)U)U)>?-?(N(NCDN-.0)DLC-U)02coro>U)CoCJOCo-CD0r?-?CD0)c(C>CoLOCN(N_?I?CoCoN-Q)r-U)OCICo0)N-C?JCDCDU)>?-c?.icO(N00CD>CDCo?-?N?U)o?CrcNo0)CoU)CDCoCo0OCoU)r?IH-r?-(N000)DCCC(NN-N-0)N-(NU)U)CDCoCDOCDO)N-??>?ci)>?-00000000??C/)(OU)CI)4JC-pC-PIci)ci)CCCDCD(I)-?.?Cl)> i)COCI)Cl)Cl)CI)a- 00000000m 0 CD 0) 0)01 - C) .3 -QCDI- .- r?j -.<(.) -r\)?0)0)- -.I?.) I\) -.<0CD--1... . 0)CD0)L?3O0)CD CD)CD 4Q)() 0 CDF?,) - - 0) C) -- C..) 0) C..)F?) - C..) 0) - --.IC)1 0?010r\).J? 4C..) 01CD(0> (0COCOCI)(OCI)a- 00000000, - 0 CD 0) 0) 01 - w F?.) h.-1CD01 . - F?.) - - C..) -Q) 0) - 01-1 - CD. --.CD oooi-60) - 0 C..) CD 0) CD -J01 C..) F?.) - - F?) F?.)910Oz.I(110 4 L0CD C00 -0) 0) F?.) . F?)CD 0) C..) F?) - C.)10? k)CDF?)-4 CD0b0-F?.)CD F?) F?.) - 0 C.) 0) C..)?co C..)C..) 0)-h919)F.;.)CD 0(10) 40 ---910-4 -0C,) O)F?.)4.CJl. . F?JQ1(;j0)C)1 F?.)- - 01 - -1 C.) -p aP?91.cD91091 40)- 4oDo1- 01k)1p9lC*)01 -CD- - 01 CD C,)co91..CD F?) 01 0 CD C.) -.1-10) 0)CDCDC.)F?)F?)0,0,C.)01CD0)?4t?)-10)0-4 b0, F?)0,CD0,F?)C-&(0> 0Co0)Co(o(/)a <- -m 0 CD 0) 0)01 . C.) F?) ? --I-?CD0) 0) C.) - 0) -:p k)r):?-010) - F?) 9101. o0 C0)0) -0)O1C,) .0)F?) CDCD. ;1.. .CD0C91C,)01-0k)CDC..)0)F?) 0)- k)F?) C.)0?0)-Ljj?,CD ?b??Cw0)gCDCD!0)- wF.) -I0)CD0)-101 0(, 4 () -- C..)-. F?)F?;.)- rc- i <- 0) CO 0 0). C..) F?)CD 0) C.) F?) CO - -P?:? ppp..) Ci.)F..) 00) - 0 - CF?.) F?)0) CD . - - -- C.)- k)0)0)F?)C..)jk)- C.)-)C)C..)0 -CDC.))F?). o N.e)1 1?F?)-LI.dCDCD CD?cJCCDCD I(0> C0Ci)Ci)(i)C0C?)a- 0 0 000 0 0 0 -m 0 (0 0) 0) 01 . C,) k) -RCD-r.-1. C)14 <50p JCDN?01 O)CJ1C,) <o 04.D? 0)010)0 o01o,?.J C,) Q(.) 0) - - 01-1 0 C)--- -).I%) <-4 -o k)A A - k0101-4(D010)O) k)CD k) - - - 01k) - <0 -cojP?o, k)oo1o1a Q401k)4C(0k) ? -k)k)<?C.) S?0)0)C,) (0CDPoo.ODk) 0)? -.i4 IDC,)(0> 0cDcI)CI)C0cI)a- 00000000m 0 CD 0) 0) 01 C,) k) -aCD9Z0)(D9)L?I 04(,30)(,)0.A ? S01 &o k) 4 (DO) - - - 0) -0). . CD. .?.1.. k) 0:,F3IDk)C.) - - I?) - CD .1?) 0) C C,) 01 - (31 CD1 -.0. C,)?4kCD C,)k)c,)C,)z.)CD0O. k)01C.)01C,)4ID0 - 0) C.) - ..k 00) M - -0)0)-4p-4C,) 0)(31 (D 00 C,) - IDJ010) )k)O)(0C.)4.k)01-.Ik)O01(D9)IC.) CD k) 01 . (001(00) k)k)-OC,3c,)-4PoP:-0)O)(D-4J k)W -C,)ID3.0)k) 01-N) N) - - (Fl 01(3101k)9 Ib,,)ID(00) N)1\)- k)- 0) <0101 C,) o01o0)C..)(.). . . 001. 01. .0,CD-40- ID(.)0 --0)a)0(0O)0) C,)(0> (0(0(0(0(0(0a <- 00000000 -rn 0 (00) 0) (31 C,) N) - --I-,CD0) - - CD - N) -0 -.J N) 0) (31 0-.b (31O)O?)Q). 60)0) 4 co0)0 C.)?? <9)-;-- 01 01. - 0)? 01SC,) 0)0-.IN)k)-_.. N)N)C,) <-J01N) N)C,)N)9)91 ?po).c.). N) 0. . CD ID0)0) CDN)CD4 -(D N)-(,)C,)Noij. ICD4.0)0,C.CD,)N) IDN)0CD010CD0)0)C.) N)- N) N) . o-i001N) <9i:CD N)4C,),?oI0)0)b0)04-.ID010 - 00) .- 0)C,)? N) (D? <- 0)-1 N) - 01 C,)I I I ICl)> Cl)Cl)Cl)Cl)Cl)C/)a <- 00000000 -m 0 CD 0) 0) 01 C,) N) --,-ICD(.) C,) . N) - a) - N) <CD - 0) (.) - . .-4 N) -bo 6C,) 0) CD00 . a,() C,) C,) - N) - 0) -CD . C,) 01 - 0). 01 CD 91a)ol 01 C)0) C,) 01- (,) a, N) 1 - N)01N)?0)?