The effects of changes in the sagittal plane alignment of running-specific transtibial prostheses on ground reaction forces

Abstract

[Purpose] To verify the effects of sagittal plane alignment changes in running-specific transtibial prostheses on ground reaction forces (GRFs). [Subjects and Methods] Eight transtibial amputees who used running-specific prostheses during sprinting participated. The sprint movements were recorded using a Vicon-MX system and GRF measuring devices. The experiment levels were set as regularly recommended alignment (REG; the normal alignment for the subjects) and dorsiflexion or plantar flexion from the REG. [Results] The subjects were classified into fast (100-m personal best < 12.50 s) and slow (100-m personal best ≥ 12.50 s) groups. In both groups, there were no significant differences in the center of gravity speed; further, the difference in the stance time was significant in the slow group but not in the fast group. Significant differences were observed in the step length for the fast group, whereas the stance time and step rate significantly differed in the slow group. The GRF impulse showed significant differences in the vertical and braking directions in both groups. [Conclusion] The GRFs are affected by sagittal plane alignment changes in running-specific prostheses. Moreover, our results suggest that the change in GRFs along with the altered sagittal plane alignment influenced the step length and step rate.

Full text

The eects of changes in the sagial plane
alignment of running-specic transtibial prostheses
on ground reaction forces
Shuichi Tominaga, PO
1, 2)*
, KeiSyoKu SaKuraba, MD, PhD
1)
, Fumio uSui, PO
3)
1)
Department of Sports Medicine, Graduate School of Medicine, Juntendo University: 2-1-1 Hongo,
Bunkyo-ku, Tokyo 113-8421, Japan
2)
Faculty of Health Sciences, Department of Rehabilitation, University of Human Arts and Sciences,
Japan
3)
Prosthetics and Orthotics Support Center, Tetsudo Kosaikai Foundation, Japan
Abstract. [Purpose]Toverifytheeffectsofsagittalplanealignmentchangesinrunning-specictranstibialpros-
thesesongroundreactionforces(GRFs).[SubjectsandMethods]Eighttranstibialamputeeswhousedrunning-spe-
cicprosthesesduringsprintingparticipated.ThesprintmovementswererecordedusingaVicon-MXsystemand
GRFmeasuringdevices.Theexperimentlevelsweresetasregularlyrecommendedalignment(REG;thenormal
alignmentforthesubjects)anddorsiexionorplantarexionfromtheREG.[Results]Thesubjectswereclassied
intofast(100-mpersonalbest<12.50s)andslow(100-mpersonalbest≥12.50s)groups.Inbothgroups,therewere
nosignicantdifferencesinthecenterofgravityspeed;further,thedifferenceinthestancetimewassignicantin
theslowgroupbutnotinthefastgroup.Signicantdifferenceswereobservedinthesteplengthforthefastgroup,
whereasthestancetimeandstepratesignicantlydifferedintheslowgroup.TheGRFimpulseshowedsignicant
differencesintheverticalandbrakingdirectionsinbothgroups.[Conclusion]TheGRFsareaffectedbysagittal
planealignmentchangesinrunning-specicprostheses.Moreover,ourresultssuggestthatthechangeinGRFs
alongwiththealteredsagittalplanealignmentinuencedthesteplengthandsteprate.
Key words:Transtibialamputee,running-specicprosthesis,groundreactionforce
(This article was submitted Dec. 1, 2014, and was accepted Jan. 11, 2015)
INTRODUCTION
Studies on able-bodied runners have been conducted
fromvariousviewpointsincludingkinematicsofthelower
limbjointanglesandchangesinangularspeed
1, 2)
,kinetics
of ground reaction forces (GRFs) and joint torque
3)
, and
physiological aspects such as the muscular activities of
lowerlimbs
4)
.Recently,therehavebeenanincreasingnum-
berofstudiesonamputeesprinters.Prince
5)
examined the
characteristicsof9transtibialamputees,includingthepeak
values of the GRF and impulse. According to their study, the
impulseexpressedthedifferencebetweenthesoundfootand
theprostheticfootbetterthanthepeakvalue,andtheasym-
metry varied depending on the properties of the foot section
oftheprosthesis.Grabowski
6)
examinedbilateralamputee
sprinters and reported that the GRFs needed to maintain
maximum speed when using running-specic transtibial
prosthesesweresignicantlysmallerthanthoseneededby
able-bodied runners. Brüggemann et al.
7)
and Weyand et
al.
