doi: 10.2522/ptj.20100391Originally published online October 14, 2011

2011; 91:1740-1751.PHYS THER. Brach, David Wert and Stephanie A. StudenskiJessie M. VanSwearingen, Subashan Perera, Jennifer S.Mobility Limitations: A Randomized Controlled TrialActivity and Participation in Older Adults With Impact of Exercise to Improve Gait Efficiency on

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Impact of Exercise to ImproveGait Efficiency on Activity andParticipation in Older AdultsWith Mobility Limitations:A Randomized Controlled TrialJessie M. VanSwearingen, Subashan Perera, Jennifer S. Brach, David Wert,Stephanie A. Studenski

Background. Definitive evidence that exercise interventions that improve gait alsoreduce disability is lacking. A task-oriented, motor sequence learning exercise inter-vention has been shown to reduce the energy cost of walking and improve gait speed,but whether the intervention also improves activity and participation has not beendemonstrated.

Objective. The objective of this study was to compare the impact of a task-oriented,motor sequence learning exercise (TO) intervention and the impact of an impairment-oriented, multicomponent exercise (IO) intervention on activity and participation out-comes in older adults with mobility limitations. The mediating effects of a change in theenergy cost of walking on changes in activity and participation also were determined.

Design. This study was a single-blind, randomized controlled trial.

Setting. The study was conducted in an ambulatory clinical research training center.

Participants. The study participants were 47 older adults (mean age�77.2 years,SD�5.5) with slow and variable gait.

Intervention. The intervention was a 12-week, physical therapist–guided program ofTO or IO.

Measurements. Measures of activity (gait speed over an instrumented walkway;daily physical activity measured with an accelerometer; confidence in walking determinedwith the Gait Efficacy Scale; and physical function determined with the total, basiclower-extremity, and advanced lower-extremity components of the Late-Life Function andDisability Instrument [Late-Life FDI]) and participation (disability limitation dimensionand instrumental role [home and community task performance] domain components ofthe Late-Life FDI) were recorded before and after the intervention. The energy cost ofwalking was determined from the rate of oxygen consumption during self-paced treadmillwalking at the physiological steady state standardized by walking speed. An adjustedcomparison of activity and participation outcomes in the treatment arms was made by useof an analysis of covariance model, with baseline and change in energy cost of walkingadded to the model to test for mediation. Tests were used to determine the significanceof the mediating effects.

Results. Activity improved in TO but not in IO for confidence in walking (Gait EfficacyScale; mean adjusted difference�9.8 [SD�3.5]) and physical function (Late-Life FDI basiclower-extremity component; mean adjusted difference�3.5 [SD�1.7]). Improvements inTO were marginally greater than those in IO for gait speed, physical activity, and totalphysical function. Participation improved marginally more in TO than in IO for disabilitylimitations and instrumental role.

Limitations. The older adults were randomized to the intervention group, but differ-ences in baseline measures had to be accounted for in the analyses.

Conclusions. A TO intervention that improved gait also led to improvements in someactivity and participation outcomes in older adults with mobility limitations.

J.M. VanSwearingen, PT, PhD,FAPTA, Department of PhysicalTherapy, School of Health andRehabilitation Sciences, Univer-sity of Pittsburgh, 6035 ForbesTower, Pittsburgh, PA 15260(USA). Address all correspon-dence to Dr VanSwearingen at:jessievs@pitt.edu.

S. Perera, PhD, Division of Geriat-ric Medicine, Department of Med-icine, University of Pittsburgh.

J.S. Brach, PT, PhD, Department ofPhysical Therapy, School of Healthand Rehabilitation Sciences, Uni-versity of Pittsburgh.

D. Wert, PT, MPT, Department ofPhysical Therapy, School of Healthand Rehabilitation Sciences, Uni-versity of Pittsburgh.

S.A. Studenski, MD, MPH, Divisionof Geriatric Medicine, Depart-ment of Medicine, University ofPittsburgh.

[VanSwearingen JM, Perera S,Brach JS, et al. Impact of exerciseto improve gait efficiency on activ-ity and participation in olderadults with mobility limitations: arandomized controlled trial. PhysTher. 2011;91:1740–1751.]

© 2011 American Physical TherapyAssociation

Published Ahead of Print: October14, 2011

Accepted: May 7, 2011Submitted: November 15, 2010

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Difficulty walking is associatedwith reduced activity and par-ticipation, a path of decline

in physical and social function, anda loss of independence.1–5 Walk-ing underlies many activities ofdaily living,6,7 and walking ability(eg, gait speed) can be used topredict future mobility and physi-cal disability.6,8,9 Therapeutic exer-cise interventions for older adultswith mobility limitations havefocused on improving walking(speed, endurance, and gait charac-teristics) as a means to reduce ordelay physical disability.10–12 Multi-component exercise programs,including strength, balance, walking,and endurance, are intended toreduce impairments and improvephysiological capacity for walking inolder adults. Such exercise programshave resulted in modest gains inwalking ability (eg, an approximate5% increase in speed, with a range of0%–16%),11,13–23 with only one studyreporting disability outcomes (areduction in emotional disability).21

