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Instantaneous cardioacceleration in response to high-intensity, short-duration isometric contractions Kitagawa, Eiji 1976

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INSTANTANEOUS CARDIOACCELERATION IN RESPONSE TO HIGH-INTENSITY, SHORT-DURATION ISOMETRIC CONTRACTIONS  by  E i j i Kitagawa B.P.E., University of B r i t i s h Columbia, 1970  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF PHYSICAL EDUCATION in the School of Physical Education and Recreation  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA September, 1976  ( 6 ) E i j i Kitagawa  In p r e s e n t i n g  this  an a d v a n c e d d e g r e e the L i b r a r y I  further  for  of  at  agree  written  thesis  for  of  British  available  the  requirements  Columbia, reference  copying of  I agree and this  gain shall  that  not  copying or  RRptRTDhBr 1 1 .  1976  Columbia  that  thesis or  publication  be a l l o w e d w i t h o u t  School o f Physical Education and Recreation  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  for  study.  by t h e Head o f my D e p a r t m e n t  is understood  financial  for  for extensive  p u r p o s e s may be g r a n t e d It  fulfilment of  permission.  -Dopo N:-mefrt—of-  Date  freely  that permission  representatives.  this  in p a r t i a l  the U n i v e r s i t y  s h a l l make i t  scholarly  by h i s  thesis  my  i ABSTRACT  The purpose of t h i s study was  to investigate on a beat-by-beat  basis, the nature of the instantaneous cardioacceleration r e s u l t i n g from short-duration, high-intensity, isometric contractions; to determine the r e l a t i o n s h i p between r e l a t i v e muscular tension and cycle time, actual c  change i n cycle time and r e l a t i v e change i n cycle time; and to determine the e f f e c t of short-duration, high-intensity, isometric contractions the recovery rate.of cycle time.  on  Muscular tensions and electrocardio-  grams were recorded before, during and a f t e r the isometric task  and  r e l a t i v e muscular tension, cycle time, actual change i n cycle time and r e l a t i v e change i n cycle time were calculated from these The sample population Each subject was  The  recordings.  consisted of t h i r t y u n i v e r s i t y males.  randomly assigned to one of three groups.  task consisted of either a 50% MVC,  to be held for 10-seconds.  Dynamometer and ECG  75% MVC  or 100%  MVC  recordings were monitered  for the 15-seconds immediately before the contraction, the 10-seoonds during the contraction and the 15-seconds immediately following the contraction.  The hypotheses were: at the onset of an isometric  contraction,  the i n i t i a l rate of increase of the r e l a t i v e change i n cycle time i s d i r e c t l y r e l a t e d to the magnitude of the percent maximal voluntary  con-  ii t r a c t i o n ; during the isometric contraction, the r e l a t i v e muscular tension i s more c l o s e l y related to the r e l a t i v e change i n cycle time than either cycle time or actual change i n cycle time; and, upon release of the i s o metric  contraction, the i n i t i a l rate of decrease of the r e l a t i v e change  i n cycle time i s d i r e c t l y related to the magnitude of the percent maximal voluntary  contraction.  The trend analysis of the r e l a t i v e change i n cycle time, during contraction, indicated that the l i n e a r and quadratic d i f f e r e n t between the three groups.  trends were  However, trend analyses of paired  comparisons between the three groups indicated that the trends of the 50% MVC  and  75% MVC  of the 100% MVC  groups were s i g n i f i c a n t l y d i f f e r e n t from the  trend  group, but, were not s i g n i f i c a n t l y d i f f e r e n t from each  other.  The post-hoc Newman-Keuls analysis indicated that the heart responded d i f f e r e n t l y over the f i r s t f i v e beats than over the l a s t f i v e beats, suggesting that there are at l e a s t two phases i n the cardioacceleratory response to isometric contractions and may  these two  phases  be a r e s u l t of a central and a peripheral heart-trigger mechanism.  The  trend analysis of the r e l a t i v e change i n cycle time,  during recovery, indicated a s i g n i f i c a n t l i n e a r trend i n beats with a s i g n i f i c a n t difference i n t h i s trend between groups.  However, observa-  tion of the graphic p l o t of means indicated that the data did not support  iii the hypothesis, that the i n i t i a l rate of decrease of r e l a t i v e change i n cycle time was d i r e c t l y related to the magnitude of the ZMVC.  The  non-support may have been due to the masking effect of r e s p i r a t i o n .  iv ACKNOWLEDGMENTS  The author would l i k e to express h i s sincere gratitude to the following people: Dr. Kenneth Coutts, committee chairman, and Dr. Robert Schutz f o r being physiological and s t a t i s t i c a l mentors, respectively, during h i s Master's programme; Dr. Michael Patterson f o r h i s stimulation and support i n c a r d i o l o g i c a l matters; and, l a s t but by no means l e a s t , Mr. Chiu and, my wife, Robin f o r t h e i r i n v a l uable assistance during the data c o l l e c t i o n .  Furthermore, the author's Master's degree would not have been as e a s i l y attainable without the f i n a n c i a l , emotional and moral support of h i s wife.  V  TABLE OF CONTENTS  Chapter  I.  Page  STATEMENT OF THE PROBLEM  1  Introduction  1  Problem  3  Subproblems  3  D e f i n i t i o n of Terms. ,  4  Assumption  7 .  <•  7  Justification  8  REVIEW OF THE LITERATURE  9  Introduction  9  Minimal-Duration Studies.....  9  Short-Duration Studies Long-Duration Studies  III.  3  Hypotheses  Limitations  II.  •  10 .  13  Peripheral Heart Trigger Mechanism(s)  15  Summary  19  MATERIALS AND METHODS  20  Experimental Design.  20  Subjects........  20  Experimental Procedure  20  Preparation...  22  vi Chapter  P a  22  Commands and I n s t r u c t i o n s  23  S t a t i s t i c a l Analyses  • •• ••  Contraction Condition Recovery Condition  24 25  Resting Condition  30 .  30  .•  31  RESULTS AND DISCUSSION  32  Results  32 Resting  32  Contraction  37  Recovery  39  Discussion  V.  e  100% MVC Determinations  Data Recording  IV.  8  ....  59  Resting  59  Contraction  60  Recovery  64  SUMMARY AND CONCLUSIONS  66  Summary  66  Conclusions  68  BIBLIOGRAPHY  69  APPENDICES  72  A.  I n d i v i d u a l Raw Scores  72  B.  I n d i v i d u a l Computed Scores......  82  vii Chapter  Page  C.  ANOVA Paired Comparisons of RCCT f o r C  the Three Levels of %MVC D.  93  Recovery Condition - Means and Standard Deviations of Cycle Time and Actual Change i n Cycle Time with Graphical Presentations  97  viii LIST OF TABLES  Table  I II  P a  R e l a t i o n s h i p between Cycle Time and Heart Rate....  S  e  26  Resting Condition - Means and Standard Deviations of Cycle Time  33  III  Summary of ANOVA f o r Resting Condition - Cycle Time 35  IV  Newman-Keuls Analyses f o r Resting Condition - Cycle Time 36 Contraction Condition - Means and Standard Deviations of R e l a t i v e Muscular Tension 40  V VI VII(A) VII(B) VII(C)  Summary o f ANOVA f o r Contraction Condition - R e l a t i v e Muscular Tension 42 Newman-Keuls Analyses f o r Contraction Condition R e l a t i v e Muscular Tension 100% MVC Group  43  Newman-Keuls Analyses f o r Contraction Condition R e l a t i v e Muscular Tension 75% MVC Group  44  Newman-Keuls Analyses f o r Contraction Condition R e l a t i v e Muscular Tension 50% MVC Group  44  VIII  Contraction Condition - Means and Standard Deviations of R e l a t i v e Change i n Cycle Time... 45  IX  Summary of ANOVA f o r Contraction Condition - R e l a t i v e Change i n Cycle Time... 47  X(A) X(B) X(C)  Newman-Keuls Analyses f o r Contraction Condition R e l a t i v e Change i n Cycle Time 100% MVC Group Newman-Keuls Analyses f o r Contraction Condition R e l a t i v e Change i n Cycle Time 75% MVC Group Newman-Keuls Analyses f o r Contraction Condition R e l a t i v e Change i n Cycle Time 50% MVC Group..  48 49 49  ix  Page  Contraction Condition - Means and Standard Deviations of Cycle Time  '  Summary of ANOVA f o r Contraction Condition Cycle Time ••• Contraction Condition - Means and Standard Deviations of Actual Change i n Cycle Time Summary of ANOVA f o r Contraction Condition - Actual Change i n Cycle Time Recovery Condition - Means and Standard Deviations of Relative Change i n Cycle Time Summary of ANOVA f o r Recovery Condition - Relative Change i n Cycle Time  X  LIST OF FIGURES  Figure  Page  1  Experimental Design  21  2  Graphical Presentation of the Relationship between Cycle Time and Heart Rate  27  3  S t a t i s t i c a l Design.  29  4  Graphical Presentation of Cycle Time during the 10 Resting Heart Beats  34  Graphical Presentation of Relative Muscular Tension during the 10 Contraction Heart Beats  41  Graphical Presentation of Relative Change i n Cycle Time during the 10 Contraction Heart Beats  46  Graphical Presentation of Cycle Time during the 10 Contraction Heart Beats  51  Graphical Presentation of Actual Change i n Cycle Time during the 10 Contraction Heart Beats.  54  Graphical Presentation of Relative Change i n Cycle Time during the 10 Recovery Heart Beats..  57  5 6 7 8  9  1 CHAPTER I  STATEMENT OF THE PROBLEM  Introduction  To date, the majority of physiological investigations on the heart rate response to exercise have been concerned with dynamic, steadystate exercises of varying degrees of i n t e n s i t y i n v a r i a b l e environments (Rowell,  1974) .  U n t i l recently, only a few investigations have studied  the e f f e c t of s t a t i c (isometric) exercise on the heart rate response. These investigations f a l l into two general categories, according to the nature of the cardiovascular response studied:  (1) studies of the i n i t i a l  cardiovascular response; and (2) studies of the pressor response and i t s related cardioacceleration.  The category (1) studies required  to be held for 1-second or less and analyzed  contractions  cycle time on a beat-by-beat  basis; whereas, category (2) studies involving contractions of more than 1-seconds duration either reported maximal change i n heart rate (beats/min.) or reported heart rate (beats/min.) at 10- to 30-second i n t e r v a l s .  A study by T u t t l e and Horvath (1957) indicat es that the major portion of cardioacceleration occurs within the f i r s t  15-seconds of a  maximal voluntary contraction (100% MVC) held f o r 1-minute.  Flessas et a l . (1970) compared a time-based and a beat-by-beat  analyses of heart rate during a 12-second Valsalva Maneuver (VM) and found that the beat-by-beat analysis resulted i n a smaller c o e f f i c i e n t of v a r i ation through a l l phases of the maneuver.  Studies by Paulev (1973), Humphreys and Lind (1963), and Freyschuss (1970b) reported d i f f i c u l t y i n detecting a relationship between the change i n heart rate and the percent maximal voluntary contraction (% MVC) range 50% MVC  - 100%  i n the  MVC.  Recent s t a t i s t i c a l studies by Khachaturian and Kerr (1972) and Jennings et a l . (1974) suggest that cycle time i s a more e f f e c t i v e measure to use i n the analysis of evoked cardiac responses, than heart rate (beats/min  The study by T u t t l e and Horvath (1957) indicates that the major portion of cardioacceleration, i n response to an isometric  contraction,  occurs i n a time span of more than 1-second, but less than  15-seconds.  Unfortunately,  the category (1) studies were of too short a duration to  determine the time course of the change i n cardioacceleration and the category (2) studies tended to mask the time course of the change i n cardioacceleration by summing the heart beats over 10- to 30-second intervals.  I f , the findings of T u t t l e and Horvath (1957) were to be  considered  i n conjunction with the r e s u l t s of Flessas et a l . (1970),  Khachaturian and Kerr (1972), and Jennings et a l . (1974), i t would seem reasonable to assume that a beat-by-beat analysis of cycle time, during a 10- to 15-second contraction, should lead to a better under-  3 standing of the r e l a t i o n s h i p between r e l a t i v e muscular tension and the r e s u l t i n g cardioacceleration.  In f a c t , an experiment of t h i s nature  may detect a r e l a t i o n s h i p between the change i n heart rate and the percent maximal voluntary  contraction i n the 50% - 100% MVC range.  Problem  The purpose of t h i s study i s to investigate, on a beat-by-beat basis, the nature of the instantaneous cardioacceleration r e s u l t i n g from short-duration, high-intensity, isometric  contractions.  Subproblems  1.  To determine the r e l a t i o n s h i p between r e l a t i v e muscular  tension and cycle time, actual change i n cycle time, and r e l a t i v e change i n cycle time.  2.  To determine the e f f e c t of short-duration 50%, 75%, and 100%  maximal voluntary  contractions on the recovery rate of cycle time.  Hypotheses  1.  At the onset of an isometric contraction, the i n i t i a l rate  of increase of the r e l a t i v e change i n cycle time (RCCT ) i s d i r e c t l y C  related to the magnitude of the percent maximal voluntary  contraction (%MVC).  4 2.  During the isometric contraction, the r e l a t i v e muscular  tension (MT ) i s more closely related to the r e l a t i v e change i n cycle K time (RCCT^) than either cycle time (CT^) or actual change i n cycle time (ACCT ). C  3.  Upon release of the isometric contraction, the i n i t i a l  rate of decrease of the r e l a t i v e change i n cycle time (RCCT ) i s d i r e c t l y related to the magnitude of the percent maximal voluntary (Z MVC)  contraction  prescribed f o r the contraction condition.  