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Changes in executive functions and self-efficacy are independently associated with improved usual gait… Liu-Ambrose, Teresa; Davis, Jennifer C; Nagamatsu, Lindsay S; Hsu, Liang C; Katarynych, Lindsay A; Khan, Karim M May 19, 2010

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Liu-Ambrose et al. BMC Geriatrics 2010, 10:25http://www.biomedcentral.com/1471-2318/10/25Open AccessR E S E A R C H  A R T I C L EResearch articleChanges in executive functions and self-efficacy are independently associated with improved usual gait speed in older womenTeresa Liu-Ambrose*1,2, Jennifer C Davis1, Lindsay S Nagamatsu1,3, Chun Liang Hsu1, Lindsay A Katarynych1 and Karim M Khan1,4AbstractBackground: Improved usual gait speed predicts substantial reduction in mortality. A better understanding of the modifiable factors that are independently associated with improved gait speed would ensure that intervention strategies are developed based on a valid theoretical framework. Thus, we examined the independent association of change in executive functions and change in falls-related self-efficacy with improved gait speed among community-dwelling senior women.Methods: A secondary analysis of the 135 senior women aged 65 to 75 years old who completed a 12-month randomized controlled trial of resistance training. Usual gait speed was assessed using a 4-meter walk. Three executive processes were assessed by standard neuropsychological tests: 1) set shifting; 2) working memory; and 3) selective attention and response inhibition. A linear regression model was constructed to determine the independent association of change in executive functions and falls-related self-efficacy with change in gait speed.Results: Improved selective attention and conflict resolution, and falls-related self-efficacy, were independently associated with improved gait speed after accounting for age, global cognition, baseline gait speed, and change in quadriceps strength. The total variance explained was 24%.Conclusions: Interventions that target executive functions and falls-related self-efficacy, in addition to physical functions, to improve gait speed may be more efficacious than those that do not.Trial Registration: ClinicalTrials.gov Identifier: NCT00426881BackgroundGait speed is a global indicator of functional mobility andstatus. Reduced speed is associated with risk of majorhealth-related outcomes [1], including falls [2] and frac-ture [3], in older adults. It is also associated with sub-clin-ical structural brain abnormalities [4] and cognitivefunction [5]. Improved usual gait speed over a 12-monthperiod predicts substantial reduction in mortality [6].Although there has been a call for research to deter-mine whether interventions to improve gait speed affectsurvival [6], a better understanding of the modifiable fac-tors that are independently associated with improved gaitspeed is needed. Candidates include cognitive function,self-efficacy, and physiological function, such as muscularstrength. A better understanding of these key factorswould ensure that intervention strategies to improve gaitspeed are based on a valid theoretical framework.Current evidence suggests that executive functionsshould be considered in interventions to improve gaitspeed in older adults. The Health, Aging and Body Com-position Study [7] highlighted that baseline lower execu-tive functions predict subsequent decline in gait speed.Conversely, prospective studies demonstrate that base-line gait speed predicts subsequent cognitive decline [8].Together, evidence supports the hypothesis that cognitiveand physical functions are inter-related.