--.0))0) -0)ON)50 N) 0 N) 0) C,) C,) C.)0)0) ? - N) . - N) N)j:,-Po,k)P-.1 - - 0101 0 -401 (,) - 01 - 01 -cx, a, - N) 0) . -91DICD N)CD4b000) 01- N) _ CD . - 0) N)0)0) - C,) - 0) N) .P?o910 N) 0 C,) 0 ?1 CD 0) QCDCD C,)- 01 C,) N) N) - 0101P? ICoN) 01C,)01CDCD C- 0 CD 0) -4 0)0) -J - I?) - 0) C,) -ppp0,IC,)01 CDCO4?,0)01 CC,)0 CD - CD 01- C?) N) N) --4. 0) - N) 01 N) - N) C??CDC,)C/)> CflCflC/)C/)CflC/)a-m 0 CD 0) 0) 01 4. C,) N)-q)CD01 - - - Co -2- p9?910)_i N)-4 N) N)_)0)SDP1? a,- ().f._.1 -J0O..01O.01 N)0) C,)01 CD 01- 1 -D. CDCDC,)cn . C 0c0 01 o o 0) C,)- N)- - N)_. <00)N) 0N)0N)CDN)CD 0) k N)C)CD t)o N) C01-4 N)-?.-N)-? - C.)-?0Co.. C,)01C,)00)N)0)0) -4 01. N). a,.-4a,01 01CD - - 0) . -(D 910)P?..- 0)0)?CD 0 a, -J C.) 0) a, 0)-C,)-?.__.N) N)C_ON) C_ON)a,a,044C.)a .& . N) C,)0) - . .Ia, - CD? CD .Cl)> C/)COCl)Cl)C/)(f)a <- 00000000m 0 CD 0) 0) 01 C,) N)-?-?CD01C..) a,010a,4. <PPP!?- C,)? -0)C.) a,N)0)Q- -4 - N) 0)0) C,)-01 . N) - -- N)0104C,)Q -JCDN)CN) 00) -J0 .r. C,) 0)Co0) C_ON)N) <2cx001CD401 CC,)-40):-?-j:-coP-I-401 -J000,4C0)01CD01a,40) --?..N)N) <F;)L0101N) C0N)04,30N)C,) N)<p, p:-4P): IS;.)N) 04C,0 CC,) - - 01 -.- N) N) N)_D4? 0)C,);CD0) 0C.) . CD-. N) N) - - N) N)91p).). 0,0)0)N)C,)C0) CO CD0)- 01--- C,) C,)0). 0 0) CD 01 C,)N)-40.. CD. . 0)... CD 0) C,)C,) 0 C,)CrrC)00)> C/)C1)COCOCi)CI)a- 0 0000000 o- 0 CD 0) 0) C.fl . C.) r\) - (1)E??-iDCD09999999999? - - 01 01 01 0)01 ?.3 C.) -1.C.)-J 0.0)0)F?)O)-0) D<09999999999-o1 01O)o?.j-4-- IDcok)r?3co<09909999999-k0) 01 0) CD - C.) 01010. 0) CY1 ?1 0) ?.I 0101 - 0 c<00009900999 I?Jb -. k, .- - - -. b - k)Q)J0I\)CD01CD0<09909999999 r.)o- F?J-3k)--0)0) 01014C.)C.)011\)CDC.)j<09909999999 rzb__i Q010) 0)-J-J0C.)0)0)<00000000900 C.)bI ok(DO) 0?0)0-C.)0)C.)0<0900999900CC.)o-?k)-010) CD C.)C.)-C)10)<00009000999 C.)b.- br?.-.-.0) 0)0I?3(,)?CDC.)CD0)C,)(0> C/)0)Ci)C0C/)C/)a <- 00000000 C,,- 0 CD 0) 0)01 - C.) I?.) - CDI?C)-?CD99999999999.)0J0)0iI.r.C.) 00)C.)0CD?4?-?A<00099099909-b-1.01010)C.)01 60) CD 0) 0- - 01 C.) t\) CD -<99999999999--01 01 .010)0)C31-4-0)6(.3(0 O))-C.)-0)C.)<00099999999 1%.)o:ID010) k)01-0)--.I--.JC.)-4-<99999999999 %)o o-r 6CD-I. -00)00)CD-0)r.?)<00000009000 tb o? 60)0)- - - 0) CD - -<00000000000 C.)b-.- -k 60) CD 1.) 01- I?.) - - 1%) CD 0 -<00000000000 C.)b?h k-.-- 60)-4 k)01C.)0)I)04.C,)4.<90099999909 C.)0 ---0NQ0)0) ?I0)C.)00)O)O)oir?.)(.3ci> cl)C/)COcO(Oc/)a- 00000000 ,,- 0 CD 0) 0) 01 - C.) k) - CDmC)RaCD0099999999901 C.) 4 010) 0) 0101 - 0)-0)?-0)0)-0)O).<09999999999-?01 4.O)010)C.)?i01C,)01 IDrs3- 0)0)01-0)-0)0)- j.j<00990999999-30)0)010) CD - 0) ?.i 01 C.) ID)0) 01CD0)-0)-.0C.)<00900990999 rID0) 0) C.) F?-3 00)- s) C.) 01 .<00000000000 IS.)?- k- 60) CD 010) 0) -.1- 01 . 010<00000900990 Mb:0)(D01-I----JCDO)010101<00000000000 C.)b.- ?bj-.-& ID0)01 0)0)?J0)--.1<00900900009 C,)0 - - 3 - 1%) - - 1?) ID01(0 C)0)CD011\)CD0)-.I01<00900999999 C.)b- IDCD0) CD CDI\)-I0)C.)100Ii)C-4-.