D e f i n i t i o n of Terms  Heart Beat.  In the s t r i c t e s t sense, a heart beat consists of  a t r i a l and v e n t r i c u l a r systole. of the R-wave was  For the purpose of this study, the peak  used as the reference point for any given heart beat.  Resting Condition.  This condition consisted of the 10  heart  beats immediately preceding the f i r s t heart beat i n the contraction condition.  Contraction Condition.  This condition consisted of the  10 heart beats a f t e r the onset of contraction. following the onset of contraction was of the contraction condition.  first  The R-wave immediately  considered  as the f i r s t heart beat  The onset of contraction was  determined as  Being that point at which the dynamometer recording pen noticeably deflected  5 from the baseline.  Recovery Condition.  This condition consisted of the f i r s t 10  heart beats a f t e r the point of release of the dynamometer.  The f i r s t  R-wave a f t e r the point of release was considered as the f i r s t heart beat of the recovery condition.  The point of release was determined as being  the i n f l e c t i o n point on the dynamometer recording paper.  Cycle Length.  The distance between the peaks of two consecutive  R-waves on an electrocardiogram  (ECG).  Often referred to as cardiac cycle  length, R-R i n t e r v a l , or P-P i n t e r v a l .  Cycle Time (CT). Cycle length expressed i n milliseconds. conversion depends on the speed of the ECG recorder.  The  For example, at a  recording speed of 100 mm./sec:  Cycle Time (msec.) = Cycle Length (mm.) x 10  The cycle time immediately preceding an R-wave was taken to be the cycle time f o r that given heart beat.  Actual Change i n Cycle Time (ACCT). (CT  v*Li  The control cycle time  ) f o r a given subject minus h i s cycle time i n the contraction condi-  t i o n (CT,,) or i n the recovery condition (CT^)•  6 Contraction:  ACCT  Recovery:  ACCT  C  (msec.) = C T (msec.) = CT„  C L  T  (msec.) - CT (msec.) - CT  Relative Change i n Cycle Time (RCCT).  C  (msec.) (msec.)  The actual change i n  cycle time (ACCT) f o r a given subject i n the contraction condition (ACCT ) C  or i n the recovery condition (ACCT ) expressed R control cycle time (CT ). • *  Contraction:  as a percentage of h i s  ACCT„ (msec.) . C x 100 CT (msec.)  RCCT =  n n  C  C L  Recovery:  RCCT  =  R CT  x 100  A C C T  C L  (msec.)  Percent/Relative Muscular Voluntary Contraction (100% MVC). The force that a subject was required to exert on the handgrip dynamometer (50%, 75%, or 100%) i n r e l a t i o n to h i s maximal voluntary contraction.  Maximal Voluntary Contraction (100% MVC).  The method f o r deter-  mining 100% MVC i s discussed i n Chapter I I I .  Relative Muscular Tension %MVC are synonymous.  (MT„).  Relative muscular tension and  To avoid confusion, %MVC w i l l only be used i n r e f e r -  ence to the muscular tension "prescribed" f o r a subject or h i s given group by the experimenter.  Since subjects cannot i n s t a n t l y a t t a i n and hold t h e i r  "prescribed" muscular tension without  some i n t e r - and i n t r a - i n d i v i d u a l v a r i -  7 a b i l i t y , r e l a t i v e muscular tension w i l l only be used i n reference to the dependent measure obtained from the subject during the t e s t i n g .  Relative  muscular tension was determined from the calibrated recording on the cardiog r a p h y paper and expressed as a.percentage of the maximal voluntary cont r a c t i o n , which was also determined from the paper recording.  The r e l a t i v e  muscular tension for any given heart beat was determined by using the peak of the preceding R-wave as the a f b r i t r a r y reference point.  Assumption  The underlying assumption f o r hypothesis (1) i s that a l l three groups w i l l have equal response times i n terms of attaining t h e i r p r e s c r i bed %MVC's.  A post-hoc analysis was done to determine the v a l i d i t y of  this assumption.  Limitations  The study i s l i m i t e d by the sample size of 30 subjects of the male sex between the ages of 18 - 28 years.  Furthermore, the subjects  were predominantly students i n the School of Physical Education and Recreation at the University of B r i t i s h Columbia and therefore cannot be considered as a random sample of the population.  8 Justification  This study w i l l lead to a better understanding of the i n i t i a l cardioacceleratory response to isometric exercise and may lead to the development of a more e f f e c t i v e method of analyzing evoked cardiac r e sponses.  Furthermore, i t may give some insight to the time course of  action of the heart trigger mechanisms that have been proposed to be operating during a normal cardiovascular response to isometric exercise.  9 CHAPTER II REVIEW OF THE LITERATURE  Introduction  Most studies of the c i r c u l a t o r y response to voluntary muscle contractions, commonly termed isometric or s t a t i c exercise, can be c l a s s i f i e d according to the duration of the required contraction.  The.follow-  ing c l a s s i f i c a t i o n s w i l l be used to present related studies: 1.  Minimal-Duration Studies  2.  Short-Duration  3.  Long-Duration Studies  Studies  (less than 1-second)  (1-10  seconds)  (1-minute or more)  Minimal-Duration Studies  Petro et a l . (1970) found that a 100% MVC  with the biceps re-  sulted i n a s i g n i f i c a n t shortening of the f i r s t R-R the onset of the contraction.  i n t e r v a l following  He estimated the cardiac latency  (i.e.,  the latency between the onset of the contraction and the cardioacceleratory response) to be approximately 500 milliseconds.  A study by Borst et a l . (1972) shows that a 100% MVC  of either  the plantar flexors or masticatory muscles e l i c i t e d a substantial  R-R  i n t e r v a l decrease (up to 18%) with no s i g n i f i c a n t difference i n responses between u n i l a t e r a l and b i l a t e r a l plantar f l e x i o n .  Their r e s u l t s indicated  10 that a stronger contraction (relative) tended to e l i c i t a larger i n t e r v a l decrease, but no clear r e l a t i o n could be demonstrated between response magnitude and exerted force i n the range 33.3% - 100% MVC.  They approx-  imated cardiac latency at 400 - 600 milliseconds.  Paulev (1973) found that the average heart rate increments of s i x subjects was between 10 - 30%; and that heart rate increments were related to %MVC when the average force was below 50% MVC, but above 50% MVC the increments were f a i r l y constant.  He determined cardiac latency  to be 550 milliseconds and composed of the following: "The cardiac latency consisted of an intracardiac e f f e c t o r time (estimated as the P-R i n t e r v a l : 200 m s e c ) , plus a conduction period i n the vagal nerve and synapse (approx. 300 msec.) and an afferent trigger period. The afferent t r i g g e r period i s so long that i t permits the operation of most heart trigger mechanisms currently proposed (e.g., Golgi tendon organs, cerebral o r i g i n ) . "  Short-Duration  Studies  Freyschuss (1970a) obtained pre- and post-values and a o r t i c pressure  of heart rate  on 10 male subjects (22 - 28 yrs.) i n response to  varying %MVC's (range 50% - 95% MVC, mean 73% MVC) held f o r 5 - 1 0 seconds. In addition, he administered  atropine  phentolamine (alpha-adrenergic phentolamirie  combined.  (parasympathetic blocking  agent),  blocking agent) and both atropine and  In r e l a t i o n to the change i n values obtained  under  the control condition, he found that: (1) atropine s i g n i f i c a n t l y decreased heart rate acceleration (p<.01) and a o r t i c pressure r i s e (p<.05); (2)  1.1 phentolamine did not s i g n i f i c a n t l y a l t e r heart rate acceleration, but s i g n i f i c a n t l y decreased a o r t i c pressure r i s e (p<.05); and (3) atropine plus phentolamine s i g n i f i c a n t l y reduced  (and i n many cases abolished)  heart rate a c c e l e r a t i o n (p<.01) and s i g n i f i c a n t l y reduced a o r t i c pressure r i s e (p<„01).  These findings suggest an interacting influence of symp-  athetic and parasympathetic  Freyschuss  activity.  (1970b) duplicated h i s previous study (1970a) except  that the subjects were eight tetraplegia males (21 - 42 yrs.) having a complete transverse spinal syndrome below segments  - C-^; who had pre-  viously passed courses of physical training and r e h a b i l i t a t i o n .  He  the r e s u l t s were not s i g n i f i c a n t l y d i f f e r e n t from those of healthy  found men  a f t e r the administration of atropine and phentolamine; i n d i c a t i n g the p o s s i b i l i t y that the tetraplegics were unable to u t i l i z e a peripheral beta-adrenergic mechanism even though beta-adrenergic a c t i v i t y i s usuallyassociated with i n o t r o p i c e f f e c t s .  Freyschuss  (1970b) obtained control values for heart rate and  a o r t i c pressure responses to isometric exercise from six healthy males (24 - 29 y r s . ) .  Then obtained comparative  succinylcholine (neuromuscular  blockade).  values a f t e r administering The heart rate increase and  blood pressure r i s e of the "intended" handgrips were 64% and 55%, respecti v e l y , of the values observed during performed handgrips. the prescence of a central heart trigger mechanism.  This suggests  12 A l l of the preceding minimal- and short-duration studies ascribed the c a r d i o a c c e l e r a t i o n at the i n i t i a t i o n of isometric contractions to a withdrawal of vagal tone.  A r r i v i n g at t h i s hypothesis from the r e s u l t s  of s t u d i e s i n v o l v i n g vagotomies, sympathectomies or pharmacological blocking agents could lead to tenuous conclusions; since i t i s generally accepted that t o n i c a c t i v i t y u s u a l l y e x i s t s i n both d i v i s i o n s of the autonomic system.  Therefore, a s a t i s f a c t o r y q u a n t i t a t i v e d e s c r i p t i o n of autonomic  c o n t r o l must take i n t o account the response to simultaneous a c t i v i t y i n both the sympathetic and parasympathetic nerves.  On t h i s premise, Levy  and Zieske (1969) studied the e f f e c t of sympathetic-parasympathetic i n t e r a c t i o n on the canine heart r a t e . l i g a t i n g the c e r e b r a l a r t e r i e s .  They i s c h e m i c a l l y destroyed the CNS  by  Using a 5 x 5 f a c t o r i a l design, they stim-  ulated the r i g h t s t e l l a t e ganglion (0,1,2,3,4 pulses/sec.) and the l e f t c e r v i c a l vago-sympathetic combinations.  trunk (0,2,4,6,8 pulses/sec.) under the appropriate  They reported a pronounced negative  sympathetic-parasympa-  t h e t i c i n t e r a c t i o n , such t h a t , at high l e v e l s of vagal a c t i v i t y , changes i n sympathetic a c t i v i t y had only a n e g l i g i b l e e f f e c t on heart r a t e .  This  marked a t t e n u a t i o n or a c t u a l masking of the sympathetic influence on heart r a t e by a c o e x i s t i n g high l e v e l of vagal a c t i v i t y was reported as being c h a r a c t e r i s t i c of a l l the experiments i n the s e r i e s . that a s i m i l a r negative i n t e r a c t i o n occurs i n man,  On the assumption  these f i n d i n g s i n d i c a t e  that vagal withdrawal must occur i n order f o r the sympathetic system to e f f e c t i v e l y i n f l u e n c e heart r a t e .  Furthermore, Toda and Shimamoto (1968)  found that s t i m u l a t i o n of the sympathetic nerves does not r e s u l t i n an increased heart rate u n t i l a f t e r an i n t e r v a l of 3 - 6 seconds.  I t there-  13 fore may  be reasonable to assume that cardioacceleration during isometric  exercise i s i n i t i a l l y  a r e s u l t of the withdrawal of vagal tone followed  by sympathetic influence.  Long-Duration Studies  T u t t l e and Horvath (1957) had nine subjects perform a 100% for  1-minute.  MVC  They found that at the end of 15-seconds the heart rate  (93±10.0 beats/min.) was  s i g n i f i c a n t l y greater (t=10.38, p<.01) than at  the r e s t i n g l e v e l (66±8.6 beats/min.).  No further s i g n i f i c a n t changes i n  heart rate were evident during the work period, although, a trend of progressive increase was  indicated by the following three 15-second i n t e r v a l s .  Ten seconds a f t e r the cessation of work, the heart rate, although s l i g h t l y greater  (71±10.7 beats/min.), was  not s i g n i f i c a n t l y d i f f e r e n t from the  r e s t i n g l e v e l (t=1.82, p>.05).  Eklund et a l . (1974) reported that a 2-minute, 50% MVC  dorsi-  f l e x i o n of the foot increased the heart rate from 60-86 beats/min. by the end of the contraction.  Lind et a l . (1964) studied four young healthy males performing handgrips of 10% MVC, and  1-2  20% MVC  and 50% MVC  minutes, r e s p e c t i v e l y .  held for 5-minutes, 5-minutes,  On a 30-second basis, t h e i r heart rate  data i n d i c a t e : a progressive r i s e at 10% MVC;  while at 20% MVC  there i s a rapid i n i t i a l r i s e followed by a slower progressive  and 50% rise.  MVC  14 After the abrupt cessation of the contraction the heart rate returned to resting control l e v e l s within 1-minute.  They reported that the tension  was c l o s e l y correlated with the magnitude and rate of increase of the cardiovascular response.  Donald et a l . (1967) reported a study involving a subject with syringomyelia at  of one arm.  Separate handgrip contractions were performed  10% MVC (5 min.), 30% MVC (3 min.) and 50% MVC (1 min.) with the affected  and unaffected hand.  The heart rate response of the affected hand was  s i m i l a r to the response of the unaffected hand for a l l %MVC's, but, n o t i c e ably attenuated;  suggesting  the p o s s i b i l i t y of an impaired  peripheral  heart t r i g g e r mechanism.  