Do exercise interventions thatimprove walking ability also reducedisability? Keysor and Jette24 con-ducted a systematic review of theeffects of exercise interventions onphysical function and disability out-comes in older adults. Thirty-onerandomized controlled trials (RCTs)of flexibility, strengthening, aerobicconditioning, balance, and multi-component exercise interventionspublished between 1985 and 2000were reviewed; 14 studies includedphysical disability outcomes (evenfewer included social, emotional,or overall disability outcomes), andonly 5 studies reported improve-ments in participation. The physicaldisability findings varied. The effectson physical disability were gener-ally small to modest effect sizes andmean differences; larger effectswere seen in older adults with sub-stantial disabilities and in one studyof older adults with osteoarthritis.24

We reviewed more recent RCTs ofexercise interventions for effectson physical function and disabilityoutcomes in older adults.15,25–28 Ofthe 5 RCTs identified, 2 includeddisability outcomes27,28; 1 study ofolder adults with osteoarthritisshowed improvements in participa-tion after interventions.27

Schrack et al29 and Ferrucci30 pro-posed an energetic model of frailtyin which the physical exertion ofwalking with mobility limitationsmay be a major factor in reducedactivity and participation (disabil-ity) in some older adults.2,31,32 Inolder adults with mobility limita-tions, abnormalities in posture andgait contributed to a greater energycost of walking (eg, inefficient gait),with adjustments for age and gaitspeed.33 Therapeutic exercise withtask-oriented motor sequence learn-ing (motor skill)34–37 to improve theefficiency of gait through training inthe timing and coordination of thesequences of movements in walkingmay be an alternative to traditionalmulticomponent, impairment-basedexercise. For motor tasks, expertmovers, or those with greater motorskill for a specific activity, tired lesseasily than novices because of thegreater efficiency of skilled motorperformance.35,37,38 After a stroke,task-oriented, gait-related exercisetreatment approaches enhanced theefficiency of gait,39,40 the efficiencyof limb movement,41 and function indaily activities.42 In people with mul-tiple sclerosis, task-oriented, tread-mill gait exercise reduced the effortof walking.43 A task-oriented, motorsequence learning, therapeutic exer-cise gait intervention reduced theenergy cost of walking and improvedgait speed more than an impairment-oriented, walking, endurance, bal-ance, and strengthening exercisegait intervention in older adults withmobility limitations.44 Although thetask-oriented, motor sequence learn-ing gait intervention appeared to

reduce energy cost and increase gaitspeed, the impact of the interven-tion on activity and participation isunknown.

Definitive evidence that exercisethat improves gait also reduces dis-ability and, particularly, that exercisethat reduces energy expenditurefor walking positively influencesactivity and participation is lack-ing. In an RCT of 2 gait inter-ventions, we compared the impactof task-oriented, motor sequencelearning exercise (TO)—designedto emphasize timing and coordina-tion to make walking easier—andthe impact of impairment-oriented,multicomponent exercise (IO)—designed to emphasize strength,balance, and endurance and correctgait abnormalities to increase thecapacity to walk—on activity andparticipation outcomes in olderadults with mobility disabilities.We also determined whether anintervention-related change in gaitefficiency (energy cost of walking)mediated changes in activity andparticipation. We expected that anexercise intervention that reducesexertion and improves the ease ofwalking also might improve activityand participation in older adults withmobility limitations.

MethodOverviewThe study methods are describedin detail elsewhere.44 In brief,we conducted a single-blind clini-

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cal RCT to compare two 12-week,protocol-driven, physical therapist–guided gait interventions basedon either TO or IO (to improvethe performance of body systemcomponents) for older adults withquantitative evidence of walkingdifficulty. In the earlier report ofthe RCT,44 the TO interventionwas referred to as timing and coor-dination (TC) exercise, and theIO intervention was described aswalking, endurance, balance, andstrengthening (WEBS) exercise. Allparticipants gave informed consentto participate.

ParticipantsThe target population was olderadults with mild to moderate mobil-ity difficulties. Potential participantswere recruited from the PittsburghPepper Center Registry of olderadults who were interested in par-ticipating in studies of balance andmobility and who reported walkingdifficulties. Eligibility was based onthe ability to walk independentlywith or without a cane; medicalsafety, including a personal physi-cian’s approval to participate in alow- to moderate-intensity exerciseprogram; adequate cognitive func-tion to provide informed consentand participate in the exercise inter-ventions (Mini-Mental State Examina-tion [MMSE]45 score of �24); andquantitative evidence of mobilitydifficulties, defined as slow and vari-able gait (see below). Randomizationwas based on a concealed block sizeof 4. The study staff was unaware ofthe randomization code, and partici-pants were notified of their assign-ments at the first treatment visit,after consent was given and baselinedata were collected. The flow dia-gram for the study is available in theearlier report of the RCT.44

MeasuresAll measurements except demo-graphic data were collected twice, atbaseline (before randomization) and

after 12 weeks of exercise, by asses-sors who were unaware of treatmentarm assignments.

