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Acute effects of barefoot, minimal shoes and runningshoes on lower limb mechanics in rear and forefootstrike runnersMax Robert Paquette a , Songning Zhang a & Lucas Dahl Baumgartner aa Department of Kinesiology, Recreation and Sport Studies, University of Tennessee,Knoxville, TN, USA

To cite this article: Max Robert Paquette , Songning Zhang & Lucas Dahl Baumgartner (2013): Acute effects of barefoot,minimal shoes and running shoes on lower limb mechanics in rear and forefoot strike runners, Footwear Science, 5:1, 9-18

To link to this article: http://dx.doi.org/10.1080/19424280.2012.692724

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Footwear Science, 2013Vol. 5, No. 1, 9–18, http://dx.doi.org/10.1080/19424280.2012.692724

Acute effects of barefoot, minimal shoes and running shoes on lower limb mechanics inrear and forefoot strike runners

Max Robert Paquette*, Songning Zhang and Lucas Dahl Baumgartner

Department of Kinesiology, Recreation and Sport Studies, University of Tennessee, Knoxville, TN, USA

(Received 20 April 2012; final version received 8 May 2012)

Barefoot or minimal footwear running is currently a highly debated topic among runners and researchers. Severalfootwear companies have developed minimal running footwear to simulate barefoot running but few studies havecompared minimal footwear to barefoot and shoes during running. The primary goal of this study was tocompare acute changes in three-dimensional (3D) ground reaction forces (GRFs) and lower limb kinematics andkinetics of habitually shod rearfoot strike (RFS) and forefoot strike (FFS) runners between minimal shoes(MSH), barefoot and neutral cushion running shoes (SH). Lower extremity joint biomechanical variables of RFSand FFS runners were analysed using a 3D motion capture system and a force platform during overgroundrunning in barefoot, MSH and running shoes. Barefoot and MSH showed a more anterior foot strike than shoes.The loading rate of the impact peak GRF was greater in barefoot and MSH than in shoes. MSH showed greaterankle plantarflexor moment and negative power in early stance compared to shoes, which indicates greatereccentric plantarflexor muscle involvement in MSH than in shoes. Running shoes had greater peak knee extensormoment, early stance eccentric knee power and late stance concentric knee power compared to MSH andbarefoot indicating less knee joint involvement. The current findings only pertain to acute changes between shoeconditions, and therefore training interventions in minimal footwear are warranted to further understand theadaptation effects of shod to barefoot or RFS to FFS running on lower limb biomechanics and runningperformance.

Keywords: Barefoot; minimal shoes; ankle; knee; running

1. Introduction

Recently, barefoot or minimal footwear running hasbeen at the forefront of running research, and hasbecome a highly debated topic. Barefoot running onoutdoor surfaces may lead to skin abrasions anddiscomfort. Minimal shoes (MSH; for example,Vibram FiveFingersTM, Nike FreeTM, New BalanceMinimusTM) have recently gained popularity with thepurpose of simulating barefoot running while provid-ing cutaneous protection. One research study found amore anterior foot strike, a flatter sole angle beforefoot strike, smaller impact peak ground reaction force(GRF) and greater ankle range of motion (ROM) inMSH (FiveFingersTM) and barefoot compared to shodin habitual barefoot rearfoot strike (RFS) runnersduring treadmill running (Squadrone and Gallozzi2009). These findings may indicate that the use ofMSH may promote a running style closely resemblingbarefoot running. However, their study did not includefrontal plane kinematics or lower limb joint kinetics intheir analysis. Another group of researchers conducted

an MSH (FiveFingersTM) training study and showed

that a large number of habitually shod runners

transitioned from an RFS pattern to a midfoot

(MFS) or a forefoot strike (FFS) pattern (Lieberman

et al. 2010). These studies provide important informa-

tion regarding biomechanical differences between

barefoot, MSH and shod running but comprehensive

analyses of the effects of MSH on lower limb running

biomechanics comparing to barefoot and standard

running shoes are still lacking in the literature.Some research has been conducted on the biome-

chanical differences between barefoot and shod run-

ning. Studies have argued that barefoot running allows

natural foot motions that optimize shock absorption to

potentially reduce the risk of running injuries (Robbins

and Hanna 1987, Hreljac 2004). Previous studies have

shown a more anterior foot strike and a flatter sole

angle at foot strike in barefoot compared to shod

running (De Wit et al. 2000, Lieberman et al. 2010).

Divert et al. (2005) found a smaller impact peak in

barefoot compared to shod but other researchers have

*Corresponding author. Email: mpaquett@utk.edu

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10 M.R. Paquette et al.

shown no differences in impact peak GRF betweenbarefoot and shod (De Wit et al. 2000, Divert et al.2008, Lieberman et al. 2010). The loading rate ofimpact peak GRF is typically greater in barefootcompared to shoes in RFS runners (De Wit et al. 2000,Lieberman et al. 2010). Push-off vertical GRF duringrunning has been shown to be similar in barefoot andshod (De Wit et al. 2000, Squadrone and Gallozzi2009), but also smaller in barefoot than in shod (Divertet al. 2005). Squadrone and Gallozzi (2009) did notfind any differences in knee flexion ROM betweenbarefoot and shod but other research has reportedsmaller knee ROM in barefoot compared shod duringstance (De Wit et al. 2000). One study on frontal planeknee kinematics of running barefoot and shod foundreduced knee angular motion in barefoot compared toshod during 3-min treadmill running trials (Burkettet al. 1985). However, research is limited in comparingbarefoot or MSH and shod on frontal plane ankle andknee motions during running.