* Correspondence: tlambrose@exchange.ubc.ca1BioMed Central© 2010 Liu-Ambrose et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Com-mons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduc-tion in any medium, provided the original work is properly cited.Executive functions are higher order cognitive pro-cesses that control, integrate, organize, and maintain Centre for Hip Health and Mobility, Vancouver Coastal Health Research Institute, University of British Columbia, Vancouver, BC, CanadaFull list of author information is available at the end of the articleLiu-Ambrose et al. BMC Geriatrics 2010, 10:25http://www.biomedcentral.com/1471-2318/10/25Page 2 of 8other cognitive abilities [9]. These cognitive processesinclude the ability to concentrate, to attend selectively,and to plan and to strategize. Executive functions declinesubstantially with aging [10] as does the correspondingvolume of the frontal-subcortical neuronal system [9,11-13]. Importantly, reduced executive functioning is preva-lent even among healthy, community-dwelling seniorswith intact global cognitive function [14,15]. This is notsurprising given many of the pathological changes (e.g.,white matter lesions, reduced frontal-subcortical volume)associated with reduced executive functions are prevalentbut clinically silent [16].Evidence from neuro-imaging studies provides insightto possible mechanisms underlying the associationbetween executive functions and gait speed. Specifically,cerebral white matter lesions -- which are associated withreduced executive functioning [16] - are also associatedwith gait and balance abnormalities [17,18]. Cerebralwhite matter lesions may interrupt frontal lobe circuitsresponsible for normal gait and balance or they mayinterfere with long loop reflexes mediated by deep whitematter sensory and motor tracts [19]. In addition, theperiventricular and subcortical distribution of white mat-ter lesions could interrupt the descending motor fibersarising from medial cortical areas, which are importantfor lower extremity motor control [20].Falls-related self-efficacy is associated with gait perfor-mance [21,22] and hence, should also be considered ininterventions to improve gait speed. Based on Bandura'sSocial Cognitive Theory [23], which states that perceivedcapability predicts activity better than does actual physi-cal ability, improved self-efficacy should be related toimproved gait speed. Using bivariate correlation analysis,we previously demonstrated that change in falls-relatedself-efficacy was not significantly associated with changein gait speed [24]. However, we did not consider execu-tive functions in these models -- these cognitive pro-cesses may play a significant role in older adults' ability toaccurately perceive their actual physical capacity [25].To our knowledge, it is currently unknown whetherchange in executive functions and falls-related self-effi-cacy are independently associated with change in gaitspeed in older adults after accounting for relevant factorssuch as age and global cognitive function. Yet, suchknowledge would facilitate the development and refine-ment of targeted interventions to improve gait speed inolder adults. For example, if improved executive func-tioning were independently associated with improvedgait speed, it would be logical to incorporate cognitivetraining that focused specifically on executive function-ing rather than other domains of cognition such as mem-community-dwelling senior women after accounting forage, global cognition, baseline gait speed, and change inquadriceps strength.MethodsStudy Design and ParticipantsThe sample for this analysis consisted of 135 women whoconsented and completed a 12-month randomized con-trolled trial of exercise that aimed to examine the effect ofonce-weekly or twice-weekly resistance training com-pared with a twice-weekly balance and tone exerciseintervention on cognitive performance of executive func-tions. The design and the primary results of the studyhave been reported elsewhere [26].We recruited women who: 1) were aged 65 to 75 years;2) were living independently in their own home; 3) scored> 24 on the Mini-Mental State Examination (MMSE); and4) had a visual acuity of at least 20/40, with or withoutcorrective lenses. Recruitment strategies have beendescribed previously [26]. Ethical approval was obtainedfrom the Vancouver Coastal Health Research Institute(V06-0326) and the University of British Columbia's Clin-ical Research Ethics Board (H06-0326). All participantsprovided written informed consent.Exercise InterventionResistance TrainingAll classes were 60 minutes in duration. The protocol forthis program was progressive and high-intensity innature. Both a Keiser® Pressurized Air system and