Descriptive MeasuresDemographics and comorbidconditions. Data on age, sex, levelof education, and coexisting medicalconditions were collected throughparticipant report. The Comorbid-ity Index46 was used to define med-ical history. Participants reportedwhether a physician had ever toldthem that they had any of 18 com-mon conditions expected to influ-ence physical function. Comorbidi-ties were categorized into 8 domains(cardiovascular, respiratory, muscu-loskeletal, neurologic, general, can-cer, diabetes, and visual) andsummed to generate a summaryscore from the report of the 18conditions.46 Potential participantsalso completed the MMSE measureof general cognitive function.45

The MMSE was used to determinewhether potential participants hadadequate cognitive function to pro-vide informed consent and as apotential covariate in the analyses ofthe findings.

Mobility performance measures.Gait speed and variability wererecorded to determine eligibility toparticipate. Potential participantswere instructed to walk at theirusual speed on a 4-m instrumentedwalkway (GaitMatII, E.Q. Inc, Chal-font, Pennsylvania)47 with a 2-m non-instrumented section at each endto allow for acceleration and decel-eration. After 2 practice walks onthe mat, the potential partici-pants performed 2 walks for data col-lection. Gait speed was defined asthe average from the 2 walks. Steplength variability and step width vari-ability were derived from the stan-dard deviations of all right and leftsteps recorded during the 2 walksand were reported as the coefficientof variation, defined as (standarddeviation/mean step length or step

width) � 100.48,49 Potential partici-pants who demonstrated mobilitylimitations, defined as slow or vari-able gait, were eligible to participate.Slow gait was a walking speed of lessthan or equal to 1.0 m/s and greaterthan or equal to 0.6 m/s (slow, butnot so slow as to limit the ability toparticipate in walking-based inter-ventions). Variable gait was eitherstep length variability (coefficient ofvariation of �4.5%)5 or step widthvariability (coefficient of variation of�7% or �30%).50

Activity MeasuresGait speed. Gait speed outcomeswere previously reported44 but areincluded in the present report (asactivity-level outcomes) to providea comprehensive description ofthe intervention effects. The exer-cise interventions were designedto improve gait; thus, informationon the intermediate outcome of achange in gait speed may be helpfulin understanding the more distalactivity and participation outcomes.

Physical activity. To capture dailyphysical activity, participants worea CSA/MTI Actigraph accelerometer(Actigraph LLC, Pensacola, Flor-ida)51,52 at waist level for 7 consecu-tive days from rising until retiringto bed at night. Activity was reportedin counts per minute, represent-ing mean activity counts per day,divided by the mean minutes wornper day, averaged over days worn.Data were available for 44 partici-pants, and all but 1 participant pro-vided 6 or more days of monitoring.

Gait Efficacy Scale (GES). TheGES53,54 is a self-report 10-item scaleof perceived confidence in walkingability. Individual items in the GESare rated from 1 (no confidence) to10 (complete confidence). The itemsrepresent a range of challenges fromlevel walking to walking on unevensurfaces, curbs, or stairs. The GEStotal score is the sum of the scores

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for the items, with a range of 10 to100.53,54

Late-Life Function and Disabil-ity Instrument (Late-Life FDI)function component. We usedthe Late-Life FDI function compo-nent7 (scores for overall function-ing, basic lower-extremity function-ing, and advanced lower-extremityfunctioning) to assess the relation-ship between perceived changes inphysical function and walking abil-ity. The Late-Life FDI total func-tioning scale includes 32 itemsabout the usual ability to performphysical activities that are typicallypart of an everyday routine. Thebasic lower-extremity functioningsubscale includes 14 activities thatmainly involve standing and essen-tial walking. The advanced lower-extremity functioning subscale (11items) involves more physically chal-lenging activities and endurance.The Late-Life FDI function compo-nent scales have scores rangingfrom 0 to 100, with higher scoresindicating better function, and excel-lent reproducibility (intraclass corre-lation coefficient of �.91).7

Participation Measure: Late-LifeFDI Disability ComponentWe used the Late-Life FDI disabil-ity component55 (scores for dis-ability limitation dimension andinstrumental role domain) to reflectchanges in the ability to performsocially defined life tasks. The dis-ability limitation dimension includes16 items about participation insocial, work, leisure, and travel activ-ities and taking care of financesand health. The instrumental roledomain reflects perceived limitationsin home and community tasks.55

The Late-Life FDI disability compo-nent scales have scores rangingfrom 0 to 100, with higher scoresindicating less disability, and excel-lent reproducibility (intraclass corre-lation coefficient of �.81).55

Measure of Potential Mediation:Energy Cost of WalkingThe energy cost of walking reflectsgait efficiency and is defined asthe mean rate of oxygen consump-tion divided by walking speed.Lower energy cost reflects highergait efficiency.38,56 Standardizedmethods for determining the energycost of walking from the rate ofoxygen consumption during walk-ing were established in previousstudies.39,57–61 The energy cost ofwalking (mL/kg�m)56,62 is a time-independent, repeatable measureof the physiological cost of gait63–65

and is influenced little by changes inoxygen consumption related to aer-obic exercise64,65; the energy costsof walking can be compared acrossindividuals and over time, regardlessof changes in gait speed.60,64,65 Par-ticipants walked on a treadmill at aself-selected pace while oxygenconsumption data were collectedwith open-circuit spirometry andexpired gases were analyzed with aMedgraphics VO2000 portable met-abolic measurement system (MedicalGraphics Corp, St Paul, Minnesota).