-FCO?O)(NCOj-COC-QCo>(N0).?LoeC4vCO>?QC?C.-0.-CCO>ccDc?.jodoooooooo0)00O.-(N>?(NCc?.i>CoCCQwrco.->(NCOCOccr?cc..--ooQj-c.->?-.-00000000000a)I.-)a).-LC?)00000000.?OCi)Co0LO-CoUQNCO>CNcNCO.-i-ccccu)O,.-UQ.-.1.-OCNCO>?-UCO>CoCo.--cOLLcc-cO0U(Naaaaaaaaa>(NCo.-.-.-U->?-UCC?1.-.-(Nc?.i>?O)COCCLD?().->0)000)Uocc-r.->0)O.-1---rIt)c0ccIQLC00000000000ci)C.)CUU)(NCi)00000000.-?Cl)(O(OU)C1)CoCoQ..cN..-.-?QCo>(N(NCoC?.1COCOrCOCCQCO>SQ.-CNQCO>0)900000000000CNOCOCOCOCOLOLOO).?U(-?I>?-U?-0(N>?.-CoF?-CoCO0CoCO90CN.->CNCOF?CO1--0)r--LO(NLc)eCoLCC.->LC)0)CN0-Q)Lc)0COIdddddoddda)0(1).?Cl)00000000.-?CI)Cf)CI)(1)C-FCI-C)C)C.-C)>C)CC14C)O)C)cOc,>C\1?Dc>?-D-?-Qc>C)(NCw)C1)e?-000000000000(NOOCDC?l0cOC?4LOcO?---(NOci>?(Nc..j>?-UCD?-00000000000>(Nococ?icoeU-1:(c?-00000000000>((NO)(DO)LOddddodddoci)C)Cl)(N(I)U)Cl)00000000?OCOCI)?C/)C1)(N0c1)C1)U)r?.O)-U?Qcc>(NU)??O)(N(NCDCN?-U??-N?-c>?-Uc1)>CDC1)?ctC\jcOO)0)cOU??0dddocSdoooCNCDC1)0)O)C1)O)CDCDUc?.>?UcJ?-o?-(NocN>c1)C1)CD0??F?-CNLC)r-0Ur?C?.i?->(NOCDOI??LOOCNF?-.O)UU)CNv-do>U)(1)oodooooooa)DbC.)CI)-Cl)00000000??)COCl)Cl)Cl)CI)C?)CD00C1)CNOC.4C1)r?o)U?-0c)>0O)O(NCDC?)U?-oC?)dddddoodo>?-?-?-0(N00C1)>C?)(DC1)U)OC1F?CDOUodooooooo>(NCCDCDC?)(NcF?U?-o--(N0c>?-Uc?.i>C?)CDCDC?)r?-OcOOLOO)QCDF?.-U)COGOGOCDLDCD?->F??eCDCO?->?dddddoddoa)C)(1)?-Cl)Cl)COU)Cl)CD(OCl)?CI)a)a)?I.Ci)ta)0a)C)C-F0CDCDCDCCD-?CCDCDCD> )COCDCD(/)a- 00000000 Cj)- 0 (0 C) C) 01 . k) - CDE1DCD-.?CDC)W01CYIC3W I-I) -0I01-4.-<0990999999901 010101 QC)C) -.I(DC)0C)C).<02 99999999-C)C)C)CY10-JC)(Ok) k)-40,()<99999999999 i0 ? - . a - - - -0101 0.0WC).f.-<02999929992k)b- - F?, F?, F?)C) CO W 0101 C) 0 C) - C) C) F?)<000000099001?,bi?jC)0 0(iF?J-1.W<00 000009000W00101 C) 0C,)-00?<00009090990WJI%3WCC) k)W-W0-k)C)COF?J<09009990990Wb ? ? ? 1)00 ? F?) N)C)C) C)F?3CDCDCD..0 wCD> I)CI)COCDCI)a <- 00000000 ,m 0 CD 0) C) 01 W N)? CDC)CD99099999999? . C) F?) 0101 - - - 01 C)01 CD 001 F?) CO - 001 - F?) ?<00099090999?N)01 0)W01C)01JCD01F?) 6OC) -C)W--JN)01N)C)C)N)<00000009009?01 O)WC)C)C)-W 6CD--C)-00CD.CO W<00099099099 N)b-C) 0101 C) JW C) CD - - () ?<99999999999k)a - s a - - - - C.) - 0001 F?) C.) C) . N) C.) CD . W N)00000000000o-- --??o 6C) C) 01 - 0(0 C.) - C) 01 ?1 W<00000000000W?- 6C)C) C)CYiC)1-k)k)??W?<99099999990W0- - ? ? ? ? ? F?) ? 0 j-.I. F?) C.) 0001 CD W W N)<00 000000099W?o 60 C) 0 4 010 F?) C) 0 F?) C.)C.)CD> I)CDCDCOCDCI)a- 00000000 (l- 0 CD 0) C) C)1 - W F?) - CDm0CD00000000000)IC)W 0C)-.CD01CDr?,-? C<09990909999-k.o, C) 01 C) CD C.) . C) C)-01C) CD-C)CDC)-.I00 N)<09 900-99999-) -J CO . 001 C) CD -.1 01001 W0-0-W-C.)<99999999999 )0 - F?) -? - - k () - F?)C) C) 0 C)- C.) N) - 0 C) - ?<99999999999 FOF?) Q(DO 010101-F?)W01CD0iF?)<00000000900 1%),OF?) J-WN)-IF?) COC)01--0CDW--J W<00000000900Wb- ?--W-C,)(0(0OC.)C)0CY1F?)C)C)? ?<99990999999W0-(DC) ?--(D01C)-.COWCDF?)<00000000900W0? CiC) 001 C) N) CO- C) W - C.)-ea?a?Inr.ja?-..Cy)C?)C\1U)-U)J-0)U)0QCNC1?