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Recovery of gait after quadriceps muscle fatigue.

van Dieen, J.H.; Barbieri, F.A.; Beretta, S.S.; Pereira, V.A.

published in

Gait and Posture

2016

DOI (link to publisher)

10.1016/j.gaitpost.2015.10.015

Link to publication in VU Research Portal

citation for published version (APA)

van Dieen, J. H., Barbieri, F. A., Beretta, S. S., & Pereira, V. A. (2016). Recovery of gait after quadriceps muscle

fatigue. Gait and Posture, 43, 270-274. https://doi.org/10.1016/j.gaitpost.2015.10.015

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Recovery

of

gait

after

quadriceps

muscle

fatigue

Fabio

Augusto

Barbieri

*

,

Stephannie

Spiandor

Beretta

,

Vinicius

A.I.

Pereira

,

Lucas

Simieli

,

Diego

Orcioli-Silva

,

Paulo

Cezar

Rocha

dos

Santos

,

Jaap

H.

van

Diee¨n

,

Lilian

Teresa

Bucken

Gobbi

a_{UnivEstadualPaulista,PostureandGaitStudiesLaboratory,RioClaro,Brazil} b

UnivEstadualPaulista,LaboratoryofInformation,Vision,andAction,Bauru,Brazil

c

MOVEResearchInstituteAmsterdam,FacultyofHumanMovementSciences,VUUniversityAmsterdam,Amsterdam,TheNetherlands

1. Introduction

Musclefatiguehasbeendefinedasalossofcontractilecapacity

ofthemuscle asa consequenceof muscleactivity,reflected in

failure to maintain a required or expected force, in failure to

continue working at a given exerciseintensity, or in a loss of

performanceduringrepeatedorcontinuousactivation[1]Muscle

fatigue negatively affects aspects related to balance, such as

muscle contractile capacity, coordination and proprioception

[2,3]. Consequently, quadriceps muscle fatigue affects gait of

youngadultsirrespectiveoftheirphysicalactivitylevel[4]and

typeofgait,suchasobstaclecrossingandsteppingdownastep

[4–7]. It coincides with adjustments in the spatio-temporal

[3,4,6,8,9],kinetic[4,7]andmuscleactivity[5,8]parametersof

gait.Youngadultswereshowntoreduceactivityofthequadriceps

muscleduringgaitafterexhaustiveexercise[5,8,10],whichmay

impair weight acceptance [4] since the quadriceps muscle

dissipates most of the energy at contact of the foot with the

ground [7,11]. In addition, muscle fatigue coincides with

compensatorygaitadjustmentsthatenhancegaitstability,such

asanincreasedstepwidthanddecreasedstepduration[4,6].

After prolonged exercise and especially after eccentric

con-tractionsfatigueandpotentiallymuscledamagemayhave

long-lastingeffects[12,13].Consideringthenegativeeffectsofmuscle

fatigueon gait, it is importanttoknowtherecoveryof

spatio-temporal, kinetics and electromyographic parameters and to

determinehow muchtimeis neededforfullrecovery.Previous

studies indicated negative effects of fatigue after exhaustive

exercise on the force generating capacity of muscle [14] and

balance[15,16]arenegativelyaffectedbymusclefatigueandneed

10–20mintorecoverafterexhaustivemusclefatigue.However,

the time needed for recovery of gait parameters after muscle

fatiguehastoourknowledgenotbeenstudied.Theperiodofrest

ARTICLE INFO Articlehistory:

Received19March2015

Receivedinrevisedform5October2015 Accepted7October2015 Keywords: Walking Musclefatigue Recoverytime Humanmovement ABSTRACT