Grossman et a l . (1973) u t i l i z e d a 50% MVC handgrip of 3-minutes duration to assess the changes i n the inotropic ( c o n t r a c t i l e ) state of the l e f t v e n t r i c l e . The eight normal subjects consisted of f i v e males and three females with an age range of 20 - 72 years. f i c a n t increases i n a o r t i c mean pressure  They found s i g n i -  (94±3.0 to 119±5.5 mm. Hg.),  heart rate (79±5 to 98±8 beats/min.), and stroke work (81±8.8 to 104±11 gm. m.); but, no s i g n i f i c a n t increases i n l e f t v e n t r i c u l a r end-diastolic pressure  (6.8±0.8 to 7.5±1.2 mm. Hg.), and systemic vascular resistance  (1606±176 to 1645±260 dynes-sec.-cm. "*). They suggest that the normal cardiovascular response to isometric exertion includes a major increase i n l e f t v e n t r i c u l a r myocardial c o n t r a c t i l i t y .  15 Quinones et a l . (1974) had nine subjects maintain a 25%  MVC  handgrip for 3-minutes and observed a s i g n i f i c a n t increase (p<,01) i n the isovolumic indices of l e f t v e n t r i c u l a r c o n t r a c t i l i t y .  In order to  test i f the increase i n l e f t v e n t r i c u l a r c o n t r a c t i l i t y during exercise was  r e l a t e d to the s i g n i f i c a n t increase i n heart rate, they re-measured  the isovolumic indices during a t r i a l pacing at a heart rate equal to the one achieved during exercise.  A t r i a l pacing was associated with a s i g -  nificant- increase (p<.05) i n a l l of the indices of c o n t r a c t i l i t y ; however, 50% of the indices achieved with a t r i a l pacing were s i g n i f i c a n t l y lower (p<.05) than those achieved during exercise.  They stated that; "The aug-  mented indices of c o n t r a c t i l i t y determined i n the normal l e f t v e n t r i c l e during isometric exercise may,  at least i n part, be r e l a t e d to the increase  i n heart rate; however, factors independent of the frequency  of contraction  also appear to be operative."  Peripheral Heart Trigger Mechanism(s)  I t has been postulated by Lind e t . a l . (1964) that: "At l e a s t two afferent channels appear to be involved. The f i r s t of these i s responsible for the pronounced cardioaccelerator response and r i s e of cardiac output, the second r e s u l t s i n baroreceptor suppression allowing rapid and very large elevation of the systemic blood pressure. The almost instantaneous return of the heart rate to the control value on r e l e a s i n g the grip i s quite remarkable. The s i m i l a r , almost immediate return of the blood pressure to control values i s equally remarkable p a r t i c u l a r l y as there i s a considerable r i s e of stroke volume i n early recovery and the cardiac output remains r a i s e d for about f i v e minutes (20 and 50% M.V.C.) afterwards. I t appears that the baros t a t i c r e f l e x e s return to their f u l l e f f i c i e n c y immediately the g r i p i s released."  16 Similar peripheral mechanisms have been postulated by Alam and Smirk (1937), Donald et a l . (1967) and Petro et a l . (1970).  Hnik et a l . (1969) found that increasing or decreasing the perfusion pressure and increasing the a r t e r i a l  did not s i g n i f i c a n t l y a l t e r  the o v e r a l l discharge frequency of the proprioceptive ( l a , l b , & II) and non-proprioceptive (III & IV) muscle afferents.  However, they did f i n d  that i n t r a - a r t e r i a l infusion of KC1 resulted i n either an enhancement of the rate of discharge or the appearance of a c t i v i t y i n previously s i l e n t endings i n both proprioceptive and non-proprioceptive sensory f i b e r s when the K  +  concentration i n the venous blood reached concentrations of 7.5 -  12.5 mEq. K  per l i t e r  +  (the range found i n venous blood following muscle  a c t i v i t y , Kjellmer, 1965).  They concluded that muscle afferents may be  activated by non-proprioceptive s t i m u l i (K ) a r i s i n g i n the muscle i n +  connection with metabolic changes.  L i u et a l . (1969) observed an increased blood pressure, heart rate, and cardiac c o n t r a c t i l e force following an i n j e c t i o n of KC1 (3.5M, 30 mg./kg.) into a femoral artery of morphine-pentobarbital-anesthetized dogs.  These responses were: (1) abolished by complete denervation; (2)  markedly diminished by the administration of phenoxybenzamine (0.7 mg./kg.) or propanolol (1.0 mg./kg.); and (3) absent following i n j e c t i o n s of NaCl (3.5M), C a C l  2  (2.5M), MgCl  2  (2.5M), and 50% glucose i n 30 mg./kg. amounts  i n place of KC1; i n d i c a t i n g that the response does not occur as a r e s u l t of changes i n osmolality or the prescence of Na , Ca  , or Mg  . They  suggest that receptors s e n s i t i v e to K  are present  i n the hindlimb and  that the K -evoked nerve impulses are transmitted through the afferent f i b e r s of the somatic nerve to the vasomotor centers of the medulla. They further suggest that the c i r c u l a t o r y responses a f t e r i n t r a - a r t e r i a l i n j e c t i o n of KC1 are mediated through the release of catecholamines at the sympathetic nerve endings of the heart and blood v e s s e l s .  Unfortunately,  the precise nature of the K -evoked peripheral stimulation i s yet to be documented.  M i t c h e l l et a l . (1968) found that stimulation of the c e n t r a l end of a canine quadriceps nerve at a frequency of 100 pulses/sec. with a strength 20 times threshold f o r the f l e x i o n response resulted i n an i n i t i a l , b r i e f depressor response followed by a pressor response, that i s , a o r t i c pressure,  l e f t v e n t r i c u l a r pressure, heart rate and maximal  rate of r i s e of l e f t v e n t r i c u l a r pressure a l l increased while l e f t ventr i c u l a r d i a s t o l i c pressure remained r e l a t i v e l y constant.  The delay from  onset of stimulation to response varied from 2 - 1 5 seconds during the series of experiments.  The pressor response was unaltered by a b i l a t e r a l  vagotomy or adrenalectomy, but, abolished by the administration of propanolol (0.8 mg./kg.).  McCloskey and M i t c h e l l (1972), Coote et a l . (1971)  and M i t c h e l l et a l . (1968) suggest that small-sized, high-threshold  (III &  IV) muscle a f f e r e n t s , when stimulated appropriately, may play some r o l e i n e l i c i t i n g the increase i n l e f t v e n t r i c u l a r c o n t r a c t i l i t y that occurs during muscular exercise.  18 Freyschuss (1970b) ascribed the heart rate acceleration at the i n i t i a t i o n of handgrip to a reduction i n the vagal tone on the heart concluded, on the basis of h i s r e s u l t s from "intended succinylcholine-blocked arm,  exercise was  exercise" of a  that the r i s e i n heart rate was  an autonomic nervous drive of central o r i g i n .  and  e l i c i t e d by  However, the r i s e by  intended  only h a l f as great as the i n i t i a l heart rate response to actual  muscular a c t i v i t y .  The r e s u l t s of t h i s study and other studies  1970b, t e t r a p l e g i c s and Donald et a l . 1967,  syringomyelia)  (Freyschuss,  tend to support  the hypothesis of an i n t e r a c t i n g peripheral-cerebral heart trigger mechanism.  This mechanism was  suggested by Paulev (1971) when he found that  the s i z e of the i n i t i a l heart rate response depends upon the s i z e of the integrated electromyogram (EMG) exercise and that two  signal during the f i r s t four seconds of  to three kicks on the b i c y c l e ergometer e l i c i t e d a  larger i n i t i a l heart rate response than only one kick.  Goodwin et a l . (1972) used a v i b r a t o r to stimulate the l a afferents i n either the biceps or t r i c e p s of their human subjects  and  cause a tonic v i b r a t i o n r e f l e x , which could r e f l e x l y a s s i s t or i n h i b i t a voluntary contraction.  They demonstrated that this procedure could  reduce or increase the amount of c e n t r a l command necessary to maintain a prescribed biceps tension. between 20 - 50% MVC.  The prescribed muscular tensions varied  They concluded that i r r a d i a t i o n of respiratory and  cardiovascular control centers by the descending central command does occur during voluntary muscular contraction i n man;  and that the cardio-  pulmonary responses of an isometric e f f o r t can be altered by a l t e r i n g  19 the magnitude of the central command.  They suggest that both central  i r r a d i a t i o n and peripheral reflexes are involved i n the cardio-pulmonary responses to exercise.  Summary  The cardioacceleratory response has been estimated to occur between 400 - 600 msec, a f t e r the onset of the contraction.  The magni-  tude of the response has been shown to be related to the %MVC up to 50% MVC, regardless of whether the contraction i s u n i l a t e r a l or b i l a t e r a l , i.  e., independent of the muscle mass involved.  However, from 50% MVC  to 100% MVC no clear r e l a r i o n s h i p has been found between the magnitude of the response and the %MVC.  Studies involving neurologically-handicapped  subjects and  drug-induced neurological blockades indicate two things: f i r s t l y , an i n t r i c a t e sympathetic-parasympathetic i n t e r a c t i o n on cardiac response e x i s t s ; and secondly, the existance of peripheral and c e n t r a l heart trigger mechanisms. based on the K  I t i s suspected that the peripheral mechanism i s  concentration and i t s e f f e c t on the proprioceptive and  non-proprioceptive  afferents; while the c e n t r a l mechanism i s based on  i r r a d i a t i o n from the c e n t r a l motor command.  I t would seem reasonable  to assume that these two mechanisms would not act simultaneously. However, no study, to date, has shown or attempted to show the time-course of the cardioacceleratroy response to isometric exercise.  20 CHAPTER I I I MATERIALS AND METHODS  Experimental  Design  This study was based on a 3 x 3 x 10 f a c t o r i a l design with r e peated measures on the l a s t two factors and 10 subjects nested under each l e v e l of the f i r s t factor, that i s , each of the three l e v e l s of %MVC  con-  tained 10 subjects and dependent measures were obtained from each of the 30 subjects for 10 consecutive heart beats i n the r e s t i n g , contraction and recovery conditions ( F i g . 1).  Subjects  The sample population consisted of 30 a l e r t , non-basal, male volunteers from the population of graduate and undergraduate students at the U n i v e r s i t y of B r i t i s h Columbia, Vancouver, B. C. from 18 - 28 years with a mean of 22 years.  The age range was  A majority of the subjects  were students i n the School of Physical Education and Recreation.  Experimental  Procedure  A l l subjects were tested once, i n random order, during the i n t e r v a l , 3 December, 1974 - 5 December, 1974,  i n the Exercise Physiology  Laboratory, U n i v e r s i t y of B r i t i s h Columbia, War Memorial Gymnasium.  FIGURE 1 EXPERIMENTAL DESIGN  Condition Resting  Subject  Heart Beat 1 2 3 4 5 6 7 8 9  Recovery  Contraction  10  Heart Beat 1 2 3 4 5 6 7 8 9  Heart Beat 1 2 3 4 5 6 7 8 9  10  1 50%  75%  100%  MVC  MVC  MVC  • • 10 11 • • • 20 21 • • 30 3 x 3 x 10 F a c t o r i a l and  Design w i t h repeated measures on the l a s t  10 s u b j e c t s n e s t e d under each l e v e l o f the f i r s t  two f a c t o r s  factor.  10  22 Ambient temperature and barometric pressure, during the testing, ranged from 24.0 - 24.5° C. and 744 - 758 t o r r . , respectively.  Preparation. his  P r i o r to testing, each subject was asked to remove  s h i r t f o r placement of the Beckman Biopotential skin electrodes.  One  of the recording electrodes was attached at the sternal apex and the other was attached at the s i x t h intercostal-space on the l e f t , l a t e r a l portion of the thoracic cage. of the l e f t scapula.  The ground electrode was attached near the apex The subject was then asked to l i e comfortably on  the testing table i n the supine p o s i t i o n .  The electrodes were connected  to a Sanborn ECG preamplifier i n conjunction with a 4-channel, paper recorder (Sanborn 500) and adjustments were made u n t i l the peak of the ECG R-wave was e a s i l y d i s c e r n i b l e at a recording speed of 100 mm./second. The handgrip dynamometer (model 76618, Lafayette Instrument Co., Lafayette, Indiana) and i t s attached rheostat was connected i n series with a dual-trace amplifier (type 3A72, Tetronix, Inc., Portland, Oregon), a Sanborn preampl i f i e r , and the 4-channel recorder.  P r i o r to each testing day, the c a l i -  bration of the dynamometer paper recording was checked and, i f necessary, adjusted so that a d e f l e c t i o n of 1 mm. was equivalent to a 2-kilogram  100% MVC Determinations.  The method f o r determining  force.  each subject's  100% MVC was e s s e n t i a l l y the same as the one established by Lind et a l . (1964).  The subject was instructed to perform three maximal handgrips,  with the r i g h t hand, on the dynamometer, using only the arm muscles.  The  three t r i a l s were recorded on the Sanborn paper recorder and the storage  23 oscilloscope (Tetronix, type 564) by using the lower beam with a time base (Tetronix, type 2B67) of 1-second/division. consistency,  To ensure between subject  the contractions were performed at 1-minute i n t e r v a l s and the  commands "contract" and "release" were given by the experimenter such that the contractions were maintained f o r approximately 2-seconds.  The mean  of the two highest values was accepted as the subject's 100% MVC.  