-Qc>(NCD)(N0CD0ccc>?QCCNC?)>C?)CD---00(N>-Uc?c(N>?Qcc(N>C?)F?CDC40CNCDCD0)CDe?-00000000000>(Nr-c?)ocNeU)(D(O(?CD(DU)CD?>?-U)U)(NLCdooddoddoa)D??()(CII,a)COO)Cl)00000000?-COCI)COCOCOCOC?)(NU)CDCOOCDC?,CDr-..C-?--cC?)>(N0(N(DC?)U)CNUCCNc?>?00)-oC?)>?)CDCDU(NQ?-C?4??C?(Ndddodddoo?4CD?QCN>?C?)U??-??CN?.J>C?)CD?C)-C?4--COCDCNULL?-00000000000>?4?0)???00000000000>F?-O)0C?)CD0C?)c?)00000000000a)ci::C.)a)U)Co00000000-COCOCi)CI)C?)C?)CDC?4O)?COCDC?4QC?)000000000>(N0(D?CDc3-C?4NQQ????C?)>?Q(N0??O(N?C?)>C?)0?C?CC?4?-?-?Qddoodoooo>(N(N(NU)t??00)??Uc..j>?-0)uo_o?oc?.i>?)t?CDCDO)r-00oCDQU)-CDc?)U)U)CDcL?>?4-(D-U)CO0)r--U)e(OL??00000000000>C?)CD0t?CD-CDCDIdddddoooda)Ct:0a)U)CO0oo00oQ?00(13(0(0(1)C)C)C-FC)C)CIC)?U0-pCCDCDCCDCD?.CDC(1)CD?.?Cl)> COCl)Cl)Cl)COCI)0. - 00000000 0-. 0 CD a) a) 01 . C,) k) - CDCD00000000000II%)- -1a)CD01CDCD01a)0<op ppppppppp-01 01 C,) a) 4 C,) - C,) 0)01 6.-J- 0a)?J0-<00000000000--.? bLa6a)? a) a)I\)01C,)-0 C,)<pp ppppppppp r30- ?00C)--0a). .-01CD0) MN)-a)<pp ppppppppp ?30- 3-0-4 CD CD.- a) . ?3 0) 1?.) 0)0)<00000000000 1%)b.- 6JCD 0r?3CD---C,)00000000000b?i --k-oo-1- C,)--C)1a)0a)a)CD<op ooopppopp C,)a)-I C,001a)-0)a)a)r?3<00000000000 C,)c)r?J 6?4 0- - - - a) ?4 - a) .Cl)> Q)Ci)(I)(OQ)Cl)a <-? 0 CD a) a)UI . C) r?) ? CDm,??aCDop opppppppp44-4C,)-.jCDk) -C,)a)01a)a)0101a)<op ppppppppp-- 01 . - C,) - 01 a) -401 0 6a)a) a) )0)C,)0.C,)<pp ppppppppp-k)a) a)0a)0)01?4CDUICD 60)CD CDa)01-a)---1C,) C,)<pp ppppppppp 1)or?j C,)??r.. 6-40L?3a)k)0?--0I?3C,) -<PP 000000020 1?)Ok) C,)?-a)k01CD010C,)-CD01a)<00000000000 1?)6CD- - a) a) a) k) - 01 - -4<00000000000 C,-1b-. b?--a)a) C,).a)CDa)a)CD0a)-<00000000200 C,)- - - 0 -a)C0 C,)0a)a)I?-)-0)a)a)<00000000000 C,)?i? ---?--6Ok) C,-1..CDU)> Cl)COCI)a- 00000000 Cl,-, 0 (.00) a) 01 - C,) ?3 -g?-tDCD00000000000-4 IL?Jk) -4a)0k)--.0)a)00<00-boi 01a)-01a)4.4 6CDC a)k)-4a)-1.0)W0)CD<00 ppppppppp-a)01a)a)?1a)-.(001 010a)-.a)--JCD0ia) C.)<00000000002k)b:_01-4 -01a)CD001000) -<pO 2220p20200 k) - rJ k) k) - C.) I?) I?) F-?)a)t?.) C.)-.k)C,)-.k)a)C,)000 0bk c,)?-a)? 01a)0?J0CD-a)k)<00 0000000op)oa)a) 01a)a)?4CDCriCDC,)- .<00000000000 C,)b-a)CD 0)-?--a)0-<00000000000 C,):.k) ?)4---b0 - 0 C,) 01 .-4 - a) - 01(0IndividualParticipantPlotsThefollowingpagescontainindividualplotsoftheparticipantmeanswithstandarddeviationbarsforeachdependentmeasure,EMGchannelandperturbationlevel.Theparticipantdisplayedineachplotisidentifiedatthetopofeachplotbythenumberfollowingthe?S?(ie.S03referstoparticipant03).EachplotdisplaystheparticipantmeanofalltrialsforeachoftheVi-Dl,Vi-D2,V2-D1andV2-D2indentationperturbations.TheViandV2perturbationvelocitiesarelabeledalongthex-axisas?low?or?high?perturbationvelocities(seesection7.1.2foranexplanationoftheselabels).TheDlperturbationdisplacementisrepresentedbythesolidlinewhiletheD2perturbationdisplacementisrepresentedbythedashedlineoneachoftheindividualparticipantplots.The?average?andpeakRMSvaluesareplottedonthefollowingpagesinmicrovolts( 