Shod runners tend to RFS while barefoot runnerstend to FFS or MFS (Lieberman et al. 2010, Lohmanet al. 2011). RFS runners generate an impact peak thatis typically absent in MFS and FFS runners (Cavanaghand Lafortune 1980, Novacheck 1998, Laughton et al.2003), and the absence of an impact peak is responsiblefor the smaller loading rate (Lieberman et al. 2010). Inaddition, FFS runners generate greater absoluteimpact peak vertical GRF, greater anterior–posteriorpush-off force (Laughton et al. 2003), lower loadingrate (Lieberman et al. 2010), less ankle dorsiflexion andknee flexion ROM, greater ankle eversion (Laughtonet al. 2003, Stackhouse et al. 2004), decreased anklestiffness and increased knee stiffness (Laughton et al.2003) compared to RFS runners.

Although research comparing barefoot and shodrunning is extensive, the findings are inconsistent. Itappears that different foot strike patterns and habitualfootwear of runners in these studies may explain theinconsistent findings (Williams et al. 2000, Stackhouseet al. 2004, Squadrone and Gallozzi 2009, Liebermanet al. 2010, Lohman et al. 2011). As barefoot and MSHrunning is becoming more popular and most modern-day runners have minimal experience of these types ofrunning, comprehensive comparisons of lower extre-mity biomechanics between barefoot, MSH and shoesin habitual shod RFS and FFS runners are warranted.The acute changes in the lower extremity joints couldprovide relevant training and injury prevention infor-mation for runners and therapists to understand thepotential immediate risks or benefits of changingfootwear from supportive shoes to minimal shoes orbarefoot. The primary purpose of the current studywas therefore to examine the acute effects of MSH,

barefoot and running shoes of habitually shod RFSand FFS runners on strike pattern, GRFs, ankle andknee kinematics and kinetics during overgroundrunning. Our primary hypotheses were that (1) MSHand barefoot would yield a more anterior foot strike,smaller impact peak, braking GRF and loading rate,greater ankle dorsiflexion and eversion ROM, peakplantarflexor moment, smaller knee flexion ROM andpeak extensor moment compared to shoes; (2) MSHand running shoes would yield greater peak push-offand propulsive GRF and peak concentric ankle powerin late stance compared to barefoot while runningshoes would yield greater peak concentric knee powerin late stance compared to barefoot and MSH. Inaddition, the secondary hypothesis was that RFSrunners would yield a more posterior foot strike,greater impact peak GRF, loading rate and push-offpeak GRF, smaller ankle dorsiflexion and eversionROM, peak plantarflexor moment, and peak kneeextensor moment compared to FFS runners.

2. Methods

Fourteen well-trained male distance runners, who ranat least 35 km/week, were recruited for this study. Allrunners reported that they did not have previousbarefoot or MSH running experience. Seven runnerswere classified as habitual RFS runners and seven ashabitual FFS runners; these made up the two footstrike groups (Table 1). Participants provided writteninformed consent approved by the Institutional ReviewBoard for ethical human subject research prior to thetesting session.

A nine-camera motion analysis system (240Hz,Vicon Motion Analysis Inc., Oxford, UK) was used toobtain the three-dimensional (3D) kinematic data.Data were collected on the dominant leg of eachrunner and all runners included in the study were right-leg dominant. Anatomical reflective markers wereplaced on the iliac crests, greater trochanters, femoralepicondyles, malleoli, and head of the first and fifthmetatarsals to define the pelvis, thighs, legs and feet,respectively. In addition, tracking markers wereattached to pelvis, thigh and leg using a four-markersemi-rigid thermoplastic shell. For the MSH and shodconditions, two tracking markers were placed indivi-dually on the lateral and medial aspects of the heelcounter while two additional markers (superior andinferior) were placed on the posterior heel counterusing a two-marker wand on a thermoplastic base. Forthe barefoot condition, foot tracking markers wereplaced directly on the skin at the same locationsmentioned for MSH and shod conditions. The same

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Footwear Science 11

shown no differences in impact peak GRF betweenbarefoot and shod (De Wit et al. 2000, Divert et al.2008, Lieberman et al. 2010). The loading rate ofimpact peak GRF is typically greater in barefootcompared to shoes in RFS runners (De Wit et al. 2000,Lieberman et al. 2010). Push-off vertical GRF duringrunning has been shown to be similar in barefoot andshod (De Wit et al. 2000, Squadrone and Gallozzi2009), but also smaller in barefoot than in shod (Divertet al. 2005). Squadrone and Gallozzi (2009) did notfind any differences in knee flexion ROM betweenbarefoot and shod but other research has reportedsmaller knee ROM in barefoot compared shod duringstance (De Wit et al. 2000). One study on frontal planeknee kinematics of running barefoot and shod foundreduced knee angular motion in barefoot compared toshod during 3-min treadmill running trials (Burkettet al. 1985). However, research is limited in comparingbarefoot or MSH and shod on frontal plane ankle andknee motions during running.

Shod runners tend to RFS while barefoot runnerstend to FFS or MFS (Lieberman et al. 2010, Lohmanet al. 2011). RFS runners generate an impact peak thatis typically absent in MFS and FFS runners (Cavanaghand Lafortune 1980, Novacheck 1998, Laughton et al.2003), and the absence of an impact peak is responsiblefor the smaller loading rate (Lieberman et al. 2010). Inaddition, FFS runners generate greater absoluteimpact peak vertical GRF, greater anterior–posteriorpush-off force (Laughton et al. 2003), lower loadingrate (Lieberman et al. 2010), less ankle dorsiflexion andknee flexion ROM, greater ankle eversion (Laughtonet al. 2003, Stackhouse et al. 2004), decreased anklestiffness and increased knee stiffness (Laughton et al.2003) compared to RFS runners.