This  was followed by a 5-minute rest period during which both beams of the dual-beam oscilloscope were converted to horizontal l i n e s using a time base of 0.5 msec./division.  Using the stored o s c i l l o s c o p e contractions  as reference points, the upper beam was positioned to i n d i c a t e the muscular force required of the subject to a t t a i n his prescribed %MVC. contraction force was displayed by the lower beam.  The  The o s c i l l o s c o p e screen  was not v i s i b l e to the subject throughout t h i s portion of the procedure.  Commands and Instructions.  The stored o s c i l l o s c o p e contractions  were erased and o s c i l l o s c o p e was released from the storage p o s i t i o n . The oscilloscope screen was then positioned so that the subject could e a s i l y see the screen by turning h i s head s l i g h t l y to the r i g h t .  He was then  given the following commands and i n s t r u c t i o n s : 1. that he should 2.  "Inspire" - Upon hearing t h i s command the subject was t o l d take a comfortable i n s p i r a t i o n . "Hold" - Upon hearing this command the subject was instructed  to block h i s respiratory movements without f o r c e f u l l y contracting his abdominal muscles, u n t i l he was given the "release" command. the occurrence of a Valsalva Maneuver.  This prevented  24 3.  "Contract" - Upon hearing this command the subject was t o l d  to perform a contraction as quickly as possible so that the lower o s c i l l o scope l i n e would match the upper oscilloscope l i n e and to maintain this match u n t i l he was given the "release" command.  Then the experimenter  demonstrated the required response to prevent the subject from obtaining information concerning 4.  his prescribed %MVC.  "Release" - Upon hearing this command the subject was instructed  to release the dynamometer immediately, resume normal breathing, and l i e quietly on the t e s t i n g table.  The preceding  procedure was developed from previous studies, that  have demonstrated the e f f e c t s of r e s p i r a t i o n (Davies and Nielson, 1967), breath-holding  (Petro et a l . , 1970), and the Valsalva Maneuver (Flessas  et a l . , 1970) on heart rate.  Furthermore, Borst et a l . (1972) and Petro  et a l . (1970) found that their subjects n a t u r a l l y blocked  their respir-  ation during isometric contractions; and Paulev (1971) found the change i n v e n t i l a t i o n , either a r i s e or reduction, occurs i n s t a n t l y at the s t a r t and end of exercise before the heart rate response.  Data Recording.  At the end of the 5-minute rest period, muscle  tension and ECG's were simultaneously mm./sec. f o r a l l three conditions.  recorded  at a paper speed of 100  The r e s t i n g (actually pre-contraction),  contraction and recovery values were recorded  continuously  for 40-seconds.  The commands " i n s p i r e " and "hold" were given 4- and 3-seconds, respectively, p r i o r to the "contract" command, which was followed by the "release"  25 command a f t e r a 10-second period.  Recovery values were recorded f o r the  l a s t 15-seconds.  Cycle time (msec.) was chosen as the dependent measure of cardiac response i n preference to heart rate (beats/min.) f o r three main reasons: (1) i t i s predominantly  the shortening of d i a s t o l e that indicates the  occurence of cardioacceleration; "(2) expressing the cycle time of a single heart beat i n beats per minute requires j u s t i f i c a t i o n ; and (3) due to the non-linearity of the relationship between cycle time and heart rate (as demonstrated by Table I and F i g . 2) a transformation would a l t e r the magnitude of any comparative changes.  This choice i s supported by the study  of Jennings et a l . (1974), which indicated that the cycle time d i s t r i b u t i o n of 10 males between 16- and 25-years old was not s i g n i f i c a n t l y d i f f e r e n t from a normal d i s t r i b u t i o n , whereas, the heart rate d i s t r i b u t i o n was s i g nificantly different.  Khachaturian and Kerr (1972) reported that s i g n i f i -  cant differences i n variance are introduced by transforming cycle time data.into heart rate.  They suggested  that this problem becomes p a r t i c u -  l a r l y important when the study i n question involves averaging ECG r e sponses across t r i a l s or states.  Statistical  Analyses  The raw scores, cycle length (mm.) and muscular tension (mm.), for each subject under each of the three conditions were obtained from the 2-channel Sanborn recording paper as defined i n Chapter I . Cycle time (msec.) and muscular tension (kg.) were calculated according to the follow  26 TABLE I Relationship between cycle time (R-R i n t e r v a l ) and the corresponding heart rates. Cycle Time (msec.)  Heart Rate (bpm)  Heart Rate Change  1400  42.9  1.5  1350  44.4  1.8  1300  46.2  1.8  1250  48.0  2.0  1200  50.0  2.2  1150  52.2  2.3  1100  54.5  2.6  1050  57.1  2.9  1000  60.0  3.2  950  63.2  3.4  900  66.7  3.9  850  70.6  4.4  800  75.0  5.0  750  80.0  5.7  700  85.7  6.6  650  92.3  7.7  600  100.0  9.1  550  109.1  10.9  500  120.0  13.3  450  133.3  16.7  400  150.0  FIGURE 2  Cycle Time ( m i l l i s e c o n d s )  M  28 ing  formulas:  1.  Cycle Time (msec.) = Cycle Length  (mm.)  x 10  (recording paper speed = 100 mm./sec.) 2.  Muscular Tension (kg.) = Muscular Tension (mm.) (calibration:  1 mm.  x 2  = 2 kg.)  and recorded on computer coding sheets p r i o r to being key-punched onto computer data cards.  In addition each subject's maximal voluntary con-  t r a c t i o n was obtained from the recording paper and determined as outlined previously.  Then expressed i n kilograms according to formula (2.) and  recorded on the computer coding sheets.  The experimental design ( F i g . 1) was not an appropriate design for the s t a t i s t i c a l analysis of the experimental data, because, the l e v e l s of the f i r s t f a c t o r could not be crossed with a l l l e v e l s of the l a s t factors and s t i l l be meaningful.  two  Therefore, the experimental data obtained  under each condition were analyzed according to the s t a t i s t i c a l design illustrated  by Figure 3.  A l l two-way analyses of variance (ANOVA) and trend analyses were performed  on the University of B r i t i s h Columbia's IBM 360/67 computer  using the "canned" program, "Repeated Measures Analysis of Variance  (UBC  BMDP2V)," (Sampson, 1974), and a l l post-hoc Newman-Keuls analyses were performed  as outlined by Winer (1971).  29 FIGURE 3 STATISTICAL DESIGN Condition (Resting, Contraction, or Recovery)  Subject  50% MVC  o  •r) •W O rt •p  c o o  f>N  M  rt  4-1  75% MVC  9  o >  rt S  •H  3 cu  100%  MVC  1  2  3  Heart Beat 4 5 6 7  8  9  10  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  3 x 10 F a c t o r i a l Design with repeated measures on the second factor and 10 subjects nested under the f i r s t  factor.  30 Resting Condition.  A two-way ANOVA and trend analysis was per-  formed on the dependent variable (CT) to test the effectiveness of the random assignment.  Followed by a post-hoc Newman-Keuls analysis to deter-  mine the e f f e c t of the i n s p i r a t i o n r e s u l t i n g from the " i n s p i r e " and "hold" commands.  The post-hoc Newman-Keuls analysis indicated that each subject's CT j u s t p r i o r to contraction (resting heart beat 10) would be appropriate to use as h i s CT  . A Fortran program was written and developed to compute  each subject's MT_, ACCT . RCCT , ACCT , and RCCT ; and appropriately punch R C C R K each subject's dependent variables f o r the contraction and recovery tion onto data cards i n preparation f o r s t a t i s t i c a l  Contraction Condition.  condi-  analyses.  Four two-way ANOVA's and trend  analyses  were performed on the four dependent variables (CT , ACCT , RCCT , and MT ) D  C  to test hypotheses 1 and 2.  C*  C  Followed by a post-hoc Newman-Keuls analysis  of MT , within each l e v e l of %MVC, to test the v a l i d i t y of the assumption R underlying hypothesis  1.  This was followed by a post-hoc Newman-Keuls  analysis of RCCT , within each l e v e l of %MVC, to indicate the beats at which the changes i n trend were occurring.  Then, three two-way ANOVA's  were performed on RCCT^ i n order to make the following comparisons: 1.  50% MVC  Vs.  75% MVC  2.  50% MVC  Vs.  100% MVC  3.  75% MVC  Vs.  100% MVC  to further test hypothesis  1.  These comparisons should normally be made  R  with a post-hoc procedure.  However, on the advice of a s t a t i s t i c i a n ,  preceding procedure was considered to be more meaningful.  Recovery Condition. formed on RCCT  K  A two-way ANOVA and trend analysis was  to test hypothesis 3.  32  CHAPTER IV RESULTS AND DISCUSSION  Results  Each subject's age, three maximal voluntary contractions scores, and determined  100% MVC  are presented i n Table I of Appendix A.  The l e v e l of confidence f o r a l l s t a t i s t i c a l tests was 0.05  set at  unless otherwise s p e c i f i e d .  Resting  Descriptive S t a t i s t i c s .  Individual cycle times f o r a l l subjects  and a l l 10 beats (heart beats) are presented i n Table I I of Appendix A. Means and standard deviations were calculated from these scores f o r each of the 10 beats of each group (%MVC) and are presented i n Table I I with a graphic p l o t of the pooled means displayed i n Figure 4.  S t a t i s t i c a l Analyses.  The ANOVA (Table III) indicated a non-  s i g n i f i c a n t groups e f f e c t and i n t e r a c t i o n (%MVC cant beats e f f e c t was  x Beats), but a s i g n i f i -  found.  The post-hoc Newman-Keuls analysis (Table IV) showed that the mean pooled CT's of beats 7, 8 and 9 were s i g n i f i c a n t l y d i f f e r e n t than  TABLE I I  Resting Condition -  M e a n s and  Standard Deviations of Cycle T i m e (CT)  Expressed in Milliseconds for all G r o u p sa n d all 10  Heart Beats.  Heart B e a t G r o u p  50$  MVC  75£ MVC 10C#  MVC  Pooled  1  2  3  4  5  6  7  8  9  10  936.0 ±186.1  945.5 ±193.5  908.5 ±153.4  925.0 ±199.9  975.5 ±247.3  947.5 ±232.7  855.0 ±173.7  820.5 -±142.1  829.0 ±107.5  881.0 ±101.7  923.0 ±168.4  922.0 ±152.1  901.5 ±135.3  932.0 ±134.4  948.5 ±167.0  893.0 ±159.1  847.5 ±142.6  809.5 ±68.2  858.0 ±82.3  954.0 ±169.8  876.0 ±161.0  890.5 ±164.2  893.5 ±165.5  863.5 ±134.4  863.5 ±149.2  836.5 ±160.8  788.0 ±171.0  768.5 ±152.7  777.5 ±129.3  870.0 ±136.3  911.7  919.3  901.2  . 906.8  929.2  892.3  830.2  799.5  821.5  901.7  ;  LO  FIGURE 4  Heart Beat The e f f e c t o f i n s p i r a t i o n on Resting Cycle Time.  The arrow  approximates the p o i n t a t which the subjects were t o l d t o comfortably i n s p i r e and block t h e i r breathing i n p r e p a r a t i o n f o r the c o n t r a c t i o n .  TABLE III Summary o f ANOVA Resting -  Cycle Time (CT)  Source  df  Between Subjects  MS  F  P  2  111942.0  0.60  NS  27  188123.3  9  63748.8  S.84  < .01  29  Ss w. $MVC c  W i t h i n Subjects  270  Beats (lin.)  1  218405.5  9.97  < .01  B e a t s  (quad.)  1  6112.4  0.42  NS  B e a t 3  (cubic)  1  187691.6  23.34  < .01  18  4868.6  0.68  NS  243  7210.4  B e a f c 3  %MVC x Beats Beats x Ss w. %WC Beats x Ss w. $ M V C ( Beats x S 3 w. %^ f c  N )  quad  Beats x Ss w. # M V C  *  lin  cubic  \  27  21906.9  27  14429.7  27  8042.5  NS denotes that the F - r a t i o i s not s i g n i f i c a n t a t the 0 . 0 5 l e v e l o f confidence.  TABLE  IV 36  N e w m a n K e u l s Analyses of Paired C o m p a r i s o n s  Resting -  Cycle T i m e (CT)  S5 = 15.503  r = Sgq>95(r,243) =  2 2.77  3 3.31  *5 3.86 3.63 4  6  7  4.03 4.17  8  9  4.29  4.39  10 4.47  Ordered M e a n s Beats 8  799.5 8  8 2 1 . 5 830.2  3  10  4  -*  *  #  *  *  •M-  *  •*  -  - . -.  -  7  6  -  -  *  9  -  7  .  6  *  901.2  9  *  901.7  906.8  .911.7  892.3  1  #  919.3  929.2  2  5  #  -K-  *#  .  -  D e n o t e s that the paired m e a n s aresignificantly different at the 0.05 level of confidence.  -  D e n o t e s that the paired m e a n s arenot significantly different at the 0.05  level of confidence.  —  37  the mean pooled CT's of the remaining beats, which were not s i g n i f i c a n t l y d i f f e r e n t from each other.  On the basis of these r e s u l t s , the f i r s t beat  p r i o r to contraction was used i n determining each subject's control cycle time.  Contraction  Descriptive S t a t i s t i c s .  Individual raw scores (CT and MT) C  and i n d i v i d u a l computed scores (ACCT , RCCT , and MT ) f o r a l l subjects C C R and a l l 10 beats are presented i n Tables I I I and IV of Appendix A, and Tables I, I I and I I I of Appendix B, respectively.  From the appropriate  preceding r e s u l t s , means and standard deviations of MT , RCCT^,, CT^, and R  ACCT^, were calculated f o r each of the 10 beats of each group and are presented i n Tables V, VIII, XI and XIII, respectively, with a graphic p l o t of the means displayed i n Figures 5, 6, 7 and 8, respectively.  S t a t i s t i c a l Analyses.  The MT  R  ANOVA (Table VI) indicated a  s i g n i f i c a n t beats e f f e c t , groups e f f e c t and i n t e r a c t i o n .  The trend analysis indicated that there was a s i g n i f i c a n t l i n e a r , quadratic, and cubic trend through beats with a s i g n i f i c a n t difference i n these trends between groups.  Post-hoc Newman-Keuls analyses was performed  on the means of  the 10 beats f o r the 100% MVC group (Table VII A), 75% MVC group (Table VII B) and 50% MVC group (Table VII C).  The analyses indicated that the  38 mean MT  K  's were not s i g n i f i c a n t l y d i f f e r e n t after the fourth beat for  the 100% MVC  group and after the t h i r d beat for the 75% and 50%  MVC  groups.  