1iV).TheamplitudeofeachEMGchannelwasnotnormalizedandthusthey-axisscaleforeachparticipantwasdifferentandisnotdisplayedintheplots.Todeterminetheactualmeanvaluesforeachparticipantrefertotheprecedingtablesinthisappendix.Thelastsetofplotsdisplaythetime-to-peakRMSvaluesinsecondsforeachparticipant,EMGchannelandperturbationlevel.Thetime-to-peakRMSplotsforallparticipants,levelsandEMGchannelsaredisplayedwithay-axisscaleof1second.ToevaluatethedifferencebetweentheDlandD2displacementattheV1perturbationvelocity(PartAanalysis,section7.2.1),thedifferencebetweenthesolidanddashedlinesatthe?low?perturbationvelocity(leftsideofeachplot)mustbeexamined.Toevaluatethedifferencebetweenthe?low?and?high?perturbationvelocitiesateachperturbationdisplacement(PartBanalysis,section7.2.2),theslopeofeachperturbationdisplacementline(DlandD2)mustbeexaminedacrossthe?low?and?high?perturbationvelocities.154V.?0>0I.-,RMS: L3 perturbation levelEMG channel: L3 deepLOW HIGHPerturbation velocitySb501 S02 S03 ?ZLZ4LOW HIGHS04?------HLOW HIGHLOW HIGH LOW HIGH505 1 S06LOW HIGHS08????509?UiUiLOW HIGHLOW HIGHHLOW HIGH4-.,0>0RMS: L4 perturbation levelEMG channel: L3 deepS02 jLOW HIGH503S04 S05LOW HIGHLOW506HIGH508LOW HIGHs09cJLOWLOW HIGHSbHIGH LOW HIGH LOW HIGHPerturbation velocityRMS: L5 perturbation levelEMG channel: L3 deep4-,0>0l)501LOW HIGH?1S02LOW HIGH503504 505LOW HIGH506LOW HIGHS08LOW HIGHcJLOW HIGHs09LOW HIGHSbLOW HIGH LOW HIGHPerturbation velocityLOW HIGHHIGH LOW HIGH LOWSbRMS: L3 perturbation levelEMG channel: L3 superficial502 503504>4-.?0>0LOW HIGH505LOW HIGH506S08LOW HIGH LOW HIGH LOW HIGH50900LOW HIGHPerturbation velocityRMS: L4 perturbation levelV.)4-I0>0LOW HIGHEMG channel: L3 superficial502-.--JLOW HIGH LOW HIGHSO 1 503504LOW HIGH505- -LOW HIGH506508 s09LOW HIGHLOW HIGHLOW HIGH LOW HIGHPerturbation velocitySO 1RMS: L5 perturbation levelEMG channel: L3 superficial502LOWS034-.0>0HIGH504F-HLOW HIGHLOW HIGH LOW HIGH505 506S08LOW HIGH509LOW HIGHONLOWSbHIGH LOW HIGH LOW HIGHPerturbation velocityRMS: L3 perturbation levelEMG channel: L4 deep4-I0>0LOW HIGH LOW HIGH LOW HIGH501 502 503504 505LOW HIGH506508LOW HIGHLOWs09LOW HIGHSbLOW HIGHHIGH LOW HIGHPerturbation velocityRMS: L4 perturbation level506510EMG channel: L4 deepS02 503V.?4-?0>0LOW HIGH LOW HIGH LOW HIGH504 505LOW HIGHLOW HIGH508LOW HIGH509LOW HIGH LOW HIGH LOW HIGHPerturbation velocity501LOW HIGH504RMS: L5 perturbation levelEMG channel: L4 deepLOW HIGH- HLOW HIGH502 5034-I0>0ULOW HIGH505LOW HIGH506LOW HIGH LOW HIGH LOW508 s09HIGHLOW510HIGHPerturbation velocity501LOW HIGHRMS: L3 perturbation levelEMG channel: L4 superficialS02:L0>04-r_zzz_ZZ503I?504LOW HIGH505LOW HIGHLOW HIGH506508LOW HIGHS09LOW HIGH510LOW HIGH LOW HIGH LOW HIGHPerturbation velocityRMS: L4 perturbation levelS08-_E_zzzEMG channel: L4 superficial502LOW HIGHLOW HIGHs09solLOWS03HIGH5044-..0>0?