Although research comparing barefoot and shodrunning is extensive, the findings are inconsistent. Itappears that different foot strike patterns and habitualfootwear of runners in these studies may explain theinconsistent findings (Williams et al. 2000, Stackhouseet al. 2004, Squadrone and Gallozzi 2009, Liebermanet al. 2010, Lohman et al. 2011). As barefoot and MSHrunning is becoming more popular and most modern-day runners have minimal experience of these types ofrunning, comprehensive comparisons of lower extre-mity biomechanics between barefoot, MSH and shoesin habitual shod RFS and FFS runners are warranted.The acute changes in the lower extremity joints couldprovide relevant training and injury prevention infor-mation for runners and therapists to understand thepotential immediate risks or benefits of changingfootwear from supportive shoes to minimal shoes orbarefoot. The primary purpose of the current studywas therefore to examine the acute effects of MSH,

barefoot and running shoes of habitually shod RFSand FFS runners on strike pattern, GRFs, ankle andknee kinematics and kinetics during overgroundrunning. Our primary hypotheses were that (1) MSHand barefoot would yield a more anterior foot strike,smaller impact peak, braking GRF and loading rate,greater ankle dorsiflexion and eversion ROM, peakplantarflexor moment, smaller knee flexion ROM andpeak extensor moment compared to shoes; (2) MSHand running shoes would yield greater peak push-offand propulsive GRF and peak concentric ankle powerin late stance compared to barefoot while runningshoes would yield greater peak concentric knee powerin late stance compared to barefoot and MSH. Inaddition, the secondary hypothesis was that RFSrunners would yield a more posterior foot strike,greater impact peak GRF, loading rate and push-offpeak GRF, smaller ankle dorsiflexion and eversionROM, peak plantarflexor moment, and peak kneeextensor moment compared to FFS runners.

2. Methods

Fourteen well-trained male distance runners, who ranat least 35 km/week, were recruited for this study. Allrunners reported that they did not have previousbarefoot or MSH running experience. Seven runnerswere classified as habitual RFS runners and seven ashabitual FFS runners; these made up the two footstrike groups (Table 1). Participants provided writteninformed consent approved by the Institutional ReviewBoard for ethical human subject research prior to thetesting session.

A nine-camera motion analysis system (240Hz,Vicon Motion Analysis Inc., Oxford, UK) was used toobtain the three-dimensional (3D) kinematic data.Data were collected on the dominant leg of eachrunner and all runners included in the study were right-leg dominant. Anatomical reflective markers wereplaced on the iliac crests, greater trochanters, femoralepicondyles, malleoli, and head of the first and fifthmetatarsals to define the pelvis, thighs, legs and feet,respectively. In addition, tracking markers wereattached to pelvis, thigh and leg using a four-markersemi-rigid thermoplastic shell. For the MSH and shodconditions, two tracking markers were placed indivi-dually on the lateral and medial aspects of the heelcounter while two additional markers (superior andinferior) were placed on the posterior heel counterusing a two-marker wand on a thermoplastic base. Forthe barefoot condition, foot tracking markers wereplaced directly on the skin at the same locationsmentioned for MSH and shod conditions. The same

researcher placed markers on all participants to reducemarker placement errors and ensure consistent markerplacement between participants. A different static trialwas performed for all three shoe conditions and theanatomical markers were removed during runningtrials. A force platform (1200Hz, AMTI, Watertown,MA, USA) was used to collect GRFs simultaneouslywith 3D kinematic data using the VICON Workstationduring the running trials.

Participants performed five overground runningtrials over a 20 -m hardwood floor runway in each ofthree conditions: barefoot (BF), MSH (FiveFingersTM

KSO, Vibram Inc., Concord, MA, USA) and shod(SH; neutral cushioning, Noveto, Adidas, Portland,OR, USA). Footwear conditions were randomized toavoid an order effect. Participants were asked tomaintain a running speed of 3.3m/s (�5%) to facilitateinterstudy comparisons (De Wit et al. 2000, Divertet al. 2005, Squadrone and Gallozzi 2009). Runningspeed was monitored with a pair of photocells (63501IR, Lafayette Instrument Inc., IN, USA) placed atshoulder height level 3m apart before and after theforce platform and, an electronic timer (54035A,Lafayette Instrument Inc.). Participants needed twoto four practice trials to successfully perform runningtrials at the correct speed while contacting the forceplatform with the tested limb. An adaptation period inbarefoot and MSH was not provided as the primarypurpose of this study was to investigate the acuteeffects of different footwear on running mechanics.