8)
reported that improving the GRF value of prostheses
contributedtoimprovingtheperformanceofamputeesprint-
ers.Inaddition,Grabowski
6)
reportedarelationshipbetween
impulseandsteprate;theyfoundthatrunningatahighstep
ratecouldbeachievedbyreducingtheimpulseinthevertical
directionwhilesprintingatone’smaximumspeed.However,
todate,therehavebeennoreportscomparingGRF,steprate,
andsteplengthduringrunningbetweenamputeesprintersat
lowandhighcompetitionlevels,andwespeculatethatthe
knowledge necessary for improving running performance
can be obtained by elucidating the characteristics of high
competition level-amputee sprinters.
The recent improvements in the competitiveness of am-
puteesprintersareremarkable,withtheworldrecords(asof
April18,2014)fortrackandeldsports(T43class)being
10.57sfor100m,20.66sfor200m,and45.39sfor400m.
Amputee sprinters exceed the range of disabled athletes
andarecatchingupwithgeneralathletes.Itisobviousthat
extensiveadjustmentsintherunning-specicprostheseswill
needtooccurinordertokeepupwiththehighcompetitive-
ness of amputee sprinters. Accordingly, one report indicated
the possibility that the maximum sprint speed can be im-
provedconsiderablydependingonthelengthandproperties
of the prosthesis
9)
. One such property is the alignment of the
running-specicprosthesis;therefore,alteringthealignment
J. Phys. Ther. Sci.
27: 1347–1351, 2015
*Correspondingauthor.ShuichiTominaga(E-mail:
shuichi_tominaga@human.ac.jp)
©2015TheSocietyofPhysicalTherapyScience.PublishedbyIPECInc.
Thisisanopen-accessarticledistributedunderthetermsoftheCre-
ativeCommonsAttributionNon-CommercialNoDerivatives(by-nc-
nd)License<http://creativecommons.org/licenses/by-nc-nd/3.0/>.
Original Article

J. Phys. Ther. Sci. Vol. 27, No. 5, 20151348
of running-specic prostheses may help improve running
performance through the modulation of GRF during running.
Accordingly,thepurposeof thisstudywastoelucidate
the effects of changes in the sagittal plane alignment of
running-specic prostheses on the GRF, step length, and
stepratein transtibialamputeesprinters.Wehypothesized
that changes in the sagittal plane alignment of the running-
specic transtibial prosthesis will lead to changes in the
GRF. Furthermore, we also hypothesized that the stance
time,steprate,andsteplengthwouldchangeuponaltering
the alignment.
SUBJECTS AND METHODS
Subjects
Eightunilateraltranstibialamputeesparticipatingintrack
andeldsportsusingspecialprostheticfeetforrunning(7
males, 1 female) were included in the study. None of the
testsubjectshadamputatedlegsduetoangiogenicdiseases
or had an abnormality in the stump skin.All participants
belongedtoclubteamsfortrackandeldsportsandwere
training regularly. Their 100-m personal best (PB) ranged
between 12.30 and 17.90s (mean ± standard deviation,
14.85±2.31s).Theanalysiswasconductedbydividingthe
testsubjectsintofast(100-mPB<12.50s)andslowgroups
(100-mPB≥12.50s)toreducetheinuenceof speed on
GRF, owing to the fact that the GRF, the main outcome
measureofthisstudy,inuencestherunningspeed.Thesub-
jectsweredividedinto2groupsaccordingtotheirrunning
performancetoreducetheinuenceofthespeedonGRF.In
addition,thecutoffof12.50swasbasedontheParalympics
participation“B”standardrecord.
Thephysicalcharacteristicsoftheparticipantsareshown
in Table 1. The running-specic prosthetic feet were the
Cheetah(Össur,Reykjavík,Iceland)in2subjects,Flex-Run
(Össur)in2subjects,andKATANA(IMASENEngineering
Corp.,Kakamihara,Japan)intheremaining4subjects.Fur-
thermore,participants4and8ranbyattachingtheFlex-Run
totheirdailyprosthesissockettoformatranstibialprosthesis
(Table1).Consentwasobtainedfromeachparticipantafter
explainingthepurposeofthestudyandtherisksthatmaybe
involved.ThisstudywasapprovedbytheResearchEthics
Committee,FacultyofHealthandSportsScience,Juntendo
University(JUSE25-20)andcompliedwiththeguidelines
setoutintheDeclarationofHelsinki(1983).