-I505LOW HIGHLOW HIGH506LOW HIGHU?LOW HIGHI SbLOW HIGH LOW HIGHPerturbation velocityLOW HIGHRMS: L5 perturbation levelEMG channel: L4 superficial501- -502 S03:iV)4-,0>0L3S05LOW HIGH LOW HIGH LOW HIGH504 506508LOW HIGH509LOW HIGHLOWSbHIGH LOW HIGH LOW HIGHPerturbation velocity4-,0>0ULOW HIGH501RMS: L3 perturbation levelEMG channel: L5 deep502LOWS03ii504 505HIGH LOW HIGH LOW HIGH506-I??LOW HIGH508 509?aLOW HIGH510LOW HIGH LOW HIGH LOW HIGHPerturbation velocityV..0>0L)508HIGH501RMS: L4 perturbation levelEMG channel: L5 deep502 503504LOW HIGH LOW HIGH LOW HIGH?505LOW HIGH506LOW HIGH LOW HIGH509LOW510LOW HIGH LOW HIGHPerturbation velocity0>0ULOW HIGH LOW HIGH501RMS: L5 perturbation levelEMG channel: L5 deep502 503504LOW HIGH LOW HIGH LOW HIGH505LOW HIGH506508LOW HIGH509LOW HIGHLOW HIGHSb-Perturbation velocityRMS: L3 perturbation levelEMG channel: L5 superficial0>0SO 1LOW HIGH502 503S04LOW HIGHLOW HIGHS05LOW HIGH506S08LOW HIGHH.zL___509LOW HIGHCSbLOW HIGH LOW HIGH LOW HIGHPerturbation velocityLOW HIGHHIGH501RMS: L4 perturbation levelEMG channel: L5 superficialS02 5034-?0>C505LOW HIGH LOW HIGH LOW HIGH504 506S08LOW HIGH509LOW HIGHLOWSbLOW HIGH LOW HIGHPerturbation velocityrI4-?0>0I-)RMS: L5 perturbation levelEMG channel: L5 superficial502LOW HIGH501 S03LOW HIGHS04LOW HIGH505LOW HIGH506508LOW HIGHs09LOW HIGHSbLOW HIGH LOW-.HIGH LOW HIGHPerturbation velocityVI4-?0>0IPeak RMS: L3 perturbation levelHIGH510LOW HIGH501EMG channel: L3 deep502 S03LOW HIGH504LOW HIGH505LOW HIGHS06508LOW HIGH LOW HIGHLOW LOW HIGHPerturbation velocity4-?0>0solPeak RMS: L4 perturbation levelEMG channel: L3 deepS02S04LOW HIGH LOW HIGH LOW HIGHS05LOW HIGHS06LOWS08LOW HIGH509LOW HIGH510HIGH LOW HIGH LOW HIGHPerturbation velocity4-,0>0I.-,Peak RMS: L5 perturbation levelEMG channel: L3 deep?1- -- ISb501?--502? I----LOW HIGHS03LOW HIGH504zZJ505LOW HIGH506LOW HIGH LOW HIGH508 S09LOW HIGHLOW HIGH LOW HIGH LOW HIGHPerturbation velocityLOW HIGH508;? IHIGHPeak RMS: L3 perturbation levelEMG channel: L3 superficial501 502LOW HIGH5045034-?0>0LILOW HIGHLOW HIGH505=?-LOW HIGH506509LOW HIGHLOW510LOW HIGH LOW HIGHPerturbation velocityLt4-..0>0UPeak RMS: L4 perturbation levelEMG channel: L3 superficialHIGHs09LOW HIGH LOW HIGH501 502IIS03LOW HIGH LOW HIGH LOW HIGH504---=--=?--_?--???-- S05HLOW HIGH LOW HIGH LOW HIGH506508LOWSbPerturbation velocity>0>0Peak RMS: L5 perturbation level501EMG channel: L3 superficial502LOW HIGH504 --HLOW HIGHS08 HHIGH503- TILOW HIGH- 506HiLOW HIGHSbIiLOW HIGH50900LOW LOW HIGH LOW HIGHPerturbation velocityPeak RMS: L3 perturbation level>4-.0>0501LOW HIGHEMG channel: L4 deepLOW HIGHS02 S03504LOW HIGHS05 506LOW HIGH508 509LOWLOW HIGHSlOzZHIGH LOW HIGH LOW HIGHPerturbation velocity509?LOW HIGH LOW HIGH501Peak RMS: L4 perturbation levelEMG channel: L4 deep502?503>V.,4-..0>0505LOW HIGH LOW HIGH LOW HIGH504-P--? S06H-????LOW HIGH LOW HIGH LOW HIGHS0800CLOW HIGH510Perturbation velocityPeak RMS: L5 perturbation level-LOW HIGHso1EMG channel: L4 deepS02:iin.1-I0>0503-LOW HIGH1LOW HIGHS04LOW HIGH505LOW HIGH506508LOW HIGHLOW HIGHs09LOW HIGH510LOW ? HIGHPerturbation velocityV?l4-,0>0c-)LOW HIGHPeak RMS: L3 perturbation levelEMG channel: L4 superficialLOW HIGH502 S03504LOW HIGHLOW HIGHS08LOW HIGHGos09ZZzzz_?