freeweights were used to provide the training stimulus. Otherkey strength exercises included mini-squats, mini-lunges,and lunge walks.Balance and ToneThis program consisted of stretching exercises, range ofmotion exercises, kegals, balance exercises, and relax-ation techniques. This group served to control for con-founding variables such as physical training received bytraveling to the training centres, social interaction, andlifestyle changes secondary to study participation.Descriptive VariablesGlobal cognition was assessed using the MMSE [27]. Weused the 15-item Geriatric Depression Scale (GDS) [28]to screen for depression. Functional Comorbidity Indexwas calculated to estimate the degree of comorbidityassociated with physical functioning [29]. This scale'sscore is the total number of comorbidities.Dependent Variable: Gait SpeedParticipants were asked to walk at their usual pace along a4-meter path. Gait speed (m/s) was calculated from theory. Thus, we examined the independent association ofchange in three key executive processes and change infalls-related self-efficacy with improved gait speed amongmean of two trials. The test-retest reliability of gait speedin our laboratory is 0.95 (ICC) [21].Liu-Ambrose et al. BMC Geriatrics 2010, 10:25http://www.biomedcentral.com/1471-2318/10/25Page 3 of 8Independent Variables of InterestDominant Quadriceps StrengthA simple strain gauge was used to assess dominant quad-riceps (isometric) strength to the nearest 0.5 kilogram[30]. Participants were seated with the hip and the kneejoint at 90 degrees of flexion. The best of three trials wasrecorded.Cognitive Performance of Executive ProcessesFor this study, we referred to the work by Miyake and col-leagues [31] who identified three key executive processesthat are moderately correlated with one another but eachhas a distinct purpose; they are: 1) set shifting; 2) workingmemory; and 3) selective attention and conflict resolu-tion.Set Shifting We used the Trail Making Tests (Part A & B)to assess set shifting [32]. Part A assesses psychomotorspeed and requires the participant to draw lines that con-nect encircled numbers sequentially. Part B consists ofencircled numbers and letters. Participants wereinstructed to draw a line as quickly and as accurately aspossible from 1 to A, A to 2, 2 to B, B to 3, and so on, untilthey completed the task. We recorded the amount of time(in seconds) it took to complete each task. To index setshifting, we calculated the difference between Part B andPart A completion time. Smaller difference scores indi-cate better set shifting.Working Memory We used the verbal digits forward andverbal digits backward tests to index the central executivecomponent of working memory [32]. Both tests consist ofseven pairs of random number sequences that the asses-sor reads aloud at the rate of one per second. Thesequence begins with three digits and increases by one ata time up to a length of nine digits. The test includes twosequences of each length and testing ceases when the par-ticipant fails to recollect any two with the same length.The score recorded, ranging from 0 to 14, is the numberof successful sequences. For the verbal digits forward test,the participant's task is to repeat each sequence exactly asit is given. For the verbal digits backward test, the partici-pant's task is to repeat each sequence in the reversedorder. The difference between the verbal digits forwardtest score and the verbal digits backward test score wasused as an index of the central executive component ofworking memory. Smaller difference scores indicate bet-ter working memory.Selective Attention and Conflict Resolution We usedGraf, Uttl and Tuokko's [33] version of the Stroop Test toassess selective attention and conflict resolution. For theStroop Test, there were three conditions. First, partici-pants were instructed to read out words printed in blackink (e.g., BLUE). Second, they were instructed to read outpants were asked to name the ink colour in which thewords are printed (while ignoring the word itself ). Therewere 80 trials for each condition and we recorded thetime participants took to read each condition. The abilityto selectively attend and control response