Methods
Theexperimentwasconductedonastraightindoor15-m
track after the subjects had warmed up sufciently. They
restedbrieybetweenthetrials,asneeded,inordertoelimi-
natetheeffectsoffatigue.Reectivemarkerswereattached
totheparticipantsonthetopofthehead,shoulders,elbows,
hands,hipjoints,heels,andtoes,aswellasontheinsideand
outsideoftheknees,feet,andmetacarpophalangealjoints.
Further, markers were placed on the prosthetic socket, at
apositioncorrespondingtotheunderlyingkneecenter,on
thecarbon-berfoot keel,eitheratthesameheightasthe
lateralmalleolusoftheintactlimbwhenstandingontip-toe
oronthetopsurfaceofthekeel,2cmproximaltothemost
distal point
10, 11)
. For the experiment, a 3-dimensional opti-
cal position measuring instrument (Vicon-MX series T10
camerasystem;Vicon Motion Systems, LosAngeles,CA,
USA)wasusedtorecordthesprintmovementswithinthe
analysisblockatasamplingfrequencyof250Hz.TheGRFs
duringthefootcontacttimewerealsomeasuredbyusing4
GRFmeasuringdevices(40cm×60cm,BP400600-2000;
Advanced Mechanical Technology, Inc., Watertown, MA,
USA) at a sampling frequency of 1,000Hz. The data for
body coordinates and GRF while sprinting were synchro-
nized within theViconsystem usingsynchronous signals.
Three experiment levels were set up by plantarexing or
dorsiexing the running-specic prosthetic feet: the regu-
larlyrecommendedalignment(REG),thenormalalignment
foratestsubject;alevelof4°dorsiexionfromtheREG
(DOR);andalevelof4°plantarexionfromtheREG(PLA)
(Fig. 1).Thesubjectsperformedapproximately10trialsfor
eachcondition.Datafromthetrialsinwhichtheprosthetic
Table 1.Characteristicsoftheparticipants
Gender
(M/F)
Age
(years)
Height
(m)
Total
mass
(kg)
Stump
length
(cm)
RSP
Mass
(kg)
RSP
(model)
100 m
PB
(sec)
Fast
M 48 1.67 81.9 12.5 1.7
Cheetah
12.30
M 43 1.62 65.0 15.2 1.517
Cheetah
12.36
M 27 1.70 60.0 14.5 1.664
KATANA
12.43
Slow
M 44 1.78 75.9 17.0 1.143
Flexrun
14.28
M 49 1.70 63.0 32.5 1.932
Cheetah
15.80
F 50 1.61 52.5 13.5 1.51
KATANA
16.51
M 38 1.72 92.0 17.4 1.795
KATANA
17.20
M 21 1.80 60.0 10.0 1.501
Flexrun
17.90
Average 40.0 1.70 68.8 16.6 1.595 14.85
SD 10.7 0.07 13.2 6.9 0.238 2.31
Maximum 50.0 1.80 92.0 32.5 1.932 17.90
Minimum 21.0 1.61 52.5 10.0 1.143 12.30
RSP:Running-specicprostheses
Fig. 1. The experimental levels
Three levels were set up by plantarexing and dorsiexing the
special foot section of the prosthesis for running: the regularly
recommendedalignment(REG),denedasthenormalalignment
foratestsubject;alevelof4°dorsiexionfromREG(DOR);and
alevelof4°plantarexionfromREG(PLA).

1349
footcameincontactwiththeGRFmeasuringdeviceswere
adoptedandanalyzed.Thenumberofanalyzedtrialsissum-
marizedinTable1.
Thecoordinatesforeachjointandthebody’s centerof
gravity(COG)werecalculatedbasedonthepositionsofthe
bodymarkersobtainedbytheViconsystem.Thecoordinate
data for 250-Hz were smoothed with a cutoff frequency
of8Hz
12)
usingaquaternarylow-passdigitallter
13)
. The
GRF data at 1,000Hz were subjected to residual analysis
and smoothed with a cutoff frequency of 30Hz using a
quaternarylow-passdigitallter
12)
.
Therunning speed was consideredtobethe maximum
speedfor the body’sCOG during the stancephaseonthe
prosthetic side. Based on the GRF measured, the time at
whichgroundcontactbeganwassetaszero,andthetime
atwhichitendedwassetasT
contact
.Thesteplengthwasde-
nedasthedistancefromthetiptoemarkeroftheprosthetic
foottotheheelmarkerofthesoundfoot.Thestepratewas
calculatedbasedonthetimeofinitialcontactofthesound
leg from the toe off of the prosthetic foot. The maximum val-
ueswerecalculatedforthehorizontalGRF(Fy)andvertical
GRF (Fz) during the foot contact time. Subsequently, the
formulasbelowwereusedtocalculatetheimpulseforthe
GRF,anditshorizontal(Impulse
y
) and vertical components
(Impulse
z
).