The energy cost of walking wascalculated from the mean rate ofoxygen consumption during 3 min-utes of treadmill walking afterthe physiological steady state wasreached.38,62,63,65 We used the totalrather than the net energy cost ofwalking as the measure of gait effi-ciency. Net energy cost requires acorrection for energy expenditureat rest, different methods, andmore testing.66 Because we wereinterested in changes in the energycost of walking over time andbecause we expected resting energyexpenditure to be unchanged, weused total energy cost to reduce theburden of testing on participants.The mean between-group differ-ence in the energy cost of walkingafter the intervention was previ-ously reported.44 In the presentstudy, we used the energy cost of

walking as a measure of gait effi-ciency and explored the role ofchanges in gait efficiency in changesin activity and participation.

InterventionsGeneral. Both interventions were12-week, twice weekly, protocol-driven, physical therapist–led pro-grams for small groups of partici-pants (n�2 or 3). The interventionswere previously described.44 Theinterventions were conducted at dif-ferent times or on separate days toavoid cross-contamination. Thera-pists received initial training in allaspects of the protocols and wereassessed for adherence before inter-vention implementation and period-ically throughout the study. The pro-tocols provided operational criteriafor the exercise activities and stan-dards for progression and allowedfor various individual levels of initialperformance and rates of change.Progression was mandated after aset of exercises were completedwith 80% accuracy and self-reportedease of performance. The time spenton walking itself was monitored toequalize walking practice betweenthe treatment arms at 20 to 30 min-utes per session. Detailed logs oftreatment sessions were maintained,with biweekly reviews of a sampleof treatment logs for evidence ofconsistency with the protocols andprogression.

TO program. The TO programwas based on principles of motorsequence learning34,37,67–69 thatenhance “skill” or smooth, subcon-scious, and automatic control ofmovement.35 The motor sequencelearning exercise involved task-oriented stepping and walking pat-terns to promote the timing andcoordination of locomotor step-ping patterns, integrated with thephases of the gait cycle to enhancesmooth movements in walk-ing.67,70–72 Progression involved sep-arately increasing the speed, ampli-

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tude, or accuracy of performancebefore advancing to a more complexmovement task.68,71 For example,the progression of diagonal steppingpatterns was as follows: step for-ward across the midline of thebody at a self-selected pace in onedirection and then in the otherdirection, increase stepping speed,alternate the side of stepping, andalternate forward and backwardstepping. Oval and spiral walkingpatterns were used to incorporatethe motor sequence and interlimbtiming of the stepping patterns intowalking tasks. Walking patternswere advanced by altering thespeed, amplitude (eg, narrowing thewidth of the oval), or accuracy ofperformance (eg, not straying fromthe desired path). The complexity ofthe gait exercise was increased byinstructing the participants to per-form the gait activities while walkingpast others and in combination withupper-extremity tasks, such as carry-ing, rolling, bouncing, or tossing aball.67,68 To promote regular timingof the stepping patterns, treadmill-paced walking practice was per-formed for 10 to 15 minutes. Thiswalking exercise was not targeted atendurance training and did notincrease the rate of perceived exer-tion. The treadmill-paced walkingoccurred primarily at the preferredwalking speed, with brief (30–60seconds) repeated (3–5 times) inter-vals of increased speed followed bya return to a comfortable walkingspeed to reinforce the consistency ofthe timing of stepping and speed.73

IO program. The IO program wasbased on current standards of physi-cal therapy for gait and balanceretraining. The impairment-basedexercise began with a brief warm-upof gentle stretching exercises for theleg (ankle, knee, and hip) and trunkmuscles. Strength training consistedof lower-extremity progressive resis-tive exercises in sitting and standingpositions for lower-extremity muscle

groups. Progression of the strengthtraining exercises involved increas-ing the repetitions to a maximum of20 and then increasing the resis-tance. The resistance was providedby cuff weights.

The balance exercises were per-formed by redistributing the centerof mass of the body over the base ofsupport.74 The balance exercisesstarted with the feet positioned atthe participant’s self-selected com-fortable distance apart for uprightbalance. With practice, the balanceexercises progressed to a narrowerbase of support and less upper-extremity support. The enduranceexercises were performed on aNuStep (NuStep Inc, Ann Arbor,Michigan) (which provides a seated,stair-climbing–like activity) or on astationary bicycle.

The endurance exercise trainingwas conducted at a submaximalworkload, defined as a self-reportedrate of perceived exertion of 10to 13, or a somewhat hard levelof effort.75 Heart rate and bloodpressure were monitored in accor-dance with recommended guide-lines for safe exercise.76,77 Pro-gression involved increasing theduration of exercise (the ability tosustain a somewhat hard level ofeffort for up to 15 minutes) andthen on increasing the intensity ofexercise.