The Visual3D biomechanical analysis softwaresuite (C-Motion, Inc., MD, USA) was used to computethe 3D kinematic and kinetic variables of the

right limb. A right-hand rule with a Cardan rotationalsequence (X–Y–Z) was used for the 3D angularcomparisons. A customized computer program(VB_V3D) was used to determine the 3D kinematicand kinetic variables of interest. Kinematic and GRFdata were filtered using a fourth-order Butterworthlow-pass filter at 8 and 50Hz, respectively. A thresholdof 10N of the vertical GRF was used to detect the startand end of the stance phase. The runners were firstplaced in the RFS or FFS runner group based on thepresence or absence of the impact peak GRF. Thestrike index (SI) was then used to confirm the footstrike pattern of both groups during shod running asparticipants were all habitually shod runners. The SIwas calculated as the ratio of the centre of pressure(COP) location at foot strike relative to the length ofthe foot (Cavanagh and Lafortune 1980) and was usedto confirm strike patterns in runners (Squadrone andGallozzi 2009, Lieberman et al. 2010, Altman andDavis 2012). In the current study, the length of the footwas defined as the distance between the heel markerand midpoint of the first and fifth metatarsal headmarker. Thus, it was difficult to use previouslyreported SI cut-off values to confirm the foot strikepatterns of our runners. However, there was a cleardemarcation between RFS and FFS runners as all RFSrunners had an SI5 27% and all FFS runners had anSI4 80% during shod running. For that reason,runners with a SI value4 80% during shod runningwere classified as FFS runners. The sagittal plane footcontact angle (FCA) was also used to confirm thestrike pattern where positive and negative valuesindicate RFS and FFS, respectively. GRFs were

Table 1. Basic information about the participants and their training.

Group Subject No.Age

(years)Height(cm)

Mass(kg)

Yearsof running km/week

FFS 2 29 178 65.4 15.5 1043 25 178 75.1 12.5 1368 31 178 73.0 15 40

12 23 179 69.3 12 10413 36 171 65.5 20 13614 23 177 65.4 10 4015 36 183 72.8 13.5 104

Mean� SD 29� 5.6 178� 3.5 70� 4.2 14� 3.2 95� 40

RFS 1 27 178 72.6 16 404 26 183 72.6 12.5 1605 25 180 74.8 11 1206 25 182 81.2 11 887 32 181 70.3 10 969 26 180 66.7 10 80

11 30 191 80.9 15 40Mean� SD 27� 2.7 182� 4.2 74� 5.3 12� 2.4 89� 43

Overall Mean� SD 28� 4.3 180� 4.4 72� 5.2 13� 2.9 92� 40

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normalized to body weight (BW) and joint moments(Nm/kg) and powers (W/kg) were normalized to bodymass. For all variables, the average of the five trials ofeach condition was used in the statistical analyses.

A two-way (Group�Shoe) mixed design analysisof variance (ANOVA), with the shoe condition as thewithin-subject factor and the group as the between-subject factor, was used to evaluate all variables (18.0SPSS, Chicago, IL, USA). In addition, a one-wayANOVA was performed for the impact peak verticalGRF (FZ_1) for the RFS group only with shoecondition as the independent factor. Significance wasset at an � level of 0.05. Within-group pairwisecomparisons were adjusted using a Bonferroni proce-dure. When interactions were observed, paired-samplet-tests were used to compare means using a Bonferroniprocedure with an adjusted � level of 0.0056.

3. Results

3.1. Foot strike pattern

The ANOVA revealed Shoe [F(2, 11)¼ 6.62, p¼ 0.013]and Group [F(1, 12)¼ 6.902, p¼ 0.0001] main effectsfor SI (Table 2). SI was greater in barefoot ( p¼ 0.020)and MSH ( p¼ 0.008) compared to running shoe. SIwas greater in FFS compared to RFS runners. Thesagittal plane FCA was smaller in FFS compared to

RFS runners [F(1, 12)¼ 42.76, p¼ 0.0001], indicating aflatter foot position at foot strike in FFS (Table 2).

3.2. GRFs

For all three shoe conditions and both foot strikepatterns, representative vertical GRF profiles areillustrated in Figure 1 and the presence of the impactpeak vertical GRF (F1_Z) is reported in Table 2. InRFS runners, the impact peak was consistently presentin all subjects except for the shod condition of subject1. However, in FFS runners the presence of the impactpeak was inconsistent and highly variable for allsubjects. Stance time (ST) revealed a Shoe maineffect [F(2, 11)¼ 9.421, p¼ 0.004; Table 3], with greaterST in shoes compared to barefoot ( p¼ 0.004). Theloading rate (LR) of the vertical impact peak GRFrevealed a Shoe�Group interaction [F(2, 11)¼ 13.98,p¼ 0.001, Table 3]. Paired-sampled t-tests showed that,within the RFS group, the loading rate was greater inbarefoot ( p¼ 0.001) and MSH ( p¼ 0.001) comparedto shoes. The LR also revealed Shoe [F(2, 11)¼ 16.346,p¼ 0.001] and Group [F(1, 12)¼ 10.157, p¼ 0.008]main effects (Table 3). The peak push-off verticalGRF (F2_Z) indicated a Shoe main effect[F(2, 11)¼ 10.71, p¼ 0.003] with larger peaks in MSH( p¼ 0.005) and shoes ( p¼ 0.002) compared to

Table 2. Foot strike pattern variables and presence of impact ground reaction force (GRF).

Group Subject No.