The ANOVA's and trend analyses of C T  C>  ACCT  C>  and RCCT  C  are  summarized i n Tables XII, XIV and IX, respectively. They show that the F-ratios obtained using CT_ or ACCT  were consistently smaller than those  obtained using RCCT , except f o r the main effect of groups and the quadr a t i c trend i n beats.  The trend analysis of RCCT  indicated that the l i n e a r and quad-  r a t i c trends i n beats were d i f f e r e n t between the three groups. powerful  trend analyses  (the l e v e l of confidence was  More  set to 0.01)  were  performed by making the following paired comparisons: 1.  50% MVC  Vs.  75% MVC  (Table I of Appendix C) - indicated  a s i g n i f i c a n t l i n e a r trend i n beats with no difference i n l i n e a r trend between the two groups. 2.  50% MVC  Vs.  100% MVC  (Table II of Appendix C) - indicated  a s i g n i f i c a n t l i n e a r and quadratic trend i n beats with a s i g n i f i c a n t d i f f = erence i n the two trends between the two groups. 3.  75% MVC  Vs.  100% MVC  (Table III of Appendix C) - indicated  a s i g n i f i c a n t l i n e a r and quadratic trend i n beats with a s i g n i f i c a n t d i f f erence i n the two trends between the two groups.  39 The post-hoc Newman-Keuls analyses on the means of the 10 beats for  the three groups indicated the following ( i n terms of RCCT ): 1.  100% MVC (Table X A) - indicated s i g n i f i c a n t differences  between each of the f i r s t f i v e beats with a change i n the trend during the following f i v e beats. 2.  75% MVC (Table X B) - indicated that the only s i g n i f i c a n t  difference i n the f i r s t f i v e beats was between the f i r s t and the remaining of  four.  However, the l a s t f i v e beats showed a similar trend to that  the 100% MVC group. 3.  50% MVC (Table X C) - indicated that the only s i g n i f i c a n t  difference was between the f i r s t beat and the remaining nine beats.  Recovery  Descriptive S t a t i s t i c s . computed scores (ACCT  R  The i n d i v i d u a l raw scores and i n d i v i d u a l  and RCCT ) for a l l subjects and a l l 10 beats are  R  presented i n Table IV of Appendix A and Tables IV and V of Appendix B, respectively.  From these r e s u l t s , the means and standard deviations of  RCCT , CT and ACCT were calculated for each of the 10 beats of each R R R group and are presented i n Table XV, and Tables I and I I of Appendix D, respectively, with a graphic plot of the means displayed i n Figure 9, and Figures 1 and 2 of Appendix D, respectively.  S t a t i s t i c a l Analysis.  The trend analysis (Table XVI) indicated  a s i g n i f i c a n t l i n e a r trend i n beats with a s i g n i f i c a n t difference i n this trend between groups.  T A B L E  Contraction Condition -  V  M e a n s a n d Standard Deviations of  Relative Muscular Tension (MTR) Expressed in Per C e n t for all G r o u p sa n d all 1 0 Heart Beats.  G r o u p  1  2  5 C # M V C  0.00 ±0.00  J35.03 ±13.96  7 5 $M V C  0.00 ±0.00  !0C$ M V C  0.00 ±0,00  6  7  8  9  1 0  3  4  5  47.07  ±3.27  48.58 ±3.11  48.57 ±3.18  48.19 ±3.16  48.12 ±3.14  48.41 ±3.81  48.41 ±3.81  48.20 ±3.63  ,60.42 ±11.60  74.69 ±3.48  74.66 13.39  74.30 ±2.37  74.32 ±2.32  74.06 ±2.29  73.73 ±2.10  74.07 ±2.11  74.26 ±2.37  J2.49 ±20.65  85.71 ±12.66  94.51 ±5.41  96.05 ±3.16  96.46 ±3.17  96.49 ±3.55  96.43 ±3.62  96.99 ±4.05  ±3.99  96.70  F I G U R E  5  Heart B e a t >->  Contraction Condition - ' '  Relative Muscular Tension during the first 10 Heart Beats.  TABLE VI 42  Summary of ANOVA Contraction - Relative Muscular Tension (MT ) R  df  Source Betweem Subjects  MS  P  29  2 Ss w. #MVC  38757.7  < .01  367.54  105.5  27  Within Subjects  •  270  Beats  9  16280.8  514.60  < .01  (lin.)  1  64720.1  815.80  < .01  Beats  (quad.)  1  52154.3  4957.38  < .01  B e a t s  (cubic)  1  23552.6  787.57  < .01  790.4  24.98  < .01  B e a t s  %WJC x Beats  18  %WG x BeatS£ 2 M V C  j  2  3982.6  50.20  < .01  ( q u a d L )  2  2057.2  195.54  < .01  2  540.2  18.06  < .01  lin  x Beats  %MC x B e a t s  ( c u b i c )  Beats x Ss w. %W0  243  31.6  27  79.3  Beats x Ss w. %^^{qQa<l.)  27  10.5  %^(^ xc)  27  29.9  Beats x Ss w. #MVC(  Beats x Ss w.  *  F  liru  CVih  )  NS denotes that the F-ratio i s not significant at the 0.05 level of confidence.  TABLE VII 43  Newman-Keuls Analyses of Paired Comparisons Contraction - Relative Muscular Tension (MT ) R  Sg =  1.026?  r = ¥ . 9 5  (  r  2  ,243) =  3  2.77  3.31  4 3.63  5 3.86  TABLE  -  7 4.17  9  8 4.29  4.39  MVC  52.49  85.71  94.51  96.05  96.43  96.46  96.49  2  3  4  5  8  6  7  *  -X-  *  *  2  -A-  -X  X  X  #  3  #  #  •»•  •»•  #  Beats 1  0.00 1  .  10 4.47  VII(A)  10C#  Ordered Means  6 4.03  96.70  96.99  10  *  Denotes that the paired means aresignificantly different at the 0.05 level of confidence.  -  Denotes that the paired means arenot significantly different at the 0.05 level of confidence.  9  TABLE  VII(B) 44  75% MVC  Ordered Means Beats  0.00  60.42  73.73  74.06  74.07  2  8  7  9  X  tt  1  1  2  tt  74.26  74.30  74.32  74.66  74.69  5  6  4  3  tt  tt  #  «  *  *  10  tt  *  •*  8  TABLE  VII(C)  5C# MVC Ordered Means Beats 1 2  0.00 35.03 1  2 tt tt  47.07  48.12 48.19 48.20 48.41 48.41 48.57  48.58  3  7  6  10  8  9  5  4  *  tt  *  *  #  *  *  *  *  *  tt  tt  tt  tt  #  3  *  Denotes t h a t the p a i r e d means a r e s i g n i f i c a n t l y d i f f e r e n t a t the 0.05 l e v e l o f confidence.  -  Denotes t h a t the paired means a r e not s i g n i f i c a n t l y d i f f e r e n t a t the 0.05 l e v e l o f confidence.  TABLE  Contraction Condition -  VIII  M e a n s and  Standard Deviations of  Relative C h a n g e in Cycle T i m e  ( R C C T C )  Expressed in Per C e n t for all G r o u p sa n d all 10 Heart Beats.  Heart Beat G r o u p  50%  MVC  15%  MVC  100%  MVC  1  2  3  -4.83  . 0.50 112.02  112.75  113.41  . 1.95  4  , 1.05  115.77  5  . 0.39  ±18.04  6  . 1.35  ±18.46  7 . 2.09 119.09  8  , 2.42  •±19.08  9  3.17 ±17.72 4.  10  ±16.82  16.22  19.52  19.86  18.65  19.78  14.26  ±10.96  14.88 ±12.32  16.18  17.43  ±12.50  15.54 ±12.77  r0.51  . 7.95 110.35  .14.04 111.22  .19.68  22.63 ll3.01  ,23.75  .24.99  ,26.61  27.62  ,27.54 ±12.35  2.46  17.10  7.69  6.64  ,7.53  ll2.83  8.91  12.38  113.31  ±13.28  -12.55  ±12.51  4>  FIGURE  Contraction Condition Beats.  6  Relative C h a n g e in Cycle T i m e during the first 10 Heart  A r r o w s indicate the heart beat at which e a c hg r o u p attained it's prescribed level  of $ M V C ,  TABLE IX 47  Summary of ANOVA Contraction -  R e l a t i v e Change i n Cycle Time (RCCT ) P  Source  df  Between Subjects  P  2  8402.9  27  1549.1  9  5.42  < .01  830.8  40.03  < .01  1  6579.8  61.09  < .01  (quad.)  1  713.3  21.14  < .01  (cubic)  1  63.5  2.80  NS  164.1  7.91  < .01  Ss w. %WJC W i t h i n Subjects  270  Beats Beats  B e a f c s  ( l i r u )  %WC x Beats  18  %WJC x B e a t s p , y  2  1082.6  10.05  <.01  %mC x B e a t s  ( q u a d u )  2  286.6  8.50  <.01  *HVC x B e a t s  ( c u b i c )  2  52.8  2.32  NS  i r  f  Beats x Ss w. #MVC  *  F  29  %WC  B e a t 3  MS  243  Beats x Ss w. % M V C (  1 i n  j  Beats x Ss w. # M V C (  quad#  Beat3 x Ss w. # M V C (  cubic  20.8  27  107.7  )  27  33.7  )  27  22.7  NS denotes t h a t the F - r a t i o i s not s i g n i f i c a n t a t the 0.05 l e v e l o f confidence.  TABLE  X  48  Newman-Keuls Analyses of Paired Comparisons Contraction - R e l a t i v e Change i n Cycle Time (RCCTQ)  Sg = 0 . 8 3 1 7 2  r Sgq  e 9 5  ( ,243) =  3  2.77  r  3.31  4  5  3.63  6  3.86  TABLE  Beats 1  19-68  22.63  23.75  24.99  26.61  1  2  3  4  5  6  7  8  #  tt  *  * * *  *  *  10 4.47  MVC  14.04  3  6  4.39  7.95  tt  5  9  4-29  -0.51  2  4  8  4.17  X(A)  100$  Ordered Means  7 4.03  * *  tt  -  tt  27.54  27.61  10  9  tt  * •»•  tt  tt  tt  tt  tt  -  tt tt  *  Denotes t h a t the p a i r e d means a r e s i g n i f i c a n t l y d i f f e r e n t a t the 0.05 l e v e l o f confidence.  -  Denotes t h a t t h e p a i r e d means are not s i g n i f i c a n t l y d i f f e r e n t a t the 0.05 l e v e l o f confidence.  tt  TABLE  X(B)  15%  MVC  Ordered Means Beats  2.46  1  6.64  7.53  3  4  7.69  8.91  2  5 *  1  3  -  12.38  6  14.26  7  *  15.54  8  16.18  10  #  tt  _  14.88  9  *  ' * . # . # >  4  _  _  2  _  # .  •  5  • »  * •  •  . »  » •  •  * »  * #  #  *  #~ • _  6  7  _  tt  *  2.93  3.17  -  TABLE  X(C)  50$ MVC Ordered Means Beats 1  -4.83  0.39  0.50  1.05  1.35  1.95  2.09  2.42  1  5  2  4  6  3  7  8  #  *  tt  tt  10 tt  5  *  Denotes that the paired means are significantly different at the 0 . 0 5 level of confidence.  -  Denotes that the paired means are not significantly different at the 0.05 level of confidence.  9 tt  TABLE  Contraction Condition -  XI  M e a n sa n d Standard Deviations of Cycle T i m e (CTQ)  Expressed in Milliseconds for all G r o u p sa n d all 10 Heart Beats.  Heart Beat G r o u p  1  50$ M V C  925.0  873.0  ±176.1  ±115.4  859.0 ±107.8  926.0 ±142.3  873.5 ±119.1  ±119.8  870.5 ±123.7  793.5 ±110.7  739.5 ±104.4  15% MVC 100$ M V C  2  3  882.0  4  5  6  866.5 ±128.2  873.5 ±154.3  865.0 ±157.2  872.5 ±111.3  860.0 ±106.8  689.5 ±109.3  663.5 ±107.9  654.5 ±115.7  7  8  9  10  846.0  857.0 ±152.1  853.5 ±147.7  ±131.7  848.5 ±127.9  824.5  804.5  ±86.7  ±73.5  796.5 ±64.3  784.5 ±70.9  ±91.5  630.0  621.0 ±107.0  644.0 ±116.2  ±109.4  792.0  623.0 ±115.4  O  7  FIGURE 1  TTT  i  its  H950-  -90& -i-f  850  i LL I  1  ra C o o r800 T"  r m  25$.  CO OJ •H  l  •a  s  ID  750 0) rH O  M44-  n  J_L I  i  TTT  I  i  I  >» .-r o  TT  I  Si  I  I l-i-L  1 M  tti  TT?  650  4100$ MVG  -Li-  I'M 600  l  ! I  rnxnn:  !  I  !  I  I  t±  I ! 1  1  1 I  4  4-2-  4  i  5  ^T+TTfrtfr^  Heart Beat Cycle Time during the f i r s t 10 Heart C o n t r a c t i o n Condition Beat3. Arrows i n d i c a t e t h e heart beat a t which each group a t t a i n e d i t * s p r e s c r i b e d l e v e l o f $MVC.  TABLE X I I 52  Summary o f ANOVA C o n t r a c t i o n - Cycle Time (CT ) C  Between Subjects  Ss w. $MVC  Beats  B e a t s  (cubic)  882446.5  %WJC x B e a t s ( $MVC x B e a t s  7.08  < .01  27  124648.7  9  73109.7  36.34  < .01  1  578218.5  52.97  < .01  1  61966.5  22.15  < .01  1  5406.6  2.42  NS  12140.1  6.03  < .01  2  76913.2  7.05  < .01  2  22334.9  7.98  < .01  2  5027.4  2.25  NS  18  %WJC x Beats l i n #  j  ( q u a d > )  %WJC x B e a t s (  c u b i c  )  Beat3 x Ss w. $MVC  243  2011.8  27  10916.1  Beats x S 3 w. $MVC(q ^)  27  2797.5  Beats x Ss w. $ M V C (  27  2235.9  Beats x Ss w.  %^(^j ± ^) L  n  uac  *  2  (lin.)  (quad.)  P  270  W i t h i n Subjects  B e a t 3  F  29  $MVC  B e a t s  MS  df  Source  c u b i c  )  NS denotes that the F - r a t i o i s not s i g n i f i c a n t a t the 0.05 l e v e l o f confidence.  TABLE XIII  Contraction Condition -  Mean3 and Standard Deviations of  Actual Change i n Cycle Time (ACCT ) C  Expressed i n Milliseconds f o r a l l Groups and a l l 10 Heart Beats.  Heart Beat 5  6  ±127.1  ±144.0  16.0 ±147.2  %.o ±99.6  129.5  ±103.4  81.5 ±109.3  ±118.2  130.5 ±112.8  180.5 ±133.1  206.5  215.5 ±139.7  Group  1  2  3  4  50$ MVC  -44.0 ±126.7  8.0 ±98.1  22.0 ±104.1  ^ 14.5  MVC  28.0 ±63.3  80.5 ±83.6  72.0  100$ MVC  -0.5 ±65.9  • 76.5 ±101.0  15%  ±136.4  9  10  ±152.3  ±152.0  ^ 35.0 ±143.2  ±137.5  149.5 ±129.9  157.5 ±146.5  1148.7  226.0 ±140.3  240.0 ±135.5  249.0  247.0  ±136.4  ±132.8  8  7  24.0  ^  27.5  ,169.5  162.0  ±148.0  FIGURE 8  81 T»  C  o o 0) 0)  E-"  o >»  o  ©  tiO  c  CO.  Si  o CO  o  Heart Beat Contraction Condition Actual C h a n g e in Cycle T i m e during the first 1 0 Heart B e a t 3 . A r r o w s indicate the heart beat at which e a c h g r o u p attained it's prescribed level of $ M V C .  TABLE XIV 55.  Summary of ANOVA Contraction - Actual Change i n Cycle Time  Between Subjects  %WC  Within Subjects  P  4.76  < .02  73110.3  36.34  < .01  2  671885.5  27  14L221.4  9  270  Beats (lin.)  1  578224.5  52.97  < .01  Beat3  (quad.)  1  61967.A  22.15  < .01  B e a t s  (cubic)  1  5406.5  2.42  NS  12140.I  6.03  < .01  2  76913.6  7.05  < .01  2  22334.9  7.98  < .01  2  5027.4  2.25  NS  B e a t 3  18  %WJC x Beats $MVC x B e a t s ( %WJC x B e a t s  l i n >  )  ( q u a d 0  %WIC x B e a t s (  c u b i c  )  Beats x Ss w. $MVC Beats x Ss w. £ M V C (  243 liru  Beats x Ss w. $MVC(q Beats x Ss w. $MVC(  *  F  29  $MVC Ss w.  MS  df  Source  (ACCTQ)  )  2011.8  27  10916.1  uad>  )  27  2797.5  cubic  )  27  2235.9  NS denotes that the F-ratio i s not significant at the 0.05 level of confidence.  T A B L EX V  Recovery Condition -  M e a n s a n d Standard Deviations of  Relative C h a n g e in Cycle T i m e ( R C C T R ) Expressed in Per C e n t for all G r o u p sa n d all 1 0 Heart Beats.  Heart Beat G r o u p  50$ M V C  7 5 $ M V C  1 0 0 $ M V C  1  2  -1.60  3  5  6  7  -6.45 ±15.00  -7.21 ±14.46  -6.72  -7.30  ±13.55  ±13.74  ±15.64  ±17.08  9.06 ±16.18  ^8.64 ±15.07  ^ 7.27 ±14.83  17.33  10.37  10.32  8.06  ±20.63  ±21.06  ^ 2.59 ±19.65  -9.18 ±17.16  2.24 ±15.30  ±14.18  12.73 ±18.26  • 5.83 ±18.40  ^ 4.02  26.93  22.25 ±24.00  ±17.37  4  ±24.67  ±21.93  8  9  -10.82  -5.93 ±15.08  -10.69 ±15.01  ±17.17  7.52 ±12.28  ^ 6.89 ±13.64  ^ 7.41 ±13.46  -11.16  -4.53 ±24.02  ±21.42  A  ±46.72  -3.68  FIGURE 9  TABLE XVI  58  Summary o f ANOVA Recovery - R e l a t i v e Change i n Cycle Time (RCCT ) R  Between Subjects  W i t h i n Subjects  P  2.63  NS  872.5  6.41  < .01  1  6730.8  16.45  < .01  2  6566.8  27  2495.4  9  270  Beats (lin.)  B e a t 3  (quad.)  1  351.9  1.97  NS  B e a t 3  (cubic)  1  126.2  0.97  NS  422.0  3.10  < .01  2  3096.5  7.57  < .01  %MC x Beats  18  %WIC x B e a t s ^ ^ j .%MC x B e a t s  ( q u a c U )  2  18.7  0.10  NS  $MVC x B e a t s  ( c u b i c )  2  262.6  2.01  NS  Beats x Ss w. %WC  243  Beats x Ss w. $ M V C (  *  F  29  ss w. %mc  B e a t 3  MS  df  Source  lino  )  136.0  27  409.3  Beats x Ss w. $ M V C (  q u a d  j  2?  