Specific gait training involved thetherapist giving verbal instructionsaimed at correcting abnormalities ofspatial or temporal characteristics ofgait or posture during walking (eg,verbal cues to facilitate heel-strike orpush-off from the trailing limb and toencourage participants to look in thedirection in which they werewalking).

Sample SizeThe original RCT was designed asa pilot study of 2 interventions and

the impact on measures of gaitchosen to represent the complexityof walking, gait variability, and theenergy cost of walking. The samplesize for the original RCT was basedon having adequate power to testfor differences in measures of gaitvariability. On the basis of datafrom a preclinical trial of similarinterventions and mean changes inthe step length variability coefficientof variation of �3.05 (SD�1.45)for the task-oriented exercise groupand �0.80 (SD�2.80) for theimpairment-oriented exercise group,a sample size of 2 groups of 16 par-ticipants would enable testing with80% power. We included 25 partici-pants in each intervention group(for a total of 50 participants) toaccount for a potential 20% dropoutrate for older adults with disabilitiesand a mean expected age of greaterthan 80 years and to account forthe potential wide variations in per-formance and inability to completesome measures for older adults withmobility disabilities. Given the pilotnature of the original RCT and thecost and burden of conducting anRCT, we also measured activity andparticipation outcomes. We reportthe activity and participation out-comes of the original RCT here andacknowledge that the original RCTwas not powered to study the sec-ondary outcomes described.

Data AnalysisAll statistical analyses were per-formed with SAS version 9.2 (SASInstitute Inc, Cary, North Carolina).Participant characteristics and base-line measurements in the treatmentarms were compared by use of t testsfor continuous variables and chi-square tests for categorical variables.To make an adjusted comparison ofactivity and participation outcomesin the treatment arms, we fitted ananalysis of covariance model withthe change in each outcome frombaseline to follow-up as the responsevariable; with treatment arm as the

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main factor of interest; and withage, sex, and baseline value for theoutcome variable as covariates. Toobtain estimates of the mediatingeffects of changes in gait efficiencyon changes in activity and participa-tion outcomes, we fitted an analysisof covariance model with the changein each outcome from baseline tofollow-up as the response variable;treatment arm as the main factorof interest; and age, sex, baselinevalue for the outcome variable, base-line value for the energy cost ofwalking, and change in the energycost of walking as covariates. Achange in gait efficiency was consid-ered to be a partial mediator of theactivity or participation outcome ifthe between–intervention group dif-ference estimate was reduced withthe addition of the variable “changein energy cost” to the analysis ofcovariance. We used methods pro-posed to test the significance of amediating or indirect effect,78,79

including a bootstrap approach toobtain confidence intervals for amediating effect.

In brief, the standard approach fortesting the statistical significance of achange in an effect (ie, the between–intervention arm difference) is theSobel test, but it is based on certainassumptions about the stochasticindependence of underlying randomvariables. Although this assumptionfacilitates mathematical derivationsrequired to obtain the necessaryformulas in an otherwise intractableproblem, it also makes the Sobeltest vulnerable to any violation ofthe said assumptions. Statisticalbootstrapping is a relatively newcomputation-intensive method basedon repeated Monte Carlo simulationsto obtain confidence intervals withoutrelying on restrictive assumptions.

Role of the Funding SourceThis work was supported by thePittsburgh Older Americans Indepen-dence Center (NIA P30 AG024827)

and a Beeson Career DevelopmentAward (NIA K23 AG026766).

ResultsFifty participants were randomized,and 47 completed the study—23 inthe TO group and 24 in the IOgroup. The 3 participants who didnot complete the study withdrewbecause of medical conditions unre-lated to study participation. The par-ticipants who withdrew did not dif-fer at baseline from the participantswho completed the interventions.The mean age of the older adultscompleting the study was 77.2(SD�5.5) years (in the TO group, themean age was 76.5 [SD�5.5] years;in the IO group, the mean age was78.4 [SD�5.5] years), 65% werewomen, 12% were black, 67% hadmore than a high school education,and all had generally good cognitivefunction (mean Mini-Mental StateExamination score of 28.7 [SD�1.4]). On average, the participantshad few of the 18 comorbiditiessurveyed (mean Comorbidity Indexof 2.6 [SD�1.1]), and the comor-bidities were predominantly in thedomains of arthritis (72%), vision(66%), osteoporosis (38%), and hear-ing (32%). Most (72.3%) of the par-ticipants reported some difficultywalking 2 or 3 blocks. All partici-pants demonstrated slow gait (meangait speed of 0.85 [SD�0.13] m/s)and variable gait (step length vari-ability of 78%; step width variabilityof 78%).

Despite random assignment, base-line differences between the treat-ment arms were observed. Com-pared with participants in the IOgroup, participants in the TO grouphad a lower energy cost of walking,fewer gait abnormalities, and nonsig-nificant but potentially meaningfulbetween-group differences in sex,gait speed, and self-reported func-tional limitations. All 47 participantswho completed the study partici-

pated in at least 22 of the 24 treat-ment sessions.