SI (%)a,b FCA (�)a F1_Z presence

BF MSH SH BF MSH SH BF MSH SH

RFS 1 53� 17 67� 8 25� 6 12.1� 1.6 4.2� 0.7 6.2� 0.9 Y Y M4 22� 2 17� 6 7� 2 8.4� 1.1 9.2� 1.7 13.1� 1.8 Y Y Y5 17� 1 23� 5 24� 20 16.6� 1.9 17.7� 0.4 21.2� 3.3 Y Y Y6 11� 11 5� 2 13� 4 10.1� 0.8 11.1� 1.5 14.2� 2.1 Y Y Y7 25� 1 26� 9 18� 3 15.3� 0.4 15.7� 3.7 19.5� 1.3 Y Y Y9 47� 19 36� 8 28� 9 7.0� 1.4 6.3� 0.6 7.0� 2.6 Y Y Y11 23� 1 23� 2 11� 3 15.7� 0.7 19.7� 0.5 26.7� 1.2 Y Y Y

Mean� SD 28� 16 28� 19 18� 8 12.0� 5.9 12.2� 3.8 15.4� 7.5

FFS 2 95� 2 96� 2 91� 6 �1.0� 1.9 �4.9� 1.3 0.001� 1.0 M M N3 100� 2 102� 3 92� 6 1.6� 2.0 6.0� 0.5 3.1� 0.5 N N N8 103� 3 110� 2 100� 2 �3.8� 4.7 0.7� 1.5 �0.9� 2.2 N N N

12 116� 7 122� 7 83� 8 5.5� 0.7 6.2� 0.4 2.2� 1.0 Y N N13 144� 25 116� 20 97� 25 �6.1� 2.7 3.8� 3.1 8.0� 2.4 Y M M14 99� 8 110� 4 99� 22 5.4� 1.4 3.7� 1.5 �2.6� 1.4 N M N15 141� 6 123� 5 87� 19 3.9� 0.5 2.0� 2.2 4.3� 1.2 Y Y M

Mean� SD 114� 21 111� 10 92� 6 2.5� 3.8 0.77� 4.6 2.0� 3.6

Overall Mean� SD 71� 48 70� 46 55� 39c,d 6.5� 7.2 7.2� 6.9 8.7� 9.0

Notes: F1_Z presence demonstrates the presence (Y), absence (N) or mix (M) of the impact peak GRF for all three shoeconditions: barefoot (BF), minimal shoe (MSH) and neutral cushion running shoes (SH).aSignificant Group main effect. bSignificant Shoe main effect. cSignificantly different from BF. dSignificantly different fromMSH.

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Footwear Science 13

normalized to body weight (BW) and joint moments(Nm/kg) and powers (W/kg) were normalized to bodymass. For all variables, the average of the five trials ofeach condition was used in the statistical analyses.

A two-way (Group�Shoe) mixed design analysisof variance (ANOVA), with the shoe condition as thewithin-subject factor and the group as the between-subject factor, was used to evaluate all variables (18.0SPSS, Chicago, IL, USA). In addition, a one-wayANOVA was performed for the impact peak verticalGRF (FZ_1) for the RFS group only with shoecondition as the independent factor. Significance wasset at an � level of 0.05. Within-group pairwisecomparisons were adjusted using a Bonferroni proce-dure. When interactions were observed, paired-samplet-tests were used to compare means using a Bonferroniprocedure with an adjusted � level of 0.0056.

3. Results

3.1. Foot strike pattern

The ANOVA revealed Shoe [F(2, 11)¼ 6.62, p¼ 0.013]and Group [F(1, 12)¼ 6.902, p¼ 0.0001] main effectsfor SI (Table 2). SI was greater in barefoot ( p¼ 0.020)and MSH ( p¼ 0.008) compared to running shoe. SIwas greater in FFS compared to RFS runners. Thesagittal plane FCA was smaller in FFS compared to

RFS runners [F(1, 12)¼ 42.76, p¼ 0.0001], indicating aflatter foot position at foot strike in FFS (Table 2).

3.2. GRFs

For all three shoe conditions and both foot strikepatterns, representative vertical GRF profiles areillustrated in Figure 1 and the presence of the impactpeak vertical GRF (F1_Z) is reported in Table 2. InRFS runners, the impact peak was consistently presentin all subjects except for the shod condition of subject1. However, in FFS runners the presence of the impactpeak was inconsistent and highly variable for allsubjects. Stance time (ST) revealed a Shoe maineffect [F(2, 11)¼ 9.421, p¼ 0.004; Table 3], with greaterST in shoes compared to barefoot ( p¼ 0.004). Theloading rate (LR) of the vertical impact peak GRFrevealed a Shoe�Group interaction [F(2, 11)¼ 13.98,p¼ 0.001, Table 3]. Paired-sampled t-tests showed that,within the RFS group, the loading rate was greater inbarefoot ( p¼ 0.001) and MSH ( p¼ 0.001) comparedto shoes. The LR also revealed Shoe [F(2, 11)¼ 16.346,p¼ 0.001] and Group [F(1, 12)¼ 10.157, p¼ 0.008]main effects (Table 3). The peak push-off verticalGRF (F2_Z) indicated a Shoe main effect[F(2, 11)¼ 10.71, p¼ 0.003] with larger peaks in MSH( p¼ 0.005) and shoes ( p¼ 0.002) compared to

Table 2. Foot strike pattern variables and presence of impact ground reaction force (GRF).

Group Subject No.

SI (%)a,b FCA (�)a F1_Z presence

BF MSH SH BF MSH SH BF MSH SH

RFS 1 53� 17 67� 8 25� 6 12.1� 1.6 4.2� 0.7 6.2� 0.9 Y Y M4 22� 2 17� 6 7� 2 8.4� 1.1 9.2� 1.7 13.1� 1.8 Y Y Y5 17� 1 23� 5 24� 20 16.6� 1.9 17.7� 0.4 21.2� 3.3 Y Y Y6 11� 11 5� 2 13� 4 10.1� 0.8 11.1� 1.5 14.2� 2.1 Y Y Y7 25� 1 26� 9 18� 3 15.3� 0.4 15.7� 3.7 19.5� 1.3 Y Y Y9 47� 19 36� 8 28� 9 7.0� 1.4 6.3� 0.6 7.0� 2.6 Y Y Y11 23� 1 23� 2 11� 3 15.7� 0.7 19.7� 0.5 26.7� 1.2 Y Y Y