0
contact
T
yy
Impulse F dt=
∫
(1)
0
contact
z
T
z
Impulse F dt=
∫
(2)
The differences between the levels were examined by
one-wayanalysisofvariance(ANOVA).Ifthepvaluewas
consideredsignicantuponone-wayANOVA,theTukey’s
multiple comparison test was used to examine the differ-
encesintheaveragevalues.Inalltests,asignicancelevel
smallerthan5%(p<0.05)wasconsideredsignicant.The
statisticalcalculations were conductedusingthe JMPver-
sion10.0.2(SASInstituteInc.,Cary,NC,USA).
RESULTS
Tables1–3showtheanalyzedoutcomesforthefast(100-
m PB < 12.50s) and slow groups (100-m PB ≥ 12.50s).
Sampledataofthewaveformsandanalysisoftheinvesti-
gatedparametersareshowninFig.2.Nosignicantdiffer-
enceswereobservedineithergroupintermsofthe COG
speed.Ontheotherhand,signicantdifferenceswereob-
served in the step length for the fast group and for the stance
timeandsteprateintheslowgroup.Moreover,signicant
differenceswereobservedinsomeGRFparametersforthe
fastgroup,whileonlythepeakvaluesandaveragevaluesof
GRFsignicantly differedin the slowgroup.With regard
totheimpulse,signicantdifferenceswereobservedinthe
vertical direction for both groups; however,nosignicant
differenceswereseeninthefastgroupintermsofthedirec-
tionofpropulsionorstancetime,whereasthesesignicantly
differedintheslowgroup.
Table 2.TheeffectofalignmentchangesontheCOGvelocity,stancetime,steplength,andstep
rate(fastgroupvs.slowgroup)
COGvelocity(m/s) Stance time (s) Step length (m) Steprate(Hz)
Fast DOR (n=27) 6.06±0.17
0.14±0.01
1.69±0.10 3.47±0.24
PLA (n=22) 6.18±0.17
0.14±0.01
1.78±0.08* 3.41±0.22
REG(n=25) 6.07±0.22
0.14±0.01
1.75±0.07 3.40±0.25
Slow DOR (n=47) 5.46±0.61
0.17±0.01
1.47±0.16 3.52±0.33
PLA (n=43) 5.51±0.35
0.16±0.01*
1.46±0.17 3.69±0.27*
REG(n=49) 5.53±0.51
0.16±0.01
1.50±0.15 3.52±0.24*
*:p<0.05
Thenumberofsampleswasatotalofthetrialsthateachsubjectperformedforeachcondition.
Table 3.Theeffectofalignmentchangesonthegroundreactionforces(fastgroupvs.slowgroup)
Peak(N/BW) Impulse(Ns/BW)
Vertical Braking Propulsive Vertical Braking Propulsive
Fast
DOR (n=27) 2.846±0.290 −0.374±0.100 0.303±0.087 0.241±0.013 −0.011±0.005 0.015±0.005
PLA (n=22) 2.685±0.188 −0.319±0.062 0.312±0.086 0.222±0.017
*
−0.006±0.006 0.016±0.004
REG(n=25) 2.825±0.235 −0.370±0.132 0.317±0.082 0.242±0.024 −0.011±0.009
*
0.017±0.005
Slow
DOR (n=47) 2.529±0.246 −0.357±0.069 0.260±0.077 0.254±0.032 −0.013±0.007 0.016±0.005
PLA (n=43) 2.293±0.275
*
−0.302±0.070
*
0.268±0.064 0.230±0.027
*
−0.007±0.004
*
0.019±0.006
*
REG(n=49) 2.487±0.259 −0.355±0.055
*
0.272±0.083 0.246±0.033 −0.011±0.005
*
0.017±0.005
*:p<0.05
Thenumberofsampleswasatotalofthetrialsthateachsubjectperformedforeachcondition.