output was cal-culated as the time difference between the third condi-tion and the second condition. Smaller time differencesindicate better selective attention and conflict resolution.Falls-Related Self-EfficacyThe 16-item Activities-specific Balance Confidence(ABC) Scale [34] assessed fall-related self-efficacy witheach item rated from 0% (no confidence) to 100% (com-plete confidence); it provides a score out of 100%.Data AnalysesDescriptive data are reported for variables of interest.Data were analyzed using SPSS Windows Version 17.0(SPSS Inc., Chicago, IL). The associations between thevariables were determined using the Pearson productmoment coefficient of correlation.A multiple linear regression model was constructed todetermine the independent association of change in exec-utive processes and change in falls-related self-efficacywith change in gait speed over a 12-month period.Change in gait speed, falls-related self-efficacy, and domi-nant quadriceps strength was calculated by subtractingthe baseline value from the trial completion value.Change in the three executive functions was calculated bysubtracting the trial completion value from the baselinevalue. Experimental group, age, global cognition, baselinegait speed, and the change in dominant quadricepsstrength were statistically controlled by entering thesefour variables into the regression model first. These inde-pendent variables were determined from the results ofthe Pearson product moment coefficient of correlationanalyses and based on biological relevance, such as exper-imental group, baseline global cognition, and change indominant quadriceps strength.The three executive processes were then entered intoregression model and only those that significantlyimproved the model were kept in the model (i.e., signifi-cant Rsq change). The ABC Scale score was entered lastinto each model. Alpha was set at P < 0.05.ResultsParticipants and Change in Variables of InterestOf the 155 participants who consented and were random-ized at baseline, 135 completed the 12-month exercisetrial. Table 1 reports the baseline descriptive statistics forthis cohort.At the end of the 12-month trial, the 135 women dem-the colour of coloured-X's. Finally, they were shown apage with colour-words printed in incongruent colouredinks (e.g., the word "BLUE" printed in red ink). Partici-onstrated a mean increase of 7 kilograms in dominantquadriceps strength and a four- and nine-second reduc-tion in Stroop Test and Trails Making Tests completionLiu-Ambrose et al. BMC Geriatrics 2010, 10:25http://www.biomedcentral.com/1471-2318/10/25Page 4 of 8Table 1: Descriptive statistics for variables of interest at baseline.Variable * BAT (n = 42) Mean (SD)1× RT (n = 47) Mean (SD)2× RT (n = 46) Mean (SD)Total (N = 135) Mean (SD)Age (yr) 69.9 (3.0) 69.5 (2.6) 69.4 (3.0) 69.6 (2.9)Height (cm) 161.3 (6.9) 161.7 (6.9) 162.2 (6.2) 161.7 (6.6)Weight (kg) 67.9 (11.0) 70.7 (15.5) 70.0 (14.6) 69.6 (13.9)EducationLess than Grade 9 † 1.0 (2) 1.0 (1.9) 1.0 (1.9) 3.0 (1.9)Grade 9 to 12 without Certificate or Diploma † 2.0 (4.1) 3.0 (5.6) 4.0 (7.7) 9.0 (5.8)High School Certificate or Diploma † 6.0 (12.2) 9.0 (16.7) 10.0 (19.2) 25.0 (16.1)Trades or Professional Certificate or Diploma † 14.0 (28.6) 10.0 (18.5) 6.0 (11.5) 30.0 (19.4)University Certificate or Diploma † 7.0 (14.3) 12.0 (22.2) 9.0 (17.3) 28.0 (18.1)University Degree † 19.0 (38.8) 19.0 (35.2) 22.0 (42.3) 60.0 (38.7)MMSE Score (max. 30 pts) 28.9 (1.2) 28.5 (1.3) 28.5 (1.5) 28.6 (1.3)Falls in the Last 12 Months (yes/no) † 16 (34) 13 (24.5) 20 (38.5) 49 (32.2)Geriatric Depression Scale (max. 15 pts) 0.5 (1.9) 0.3 (1.0) 0.9 (2.4) 0.6 (1.8)Functional Comorbidity Index (max. 18 pts) 2.2 (1.7) 1.8 (1.6) 2.2 (1.5) 2.1 (1.6)Lawton and Brody (max. 8 pts) 8.0 (0) 8.0 (0.1) 7.9 (0.5) 8.0 (0.3)Dominant Quadriceps Strength (kg) 27.9 (8.0) 30.4 (6.7) 29.8 (8.3) 29.4 (7.7)Stroop CW - Stroop C (sec) 44.03 (15.4) 45.71 (24.8) 46.07 (16.0) 45.31 (19.2)Trail B - Trail A (sec) 44.60 (36.9) 41.36 (26.2) 49.12 (37.7) 45.01 (33.8)Digit Forward - Digit Backward 3.4 (2.6) 3.4 (2.0) 3.4 (2.4) 3.4 (2.3)Gait Speed (m/sec) 1.16 (0.2) 1.18 (0.2) 1.16 (0.2) 1.17 (0.2)ABC Scale Score (%) 85.3 (15.0) 89.4 (12.1) 89.5 (10.7) 88.2 (12.7)* BAT = Balance and Tone; 1× RT = once-weekly resistance training; 2 × RT = twice-weekly resistance training; yr = year; kg = kilogram; MMSE = Mini-Mental State Examination; sec = seconds; Stroop CW = Stroop colour-words condition; Stroop C = Stroop coloured-X's condition; m/sec = meters per second; ABC Scale = Activities-specific Balance Confidence.