Mean� SD 28� 16 28� 19 18� 8 12.0� 5.9 12.2� 3.8 15.4� 7.5

FFS 2 95� 2 96� 2 91� 6 �1.0� 1.9 �4.9� 1.3 0.001� 1.0 M M N3 100� 2 102� 3 92� 6 1.6� 2.0 6.0� 0.5 3.1� 0.5 N N N8 103� 3 110� 2 100� 2 �3.8� 4.7 0.7� 1.5 �0.9� 2.2 N N N

12 116� 7 122� 7 83� 8 5.5� 0.7 6.2� 0.4 2.2� 1.0 Y N N13 144� 25 116� 20 97� 25 �6.1� 2.7 3.8� 3.1 8.0� 2.4 Y M M14 99� 8 110� 4 99� 22 5.4� 1.4 3.7� 1.5 �2.6� 1.4 N M N15 141� 6 123� 5 87� 19 3.9� 0.5 2.0� 2.2 4.3� 1.2 Y Y M

Mean� SD 114� 21 111� 10 92� 6 2.5� 3.8 0.77� 4.6 2.0� 3.6

Overall Mean� SD 71� 48 70� 46 55� 39c,d 6.5� 7.2 7.2� 6.9 8.7� 9.0

Notes: F1_Z presence demonstrates the presence (Y), absence (N) or mix (M) of the impact peak GRF for all three shoeconditions: barefoot (BF), minimal shoe (MSH) and neutral cushion running shoes (SH).aSignificant Group main effect. bSignificant Shoe main effect. cSignificantly different from BF. dSignificantly different fromMSH.

barefoot (Table 3). The peak propulsive GRF (FPR)showed a Shoe main effect [F(2, 11)¼ 11.18, p¼ 0.002,Table 3] with larger peaks in barefoot ( p¼ 0.018) andMSH ( p¼ 0.001) compared to shoes.

3.3. Joint kinematics

Peak ankle dorsiflexion angle (DF_Peak) showed aShoe main effect [F(2, 11)¼ 7.99, p¼ 0.007; Table 4]

with smaller peak dorsiflexion in barefoot comparedto MSH ( p¼ 0.005) and shoes ( p¼ 0.006). Ankledorsiflexion range of motion (DF_ROM) indicatedShoe [F(2, 11)¼ 10.34, p¼ 0.003] and Group[F(1, 12)¼ 16.60, p¼ 0.002] main effects (Table 4).These were smaller in barefoot compared to MSH( p¼ 0.002) and shoes ( p¼ 0.006) and smaller in RFScompared to FFS runners. Peak knee flexion angle(Flex_Peak) showed a Shoe main effect[F(2, 11)¼ 7.30, p¼ 0.010; Table 4] with smaller

Figure 1. Representative vertical GRF curves plotted over time normalized to 100% of the right limb stance phase for habitualRFS and FFS runners in barefoot, MSH for middle graph (MSH), vertical axis should say MSH and neutral cushion runningshoes (Shod).

Table 3. Anterio–posterior and vertical ground reaction force (GRF) variables (mean� SD).

RFS FFS

Variables BF MSH SH BF MSH SH

Stance time (s)a 0.242� 0.03 0.245� 0.03 0.253� 0.03 0.221� 0.02 0.223� 0.02 0.225� 0.02FBR (BW) �0.39� 0.07 �0.37� 0.06 �0.38� 0.07 �0.37� 0.07 �0.37� 0.05 �0.36� 0.05FPR (BW)b,d,e 0.32� 0.02 0.33� 0.02 0.30� 0.03 0.31� 0.05 0.32� 0.05 0.30� 0.05F1_Z (BW) 1.5� 0.5 1.6� 0.4 1.6� 0.3 – – –LR (BW/s)a,b,c 164.4� 57.1 147.9� 50.5 61.7� 22.3g,h 74.7� 54.7 60.5� 25.6 57.0� 12.0F2_Z (BW)b,d,f 2.5� 0.2 2.5� 0.2 2.5� 0.2 2.6� 0.2 2.7� 0.1 2.7� 0.2

Notes: aSignificant Group main effect. bSignificant Shoe main effect. cSignificant Group� Shoe interaction. dSignificantdifference between barefoot (BF) and neutral cushion running shoes (SH). eSignificant difference between minimal shoe (MSH)and SH. fSignificant difference between MSH and BF. gSignificant difference between BF and SH within foot strike group.hSignificant difference between MSH and SH within foot strike group.D

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14 M.R. Paquette et al.

values in barefoot ( p¼ 0.022) and MSH ( p¼ 0.006)compared to shoes. Knee flexion ROM (Kn_ROM)also showed a Shoe main effect [F(2, 11)¼ 12.07,p¼ 0.002; Table 4] with smaller values in barefoot( p¼ 0.001) and MSH ( p¼ 0.008) compared to shoes.In the frontal plane, the ankle eversion ROM(EV_ROM) yielded a Shoe main effect[F(2, 11)¼ 5.76, p¼ 0.019, Table 4] with smallervalues in barefoot compared to MSH ( p¼ 0.012).