178.4  Beats x Ss w. $ M V C  ( c u b i c )  27  130.5  NS denotes that the F - r a t i o i s not s i g n i f i c a n t a t the 0.05 l e v e l o f confidence.  59 Discussion  Resting  The ANOVA on resting cycle time (Table III) shows a n o n - s i g n i f i cant groups e f f e c t i n d i c a t i n g that the random assignment of subjects to groups was e f f e c t i v e .  The " i n s p i r e " command was given just p r i o r to beat s i x and the s i g n i f i c a n t difference of beats 7, 8 and 9 from the remaining beats indicated that maximum tachycardia occurred at beat 8.  This finding  supports those of Davies and Neilson (1967), who found that a fast i n s p i r a t i o n i n the supine p o s i t i o n produced maximum tachycardia i n 3-seconds and maximum bradycardia i n 4.8-seconds.  This may p a r t i a l l y  explain the negative mean values of RCCT^ for beat one. r e s p i r a t i o n was not measured during this condition.  Unfortunately,  As a r e s u l t , the  i n t e r a c t i n g e f f e c t s of i n s p i r a t i o n and contraction were d i f f i c u l t to explain.  Beat ten was u t i l i z e d as the control cycle time and selected on the basis of the N-K analysis along with the fact that i t had been u t i l i z e d as the control value i n previous studies (Borst et a l . , 1972, and Petro et a l . , 1970) and should be representative of autonomic tone just p r i o r to contraction.  This choice may have been inappropriate, as  demonstrated by some of the i n d i v i d u a l r e s t i n g cycle times, e s p e c i a l l y  60 i n the case of subject 1.  In addition, testing was done just p r i o r to  term examinations, and most subjects were unfamiliar with the testing equipment and procedure, which may have caused anxiety.  However, s e l -  ection of control cycle times on an i n d i v i d u a l basis was u n j u s t i f i a b l e .  Contraction  The mean MT 's of each beat f o r each group (Table V) indicated R that the r e l a t i v e muscular tension attained by each group was consis^tently lower than the prescribed muscular tension ( i . e . , 50%, 75% and 100%).  This consistent undershooting can be attributed to the inexact  c a l i b r a t i o n of the oscilloscope screen.  For ease of discussion the  attained muscular tension w i l l be considered equivalent to the prescribed value.  The r e s u l t s indicated that the response time assumption underl y i n g hypothesis 1 was not v i o l a t e d .  Although, the N-K analyses on MT  indicated attainment of the prescribed %MVC by beat 4, 3 and 3, f o r the 100%, 75% and 50% MVC groups, r e s p e c t i v e l y ; the time of attainment (determined by summing cycle times) 3.1 s e c , 2.7 s e c and 2.7 s e c , respect i v e l y , was e s s e n t i a l l y the same i n terms of the assumption.  Test of Hypothesis 1.  The s i g n i f i c a n t l i n e a r trend (p<.01)  and the s i g n i f i c a n t groups by l i n e a r trend i n t e r a c t i o n (p<.01) supported hypothesis 1.  The trend analyses of paired comparisons showed that the  61 the l i n e a r trend f o r the 100% MVC group was s i g n i f i c a n t l y d i f f e r e n t from the l i n e a r trends f o r the 75% MVC group (p<.01) and the 50% MVC group (p<.01).  However, the l i n e a r trend for the 75% MVC group was not s i g -  n i f i c a n t l y d i f f e r e n t from the l i n e a r trend f o r the 50% MVC group, due to the v i r t u a l abscence of a l i n e a r trend f o r the 50% MVC group ( as indicated by Figure 6).  The N-K analyses f o r RCCT  i n the 100%, 75% and 50% MVC groups  indicated the following: (1)  The f i r s t f i v e beats of the 100% MVC group were s i g n i f i cantly d i f f e r e n t from each other i n successive order.  (2)  Only beat 1 was s i g n i f i c a n t l y d i f f e r e n t from beats 2, 3, 4 and 5 i n the 75% and 50% MVC groups.  (3)  The 100% and 75% MVC groups showed s i m i l a r trends f o r beats 6 to 10, as indicated by the N-K analyses.  The  50% MVC group showed a s i m i l a r trend over tha l a s t f i v e beats, as can be seen i n Figure 6, but, the trend was not  supported i n terms of the N-K analyses as i t was f o r  the 100% and 75% MVC groups. (4)  A l l three groups showed an reversal of beats 9 and 10, i n terms of ordered means, suggesting a possible overcompensation of the heart-trigger mechanism(s).  The difference i n responses f o r the f i r s t f i v e heart beats the l a s t f i v e heart beats f o r the three groups suggests that there  62 were at l e a s t two d i f f e r e n t heart-trigger mechanisms involved.  The  f i r s t mechanism was almost instantaneous and may have been the c e n t r a l heart-trigger mechanism that has been proposed to operate on central i r r a d i a t i o n , whereas,the second mechanism was slower acting ( i n that i t did not appear to show any apparent effects u n t i l the s i x t h heart beat) and may have been the peripheral heart-trigger mechanism oper-  + ating on the basis of the K  concentration and i t s e f f e c t on the pro-  prioceptive and non-proprioceptive afferents. Previous studies (Humphreys and Lind, 1963, and Freyschuss, 1970b) reported d i f f i c u l t y i n detecting a relationship between the change i n heart rate i n the range 50% MVC - 100% MVC.  Since then,  Jennings et a l . (1974) and Khachaturian and Kerr (1972) have advocated the use of cycle time i n preference to heart rate i n the analysis of evoked cardiac responses; and this study supports their suggestion.  N-K analyses indicated, i n terms of the f i r s t f i v e beats f o r the 50% and 75% MVC groups, no s i g n i f i c a n t -change i n RCCT after the r  second beat; whereas, the prescribed muscular tension was not attained u n t i l the t h i r d beat with a s i g n i f i c a n t difference i n tension between the second and t h i r d beat.  This showed that at the onset of the con-  t r a c t i o n the cardioacceleration did not appear to be influenced by a peripheral" heart-trigger mechanism which was dependent on the r e l a t i v e muscular tension, but may have been the r e s u l t of a cerebral i r r a d i a t i o n i n i t i a t i n g vagal tone withdrawal.  This suggestion of vagal tone with-  drawal was based on the studies by Levy and Zieske (1969) on sympathetic-  63 parasympathetic i n t e r a c t i o n , and Toda and Shimamoto (1968) on sympathetic stimulation response time.  Hnik et a l . (1969) found a latency of 60 sec. or more from the time of infusion of K of the sensory f i b e r s . time required for the  +  to the onset of increased discharge frequency  They suggested this latency was a r e s u l t of the to d i f f u s e into the v i c i n i t y of the sensory  nerve endings and a t t a i n a s u f f i c i e n t l o c a l concentration to enhance the a c t i v i t y of these endings.  However, during a normal contraction  i t would be reasonable to assume that the latency would be much shorter because the d i f f u s i o n distance would be n e g l i g i b l e and the rate of increase i n l o c a l K  concentration would depend mainly on the r e l a t i v e  number of muscle f i b e r s involved and the l o c a l blood flow rate.  L i u et a l . (1969), M i t c h e l l et a l . (1968) and, Toda and Shimamoto (1968) demonstrated  that K - s e n s i t i v e , group I I I and/or IV  sensory afferents could e l i c i t a predominantly "sympathetic" cardiovascular response, s i m i l a r to that observed i n man.  Furthermore,  response was not apparent u n t i l a f t e r a delay of at least  this  2-seconds.  Humphreys and Lind (1963) reported that the blood flowed through the forearm during a handgrip contraction u n t i l the tension exceeded 70% MVC;  and Staunton et a l . (1964) found that  complete  occlusion of the active muscles potentiated the pressor r e f l e x .  These  findings, i n l i g h t of the preceding findings and postulations, suggest  64  that a s i m i l a r peripheral heart trigger mechanism i s operating during isometric contractions i n man.  Furthermore, the greater the tension,  e s p e c i a l l y above 70% MVC, the more rapid the onset of the cardiovascular response with a minimal latency of 2-seconds.  This proposed mechanism  could a s s i s t i n muscular homeostasis by increasing perfusion pressure  + to increase blood flow, r e s u l t i n g i n a decrease i n K which would r e s u l t i n a decreased  concentration  sensory afferent a c t i v i t y .  In terms of the present study, i t i s proposed that the postulated mechanism had exerted a s t a t i s t i c a l l y detectable influence by beat f i v e f o r the 75% MVC group and somewhat e a r l i e r f o r the 100% MVC group, i n f a c t , at such a time that there was a merging of cerebral-peripheral influences.  Test of Hypothesis 2. and RCCT  The trend analyses F-ratios for MT^  were consistently larger than those of either CT W  \J  with the exception of the RCCT  or ACCT , LA*  F - r a t i o f o r the quadratic trend of beats.  These r e s u l t s indicated that the use of RCCT^, as the dependent measure generally resulted i n a r e l a t i v e l y smaller unexplained  (error) variance,  thereby, supporting the hypothesis.  Recovery  Test of Hypothesis 3.  The trend analysis indicated a s i g n i f -  icant difference i n the l i n e a r trend between group?;, which  supported  65 the hypothesis.  However, as indicated by Figure 9, the s i g n i f i c a n t  l i n e a r trend and r e s u l t i n g s i g n i f i c a n t difference between groups was predominantly a result of the pronounced l i n e a r trend i n the 100% group with a s l i g h t l i n e a r trend i n the 50% MVC l i n e a r trend i n the 75% MVC  MVC  group and v i r t u a l l y no  group; and indicated non-support for the  hypothesis.  Davies and Nielson (1967) reported that forced expiration from a breath-held p o s i t i o n i n v a r i a b l y produced a s l i g h t f a l l i n heart rate followed by a r i s e .  Although, r e s p i r a t i o n was not recorded i n this  study t h i s response probably occurred and masked the trends r e s u l t i n g from the relaese of the contraction.  This may  explain the plateau or  rebound tendency observed i n Figure 9.  Paulev (1971) found, following a 100% MVC  handgrip held for  6 0 - s e c , a reduction i n heart rate after a delay and a r e l a t i v e increase i n the depth of the f i r s t two r e s p i r a t i o n s . This study, i n contrast, showed no apparent delay before the reduction occurred.  66 CHAPTER V SUMMARY AND CONCLUSIONS  Summary  The purpose of this study was to examine the e f f e c t s of i s o metric contractions on the heart and determine the time-course of the change of the cardioacceleratory response.  Further, the study examined  the degree of relatedness of muscular tension to cycle time, r e l a t i v e change i n cycle time and actual change i n cycle time.  In addition, the  study examined the time-course of the recovery of the cardiac response to the isometric contraction.  A t o t a l of 30 males between the ages of 18 - 28 years were involved i n the experiment as subjects.  Each subject was randomly  assigned to one of three groups ( 10 subjects per group) requiring either a 50% MVC, 75% MVC or 100% MVC.  Each subject's maximal voluntary contraction with a right handgrip was determined. period.  This was followed by a 5-minute recovery  Then 15-seconds of resting (pre-contraction) ECG's were  recorded.  Immediately followed by the recording of 10-seconds of  contraction ECG's and muscular tensions, and 15-seconds of recovery ECG's.  Cycle length and muscular tension values were obtained from  the recording paper and cycle time, r e l a t i v e change i n cycle time and  67 actual change i n cycle time were calculated from the appropriate values.  Analysis of variance of the results indicated that, during the pre-contraction phase, the " i n s p i r e " command caused maximum tachycardia to occur at beat 8 and maximum bradycardia to occur at either beat 10 or beat 1 of the contraction phase.  The statement that maximum  bradycarida may have occurred at beat 1 of the contraction phase i s supported by the fact that some subjects had negative values f o r their r e l a t i v e change i n cycle time f o r this beat.  The trend analyses of paired comparisons f o r the three groups showed that the l i n e a r trend for the 100% MVC group was s i g n i f i c a n t l y d i f f e r e n t from the l i n e a r trends f o r the 50% and 75% MVC groups (p<.01). However, the l i n e a r trend f o r the 75% MVC group was not s i g n i f i c a n t l y d i f f e r e n t from the l i n e a r trend f o r the 50% MVC group due to the v i r t u a l abscence of a l i n e a r trend for the 50% MVC group.  The Newman-Keuls analyses of RCCT  f o r the three groups  indicated that the cardioacceleratory response was composed of two phases and supported previous studies which postulated the existence of a f a s t - a c t i n g c e n t r a l heart-trigger mechanism and a slower-acting peripheral h e a r t - t r i g g e r mechanism.  The trend analyses F-ratios indicated that the use of RCCT as a dependent v a r i a b l e , generally, resulted i n a smaller  unexplained  68  variance than either CT or ACCT . C  C  A graphic plot of means f o r RCCT  indicated a pronounced l i n e a r  trend f o r the 100% MVC group, a s l i g h t l i n e a r trend f o r the 50% MVC group and v i r t u a l l y no l i n e a r trend f o r the 75% MVC group.  This showed that the  rate of recovery from the cardioacceleratory response does not appear to be strongly dependent on the magnitude of the %MVC.  Conclusions  1.  