† Count = number of "yes" cases within each group. % = percent of "yes" within each group.time, respectively (Table 2). There was a 1.2% increase inthe ABC Scale score. Usual gait speed increased by amean of 0.22 m/s. A paired t-test indicated that this was astatistically significant increase (P < 0.001).Correlation CoefficientsTable 3 reports the correlation coefficients of those vari-ables included in the final multi-variable regressionmodel. Of the three key executive processes only changein selective attention and conflict resolution was signifi-cantly and positively associated with improved gait speed(P < 0.01). Change in falls-related self-efficacy was alsosignificantly and positively associated with improved gaitspeed (P < 0.001).Linear Regression ModelExperimental group, age, baseline gait speed, baselineexecutive process of selective attention and conflict reso-lution to the model resulted in an R-square change of7.5% and significantly improved the regression model (FChange = 11.6, P = 0.001). Adding change in the ABCScale score to the model resulted in an R-square changeof 4.5% and significantly improved the model (F Change =7.4, P = 0.008). The total variance accounted by the finalmodel was 24.0% (Table 3).DiscussionThere is an increasing recognition that gait speed is animportant indicator of current and future functional sta-tus in older adults. We found that both improved cogni-tive performance of selective attention and conflictresolution and falls-related self-efficacy were indepen-dently associated with improved gait speed among com-munity-dwelling senior women. To our knowledge, this isglobal cognition, and change in dominant quadricepsstrength accounted for 11.9% of the variance in improvedgait speed (Table 3). Adding the change score for thethe first study that has examined the independent associ-ation of changes in executive functions and falls-relatedLiu-Ambrose et al. BMC Geriatrics 2010, 10:25http://www.biomedcentral.com/1471-2318/10/25Page 5 of 8self-efficacy with improved gait speed after accountingfor age global cognition, baseline gait speed, and changein dominant quadriceps strength.Our findings concur with previous studies demonstrat-ing the association between executive functions and gaitspeed [7,35]. Of the three key executive processes exam-ined in this study, only improved performance on theStroop Test was independently associated with improvedgait speed after accounting for relevant covariates. Thisfinding concurs with those of a previous cross-sectionalstudy of community-dwelling older adults [36]. Thatstudy found that performance on the Stroop Test, but noton the Trail Making Test (Part A & B), was independentlyassociated with usual gait speed. However, our resultscontradict those of the Lifestyle Interventions and Inde-pendence for Elders Pilot (LIFE-P) study [37]; that studyfound that improved performance on the Stroop Test wasassociated with improved balance but not with improvedgait speed. Differences in study participants and inter-ventions may contribute to this discrepancy. It is not sur-prising that global cognition was not significantlyassociated with increased gait speed in our study giventhat only individuals without cognitive impairment wereincluded.As gait speed is an independent predictor of falls [2]and fracture risk [3], our finding extends previous studiesdemonstrating an association between the Stroop Testand falls [38,39]. Specifically, in a prospective study ofinpatient falls in an urban rehabilitation hospital, perfor-mance on the Stroop Test predicted falls status beyondthat explained by age and functional motor ability [38].Neuro-imaging data also suggest that the specific execu-tive cognitive process of selective attention and conflictresolution is associated with falls and mobility. Specifi-conflict resolution -- compared