Theaimofthisstudywastoinvestigatetheeffectofrecoverytimeafterquadricepsmusclefatigueon gaitinyoungadults.Fortyyoungadults(20–40yearsold)performedthree8-mgaittrialsatpreferred velocitybeforeandaftermusclefatigue,andafter5,10and20minofpassiverest.Inaddition,ateach timepoint,twomaximalisometricvoluntarycontractionswerepreformed.Musclefatiguewasinduced by repeated sit-to-stand transfers until task failure. Spatio-temporal, kinetic and muscle activity parameters,measuredinthecentralstrideofeachtrial,wereanalyzed.Datawerecomparedbetween beforeand afterthemusclefatigue protocoland afterthe recoveryperiods byone-wayrepeated measuresANOVA.Thevoluntaryforcewasdecreasedafterthefatigueprotocol(p<0.001)andafter5, 10and20minofrecoverycomparedtobeforethefatigueprotocol.Stepwidth(p<0.001)andRMSof bicepsfemoris(p<0.05)wereincreasedimmediatelyafterthefatigueprotocolandremainedincreased aftertherecoveryperiods.Inaddition,stridedurationwasdecreasedimmediatelyafterthefatigue protocolcomparedtobeforeandtoafter10and20minofrest(p<0.001).Theanterior–posterior propulsiveimpulsewasalsodecreasedafterthefatigueprotocol(p<0.001)andremainedlowafter5, 10and20minofrest.Weconcludethat20minisnotenoughtoseefullrecoveryofgaitafterexhaustive quadricepsmusclefatigue.

ß2015ElsevierB.V.Allrightsreserved.

* Corresponding author at: Universidade Estadual Paulista-UNESP-FC-Bauru, LaboratoryofInformation,Vision,andAction,DepartmentofPhysicalEducation, Av.Eng.LuizEdmundoCarrijoCoube,14-01,VargemLimpa,CEP:17.033-360, Bauru,SP,Brazil.Tel.:+551431036082x7612.

E-mailaddress:barbieri@fc.unesp.br(F.A.Barbieri).

ContentslistsavailableatScienceDirect

Gait

&

Posture

j our na l ho me pa g e : w ww . e l se v i e r . com / l oca t e / ga i t po st

http://dx.doi.org/10.1016/j.gaitpost.2015.10.015

required to recover gait parameters after muscle fatigue is

important,since around23–30%of fallsinoccupational setting

occurbecauseoffatigue[17].Fatigueintheseincidentsmayrefer

tootherprocessesinadditiontomusclefatigue,e.g.mentalfatigue.

Nevertheless,thisstudyfocusesoneffectsofmusclefatigueonly.

Theaimofthisstudywastoinvestigatetheeffectofdifferent

recoveryperiods (5, 10 and 20min) after fatiguing quadriceps

muscleexerciseon gaitin youngadults.We hypothesizedthat

muscle fatigue would negatively affect gait, which would be

reflectedincompensatory adjustmentstoimprovestability(i.e.

greater step width, decreased step duration). Moreover, we

hypothesized that gait changes would return towards baseline

valuesover20minofrest.

2. Method

Forty individuals aged between 20 and 40 years (age:

28.95.0 years; body weight: 78.614.0kg; body height:

1.760.06m; bodymass index:24.84.0kg/m2) participatedin

thisstudy.Theexclusioncriteriaofthestudywerefactorsthatcould

interfere with gait and other experimental procedures, such as

medication use,presence ofosteomyoarticular, neuromuscular or

cardio-respiratorydiseasesandbalanceandvisiondisorders.During

thesampleselectionprocess,26initiallyrecruitedindividualsdidnot

fitthecriteriaofthestudy.ThestudywasapprovedbythelocalEthics

Committee(#2055/2008).

Participants were instructed not to perform any strenuous

physical activity 48h before evaluation. The participants

per-formedawarm-upperiodof5min,withwalkingandstretching.

Afterthisperiod,theparticipantsperformedaseriesof

familiari-zation trials in the leg press instrument (for the maximum

voluntary isometric contraction protocol). Subsequently, the

participants(Fig.1):

1)filledoutaquestionnaireonmedicalhistory;

2)performedtheunobstructedgaittask;

3)performed the maximum voluntary isometric contraction

protocol;

4)performedthefatigueprotocol(sit-to-standtask);

5)repeatedthesecondandthirditemsafterthefatigueprotocol

and after5, 10and 20min ofrest. Theperiodsof restwere

passivewiththeparticipantsseated.