The i n i t i a l rate of cardioacceleration, as determined by  the rate of change i n r e l a t i v e change i n cycle time,is d i r e c t l y dependent upon the magnitude of the r e l a t i v e maximal voluntary  contraction  i n the range 50% MVC - 100% MVC.  2.  The r e l a t i v e change i n cycle time i s a more s e n s i t i v e  measure f o r the determination of cardiac responses to isometric contractions than either the cycle time or the actual change i n cycle time.  3.  The magnitude of the r e l a t i v e maximal voluntary  contraction  held f o r 10-seconds does not a f f e c t the i n i t i a l rate of cardiodeceleration.  BIBLIOGRAPHY  69  Alam, M., and Smirk, F. H. "Observations i n Man on a Pulse Acceleration Reflex from the Voluntary Muscles of the Legs," Journal of Physiology (London), 9 2 : 1 6 7 - 1 7 7 , 1938. Astrand, P-0., and Rodahl, K. Textbook of Work Physiology, Toronto: McGraw-Hill Book Co., 1 9 7 0 . Borst, D., Hollander, A. P., and Bouman, L. N. 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"Changes i n the lonotropic State of the Left Ventricle During Isometric Exercise," British Heart Journal, 3 5 : 6 9 7 - 7 0 4 , 1973.  70 Guyton, A. C , Textbook o f Medical Physiology, 3 r d Ed., P h i l a d e l p h i a : W. B. Saunder3, 1 9 7 0 .  Hnik, P., Hudlicka, 0., Kucera, J . , and Payne, R. " A c t i v a t i o n o f Muscle A f f e r e n t s by Nonproprioceptive S t i m u l i , " American J o u r n a l o f Physiology, 217:1451-1458,  1969.  Jennings, R. J . , S t r i n g f e l l o w , J . C , and Graham, M. "A Comparison o f the S t a t i s t i c a l D i s t r i b u t i o n s o f Beat-by-Beat Heart Rate and Heart P e r i o d , " Psychophysiology. 1 1 : 2 0 7 - 2 1 0 , 1974. Khachaturian, Z. S., Kerr, J . , Kruger, R., and Schachter, J . A. "A Methodol o g i c a l Note: Comparison between Period and Rate data i n Studies o f Cardiac Function," Psychophysiology, 9=539-545, 1 9 7 2 . Leon, D. F., Shaver, J . A., and Leonard, J . J . " R e f l e x Heart Rate C o n t r o l i n Man," American Heart J o u r n a l , 80:729-739, 1 9 7 0 . Levy, M. N. "Sympathetic-Parasympathetic I n t e r a c t i o n s i n the C i r c u l a t i o n Research, 2 9 : 4 3 7 - 4 4 5 , 1 9 7 1 .  Heart,"  Levy, M. N., and Zieske, H. "Autonomic C o n t r o l o f Cardiac Pacemaker A c t i v i t y and A t r i o v e n t r i c u l a r Transmission," J o u r n a l o f Applied Physiology. 27:465-470,  1969.  L i n d , A. R. " C a r d i o v a s c u l a r Responses t o S t a t i c E x e r c i s e ( i s o m e t r i c s , Anyone?)," C i r c u l a t i o n , 41(2):173-176, 1970. L i n d , A. R,, and McNicol, G. W. " L o c a l and C e n t r a l C i r c u l a t o r y Responses t o Sustained Contractions and the E f f e c t o f Free o r R e s t r i c t e d A r t e r i a l Inflow on Post-Exerci3e Hyperemia," J o u r n a l o f Physiology (London), 192:575-593,  1967a.  L i n d , A. R., and McNicol, G. W. " C i r c u l a t o r y Responses t o Sustained Hand-Grip Contractions Performed during other E x e r c i s e , both Rhythmic and S t a t i c , " J o u r n a l o f Physiology (London), 1 9 2 : 5 9 5 - 6 0 7 , 1 9 6 7 b . L i n d , A. R., T a y l o r , S. H., Humphreys, P. W., Kennelly, B. M., and Donald, K. W. "The C i r c u l a t o r y E f f e c t s o f Sustained Voluntary Muscle C o n t r a c t i o n , " C l i n i c a l Science. 2 7 : 2 2 9 - 2 4 4 , 1 9 6 4 . L i u , C. T., Huggins, R. A., and Hoff, H. E. "Mechanisms o f I n t r a - a r t e r i a l ^ - i n d u c e d Cardiovascular and R e s p i r a t o r y Responses," American J o u r n a l of Physiology. 2 1 7 : 9 6 9 - 9 7 3 , 1 9 6 9 . McCloskey, D. I . , and M i t c h e l l , J . H. " R e f l e x Cardiovascular and Respiratory Responses O r i g i n a t i n g i n E x e r c i s i n g Muscle," J o u r n a l o f Physiology (London), 224:173-186, 1972.  1  Macdonald, H. R., Sapru, R. P., T a y l o r , S. H., and Donald, K. W. "The E f f e c t s of Intravenous Propanolol ( I n d e r a l ) on the Systemic C i r c u l a t o r y Response to Sustained Handgrip." American J o u r n a l o f Cardiology, 18:333-343, 1 9 6 6 .  71  Mitchell, J . H., Gupta, D. N., and Barnett, S. E. "Reflex Cardiovascular Responses Elicited by Stimulation of Receptor Sites with Pharmacological Agents," Circulation Research, 20(Suppl. 1):I192-I200, 1 9 6 7 . Paulev, P. E. "Cardiac Rate and Ventilatory Volume Rate Reactions to a Muscle Contraction i n Man," Journal of Applied Physiology, 3 4 ( 5 ) :  578-583, 1973.  Paulev, P. E. "Respiratory and Cardiac Responses to Exercise i n Man," Journal of Applied Physiology, 30:165-172, 1971. Perez-Oonzalez, J . F., and Coote, J . H. "Activity of Muscle Afferents and Reflex Circulatory Responses to Exercise," American Journal of Physiology, 223:138-143, 1972. Petro, J. K., Hollander, A. P., and Bouman, L. N. "Instantaneous Cardiac Acceleration i n Man Induced by a Voluntary Muscle Contraction," Journal of Applied Physiology, 29(6):794-798. 1970. Quinones, M. A., Gaasch, W. H., Waisser, E., Thiel, H. G., and Alexander, J. K. "An Analysis of Left Ventricular Response to Isometric Exercise," American Heart Journal. 88:29-36, 1974. Robinson, B. F., Epstein, S. E., Beiser, G. D., and Braunwald, E. "Control of Heartrate by the Autonomic Nervous System: Studies i n Man on the Interrelation between Baroreceptor Mechanisms and Exercise," Circulation Research. 19:400-411, 1966. Rohlf, F. J . , and Sokal, R. R. S t a t i s t i c a l Tables, San Francisco: W. H. Freeman and Co., I 9 6 9 . Rowell, L. B. "Human Cardiovascular Adjustments to Exercise and Thermal Stress," Physiological Reviews. 54(1):75-159, 1974. Sampson, P. Repeated Mea3ure3 Analysis of Variance (UBC BMDP2V), Health Sciences Computing F a c i l i t y , University of California, L03 Angeles, 1974. Storms, L. H., and Acosta, F. X. "Effects of Dynamometer Tension on Stimulus Generalisation i n Schizophrenic and Non Schizophrenic Patients," Journal of Abnormal Psychology, 83(2):204-207, 1974. Toda, N., and Shimamoto, K. "The Influence of Sympathetic Stimulation on Transmembrane Potentials i n the S. A. Node," Journal of Pharmacology and Experimental Therapy, 159:298-305, 1968. Tuttle, V/, W., and Horvath, M. "Comparison of Effects of Static and Dynamic Work on Blood Pressure and Heart Rate," Journal of Applied Physiology,  10(2):294-296, 1957-  Winer, B. J. S t a t i s t i c a l Principles in Experimental De3ign, 2nd Ed., New York: McGraw-Hill Book Co., 1971.  APPENDIX A Individual Raw Score3  73  TABLE I  Age and Maximal Voluntary Contractions  Subject 1 2 3 50$  MVC  '4 5 6  7 8  75$  100$  MVC  MVC  Age (Years)  Maximal Voluntary Contractions (kgms.) Mean of Two Trial 2 Highest Trial 1 Trial 3  22  39.6  23 22  28.0  36.4 31.2  50.8 40.6  57,5 32.0  49.2 34.6  48.0 35.8  52.0 57.6  50.0 58.0 45.2  56.0  51.0 57.8  40.0  42.6  47.0  39.2  44.5  40.0 54.0  39.0 46.0  41.0 52.0  34.0  37.2 41.2  37.1 40.8  59.0 52.0  60.1  42.0  58.0 42.6  49.4 39.6  58.0 39.0  57.3 44.3 56.3  56.0 35.0 49.6 53.8  54.0 38.2  40.0 49.6 33.6 57.0 47.0 32.0  40.0 53.0 41.6 59.2  21 21 19 21 20 21  39.4 42.0  9 10  26  11 12  22 21  42.0  13 14 15 16  24 20 21  37.0 38.8  28  17  25  50.0  58.0  40.4 61.2 41.0 54.0  18  24  19 20  23 22  49.6 56.6 46.0 54.6 38.2  21 22  22  49.0  52.0  28  36.4 44.0  40.0  23 24 25  26 27  28 29 30  21 20  18 23 24 22 21 22  51.4 40.0 52.6  50.4 42.4 38.2  46.6  53.4 36.6  58.0 47.8 35.2  60.4 45.8 34.0  38.0 27.4 44.0 42.0 46.4 32.4 46.6  38.8 29.6 54.2 41.3 48.6 35.2  50.8  39.3  50.0 52.6  47.4 34.6  TABLE  II  Resting Cycle Time ( m i l l i s e c o n d s )  Subject  50$ MVC  1  2  3  4  1 2 3  1160  1135 760  1090  1170 720  850  830  I  1120  1285  860 1100  1020  660 1110  735 1070  7 8 9 10  760 1030 740  11 12  13 75$  MVC  H  765  850  1205 745 1420  1310  1100 775  1100  745  1000  765 1015 700  785  800  1110  790 1025  865 790 960  780  785  765 745 1320  7  8  9  10  1.185 730  920  765 715  705 720  1170  715 1165  1235  990  930  725 920  750  1115  1070  765 735 1020  920 710  895  1015  905  730 830  815 950 895  905 770  875 785  885 790 940  765  785 785  620  985  780  585 1165 765  965  935  955  960  995 755 790  855  850  830  795 1025  750  865 760  760 700  695 700  735 710  1015  950  995  1055  1025  905  725  735  795  1190  875 1130 850  815 900  735  775  775 730 1250 1020  1010 910  900  19  1005  920  860  1100  6  615 1060  17 18 20  735  Heart Beat 5  950  800  705  925  1195  1265  800 1155 1270  985 925  1005  960  760  870 865  840  880  940  1010 875 810  575  910  965  970  870  920  865  835  860  780  810  885 765  830 850  740 845 810'  890  790  870  950 860 900 970  1350  950  1040  830  1000 940 1050  21 22 23 24 100$ MVC  25  26 27  28 29 30  885 765 950 635 870 710  1090 1150 915 790  925 830 865 625 920  705 1170 1115 910 840  925  860 925  630 945 710 1210 1065 850 815  875 810 930 630  945 710 1020 1065 860 790  825 795 865 640 950 715 1150 1015 905 775  770 785 735 620 900 700 1180 955 940 780  760 690 640 610 870 680 1130 985 865 650  790 685 560  840 805 580  600  600  850 680 990 1010 825 695  825 715 945 950 830 685  870 965  990 610 880 775 1075 950 850 735  TABLE  III ON  Contraction Cycle Time ( m i l l i s e c o n d s )  Subject 1 2  50$  3 4 5 MVC 6 7 8 9 10  11  .12 13 14  15 16 17  18 19 20  7  940 740 970 1360 850 1000 820 900  980  985  1060  1110  1115  725  725  725  720  720  960  965 1055 765  985  955 720  950  770  750 920  900 700 850  780  770  770  750  985  910  • 845 825  825  1250  760 1150  960  920  910  905  935 950  840 960 755  4  6  2  940 1040 845 980  3  Heart Beat 5  1  940 960 815 1000  1025  780  1025  680 845  670 830  740 900 645 830  850  840  810  725  700  690  885 845 780 1085  915  895 820 760 1115 940 910  910  820  790  1025  925  1015  750 915  955  890 775 970  895 640 820  8  9  10  1130  1135  1100  720  725  725  1070 740 1010 880 730 930  980 770 710 885 660  780  990 940 750 950  730 865 670 780  840  795  750  765 965  765 910  970  765 930  815 790  800  740  740  825  805  780  720  720  900 730  775  775  780 840  815  790  725  885  825  855 840  830  740 895  830  825 680 825  985 840  895  830 670  815 680 840 810  1080 8907 . 880  1000  660  835 655 775  835  735  745 915  790 750  780  890  715 855  735 700 945  21 22 23 24 25  100$ MVC 26 27  28 29  30  860 830 900 620 935 810 1060 1010 900 780  775 710 755 620 910  750 950 955 790 720  725 640 710 600  880 715 860  900 700 665  660 590 590 570 825 680 800 885 655 640  630 560 550 565 790 655 790 850 630 615  630 545 535  550 805 625 785 850 610 610  630 510 505  630 510 510  535  530 730  525 725  590  580 750 810 580 585  570 790 820 570 580  635 530 525 540 810 610 775 . 825  630  595  590  595  520  515 755 765 815 585  TABLE IV CO  Contraction Muscular Tension (kilograms) H e a r t Beat Subject  ,  5C#MVC :  1 2 3 4 5  2  3  4  5  OcO  4.0  18.0  18.0  14.0 24.0 20.2 20.4  14.0 25.2 21.2 20.4  18.0 14.0  18.0 24.8 28.6 18.0  18.0 24.8  18.0 24.8  22.8 30.8  10  0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  11 12 13 14 15 16 17 18 19 20  0.0 0.0 0.0 0.0 0.0 0 0 0 0 0.0  6  7 8 9  75$MVC  1  14.0  27.0 10.0 14.0 18.0  22.0 15.4 10.2 20.0 20.6 27.2 22.8 19.6 29.2 39.8 30.8 32.0 42.6 25.0  22.4 30.8  35.2 27.0 29.0 46.0 40.6 43.4 33.0 42.6 30.6  30.0 21.0  35.6 28.0  31.6 46.4 40.6 41.0 33.0 42.6 28.0  6  7  8  9  10  18.0  18.0 13.4  18.0  18.0  18.0 13.0  13.6 25.0 20.0 20.4  25.2 20.0 20.4  22.8  30.2 21.0 23.0  30.2 21.0  30.8 36.6 28.0 31.6 46.0 38.0 40.6 33.0 42.6 28.4  30.6 36.6 28.0 31.6 46.0 38.4 41.0 33.0 42.4 28.2  25.0 21.2  20.4 30.2 21.0  18.0 24.8  13.2 25.2 20.0 20.4  13.2 25.2 20.0 20.4  25.2 20.0 20.4  18.0 24.8  18.0 24.8  22.8  32.0 21.0 23.0  18.0 24.8  30.4 36.4  30.0 36.4  30.0  29.6 36.4 28.0 31.6 45.2 38.0 41.0 33.0 43.4  18.0 24.8  28.0  31.6 46.0 37.0 41.0 33.0 42,4 28.6  27.2 31.6 45.4 38.0 40.8 33.0 41.4 29.0  32.0 21.0 23.0  36.4 28.0 31.6 45.4 38.0 41.0 33.0 41.6  29.2  31.2 21.0 23.0  29.2  100$MVC  21 22 23 24 25 26  27 28  29 30  0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  30.0 26.0 32.0 26.0 9.0 12.0 15.0 36.0 27.2 30.6  46.0 36.0 47.0 43.0 30.0 30.0 35.6 53.2 48.0 32.4  53.6 36.0 48.0 52.0 36.0 44.0 40.6 54.0 48.0 32.4  53.6 36.4 48.0 52.0 37.2 50.0 40.6 54.0 48.0 32.4  53.6 37.2 48.0 52.0 37.2 51.4 40.6 54.0 48.0 32.2  53.6 37.4 48.0 52.0 36.6 51.6 40.6 54.0 48.4 32.2  53.6 37.4 48.0 52.0 36.6 51.6 40.6 54.0 48.4 32.0  53.6 37.8 48.0 52.0 36.6 54.0 40.6 54.0 48.4 32.0  52.0 37.8 48.0 52.0 36.4 54.0 40.6 54.0 48.4 32.2  TABLE V  CO  o  Recovery Cycle Time ( m i l l i s e c o n d s ) Heart Beat 5  Subject 1 2 3 4  50$ MVC  5 6  7 8 9 10 11 12 13 14  75$ MVC  15  1040 770 1025 830 760 950 770 870 705 825  1050 760 1015 990 800 965 880 950 685 810  1120 750 1015 1230 790 1190 885 1000 750 880  845 695 760  845 866  815  825  905  1055 700  1055 750  835 740 1060  16  880  17  840  980  790 700  840 700  870  990  18 19 20  925  955  1115 760  1110 770  1035  1065  1155  1100  805 925  890 980  840 945 910 1010  770 905  745  820  820 965 885 655  975 950 720 715 1010  985 885  950  705 1130  705 1105  915  910  710 1025  900 900 700 975  6  7  8  9  10  1085 755 1105 1110 835 950 895 990 750 900  1090 740  1120 760 1100 1160 865 970  1020 795 885  1105 735 1105 990 885 880 875 990 830 875  1135 815 1100 1110 845 1000 970 1160 730 855  835 895 820  810 825 865 865  825 820 885 770  710  795  850 810 840 840 870  910 950  925 950 960  775  740 980 830 840 720  1135  1125  1020 870 945 920  950 840 950 740 1145  985 730  1010  920  1110 820 890  740 915  840 780 820 790 835 875  900 985 780 1065  21 22 23 24 25  26 27  28 29 30  565 435 470 465 ' 695 615 825 795 890 540  585 445 475 470 725  630 845 795 1135 585  615 435 510 480 790 665 910 825 1130 740  640 430 840 475 840 705 1005 920  1000 890  650 430  635 520  620 680  935  955  925 530  485 815 755  960 910 1040 780  500 780  655 730 