with senior non-fallers.This alteration in neural activity may be an early indicatorof increased falls risk as the cerebellum is not onlyresponsible for normal motor function (i.e., movement),it is also involved in executive functions [41] (e.g., plan-ning of movement), and hence, may represent a criticalinterface between mobility and cognition.Our finding of an independent association betweenimproved falls-related self-efficacy and improved gaitspeed extend those of two previous cross-sectional inves-tigations [21,22]. Specifically, we demonstrated that falls-related self-efficacy was independently associated withgait speed among senior women after accounting for age,physical activity level, and relevant physiological func-tions [21]. We note that the observed change in falls-related self-efficacy was minimal in this study. This sug-gests that small changes in falls-related self-efficacy, asmeasured by the ABC Scale, are clinically significant.However, more research is needed to ascertain what con-stitutes a clinically significant change in the ABC Scalescore among high-functioning community-dwelling olderadults. The minimal change observed may also be sec-ondary to a ceiling effect of the ABC Scale [42] in ourstudy cohort.According to the LIFE-P study [43], the observedimprovement in gait speed of 0.22 m/s is a meaningfulchange. Specifically, that study reported a 0.08 m/schange in 4-meter gait speed to be substantial, with aneffect size of at least 0.5. However, participants of theLIFE-P study were likely more frail than our study partic-ipants because the LIFE-P study participants were aged70 to 89 years and had Short Physical Performance Bat-tery scores of 9 or less. Therefore, the substantial changein gait speed we observed may be, at least in part, due to aTable 2: Mean change for variables of interest.Variable * BAT (n = 42) Mean (SD)1× RT (n = 47) Mean (SD)2 × RT (n = 46) Mean (SD)Total (N = 135) Mean (SD) Dominant Quadriceps Strength (kg) ** 7.1 (7.0) 6.4 (9.1) 8.1 (6.4) 7.2 (7.6) Stroop CW - Stroop C (sec) † 0.26 (17.12) 6.22 (22.31) 5.01 (13.75) 3.94 (18.21) Trail B - Trail A (sec) † 8.64 (32.15) 7.30 (30.36) 10.96 (36.92) 8.97 (33.06) Digit Forward - Digit Backward † -0.64 (2.70) 0.06 (2.54) -0.47 (2.24) -0.34 (2.50) Gait Speed (m/sec) ** 0.22 (0.18) 0.19 (0.19) 0.24 (0.16) 0.22 (0.18) ABC Scale Score (%) ** 2.83 (9.91) 2.26 (10.27) -1.37 (10.60) 1.19 (10.37)* BAT = Balance and Tone; 1× RT = once-weekly resistance training; 2 × RT = twice-weekly resistance training; Stroop CW = Stroop colour-words condition; Stroop C = Stroop coloured-X's condition; m/sec = meters per second; ABC = Activities-Specific Balance Confidence.** Mean change = final value minus baseline value. Positive change indicates improvement.† Mean change = baseline value minus final value. Positive change indicates improvement.cally, our previous work [40] found that senior fallers hadreduced brain activation in the right cerebellum duringthe flanker task - a task requiring selective attention andgreater capacity of our participants to improve.Our finding that improved dominant quadricepsstrength was not significantly associated with improvedLiu-Ambrose et al. BMC Geriatrics 2010, 10:25http://www.biomedcentral.com/1471-2318/10/25Page 6 of 8Table 3: Multiple linear regression model summary improved usual gait speed. Usual Gait Speed (m/s)Independent Variable r R2 R2 Change Unstandardized B (Standard Error)Standardized β P - valueModel 1 0.345 0.119 0.119Group 0.082 0.014 (0.018) 0.066 0.441Age -0.19 * -0.014 (0.005) -0.239 0.007MMSE Score 0.02 0.004 (0.011) 0.028 0.749Baseline Gait Speed -0.19 * -0.249 (0.081) -0.273 0.003 Quadriceps Strength 0.11 0.003 (0.002) 0.129 0.133Model 2 0.441 0.194 0.075Group 0.082 0.008 (0.018) 0.036 0.659Age -0.19 * -0.013 (0.005) -0.217 0.011MMSE Score 0.02 0.002 (0.011) 0.015 0.859Baseline Gait Speed -0.19 * -0.283 (0.078) -0.310 < 0.001 Quadriceps Strength 0.11 0.004 (0.002) 0.173 0.038 Stroop Test 0.26 * 0.003 (0.001) 0.283 0.001Model 3 0.490 0.240 0.045Group 0.082 0.017 (0.018) 0.077 0.349Age -0.19 * -0.014 (0.005) -0.236 0.005MMSE Score 0.02 0.001 (0.011) 0.008 0.922Baseline Gait Speed -0.19 * -0.248 (0.077) -0.271 0.002 Quad Strength 