J. Phys. Ther. Sci. Vol. 27, No. 5, 20151350
DISCUSSION
Thepurposeofthisstudywastoelucidatetheeffectsof
changesinthesagittalplanealignmentofrunning-specic
prostheses on GRF in transtibial amputee sprinters. Eight
participantswereinstructedtosprintwith3differentalign-
ments.Theanalysiswasconductedbydividingthetestsub-
jectsintofast(100-mPB<12.50s)andslowgroups(100-m
PB≥12.50s);whilesignicantdifferenceswereobserved
only in some parameters in the fast group, differences in
numerousparameterswereseenintheslowgroup.Impor-
tantly,signicantdifferenceswereobservedwithregardto
theimpulseintheverticalandhorizontaldirectionsinboth
groups (Table 3). These ndings indicated that the GRFs
are affected by changes in the sagittalplane alignmentof
running-specictranstibialprostheses,thuspartlysupport-
ing our hypothesis in terms of the GRF.
Generally,therunningspeedofan able-bodied sprinter
isdeterminedbytheproductofthesteprate(thenumberof
stepsperunit)andsteplength;therefore,eitherorboththe
steprateorsteplengthmustbeincreasedinordertoincrease
therunningspeed.Inpreviousstudiesonable-bodiedsprint-
ersrunningbyvaryingconditionofrunningspeeds
13–18)
, it
wasfoundthattherunningspeedincreasedasthesteplength
increasedwhentherunningspeedwaslow,andtherunning
speedincreasedasthesteprateincreasedwhentherunning
speed was high. Since the impulse is the value obtained
byintegratingforcewithtime,theimpulseandsteplength
increaseas a result ofanincrease in thestancetime with
the ground, even if the force applied against the ground is
minimal.Meanwhile,thestancetimeandswingtimeneed
tobereducedinordertoincreasethesteprate,becausethe
stepratesizeisdeterminedbythesumofthestancetimeand
swingtime.Thus,whileanincreaseinstancetimeleadsto
an increase in step length, it has a negative effect on the step
rate.Inotherwords,thereisanegativecorrelationbetween
steprateandsteplength.Itisobviousthatahumanshould
sprintwiththeoptimalcombinationofahighsteprateand
large step length in order to achieve a high running speed
19)
;
therefore, it is assumed that changing either the step rate or
steplength(orboth)contributestoanincreaseinrunning
speed.
Sincechangeswereobservedintheimpulseinboththe
verticalandhorizontaldirectionsfortheGRFinbothgroups
in this study, this indicates that the changes in alignment
affectedthestep length.Hunter et al.
20)
indicated that the
horizontal impulse affects the horizontal moving distance
fortheCOGduringtheswingphase,whichcomprisesstep
length.Indeed, the steplength increased inthe fast group
duringthePLAconditioninthisstudy,andwespeculatethat
thiswascausedbythereductionofthebrakingforceduring
the PLA condition.
Grabowski
6)
 demonstrated the relationship between
impulse and step rate, and reported that running at a high
stepratecouldbeachievedbyreducingtheimpulseinthe
verticaldirectionduringhigh-speedsprinting.Inthepresent
study,anincreaseinthestepratewasobservedintheslow
group during the PLA condition, indicating that changes
in alignment affect the step rate. Moreover, a decrease of
the impulse in the vertical direction was observed during
thePLAcondition,andthisresultcorrespondswiththatof
Grabowski’s study. Altering alignment might reduce the
vertical impulse during stance, and we speculate that this
iscausedbyreductionsofthestancetimeduringthePLA
condition. As a result, a higher step rate might increase the
topspeedbyreducingtherequiredverticalimpulseduring
stance, thereby supporting our hypothesis in terms of the
step length and step rate.
However,theresultsofthepresentstudyintermsofthe
COGspeedwerenotstatisticallysignicant(Table2),likely
owingtothefactthattheGRFmeasuringdeviceswerelo-
cated at a 10-m distance from the starting point. Therefore,
it is thought that a difference did not emerge due to the
speed of running, and one of the limitations of this study is
thatthemeasuredrunningdistancewasonly15 m, which
is relatively short and corresponds only to the acceleration
aspectofa100-msprint.Toaddressthisissue,weplanto
conductafuturestudywithalongerrunningdistanceandto
examinethekinematicsandkineticsofalignmentchangesin
each aspect of a 100-m sprint.
Inconclusion,theGRFisaffectedbychangesinthesag-
ittalplanealignmentinrunning-specicprostheses.Atthe
sametime,anincreaseinsteplengthalongwithreductions
ofthebrakingimpulsewereobservedinthefastgroupwith
ahighlevelpersonal-recordinthe100-msprint.Intheslow
group,anincreaseinthestepratewasobservedalongwith
reductionsofthebrakingimpulseandstancetime.