Theparticipantswalkedoveran8mpathwayatself-selected

speed.Eachparticipantperformedthreetrialsbeforethefatigue

protocol,afterthefatigueprotocolandafter5,10and20minof

rest.Weanalyzedthestrideinthemiddleofthepathwayonthe

forceplates(AccuGait,AdvancedMechanicalTechnologies,Boston,

MA)–50cm50cm–withrateof200samples/s.Kineticdatawere

filteredwitha4thorderfilterwithacutofffrequencyof16Hzand

themagnitudeofthegroundreactionforcewasnormalizedbybody

weight. Kinematic data were collected by a three-dimensional

optoelectronicsystem(OPTOTRAKCertus),positionedorthogonalto

the plane of progression tothe right of the walkway, usinga

samplerateof100samples/s.Fourinfraredemitterswereplaced

overthefollowinganatomicalpoints:lateralfaceofcalcaneusand

headofthefifthmetatarsusoftherightlimb,andmedialfaceof

calcaneusandheadofthefirstmetatarsusoftheleftlimb.These

data werefiltered witha 5thorder low-pass filterwith cutoff

frequencyof6Hz.Muscleactivitywasassessedusingdisposable

Ag/AgClsurface-electrodes(lead-offarea1.0cm2_{,inter-electrode}

distance 2.0cm) in combinationwith a signal amplifier (EMG

SystemdoBrasilLtda.).Afterabrasionandcleaningwithalcohol,

electrodes were attachedover the vastus lateralis and biceps

femoris in the right limb. ElectrodesandEMG data collection

followedtheSENIAMguidelines[18].EMGsignalswereamplified

(1000times,commonmoderejectionratio>120dB)andstored

on disc (12bits AD converted, resolution 5V, sample rate

1000samples/s). Off-line, EMG signals were band-pass filtered

between20and500Hzandrectifiedandlow-passfilteredat15Hz.

In addition, values were normalized to peak values of the

correspondingsignalsintheunfatiguedtrialsofeachparticipant.

Thedataacquisitionsystemswereelectronicallysynchronized.

Thestridelength,strideduration,stridevelocity,stepwidth,

double supporttime, brakingand propulsiveanterior–posterior

impulses and root mean square (over a stride—between two

consecutive left heel contacts) of vastus lateralis and biceps

femorisEMG wereanalyzedbeforeandafterthemusclefatigue

protocolandafter5,10and20minofpassiverestineachtrial.

Maximumvoluntaryisometriccontractionswereperformedin

acustom-builtlegpressdevice[4,6](Fig.2).Asourfatigueprotocol

causes fatiguein thewhole leg and does not isolate a specific

musclegroup,wechosethelegpressdevicetotestforchangesthe

maximalforceproducedwiththewholelegandnobyanisolated

musclegroup.A loadcellwithprecision of0.98Nwasused in

combinationwithasignalamplifier(EMGSystemdoBrasilLtd.).

Theparticipantswereseatedinabackwardinclinedchair,withthe

hipjointat908(1808isfullextension)andkneejointat1108(1808

is full extension). Total contraction duration was 5s. The

participantperformedthetestwithbothlegs,withtheinstruction

togenerateasmuchforceasfastaspossible.Twoattemptswere

made with 2min rest between attempts before the fatigue

protocol,afterthefatigueprotocolandafter5,10and20minof

rest.Themaximumforcegeneratingandmedianfrequencyofthe

powerspectrumvalueoftheEMGofthevastuslateralisandbiceps

femoris in each period were determined. Results of the two

attempts at each time point (before and after fatigue, after 5,

10and20minrest)wereaveraged.

Thefatigueprotocolwasarepeated sit-to-standtaskfroma

chairwitharmsacrossthechest[4,5].Thesubjectperformedthis

task until theparticipant wasunable tocontinue orwhen the

movementfrequencyfellbelowandremainedbelow0.5Hzafter

encouragement and theduration of theprotocolwasrecorded.

RatingofperceivedexertionwasmeasuredbytheBorgScale[19]

atthebeginningandtheendofthefatigueprotocol,andafter5,

10and20minofrest.

2.1. Dataanalysis

The spatiotemporal, kinetic and muscle activity parameters

werecalculatedinMatlab(Version2012—MathWorks,Inc.).The

dependentvariables ofinterestwerestatisticallyanalyzed with

SPSS18.0forWindows.The datawerenormallydistributed,as

verifiedbytheShapiro–Wilktest.Thedependentvariableswere

comparedusingrepeatedmeasuresANOVAs,withperiod(before

fatigueafterfatigue5minofrest10minofrest20minof

rest)asmainfactor(

a

tolocalizethedifferencesamongperiods(Bonferroniadjustments

to

a

3. Results

Themeandurationofthefatigueprotocolwas12.43min(SD:

10.63min). The meansand standarddeviationsof theratingof

perceived exertion,maximal isometricvoluntarycontraction,

spa-tiotemporal,kinetic andelectromyographyparametersbeforeand

aftermusclefatigueandafter5,10and20minofrestarepresentedin

Table1.ANOVAindicatedthattheindividualshadahigherratingof

perceivedexertionaftermusclefatigueandaftertheperiodsofrest

(5,10and20min)thanbeforemusclefatigue(p<0.001).Inaddition,

theratingofperceivedexertionimmediatelyaftermusclefatiguewas

higherthanafter5,10and20minofrest(p<0.001)(Table1).Also

force generatingcapacity wasdecreasedafter musclefatigue and

remaineddecreasedaftertherestperiods(p<0.001).Withregardto

the EMG signals, vastus lateralis showed a decreased median

frequencyafterthefatigueprotocol(p<0.01),whichwasrecovered

after20minofrest(nodifferencesbetweenbeforemusclefatigueand

20min of rest). Median frequency of biceps femoris showed a

reductiononlydirectlyafterthefatigueprotocolcomparedtobefore

(p<0.05),withoutdifferencesbetweenbeforethefatigueprotocol

andafter5,10and20minofrest.

Afterthe fatigueprotocol, participantsshowedincreasedstep

width (p<0.001) and muscle activity of the biceps femoris

(p<0.005)anddecreasedstrideduration(p<0.005)andpropulsive

anterior–posteriorimpulse(p<0.001)(Table1).Twentyminutesof

restwerenotenoughforrecoveryofthesegaitparameters.Step

width (p<0.001), activityof the biceps femoris (p<0.005) and

propulsiveanterior–posteriorimpulse(p<0.001)hadnotreturned

tobaselinevaluesafter20minofrest.Onlystridedurationshowed

clearrecovery(after5minofrest).Noneoftheotherparameters

analyzeddidshoweffectsofquadricepsmusclefatigueorrest.

4. Discussion

Theaimofthisstudywastoinvestigatetheeffectofdifferent

recovery periods (5, 10 and 20min) after quadriceps muscle

fatigueongaitinyoungadults.Asweexpected,musclefatigue

coincidedwithchangesinsomegaitparameters.Afterthefatigue

protocolstepwidthwasincreasedandstridedurationdecreased.

In addition, gait propulsion (decreased propulsive anterior–

posteriorimpulse)andbicepsfemorisactivity(increasedRMSof

theEMG)weremodified afterthefatigueprotocol.Nochanges

were observedin stride length, stride velocity, double support

Fig.2.Pictureoftheequipment(custom-builtlegpressdevice)formaximum voluntaryisometriccontractionsduringkneeextension.

Table1

Meansandstandarddeviationsoftheratingofperceivedexertion,maximalisometricvoluntarycontraction,spatiotemporal,kineticsandelectromyographyparameters beforeandaftermusclefatigueandafter5,10and20minofrest.

Beforefatigue Afterfatigue 5minofrest 10minofrest 20minofrest Rateofperceivedexertion

Borgscale 7.101.39* _18.93

1.28& _8.95

2.66 9.032.81 8.732.84 Maximalisometricvoluntarycontraction

Muscleforce(kg/f) 375.6513.23*

318.3425.90 330.7912.02 326.6214.76 333.2546.11 Medianfrequencyofvastuslateralis 128.8437.52+

111.7840.30 110.8138.46 112.5240.02 118.1839.71 Medianfrequencyofbicepsfemoris 103.0635.66#

87.9428.27 91.8919.92 93.6426.03 95.3325.13 Spatial-temporalparameters Stridelength(cm) 134.9610.85 135.3811.98 134.7210.93 135.4511.83 135.6011.74 Stepwidth(cm) 11.452.31* 12.762.66 12.182.38 12.332.72 12.822.78 Strideduration(s) 1.070.08# _1.05 0.08 1.060.07 1.070.09 1.070.09 Stridevelocity(cm/s) 127.3115.16 129.3915.29 128.1514.05 127.9918.63 127.8317.97 Doublesupportduration(%) 26.792.99 26.693.29 27.843.93 26.432.93 26.432.84 Kineticsparameters

Brakinganterior–posteriorimpulse(BW) 0.040.04 0.050.04 0.050.04 0.050.04 0.050.04 Propulsiveanterior–posteriorimpulse(BW) 0.040.02*

0.030.01 0.030.01 0.030.01 0.030.01 Muscleactivity RMSvastuslateralis(%) 23.065.09 24.8913.18 24.6114.01 23.3815.55 21.89.89 RMSbicepsfemoris(%) 21.135.63* _23.63 9.77 24.8912.25 24.1211.21 25.0111.67 *

Beforefatigueissignificantlydifferentfromotherperiods.