0.11 0.002 (0.002) 0.086 0.324 Stroop Test 0.26 ** 0.002 (0.001) 0.229 0.007 ABC Scale 0.29 *** 0.004 (0.002) 0.236 0.008* P ≤ 0.05** P ≤ 0.01*** P ≤ 0.001gait speed concurs with previous findings [44]. A modelassuming nonlinear relationships may be appropriate forunderstanding how change in muscular strength affectschange in gait speed [44].An important clinical implication of these results is thatclinicians may need to consider the specific executiveprocess of selective attention and conflict resolution andfalls-related self-efficacy in the rehabilitation of gaitamong community-dwelling seniors. Our data suggestinterventions that target executive functions and falls-related self-efficacy in addition to physical functions toimprove gait speed may be more efficacious than thosethat do not.We note that our study sample consisted exclusively ofresults of our study may not generalize beyond this popu-lation of senior women and we may have underestimatedthe contribution of change in executive functions andfalls-related self-efficacy to change in gait speed. Futureprospective studies are needed to test whether the pres-ent findings also apply to larger, more heterogeneouspopulations. Finally, because the effect of selective atten-tion and conflict resolution and falls-related self-efficacyobserved in this study was small, future studies are alsoneeded to determine the clinical significance, if any, ofthe additional and unique variance accounted for by eachfactor.Conclusionsindependent community-dwelling senior women whowere without significant physical and cognitive impair-ments and without a significant history of falls. Thus, theIn conclusion, both change in executive functions andfalls-related self-efficacy are independently associatedwith improved gait speed. Clinicians may need to con-Liu-Ambrose et al. BMC Geriatrics 2010, 10:25http://www.biomedcentral.com/1471-2318/10/25Page 7 of 8sider these factors when developing rehabilitation strate-gies to improve gait speed.Competing interestsThe authors declare that they have no competing interests.Authors' contributionsTLA conceived and designed the study, acquired data, and analyzed and inter-preted the data. TLA, JCD, and KMK drafted and revised the manuscript. LSN,LK, and CLH acquired data and participated in the statistical analysis. Allauthors read and approved the final manuscript.AcknowledgementsThe authors would like to thank the Vancouver South Slope YMCA manage-ment and members who enthusiastically supported the study by allowing access to participants for the training intervention. We thank the instructors for their commitment to the participants' health and safety. TLA is a Michael Smith Foundation for Health Research (MSFHR) Scholar. LSN and JCD are MSFHR Senior Graduate trainees.Declaration of Sources of Funding: This work was supported by the Vancou-ver Foundation (BCM06-0035); and the Michael Smith Foundation for Health Research Establishment Grant (CI-SCH-063(05-1)CLIN) to TLA.Sponsor's Role: None.Author Details1Centre for Hip Health and Mobility, Vancouver Coastal Health Research Institute, University of British Columbia, Vancouver, BC, Canada, 2Department of Physical Therapy, University of British Columbia, Vancouver, BC, Canada, 3Department of Psychology, University of British Columbia, Vancouver, BC, Canada and 4Department of Family Practice, University of British Columbia, Vancouver, BC, CanadaReferences1. Cesari M, Kritchevsky SB, Penninx BW, Nicklas BJ, Simonsick EM, Newman AB, Tylavsky FA, Brach JS, Satterfield S, Bauer DC, et al.: Prognostic value of usual gait speed in well-functioning older people--results from the Health, Aging and Body Composition Study.  J Am Geriatr Soc 2005, 53(10):1675-1680.2. 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J Gerontol A Biol Sci Med Sci 1996, 51(6):M297-302.Pre-publication historyThe pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2318/10/25/prepubdoi: 10.1186/1471-2318-10-25Cite this article as: Liu-Ambrose et al., Changes in executive functions and self-efficacy are independently associated with improved usual gait speed in older women BMC Geriatrics 2010, 10:25


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