Activity OutcomesAfter treatment, gait speed improvedwith both forms of exercise (Tab. 1);the improvement was marginallygreater in the TO group than in theIO group. Physical activity increasedmarginally more in the TO groupthan in the IO group because of aslight increase in activity in the TOgroup and a slight decrease in activ-ity in the IO group. Confidence inwalking, as determined with theGES, improved 10.8 points in theTO group but did not change in theIO group. Physical function (usualdaily activities) improved in the TOgroup but not in the IO group. Par-ticipants in the TO group demon-strated greater gains in basic lower-extremity functioning than those inthe IO group (Tab. 1).

The between-group difference forTO versus IO was large for confi-dence in walking, but for physicalfunction, the difference was small;for gait speed, activity, and total andadvanced lower-extremity function-ing, the differences were marginal.Although clinically meaningful dif-ference values for gait speed areknown,80 such values have not beendefined for activity, the GES, or Late-Life FDI measures. Therefore, weestimated meaningful differencesfrom the baseline sample data forthese variables by using Cohen effectsize criteria (eg, small effect�0.2 �baseline standard deviation; mod-erate effect�0.5 � baseline standarddeviation)81,82 and applied them tothe interpretation of the results. Theadjusted mean difference for confi-dence in walking was greater than anestimated moderate effect size, andthe adjusted mean differences for theremaining activity outcomes werebetween small and moderate effectsizes (Fig. 1).

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Participation OutcomesThe improvement in participationwas marginally greater in the TOgroup than in the IO group (Tab. 1).Values for both disability limitationsand instrumental role increased mar-ginally more in the TO group than inthe IO group. Although the adjustedmean differences for the participa-tion outcomes were marginally sig-nificant, both exceeded a moderateeffect size for the measures (Fig. 1).

Mediating Effects of Changes inGait Efficiency on Activity andParticipation OutcomesGait efficiency improved in the TOgroup but did not change in the IOgroup (Tab. 1, mediator; change inthe energy cost of walking).44

We assessed the results for a mediat-ing effect of the change in gait effi-ciency by examining the change inthe between-intervention differenceestimate due to additionally includ-ing the change in the energy cost ofwalking as a predictor. The changein gait efficiency partially explainedthe intervention-related changes insome activity and participation out-comes, based on the reduction in thebetween-intervention difference esti-mate (Tab. 2, Fig. 2). The reductionin the difference estimate due tothe change in gait efficiency repre-sented a small meaningful change80

for the activity outcome of gaitspeed. The adjusted mean differenceestimate increased for the Late-LifeFDI disability limitation and instru-mental role outcomes, an indicationof no mediating effect of the changein gait efficiency on the participa-tion outcomes. The impact of thechange in the energy cost of walk-ing on the between-group differencein mean changes in activity and par-ticipation outcomes did not persistwhen additional methods (Sobel testand bootstrap confidence intervals)were used to test the significance ofthe mediating or indirect effects78,79

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Improving Gait Efficiency in Older Adults With Mobility Limitations

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DiscussionThe TO program led to greater gainsin some activity and participationoutcomes than the IO program.These greater gains appeared to bepartially mediated by the improve-ment in gait efficiency; however,these indirect effects could not besubstantiated by the formal statisticaltests of mediation.

Both task-oriented and impairment-oriented interventions improved gaitspeed. The gait speed improvementwas equal to or greater than thatobserved in previous exercise inter-vention trials for older adults withwalking problems.11,13,16,17,19–21,23

Only the task-oriented interventionimproved gait and improved someactivity and participation outcomesfor the older adults studied.

After the TO program, activityimproved in terms of daily physicalfunction, specifically, basic activitiesof daily living involving the lowerextremities, and total physical func-tion and participation improved mar-ginally. The impact of the motorsequence learning exercise on basiclower-extremity functioning, with amarginal impact on total physicalfunction and disability, may be sec-ondary to the focus of the interven-tion on “fixing” gait. The motorsequence learning intervention wastargeted at correcting deficits in themuscle patterns of stepping andintegrating posture with the phasesof gait through task-oriented, pro-gressive stepping and walking tasksand treadmill-paced practice. Manyof the items on the Late-Life FDIbasic lower-extremity functioningsubscale represent stepping activi-ties or short-distance, indoor walk-ing,7 which most likely require pathadjustments to walk around objectssuch as chairs and tables and turningto enter or exit a room. Similarly,the specificity of the exercise mayexplain the better activity and par-ticipation outcomes after the TO

program than after the IO program.The diagonal stepping and curved-path walking tasks emphasized inthe TO program are similar tothe steps, curbs, and indoor walk-ing paths represented by the Late-Life FDI basic lower-extremityfunctioning items. Although the IOintervention involved standing bal-ance activities and lower-extremitymuscle strengthening and flexi-bility exercises specific for musclegroups necessary for stepping uponto curbs, rising from chairs, bal-ancing while reaching, and provid-ing stability while turning or

changing directions, this interven-tion was not goal oriented for walk-ing and did not change basic lower-extremity functioning.