#

Beforefatigueissignificantlydifferentfromafterfatigue.

&

Afterfatigueissignificantlydifferentfromafter5,10and20minofrest.

+

time,brakingimpulseandquadricepsmuscleactivity.

Unexpect-edly,forcegeneratingcapacity,stepwidth,propulsiveanterior–

posteriorimpulseandmuscleactivityofthebicepsfemoriswere

notrecoveredafter20minof rest,incontrast withoursecond

hypothesis.Therefore,inthefollowingparagraphs,wewilldiscuss

theapparentabsenceofrecoveryoftheeffectsofmusclefatigueon

gaitparametersafter20minofrestandofferinterpretationsofthe

consequencesofsuchsustainedeffectsongait.

Several possibly interrelated considerations are to be made

regardingtheeffectsofourfatigueprotocol.First,ingeneral,gait

appearstobequiteresistantagainstfatigue[2,4–7].Thefactthat

gait is a very sub-maximal task may explain that some gait

parametersarenotaffectedbymusclefatigue.Specificallychanges

inquadricepsmuscleactivityduringgaitwere,however,expected.

Previously,adecreaseinthequadricepsactivityduringastepof

the ipsilateral leg was found with muscle fatigue during the

approachofastepdown[5].Inaddition,andinlinewithalthough

notnecessarily coincidingwithdecreasedquadricepsactivity,a

decrease in knee moments withfatigue was found during the

stancephaseofthelegfirstlandingonthelowerlevelinstepping

down[7].Alsointheapproachofastepdownandincontrastwith

thepresentfindings,bicepsfemorisactivitywasdecreasedwith

fatigue[5].Allinall,thesedatasuggestthatmusclefatigueeffects

cannot be generalized across these different gait types. The

increasedbicepsfemorisactivityanddecreasedforcegenerating

capacity of thequadriceps muscles foundin the presentstudy

might affectin particular stancephase kinematicsof theknee,

whereakneeextensormomentisusedtogeneratebodyweight

support.However,increasedankleandhipextensormoments,to

whichtheincreasedbicepsfemorisactivitymightcontribute,can

potentiallycompensateforthis[20].

Second,theMVCdatashowednoevidenceofneuromuscular

recovery. The duration of the fatigue protocol was substantial

(13min) and consequently the fatigue induced may have

required longer recovery times than shorter, high-intensity

protocolswould[21].Inducingfatigueunderdynamicconditions,

suchas thesit-to-stand task, does not involvemaximum force

generating duringtheexercise.Thelonger recoverytimes after

contractions of lower force are reportedly due to greater

involvementofperipheralfactorsthaninrecoveryaftermaximum

contractions,whereamorecentralcomponentissuggested[22].

Third,theprotocolmostlikelyaffectedthewholelegsandnot

just the quadriceps muscles. We fatigued participants by a

repetitivesit-to-standtask,whichwe choseforitsecological

validityandrepresentativenessofdailylifeconditions[2].This

fatigueprotocolrequireshighactivityofthequadricepsmuscles,

butinvolvessubstantialactivityandpossiblyfatigueofankle[5]

andhipextensors.Inaddition,themovementtomusclefatigue

may also contains eccentric components, which may lead to

microfailureandpain[12,13]andmightberelatedtothelackof

recovery. Therefore, the fatigue protocol may have affected

variousmusclesofthe(whole)legandnotanisolatedmuscle

group. Fatigue of multiple muscles simultaneously requires

more time for recovery than fatigue of an isolated muscle

[17,23].Moreover,theneuromuscular systemmay beableto

compensatethe deficits causedby muscle fatigueof a single

musclegroupbyadaptingactivityofantagonisticand

synergis-ticmuscles,whereasthismay benotpossibleif thesemuscle

groups, suchas we found in our study, are fatigued as well

[15,16].

Fourthandfinal,ithasbeensuggestedthatwithmoremuscles

fatiguedtherearechangesinthesupraspinalactivityregulating

theactivityofothermuscles,butalsoofmusclespindles[24].The

effects of fatigue-related changes on proprioception may have

contributedtodestabilizingthegait.Toourknowledge,nodataon

recoveryofproprioceptionafterfatigueisavailable.