3.4. Sagittal plane joint kinetics

Peak ankle plantarflexor moment (PF_M) showed aShoe main effect [F(2, 11)¼ 18.33, p¼ 0.0001, Table 5].MSH had greater plantarflexor moment compared tobarefoot ( p¼ 0.01) and shoes ( p¼ 0.001). Initial peakeccentric ankle power (An_P1) revealed a Shoe maineffect [F(2, 11)¼ 18.99, p¼ 0.0001; Table 5]. MSH hadsmaller peak ankle power compared to barefoot( p¼ 0.001) while both MSH ( p¼ 0.002) and barefoot( p¼ 0.001) had a smaller peak ankle power than shoes.The second peak concentric ankle power in late stance(An_P2) revealed a Shoe main effect [F(2, 11¼ 17.94,

p¼ 0.0001] with barefoot showing smaller peakscompared to MSH ( p¼ 0.001) and shoes ( p¼ 0.003)(Table 5). Peak knee extension moment (EX_M) alsoindicated a Shoe main effect [F(2, 11)¼ 17.59,p¼ 0.0001; Table 5] with barefoot ( p¼ 0.001) andMSH ( p¼ 0.001) showing smaller peaks compared toshoes. Initial peak eccentric knee power (Kn_P1)indicated a Shoe [F(2, 11)¼ 16.07, p¼ 0.001] maineffect (Table 5) with smaller peaks observed in bare-foot ( p¼ 0.001) and MSH ( p¼ 0.001) compared toshoes. Finally, the second peak concentric knee powerin late stance (Kn_P2) indicated a Shoe main effect[F(2, 11)¼ 12.44, p¼ 0.001; Table 5] with smaller peaksin barefoot ( p¼ 0.005) and MSH ( p¼ 0.001) com-pared to shoes.

4. Discussion

The purpose of the study was to examine the acuteeffects of different footwear in strike pattern, GRFs,sagittal and frontal plane ankle and knee kinematicsand kinetics during overground running. In the currentstudy, participants were well-trained RFS and FFS

Table 5. Peak ankle and knee kinetic variables (mean� SD).

RFS FFS

Variables BF MSH SH BF MSH SH

PF_M (Nm/kg)b,d,e �2.9� 0.4 �3.0� 0.3 �2.7� 0.3 �3.0� 0.3 �3.2� 0.2 �3.0� 0.2An_P1 (W/kg)b,c,d,e �5.2� 2.1 �8.6� 1.1 �6.5� 1.5 �6.2� 2.3 �9.7� 1.2 �9.0� 1.5An_P2 (W/kg)b,c,e 8.6� 3.0 11.4� 1.2 10.8� 1.3 8.5� 3.7 11.7� 3.7 11.4� 2.3EX_M (Nm/kg)b,c,d 2.9� 0.6 3.0� 0.5 3.3� 0.5 2.5� 0.3 2.7� 0.4 3.0� 0.5Kn_P1 (W/kg)a,b,c,d �10.5� 3.5 �11.2� 2.1 �13.2� 2.7 �7.4� 1.9 �8.7� 1.6 �11.1� 2.5Kn_P2 (W/kg)b,c,d 5.2� 2.1 5.5� 2.0 6.5� 2.1 5.3� 1.7 5.8� 1.6 6.8� 2.0

Notes: aSignificant Group main effect. bSignificant Shoe main effect. cSignificant difference between barefoot (BF) and neutralcushion running shoes (SH). dSignificant difference between minimal shoe (MSH) and SH. eSignificant difference between MSHand BF.

Table 4. Ankle and knee kinematic variables (mean� SD).

RFS FFS

Variables BF MSH SH BF MSH SH

DF_Peak (�)b,c,e 11.4� 3.4 15.0� 4.2 12.4� 4.2 16.2� 5.5 23.5� 3.6 22.0� 3.3DF_ROM (�)a,b,c,e 11.4� 3.4 15.0� 4.2 12.4� 4.2 16.2� 5.5 23.5� 3.6 22.0� 3.3EV_ROM (�)b,e 7.1� 2.7 9.2� 3.1 9.0� 2.9 8.39� 3.8 12.1� 3.6 11.1� 3.3Flex_Peak (�)b,c,d 7.1� 2.7 9.2� 3.1 9.0� 2.9 8.39� 3.8 12.1� 3.6 11.1� 3.3Kn_ROM (�)b,c,d 22.7� 2.7 23.3� 2.5 28.0� 4.3 21.3� 4.9 22.5� 4.3 23.7� 3.1

Notes: aSignificant Group main effect. bSignificant Shoe main effect. cSignificant difference between barefoot (BF) and neutralcushion running shoes (SH). dSignificant difference between minimal shoe (MSH) and SH. eSignificant difference between MSHand BF.

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Footwear Science 15

values in barefoot ( p¼ 0.022) and MSH ( p¼ 0.006)compared to shoes. Knee flexion ROM (Kn_ROM)also showed a Shoe main effect [F(2, 11)¼ 12.07,p¼ 0.002; Table 4] with smaller values in barefoot( p¼ 0.001) and MSH ( p¼ 0.008) compared to shoes.In the frontal plane, the ankle eversion ROM(EV_ROM) yielded a Shoe main effect[F(2, 11)¼ 5.76, p¼ 0.019, Table 4] with smallervalues in barefoot compared to MSH ( p¼ 0.012).