The motor sequence learning exer-cise also differed from the impairment-based exercise in that the steppingand walking patterns in the TO pro-gram were designed to facilitate theimplicit motor learning of move-ment patterns.37,83,84 The exerciseactivities in the TO program wereall task oriented (eg, step acrossand walk around cones [to forman oval]), but there was no mention

Figure 1.Between-group adjusted mean differences in activity and participation outcomes rela-tive to small and moderate effect sizes for the variables. The radar graph provides anoverall view of the between-group differences in the activity and participation variables.The adjusted between-group differences for each variable are plotted on separate spikesof the radar. The thick solid line connects the adjusted between-group differences forthe variables. The estimated meaningful differences for each variable are represented assmall meaningful changes (area enclosed by the dashed line) and moderate meaningfulchanges (area enclosed by the dotted line). The meaningful differences for each variablewere estimated by calculating a small effect as 0.2 � baseline standard deviation of thesample mean of the variable and a moderate effect as 0.5 � baseline standard deviationof the sample mean of the variable. The values for gait speed and activity were adjustedby a multiple of 10 so that the same scale could be used in the axes for all of thevariables. For gait speed, the actual value was the value shown times 10�2; for activity,the actual value was the value shown times 10. Asterisks indicate participation variables.cpm�counts per minute, GES�Gait Efficacy Scale, Instrumental�instrumental role,Late-Life FDI�Late-Life Function and Disability Instrument, LE�lower extremity,Limitations�disability limitations.

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Figure 2.Change in the estimates of the between-group adjusted mean differences explained by a change in gait efficiency. The black barsrepresent the between-group mean differences in the change in each variable from baseline to follow-up, adjusted for the covariatesage, sex, and baseline value for the outcome variable. The gray bars represent the between-group mean differences in each variablefrom baseline to follow-up, adjusted for the covariates age, sex, baseline value for the outcome variable, baseline value of the energycost of walking, and change in the energy cost of walking. A comparison of the gray bars with the black bars illustrates the mediatingeffects of the change in the energy cost of walking on changes in activity and participation outcomes. The values for gait speed andactivity were adjusted by a multiple of 10 so that the same scale could be used in the axes for all of the variables. For gait speed, theactual value was the value shown � 10�2; for activity, the actual value was the value shown � 10. Asterisks indicate participationvariables. cpm�counts per minute, GES�Gait Efficacy Scale, Late-Life FDI�Late-Life Function and Disability Instrument, LE�lowerextremity.

Table 2.Estimates of Adjusted Mean Between-Group Differences and Mediating Effects of a Change in Gait Efficiency on DifferenceEstimates for Activity and Participationa

MeasureEstimate

(SE)bP for

EstimateChange inEstimatec

Sobel Method Changein Estimate (95% CI)

Sobel MethodP for Change

Bootstrap MethodChange in Estimate

(95% CI)

Activity

Gait speed, m/s 0.06 (0.04) .16 �0.055 �0.030 (�0.069 to 0.008) .1255 �0.031 (�0.078 to 0.000)

Activity, cpm 16.9 (9.5) .08 �2.6 �0.78 (�6.27 to 4.70) .7794 �0.74 (�6.91 to 4.71)

GES score, 10–100 9.2 (3.7) .02 �1.3 �0.81 (�3.18 to 1.55) .5001 �0.82 (�3.47 to 1.05)

Late-Life FDI total, 0–100 2.6 (1.2) .03 �0.70 �0.27 (�1.04 to 0.50) .4904 �0.31 (�1.46 to 0.42)

Late-Life FDI basic LE, 0–100 4.6 (1.7) �.01 �0.56 �0.44 (�1.58 to 0.70) .4475 �0.49 (�2.14 to 0.59)

Late-Life advanced LE, 0–100 3.9 (1.7) .03 �0.11 �0.22 (�1.30 to 0.85) .6826 �0.25 (�1.62 to 0.80)

Participation

Late-Life FDI limitations, 0–100 5.6 (3.2) .09 1.5 0.15 (�1.84 to 2.15) .8804 0.13 (�1.32 to 1.77)

Late-Life FDI instrumental role,0–100

6.4 (3.8) .10 2.5 0.42 (�1.94 to 2.77) .7281 0.36 (�1.38 to 2.32)

a CI�confidence interval, cpm�counts per minute, GES�Gait Efficacy Scale, Late-Life FDI�Late-Life Function and Disability Instrument, Total�overallfunctioning, Basic LE�basic lower-extremity functioning, Advanced LE�advanced lower-extremity functioning.b Mean difference estimate for task-oriented, motor sequence learning exercise versus impairment-oriented, multicomponent exercise, adjusted for age, sex,baseline value for the outcome variable, and baseline value of the energy cost of walking.c Change in the mean difference estimate, adjusted for age, sex, baseline value for the outcome variable, baseline value of the energy cost of walking, andmean change in the energy cost of walking.