REFERENCES
1) DillmanCJ:Kinematicanalysesofrunning.ExercSportSciRev,1975,3:
193–218.[Medline] [CrossRef ]
2) TsujiK,SodaN,OkadaN,etal.:Acomparisonofthelowerlimbmuscles
activities betweenwalking andjogging performedatthe same speed. J
PhysTherSci,2012,24:23–26.[CrossRef]
3) MunroCF,MillerDI,FuglevandAJ:Groundreactionforcesinrunning:a
reexamination.JBiomech,1987,20:147–155.[Medline] [CrossRef ]
4) JacobsR,vanIngenSchenauGJ:Intermuscularcoordinationinasprint
push-off.JBiomech,1992,25:953–965.[Medline] [CrossRef ]
Fig. 2. Analysis of parameters
A indicates the maximum value of the ground reaction force in the
verticaldirection.Bindicatestheimpulseforthegroundreaction
forceintheverticaldirection.Cindicatesthemaximumvalueof
thegroundreactionforceinthebrakingdirection.Dindicatesthe
impulseforthegroundreactionforceinthebrakingdirection.E
indicates the maximum value of the ground reaction force in the
direction of advancement. F indicates the impulse for the ground
reaction force in the direction of advancement.

1351
5) PrinceF,AllardP,TherrienRG,etal.:Runninggaitimpulseasymmetries
inbelow-kneeamputees.ProsthetOrthotInt,1992,16:19–24.[Medline]
6) Grabowski AM, Herr HM: Leg exoskeleton reduces the metabolic cost
ofhuman hopping.J ApplPhysiol1985,2009,107:670–678.[Medline]
[CrossRef]
7) BrüggemannGP,ArampatzisA,EmrichF,etal.:Biomechanicsofdouble
transtibialamputeesprintingusingdedicatedsprintingprostheses.Sports
Technol,2009,1:220–227.[CrossRef]
8) WeyandPG,BundleMW,McGowanCP,etal.:Thefastestrunneronarti-
ciallegs:differentlimbs,similarfunction?JApplPhysiol1985,2009,107:
903–911.[Medline] [CrossRef]
9) WeyandPG,SandellRF,PrimeDN,etal.:Thebiologicallimitstorunning
speedare imposedfromthe groundup.JAppl Physiol1985,2010,108:
950–961.[Medline] [CrossRef]
10) BuckleyJG:Biomechanicaladaptationsoftranstibialamputeesprintingin
athletesusingdedicatedprostheses.ClinBiomech(Bristol,Avon),2000,
15:352–358.[Medline] [CrossRef]
11) Hosoda M, Yoshimura O,Takayanagi K, et al.:Human gaitanalysisas
viewedfromA/KandB/Kforceplate/stickgures.JPhysTherSci,1999,
11:79–85.[CrossRef]
12) Arampatzis A, Brüggemann GP, Metzler V: The effect of speed on leg
stiffnessandjointkineticsinhumanrunning.JBiomech,1999,32:1349–
1353.[Medline] [CrossRef]
13) WinterDA:Biomechanicsandmotorcontrolofhumanmovement.Hobo-
ken:Wiley,2009,p370.
14) HayJG:Thebiomechanicsofsportstechniques,4thed.NewJersey:Pren-
tice-Hall,1993,pp396–412.
15) HayJG:Cyclerate,length,andspeedofprogressioninhumanlocomotion.
JApplBiomech,2002,18:257–270.
16) MeroA,KomiPV,GregorRJ:Biomechanicsofsprintrunning.Areview.
SportsMed,1992,13:376–392.[Medline] [CrossRef]
17) MeroA,LuhtanenP,ViitasaloJT,etal.:Relationshipbetweenthemaxi-
malrunningspeed,musclebercharacteristics,forceproductionandforce
relaxationofsprinters.ScandinavianJournalofSportsSciences,1981,3:
16–22.
18) YanaiT,HayJG:Combinationsofcyclerateandlengthforminimizingthe
musclepowerrequirementinhumanrunning.JournalofAppliedNiome-
chanics,2004,20:51–70.
19) KunzH,KaufmannDA:Biomechanicalanalysisofsprinting:decathletes
versuschampions.BrJSportsMed,1981,15:177–181.[Medline] [Cross-
Ref]
20) HunterJP,MarshallRN,McNairPJ:Interactionofsteplengthandsteprate
duringsprintrunning.MedSciSportsExerc,2004,36:261–271.[Medline]
[CrossRef]