930 1420  750  840 760  950  1125  800 700 1020  915  935 1125  935 1060  905  990  1120 825  655 825  650 960  950  970  900 700 1095  840 815 670 980  900  910  1080 1005  1090  795  975  82  APPENDIX B I n d i v i d u a l Computed Scores  TABLE I  00 LO  Contraction - Actual Change i n Cycle Time ( m i l l i s e c o n d s )  Subject  <cn* mm  50% MVL  1  2  3  4  1 2 3  ^175 -5 50  -215  -295  80  -220 10 85  4  -345  -25  65  "35 _5Q  5  6  7 8  -25  -30  -10  125 -15  140 -30  7  8  9  10  80  -345 15 60  -350 15 55  -365 15 35  -370 10 30  -335 10 20  -305 -5 10  55  -10  -40  75  120  135  0  35  50  45  65  75  85  -5  0  0  55  20  175 -10  185  165 20  170 0  175 -15  10  -50  145 -30  -75 155 -15  35  0  9  40  90  110  120  145  150  130  120  70  60  20  90  95  110  110  120  160  160  165  165  11  5  15  -45  -45  -50  35 -20  -25 95 35 -10  -40  15 -95 -15 45 100  -55 85 5 -15 90  -30  12  -65 60  105  105 65 15 105  125 110 -10  130  50 20 120  115 65 -10  80  150 310  105 440 200 160 310  135 460 210 190  435 220  35 230  365 160 110  385  40 30 140  235 60 30 260  335  350  15  115  25  215  235  185  95  14  MVC  -30  6  10  13  75$  75  -15  10  Heart Beat 5  11 17  18 19 20  5 110 200  -5 10 110  265 45 50 275 70  75 270 110 60 260 70  285 110  185  115 -5 125  205  CAOlAlAUMAOO>rt -tiAtoooiAOconco^  CM - * - - *  H  O J CM H  W  H  0 > A I A O O I A I A O O O  - * U N 00 CO U N O CM - * C-- U N CM - * - * H r H n H N H  O  U M A U M A 1 A O I A O  CM - * - *  rH rH  ON r H CM  O rH  I A I A I A O O ' A Q ' A ' A O ON O N V O r>-fv_vo o cy U N - * rH O N H CM rH CM - * - *  O O U N O U N O O O O U N - J - CM ir\Of>iriOvO<l-N CM-*-* r H CM H CM H  O U N O U N O O U N O O O -*O-J--*ONCMC0OCMCM C M - * - * H CM r H CM r H  O " N O O UN UN UN UN UN UN rHC~-0-*UNONC~-vOONO CM ON - * CM H  U N U N O O O O U N O O O - * CM CO r H vO r H UN UN t^H O N CM CM <H  UNUNUNO O U N U N U N O U N ON UN ON <H ON CM CM I O H CM CM I I rH  O U N O O U N U N U N O O U N rH  t  i  l  I I I  H CM f / \ - J i A v O ! > C O O O CMCMCMCMCMCMCMCMCMON O  O rH  T A B L E II  00  Contraction - Relative C h a n g e in Cycle T i m e (per cent)  Heart Beat Subject 1  ,-22.88  2  -0.68  3 t  50$ M V C  5 6 7 8 9 1 0  11 12 13 1 4 7 5 $ M V C  1  1 5 1 6 17 1 8 19 20  4.90 -33.99 -4.29 -5.26 8.38 -1.69 5.06  2  3  4  5  6  -28.10  -28.76  -38.56  -45.10  -45.75  1.36  1.36  1.36  2.04  7.84 -2.46  8.33 6.40  7.84 5.42  2.04 5.88  -3.07 -1.05 15.64  0.00 -5.26  -3.68 -3.16 13.97 -1.69  16.20  -3.39 13.92 10.11  -3.39 15.19 11.70  2.13  11.39 9.57  -.64 1.91 -10.67 -1.81  1.91 4.46 -2.25 -.60  -8.28  -7.01  7.64 -0.56  10.83  1.20  -1.81  5.17 7.41 4.00 3.19 13.33 1.44  12.64 14.81 8.00 3.72 21.90 11.06  12.64  10.34  17.41 6.00  19.63  3.19 24.76 2.40  -.56  4.50 5.32 26.19 6.73  -0.99 4.29 -7.89 17.32 -1.69 18.35 11.70  -3.18 12.10 3.93 -1.20 8.62 20.00 11.00 6.38 24.76 6.73  5.39 -3.94 6.13 -0.53 19.55 -1.13 18.99 12.77  -3.82 13.38 5.62 2.41 13.79 27.04 16.00 11.70 27.14 10.58  7  8  9  10  -47.71 2.04  -48.37 1.36  -43.79 1.36  -39.87 -0.68  3.43  2.94  3.45 5.62  7.39 7.98 0.00  1.96 11.82  13.30  0.00 20.6? 0.00 16.46 17.02  -5.10 13.38 7.30 1.81 12.07 28.52 18.50 15.96 29.52 20.67  18.44 2.26  9.20 5.79 18.99 0.00 8,86  15.19 17.02  17.55  -5.73 14.65 7.30 -1.20 12.07 32.59 20.00 17.02 29.52 22.60  -5.73 15.92 12.36 -1.20 15.52 34.07 21.00 20.21 31.90 17.79  0.98 10.43 2.11 19.55 -1.69 7.59 17.55  -6.37 16.56 12.92 -0.60 14.37 32.22 22.00 21.81 33.33 9.13  21 22 23 24 25  100$ MVC 26 27  28 29 30  1.15 13.99 9.09 -1.64 , -6.25 -4.52 1.40 -6.32 -5.88 -6.12  27.59 43.52  6.56  27.59 41.97 44.44 7.38  6.25  10.23  8.52  19.35  6.84  15.48 26.51 10.53  22.94 12.93  16.33  10.92  16.67  26.42  33.68  24.14 38.86  28.28  40.40  1.64 0.00 7.74 20.00  12.26  23.74 -1.64 -3.41 3.23 11.63 -0.53 7.06 2.04  5.26 17.65 9.52  25.58  25.88  45.96 9.84 26.98 10.53 28.24 17.01  27.01  45-08 46.97 11.48 7.95 21.29 27.91  13.16 30.00 19.05  27.59  27.59  14.20  47.15 48.99 13.11 17.05  23.87  25.16  26.45 26.51 13.68 32.94 21.09  27.59  46.11 47.98 12.30  28.84 14.21 30.59 20.41  30.23  14.74 31.76 20.41  47.15 48.48 13.93 17.61  TABLE  III  CO  Contraction - R e l a t i v e Muscular Tension *(per cent) Heart Beat 5  Subject  50$ MVC  1 2 3 4 5 6 7 8 9 10  11 12 13 14 15 75$ MVC ^ 17 18 19 20  0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00  0.00 0.00 0.00 0.00 0.00 . 0.00 0.00 0,00 0.00  0.00  10.31  47.30  49.87 24.21  28.81 51.14  43.14 26.64 23.94  44.94 50.24 52.31  61.46 48.04 48.59 78.35 53.75 72.23 .  75.67  63.61  46.39 47.30 44.33 48.91 41.98 51.14 48.63 49.48 42.25 50.34  46.39 47.30 46.55 51.33 41.98 51.14 48.63 51.90  75.12 67.69 72.78  75.12 68.46 75.47 77.45 77.20  79.92  79.92  75.74 74.49 75.67 77.86  71.55 74.49 75.67  75.12 70.38 75.47 77.45 76.54 74.80 70.86 74.49 75.67  71.25  72.26  71.08 76.54  46.39  47.30 46.13 51.33 41.98 51.14 48.63 52.25 49.30 51.24  49.30 51.24  V  8 46.39 45.95  46.18 48.43 41.98 51.14 48.63 52.25 49.30 51.69  74.63 70.38 75.47 77.45 76.54 75.59 71.55 74.49 75.31 71.76  46.39 45.27 46.55 48.43 41.98 51.14 48,63 52.25  49.30 51.24  74.15 70.00 75.47 77.45 76.54 72.83  71.55 74.49 75.31 72.77  10  46.39 44.59 46.55 48.43 41.98 51.14 48.63 55.36 49.30 51.69  46.39  46.39  44.59 46.55 48.43 41.98 51.14 48.63 55.36 49.30 51.69  43.92  73.17 70.00  73.17 70.00 75.47 77.45 75.54 74.80  72.20  73.32  77.45 75.54 74.80 71.20 74.49 73.53 73.79  71.55  74.49 73.89 74.30  46.55 48.43 41.98 51.14 48.63 53.98 49.30 51.69  70.00 75.47 77.45 75.21 74.80 71.55 74.49 77.09 74.30  21  22 23 24 2 C  100$ MVC  2 o  27 28  29  30  0.00 o.co  0.00 0.00 - 0.00 0.00 0.00 0.00 0.00 0,00  55.56 68.06 64.00 49.43 22.50 22.64 36.06 60.81 57.38 88.44  85.19 94.24 94.00 81.75 75.00 56.60 85.58 89.86 101.27 93.64  99.26 94.24 96.00 98.86 90.00 83.02 97.60 91.22 101.27 93.64  99.26 95.29 96.00 98.86 93.00 94.34 97.60 91.22 101.27 93.64  99.26 97.38 96.00 98.86 93.00 96.98 97.60 91.22 101.27 93.06  99.26 97.91 96.00 98.86 91.50 97.36 97.60 91.22 102.11 93.06  99.26 97.91 96.00 98.86 91.50 97.36 97.60 91.22 102,11 92.49  99.26 98.95 96.00 98.86 91.50 101.89 97.60 91.22 102,11 92.49  96.30 98.95 96.00 98.86 91.00 101.89 97.60 91.22 102.11 93.06  00 oo  TABLE  IV CO  Recovery - Actual Change i n Cycle Time ( m i l l i s e c o n d s )  Subject  50$  v C  3  4  5  6  7  8  9  10  -285 -25  -355  -350  -325  -340  -355  -370  -25  -345 -35  -320  -15  0  -25  -85  A  -275 -35  3 4  -5  5 25  5 -215  -15 -140  -45 -85  55 0  15  25 -240 10  10  -25 5  5  6  9 10  11 12 13  MVC  2  2  7 8  75$  Heart Beat 1  14 15 16 17  18  19 20  185 125  -15 15  15 85 115  -65 105 130  -60  -60  90 130 -225 170 470 160 150  -95 20  -30  -35 -190 -60 110  -170  65 -225 120  -15  350  350  170  50  5  -115 40 60  -81  425 20 100  25  -5 130  290 15 55 345 -90  35  -15 -125 45  30  -35  -180  -20 -95 -20  -5 . -105 -55  0 -25  -105 40  -135 -5 55  -105  -50 -110  -25  -40  70  25 -35 160  -40  5 175 160  55 130  400  25  325 100 40  370 170 100  345  350  -65  65  155 340  50  25 -70 70 20  0  40  -80  -85  -145 -50 -20 -25 -225 -30 50  -40 65  -35 5 60  :  -65 -25 50 -10  0  -80 -80 -95 -30 -50  -75 -275  60  85  -55 5 70 40 35 475 100  160 -10  75 365 90 -10  425 50 -20  330  310  320  310  -45 270  -95  -105  30  125  -25  21 22 23 24 25  100$ MVC 26 27  28 29 30  305 530 520  145 . 185 160 250 155 -40 195  285 520  515 140 155 145 230 155 -285 150  255 530 480 130 90 110 165 125  -280 -5  230  535 150 135 40 70 70 30  -150 -155  220 535 . 55 125  65 20 115 40 -190 -45  235  445 35 110 100 25 125  35 -270 -90  250 285 65 80 40 15 -50 15  215 235  -275  -810 80 75 55 15 -210  215 140 40 -290 85 75 -20 50 -230  -170  -255  -270  60  220 5 20 -230 65 105 95 40 -240 -240  ' T A B L E -V  Recovery - Rslative Change i n Cycle Time (per cent) Heart Beat 5  Subject 1  2 3  50$ MVC  4 5 6 7 8 9  10  11 12 13  -35.95 -4.76 -0.49 18.23 6.75  -37.25 -3.40 0.49 2.46 1.84  -46.41 -2.40 0.49 -21.18 3.07  -45.75 -3.40 -1.47 -13.79 1.23  13.97 1.69 10.76 12.23  1.68 -7.34 13.29 13.83  1.12 -12.99 5.06 6.38  0.56 -10.73 2.53 3.72  -7.64 11.46  -7.64  -3.82 -21.66  -4.46 -24.20  0.00  14.61  -1.58  -10.32  7.30  -27.11  15  -27.11 19.54  17 18  16.00 15.96  2,00 10,64  33,33  33.33 4.81  14 16  19 20  34.81  16,35  13.79 31.48  -25.26  -1.69 -0.60 14.94 21.48 1.50  5.85  32.86  - 8 65 0  2.63  -6.74 13.25  17.82  25.19 5.00 2.66  32.86 -6.25  -45.10 04.76 -4.41 -8.37 -3.07  10  8  -41.83 -2.72 -8.33 -9.36 -2.45  -42.48 -0.68 -10.29 -0.49 -6.75  -44.44 0.00 -8.33 2.46  -46.41 -3.40 -7.84 -14.29  -48.37 -10.88 -7.84 -9.36 -3.68  0.00 -11.86 5.06  2.23 -11.86 -5.06 6.91  -2.79 -25.42  4.26  -2.79 -15.25 -0.63 5.85  -8.38 -31.07 7.59  -4.46 -6.37 -14.01 -22.93 0.56 7.87 21.08 6.63 14.94 18.39 :  t-3.18 -5.10 2.81 -4.22 18.39  -5.10 -4.46 0.56  17.00  16.00 -1.06  0.53 -1.68  -14.12 5.70 3.19  0.00  24.0?  27.41  10.00 4.26 33.33 6.25  31.43 -9.13  10.64  0.53  -8.59 7.37  -6.13 -2.il -3.80  5.32  29.63  27.04 9.00 -1.06  -8.28 -3.18 5.62 -1.20 0.00 31.48 5.00 -2.13  29.52  30.48  29.52  -10.10  7.23 8.62  2.88  12.02  -5.26  9.04  -7.01 0.64 7.87 4.82  4.02  35.19 10.00 -4.79 25.71 -2.40  21 22 23 24 25 26  27 28  29 30  35.06 54.92 52.53 23.77 21.02 20.65 23.26 16.32 -4.71 26.53  32.76 53.89 52.02 22.95 17.61 18.71 21.40 16.32 -33.53 20.41  29.31 54.92 48.48 21.31 10.23 14.19 15.35 13.16 -32.94 -0.68  26.44 55.44 15.15 22.13 4.55 9.03 6.51 3.16 -17.65 -21.09  25.29 55.44 5.56 20.49 7.39 2.58 10.70 4.21 -22.35 -6.12  27.01 46.11 3.54 18.03  11.36 3.23 11.63 3.68 -31.76 -12.24  28.74 29.53 6.57 13.11 4.55 1.94 -4.65 1.58 -32.356 -23.13  24.71 24.35 6.06 -132.79 9.09 9.68 5.12 1.58 -24.71 -34.69  24.71 14.51 4.04  -47.54 9.66 9.68 -1.86 5.26 -27.06 -36.73  25.29 0.52 2.02 -37.70 7.39 13.55 8.84 4.21 -28.24 -32.65  VO  to  93  APPENDIX C ANOVA. Paired Comparisons o f RCCTQ f o r the Three l e v e l s o f $MVC  94 TABLE I  Summary o f ANOVA Contraction - R e l a t i v e Change i n Cycle Time (RCCT ) C  Comparison 50$ MVC Vs. 75$ MVC  Source  df  Between Subjects  Ss w . $MVC Subjects  1  4555,7  18  1644.2  9  2.77  NS  220.6  8.23  <.01  (lin.)  1  1720.9  12.01  <.01  (quad.)  1  64.3  1.77  NS  9  46.5  1.74  NS  162  26.8  B e a t 3  $MVC x Beats Beats x Ss w. $MVC Beats x Ss w. $ M V C ( Beats x S s w. $ M V C  *  P  180  Beats  B e a t s  F  19  $MVC  Within  MS  lin  j  ( q u a d 0  18  143.3  18  36.4  NS denotes t h a t the F - r a t i o i a not s i g n i f i c a n t a t the 0.01 l e v e l o f confidence.  95 TABLE I I  Summary o f ANOVA C o n t r a c t i o n - R e l a t i v e Change i n Cycle Time (RCCT,,) Comparison 50$ MVC Vs. 100$ MVC  Between Subjects  $MVC  Bes-ta  B e a t s  1  16796.1  18  1873.7  9 (Iin.)  (quad.)  8.94  < .01  656.9  29.07  <.01  1  4837.3  43.64  <.01  1  871.8  19.00  <.01  287*6  12.73  <.01  9  $MVC x Beats $MVC x 3eat3p.. v  1  2132.1  19.24  < .01  $MVC x B e t  1  394.4  8.60  <c01  n  a  3 ( q u a d s )  162  Beats x Ss w. $MVC Beats x Ss w. $ M V C ^ Beats x Ss w. $ V ( M  *  P  180  W i t h i n Subjects  B c a f c s  F  19  $MVC Ss  MS  df  Source  in  G  q u a d  % j  .  22.6  18  110.9  18  45.9  NS denotes t h a t t h e F - r a t i o i s not s i g n i f i c a n t a t t h e 0.01 l e v e l o f confidence.  96 TABLE I I I  Summary o f ANOVA Contraction -  R e l a t i v e Change i n Cyele Time (RCCT ) C  Comparison 75$ MVC Vs. 100 $MVC  Source  df  Between' Subjects  Ss w. $MVC W i t h i n Subjects  NS  948.4  73.71  <.0i  1  7684.0  111.49  <.01  1  777.2  41.07  <.01  158.3  12.30  <.01  1  787.8  11,43  <.01  1  462.6  24.45  <.01  3856.9  18  1124.4  9 (lin.)  Beats^quadj $MVC x Beats e a t 3  9 (iin.)  $MVC x B e a t s  ( q u a d # )  162  Beats x Ss w. $MVC Beats x Ss w. %NSC^  n  Beats x S s w. $ M V C  *  3.43  1  180  Beats  $MVC x B  P  19  $MVC  B 8 3 t 3  MS  ^  ( q u a d )  12.87  18  68.9  18  18.9  NS denotes t h a t the F - r a t i o i 3 not s i g n i f i c a n t a t the 0.01 l e v e l o f confidence.  APPENDIX D Recovery C o n d i t i o n - Means and Standard Deviations o f Cycle Time and A c t u a l Change i n Cycle Time w i t h G r a p h i c a l Presentations  TABLE I  Recovery Condition - Means and Standard Deviations of Cycle Time (CT ) R  Expressed i n Milliseconds f o r a l l Groups and a l l 10 Heart Beats.  Group  1  2  3  4  50$ MVC  854.5  ±122.0  961.0 ±178.07  934.0  ±115.4  890.5  813.5 ±111.0  877.5 ±110.6  901.5 ±135.0  629.5 ±163.5  669.0 ±213.5  710.0  774.5  ±215.1  ±205.0  75$  MVC  100$ MVC  ±137.7 886.5 ±139.1  Heart Beat 5  940.5 ±130.7  6  937.5  7  941.0  8  10  971.5 ±142.0  972.0 ±153.2  ±94.7  970.0 168.5  867.0 ±93.9  ^924.0 ±224.5  ±149.0  890.5  886.0 ±141.8  927.0  ±135.3  ±124.2  ±118.8  853.5 ±127.6  857.0 ±122.9  870.0 ±123.6  868.0  776.0  795.0 ±200.3  844.5 ±199.8  ±202.5  9  99 FIGURE  1  T 1,1 1 I i.„l-l-t.-L.L. ,  Heart Beat Recovery Condition Beats.  Change in Cycle Time during the f i r s t 10 Heart  TABLE I I  Recovery Condition -  Means and Standard Deviations of  Actual Change i n Cycle Time (ACCT ) R  Expressed i n Milliseconds f o r a l l Groups and a l l 10 Heart beats.  Group  50$ MVC  75$ MVC  100$ MVC  1  2  3  4  Heart Beat 5  6  7  -60.0  8  9  10  26.5 1126.2  1112.8  -80.0 ±143.5  -53.0 1118.4  -59.5 1112.3  -56.5 1106.3  -46.0  ll08.3  ±119.9  -90.5 ±120.1  -91.0 ±138.0  .140.5 -191.8  ,76.5 1193.5  1161.2  , 52.5  , 67.5 -174.3  ,100.5 ±160.8  ,97.0 ±163.0  , 84.0 ±167.3  , 86.0 -142.5  , 84.0 ±160.6  . 87.0 ±165.4  ,240.5 1174.1  ,201.0 3225.6  ±230.6  ,160.0  , 95.5 -196.5  . 94.0 -189.3  . 75.0 ±188.2  , 25.5 ±169.0  ,-54.0 ±308.5  .-20.5 -179.2  ,-16.0 -163.4  1  o o  101 FIGURE  Z  Heart Beat Recovery Condition f i r s t 10 Heart Beats.  Change i n A c t u a l Change i n Cycle Time during the  

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