-S06? ;:;LOW HIGHSbH? 1LOW HIGHLOW HIGH LOW HIGHPerturbation velocityPeak RMS: L4 perturbation levelEMG channel: L4 superficial502I-LOW HIGHS04JJLl)?1-?0>0LOW HIGH505LOW HIGH LOW HIGHS08--z-zz--z-ILOW HIGH506----I-------LOW HIGH510GOLOW HIGH LOW? HIGH LOW HIGHPerturbation velocity4-I0>0Peak RMS: L5 perturbation levelEMG channel: L4 superficial00S08HIGH510LOW HIGHSO 1 S02S04503LOW HIGH LOW HIGH LOW HIGHS05IFLOW HIGH LOW HIGH LOW HIGH506LOW LOW HIGHPerturbation velocity00dl>4i0>0Peak RMS: L3 perturbation levelEMG channel: L5 deep501 502_.-r503LOW HIGH506LOW HIGH LOW HIGH504 S05LOW HIGH LOW HIGHS08 509I________LOW HIGHSbLOW HIGH LOW HIGH LOW HIGHPerturbation velocityHIGHPeak RMS: L4 perturbation level501EMG channel: L5 deepS02LOW4-I0>01%)LOW HIGH504LOW HIGH508SOSLOW HIGH506LOW HIGH LOW HIGHSb-LOW LOW HIGH LOW HIGHPerturbation velocity501Peak RMS: L5 perturbation level>4-.?0>0I-,LOW HIGH LOW HIGH506LOW HIGHEMG channel: L5 deepS02 S03504LOW HIGH LOW HIGH LOW HIGH505FS08 50900LOWSbiiiiHIGH LOW HIGH LOW HIGHPerturbation velocity4-.?0>0501_fPeak RMS: L3 perturbation levelEMG channel: L5 superficial502 S03Hzzzz1LOW HIGH504-----LOW HIGH505LOW HIGH506LOW HIGHSO8- -:509LOW HIGHcc00510LOW HIGH LOW HIGH LOW HIGH?Perturbation velocity004-?0>0U501Peak RMS: L4 perturbation levelEMG channel: L5 superficial502 I-F504LOW HIGH LOW HIGH LOW HIGH505zZZLOW HIGH508LOW HIGH506LOW HIGH509LOW510HIGH LOW HIGH LOW HIGHPerturbation velocityPeak RMS: L5 perturbation level4-,0>0EMG channel: L5 superficialS02LOW HIGHLOW HIGHS09ZLOW HIGH501LOW503HIGH504 SOSILOW HIGHSO6LOW HIGH508?LOW HIGH510LOW HIGH LOW HIGHPerturbation velocityv)C0wcuE0Time-to-peak RMS: L3 perturbation levelLOW HIGH501EMG channel: L3 deep502LOW HIGHS04503NILOW HIGH00LOW HIGHS081 S050 LOW HIGH1 509LOW HIGHS06NI01010LOW HIGH510LOW HIGH LOW HIGHPerturbation velocityTime-to-peak RMS: L4 perturbation level5030? 0LOW HIGH LOW HIGHLOW HIGHv, 1S04C0UId,2I?nLOW HIGHSO 1EMG channel: L3 deep1 S02S05 S060 LOW HIGH50900LOW HIGH510LOW HIGH LOW HIGH LOW HIGHPerturbation velocityV)0I-)V?IEI-Time-to-peak RMS: L5 perturbation levelEMG channel: L3 deep1 1501 502HIGH LOW HIGH LOW HIGHS03504 5050 LOW HIGH506Li0 LOW HIGH1 509n? ?LOWHIGH00LOW HIGH510LOW HIGH LOW HIGHPerturbation velocityC0cuETime-to-peak RMS: L3 perturbation levelEMG channel: L3 superficial1 1501 502LOW HIGH504503LOW HIGH5050o.0LOW HIGH508LOW HIGH50900aLOW HIGHLOW HIGH510ScLOW HIGH LOW HIGH LOW HIGHPerturbation velocityV0I-,?F)EF-Time-to-peak RMS: L4 perturbation levelEMG channel: L3 superficial1 1S020501LOW LOWS04S031HIGHIS050 0LOW HIGHLOW HIGHLOW HIGH05080100509LOW HIGH5101LOW HIGH LOW HIGH LOW HIGHPerturbation velocityTime-to-peak RMS: L5 perturbation levelEMG channel: L3 superficialLtC0cJa)a)EI-0501LOW HIGH CS02LOW HIGH10503LOW HIGHS0400506LOW HIGHS081 505 1C 0--?