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of which muscles to contract orwhere to place steps or shift bodyweight. The impairment-orientedexercise facilitated improvementsin body systems that contribute tothe ability to walk, but the IO pro-gram was not task oriented andwas not designed to facilitate theimplicit learning of how to integrateincreased physiological capacitieswith walking. Van Peppen et al42

reported a similar impact of task-oriented but not impairment-targeted physical therapy exerciseinterventions on functional out-comes after stroke. Althoughimpairment-targeted exercise inter-ventions improved range of motion,strength, and exercise tolerance,only task-oriented exercise interven-tions improved function in tasks rep-resenting activities of daily living.42

Task-oriented, gait-related exercisewas described as being effective andefficient in improving functional out-comes after stroke in a summary ofseveral systematic reviews of inter-ventions to improve mobility-relatedactivities.72

The change in gait efficiency afterthe intervention did not mediate thechanges in activity and participationoutcomes. The lack of mediation ofthe outcomes by the change in gaitefficiency may be related in part tohow gait efficiency was measured.Gait efficiency was derived fromthe energy expenditure for walkingmeasured during treadmill walking.Treadmill walking may not be repre-sentative of walking-based activitiesand physical function in daily life.The treadmill path is straight, andthe continuously moving belt drivesthe stepping pattern of walking.Physical activities typical of daily liv-ing (eg, cleaning house, taking careof oneself, shopping, and visitingothers) in the home or communitycan involve irregular paths, repeatedchanges in acceleration, starts andstops, and elevation. If the energycost of walking were measured dur-

ing the performance of physicalactivities typical of daily living, animprovement in gait efficiency mightbe found to be a better mediator ofactivity and participation outcomes.Unfortunately, measuring the energycost of walking during the perfor-mance of physical activities typicalof daily living is difficult. The rateof oxygen consumption must berecorded at the physiological steadystate to be an accurate indicatorof the energy expenditure for theactivity. Achieving the physiologicalsteady state usually requires 1 to 3minutes of continuous activity.38,63,65

The performance of many physicalactivities typical of daily living doesnot occur continuously for 1 to 3minutes. Rather, the performance ofthe activities usually is intermittentor varies in level of intensity overtime.

The present study had several limita-tions. The study was powered todetect differences in physiologicaland performance measures of gaitbut was not powered to detect dif-ferences in self-reported, more dis-tal outcomes or to test mediatingeffects.

The differences in the estimatedmediating effects across the methodsalso warrant comment. The similar-ity of the results obtained with the2 formal mediation methods (Sobelmethod and bootstrap method) isreassuring for the validity of theSobel method because it relies oncertain assumptions, whereas thebootstrap method does not. The dif-ference between mediating effectresults obtained with formal meth-ods and a simple change in the effectof an intervention is likely due to thedifferent estimation algorithms (opti-mizing different objective functions)used to obtain the estimates, withformal mediation analyses resultingin more conservative estimates. Con-sistent results across all 3 methodswould have strengthened our results

and allowed us to make a more force-ful conclusion regarding mediatingeffects.

The older adults were randomized tothe intervention group, but differ-ences in baseline measures44 had tobe accounted for in the analyses.Although the Late-Life FDI function-ing and disability component scaleswere developed to measure changesin activity and participation, someof the items from each scale havebeen found to be more representa-tive of a different domain of activityand participation than the originaldomain to which the item scorescontribute.85

ConclusionAn exercise intervention thatimproved gait also improved someactivity and participation outcomes.A task-oriented, motor sequencelearning intervention targeted to“fix” gait may have a greater poten-tial to affect activity and participa-tion. The mechanism of the effect ofsuch an intervention on disability inolder adults with mobility limitationsis not clear.

Dr VanSwearingen, Dr Brach, and DrStudenski provided concept/idea/researchdesign. Dr VanSwearingen, Dr Perera, DrBrach, and Mr Wert provided writing. DrVanSwearingen, Mr Wert, and Dr Studenskiprovided data collection. Dr VanSwearingenand Dr Perera provided data analysis. DrVanSwearingen provided project manage-ment and institutional liaisons. Dr VanSwear-ingen, Dr Brach, and Dr Studenski providedfund procurement. All authors provided con-sultation (including review of manuscriptbefore submission).

This study was approved by the University ofPittsburgh Institutional Review Board.

The data from this study were presented atthe Annual Conference of the AmericanPhysical Therapy Association; June 8–11,2011; Baltimore, Maryland.

This work was supported by the PittsburghOlder Americans Independence Center (NIAP30 AG024827) and a Beeson Career Devel-opment Award (NIA K23 AG026766).

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Trial registration: ClinicalTrials.gov Identifier:NCT00177359.

DOI: 10.2522/ptj.20100391

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Improving Gait Efficiency in Older Adults With Mobility Limitations

December 2011 Volume 91 Number 12 Physical Therapy f 1751 by guest on June 9, 2014http://ptjournal.apta.org/Downloaded from

doi: 10.2522/ptj.20100391Originally published online October 14, 2011

2011; 91:1740-1751.PHYS THER. Brach, David Wert and Stephanie A. StudenskiJessie M. VanSwearingen, Subashan Perera, Jennifer S.Mobility Limitations: A Randomized Controlled TrialActivity and Participation in Older Adults With Impact of Exercise to Improve Gait Efficiency on

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