Thegaitchangesobservedsuggestthatwalkingbecamemore

challenging after the muscle fatigue protocol, as reflected in

adjustments of gait parameters todeal withthe loss of motor

controlandtomaintainstabilityandsafety,corroboratingprevious

studies [3–9]. Specifically, participants increased the base of

support and decreased stride duration, probably to deal with

reducedbalancecontrolinthemedio-lateraldirection[4–7,25].In

addition,thereducedstepfrequencyimpliesmoretimetoplanand

executemovementsandmovementadjustments[26].Highforce

generatingcapacityoflegmusclesisimportanttoperformfastgait

adjustments,forexampletochangedirection,avoidanobject,or

recoverfromanimbalance.Absenceofrecoveryofforcegenerating

capacityafter20minofrestmaythusimplyincreasedriskoffalls

duetoperturbations.Wethereforesuggest,thattopreservegait

stabilityinthepresenceofmusclefatigue,subjectschooseamore

stablegaitpattern,toavoidhavingtomakefastgaitadjustments

andrecoveryresponses.However,thegaitchangesobservedmay

haveanegativeeffect,intermsofanincreasedenergycost[27,28],

whichmight preventrecoveryorcausefurtherfatigue

develop-ment during longer walking episodes. Previous studies have

suggestedthatenergycostdeterminestheselectionofacertain

gaitpattern[29],butourresultssuggestthatoptimizingenergy

costisnotthesoleobjectivewhenwalking.Thechoiceforacertain

gaitpatternmayberelatedtoimprovinggaitstabilityandreducing

fallriskratherthanminimizingenergycost[30].

Participantsincreasedbicepsfemorismuscleactivity,whichis

in contrast to our previous study [5]. In addition, propulsive

impulseswerefoundtobereducedafterthefatigueprotocol.The

increasedbicepsfemorisactivitymayhavebeenusedtopartially

compensatea propulsiondeficitcausedbymusclefatigueorto

compensate reduced weight support, through increased hip

extensionmoments[5,31]orthroughimprovedkneemechanical

efficiency[8,32].Reducedabilitytogeneratepropulsiveanterior–

posterior impulse diminishes the possibility to increase stride

length[30]and,consequently,toimproveorcorrectthebalancein

theforwarddirection,whichcouldincreasetheriskoffallingafter

perturbationsuchastripping.

Thepresentstudywaslimitedtolevelgaitinhealthyyoung

adults. Futurestudiesshouldinvestigate theeffects ofrecovery

after muscle fatigue in populations that are more affected by

fatigueorhaveanincreasedfallrisk,indifferenttypesofgait,such

assteppingdownastepandobstaclecrossing,aswellasrecovery

overalongertimeperiodsafterdifferentfatigueprotocols.Asecond

limitationwasaquitelargestandarddeviationoftheendurance

timeinfatigueprotocol.Althoughlevelsoffatiguemayhavediffered

between participants, maximumforce andmedian frequencyof

both muscles were decreased after the fatigue protocol in all

participants,whiletheratingofperceivedexertionwasincreased.

Wethereforebelievethatthishasnotstronglyaffectedourresults,

althoughitwillhavelimitedthestatisticalpower.Finally,wedidnot

analyzethejointkinematicsandkinetics(ankle,kneeandhipjoint

anglesandmoments).Inourexperimentalprocedures,weusedonly

fourinfraredemittersplacedoverthefeet(seeSection2),which

prevents the calculation of joint kinematics and kinetics. We

recommendforfuturestudiestheanalysisofthesevariablestohave

fullgaitanalysisandtoassessthefatigueeffectsonthedifferent

jointlevelsduringwalking.

In conclusion, our hypotheses were partially confirmed.

Changesinstepwidthandstridedurationcoincidedwithmuscle

fatigue and appear to reflect compensations for impaired gait

stability. In addition, propulsive impulses were reduced while

bicepsfemorisactivitywasincreased.Twentyminutesofrestwas

not enoughfor recoveryof thegaitparameters. These findings

indicatethatthemodulationsofgait,caused bymusclefatigue,

werequitepersistentandmaybeaneffectofthepersistentdecline

offorcegeneratingcapacityofmuscle.

Acknowledgement

The authors thank FAPESP (#2013/12774-0) for financial

support. References

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