---?LOW HIGH LOW HIGH1 1 5100 0HIGH LOW HIGH LOWHIGHLOWPerturbation velocityt5C0IJG)2I-Time-to-peak RMS: L3 perturbation level5010EMG channel: L4 deep1 502LOW HIGH50450311LOW ? HIGHLOW HIGH505LOW HIGH506000508000LOW HIGH509LOW HIGH510? LOW HIGH LOW HIGH LOW HIGHPerturbation velocityTime-to-peak RMS: L4 perturbation levelEMG channel: L4 deep-t:C0?-IEI-0509LOW - HIGHSbLOW HIGHSO 1iILOW HIGH504503502C LOW HIGH1 505r_______ _______LOW HIGH00LOW HIGH506101010508LOW HIGH LOWV10HIGHLOW HIGHPerturbation velocityV..C0L)wV..ci)2Time-to-peak RMS: L5 perturbation levelsoi1EMG channel: L4 deep1 S0201LOW HIGH504S0300LOW HIGHS05?10 LOW HIGH1 S08jLOW HIGH50600LOW HIGHS09LOW HIGHLOW HIGH0 LOW HIGHLOW HIGHPerturbation velocityC0ciiVIci)EF-Time-to-peak RMS: L3 perturbation levelEMG channel: L4 superficial501 50200LOW HIGHS0450310100LOW HIGHS05LOW HIGH506508LOW HIGH0 ?_____LOW HIGH1 510t0LOW HIGH509CC0? -.______________LOW HIGH LOWHIGH LOW HIGHPerturbation velocityV.)0UcliV.)ciiE503501LOWTime-to-peak RMS: L4 perturbation levelEMG channel: L4 superficial1 15020 01 1HIGH504LOW HIGH0505LOW HIGH506LOW HIGHS08 509000 LOW HIGH1tJ?510? LOW HIGH LOW HIGH LOW HIGHIj0Perturbation velocityTime-to-peak RMS: L5 perturbation level0EMG channel: L4 superficialS02LOW HIGH 0503LOW HIGHC0c-Ia)V.,a)E505LOW HIGHsoiLOW HIGH0S04LOW HIGH10508 S095060 ?-?--??LOW HIGH0 LOW?HIGH LOW HIGH LOW HIGHPerturbation velocityTime-to-peak RMS: L3 perturbation level503LOW HIGH506LOW HIGH5010?EMG channel: L5 deep1 5020LOW HIGH LOW HIGH10InC0UcijIna)EI?504 S050 LOW HIGH1 S080 05100LOW HIGH LOW HIGH LOW HIGHPerturbation velocityTime-to-peak RMS: L4 perturbation levelEMG channel:L5 deepC0UEI?LOW HIGH501 502 50300504LOW HIGH505000LOW HIGH506LOW HIGH000H508LOW HIGHS09LOWLOW HIGH510HIGH LOW HIGH LOW HIGHPerturbation velocityC0I-,a)?Ia)EI?Time-to-peak RMS: L5 perturbation levelEMG channel: L5 deep501 502 503LOW HIGH505b LOW HIGH1 5040 LOW HIGH1 508LOW HIGH506000010LOW HIGH509tJcMLOW HIGH510LOW HIGH LOW HIGH LOW HIGHPerturbation velocity?I,C0a)2Time-to-peak RMS: L3 perturbation levelEMG channel: L5 superficialSO 1 502LOW HIGHS04LOW503000(IHIGH505LOW HIGH000LOW HIGHS06I1ILOW HIGH 0S08 s09LOW HIGH0SbLOW HIGH LOW HIGH LOW HIGHPerturbation velocity0L)G)2I?Time-to-peak RMS: L4 perturbation level503LiSO 1LOW HIGHS04EMG channel: L5 superficialS020 - -____________LOW HIGH000V0100LOW HIGH LOW HIGHLOW HIGH506I508 1 S09LOW HIGHLOW HIGH510LOW HIGH LOW HIGHPerturbation velocityTime-to-peak RMS: L5 perturbation levelEMG channel: L5 superficial1 1501502 503LOW HIGH LOW HIGH LOW HIGHV.?S05C01)V.?cuI?_ILOW HIGHS04LOW00101(..HIGHS08111 506o LOW HIGHs09LOW HIGH LOW HIGH LOW HIGHPerturbation velocity

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