3.4. Sagittal plane joint kinetics

Peak ankle plantarflexor moment (PF_M) showed aShoe main effect [F(2, 11)¼ 18.33, p¼ 0.0001, Table 5].MSH had greater plantarflexor moment compared tobarefoot ( p¼ 0.01) and shoes ( p¼ 0.001). Initial peakeccentric ankle power (An_P1) revealed a Shoe maineffect [F(2, 11)¼ 18.99, p¼ 0.0001; Table 5]. MSH hadsmaller peak ankle power compared to barefoot( p¼ 0.001) while both MSH ( p¼ 0.002) and barefoot( p¼ 0.001) had a smaller peak ankle power than shoes.The second peak concentric ankle power in late stance(An_P2) revealed a Shoe main effect [F(2, 11¼ 17.94,

p¼ 0.0001] with barefoot showing smaller peakscompared to MSH ( p¼ 0.001) and shoes ( p¼ 0.003)(Table 5). Peak knee extension moment (EX_M) alsoindicated a Shoe main effect [F(2, 11)¼ 17.59,p¼ 0.0001; Table 5] with barefoot ( p¼ 0.001) andMSH ( p¼ 0.001) showing smaller peaks compared toshoes. Initial peak eccentric knee power (Kn_P1)indicated a Shoe [F(2, 11)¼ 16.07, p¼ 0.001] maineffect (Table 5) with smaller peaks observed in bare-foot ( p¼ 0.001) and MSH ( p¼ 0.001) compared toshoes. Finally, the second peak concentric knee powerin late stance (Kn_P2) indicated a Shoe main effect[F(2, 11)¼ 12.44, p¼ 0.001; Table 5] with smaller peaksin barefoot ( p¼ 0.005) and MSH ( p¼ 0.001) com-pared to shoes.

4. Discussion

The purpose of the study was to examine the acuteeffects of different footwear in strike pattern, GRFs,sagittal and frontal plane ankle and knee kinematicsand kinetics during overground running. In the currentstudy, participants were well-trained RFS and FFS

Table 5. Peak ankle and knee kinetic variables (mean� SD).

RFS FFS

Variables BF MSH SH BF MSH SH

PF_M (Nm/kg)b,d,e �2.9� 0.4 �3.0� 0.3 �2.7� 0.3 �3.0� 0.3 �3.2� 0.2 �3.0� 0.2An_P1 (W/kg)b,c,d,e �5.2� 2.1 �8.6� 1.1 �6.5� 1.5 �6.2� 2.3 �9.7� 1.2 �9.0� 1.5An_P2 (W/kg)b,c,e 8.6� 3.0 11.4� 1.2 10.8� 1.3 8.5� 3.7 11.7� 3.7 11.4� 2.3EX_M (Nm/kg)b,c,d 2.9� 0.6 3.0� 0.5 3.3� 0.5 2.5� 0.3 2.7� 0.4 3.0� 0.5Kn_P1 (W/kg)a,b,c,d �10.5� 3.5 �11.2� 2.1 �13.2� 2.7 �7.4� 1.9 �8.7� 1.6 �11.1� 2.5Kn_P2 (W/kg)b,c,d 5.2� 2.1 5.5� 2.0 6.5� 2.1 5.3� 1.7 5.8� 1.6 6.8� 2.0

Notes: aSignificant Group main effect. bSignificant Shoe main effect. cSignificant difference between barefoot (BF) and neutralcushion running shoes (SH). dSignificant difference between minimal shoe (MSH) and SH. eSignificant difference between MSHand BF.

Table 4. Ankle and knee kinematic variables (mean� SD).

RFS FFS

Variables BF MSH SH BF MSH SH

DF_Peak (�)b,c,e 11.4� 3.4 15.0� 4.2 12.4� 4.2 16.2� 5.5 23.5� 3.6 22.0� 3.3DF_ROM (�)a,b,c,e 11.4� 3.4 15.0� 4.2 12.4� 4.2 16.2� 5.5 23.5� 3.6 22.0� 3.3EV_ROM (�)b,e 7.1� 2.7 9.2� 3.1 9.0� 2.9 8.39� 3.8 12.1� 3.6 11.1� 3.3Flex_Peak (�)b,c,d 7.1� 2.7 9.2� 3.1 9.0� 2.9 8.39� 3.8 12.1� 3.6 11.1� 3.3Kn_ROM (�)b,c,d 22.7� 2.7 23.3� 2.5 28.0� 4.3 21.3� 4.9 22.5� 4.3 23.7� 3.1

Notes: aSignificant Group main effect. bSignificant Shoe main effect. cSignificant difference between barefoot (BF) and neutralcushion running shoes (SH). dSignificant difference between minimal shoe (MSH) and SH. eSignificant difference between MSHand BF.

runners with no previous barefoot running experience.Our results showed a greater SI in barefoot and MSHcompared to shoes, indicating a tendency towardsMFS or FFS running in barefoot and MSH. Thisfinding is consistent with previous research comparingrunning barefoot and in shoes (Lieberman et al. 2010)but our study only investigated acute effects of runningbarefoot and in MSH. Lieberman et al. (2010) showedthat a training intervention where runners couldprogressively increase the number of miles run inMSH (FiveFingersTM) over a 6-week period reducedthe number of RFS runners from 72% to 36%, andincreased the number of FFS runners from 14% to57%. Based on our findings, it appears that runnerswith no previous experience in barefoot runningimmediately adopt a more anterior foot strike whenrunning barefoot or in MSH.

The impact peak GRF is typically present in RFSrunners (Novacheck 1998, Lieberman et al. 2010) butabsent in FFS runners (Laughton et al. 2003,Lieberman et al. 2010). The majority of our FFSrunners did not show an impact peak but, interestingly,some FFS runners (subjects 12, 13 and 15) had aconsistent impact peak in the barefoot condition eventhough their SI indicated a more anterior foot strikepattern. It is possible that the FFS runners used anMFS pattern to reduce the pressures placed on theirforefoot during the overground running trials. Thisobservation deserves more attention in future studies,which should focus on the effects of surface type onfoot strike patterns in RFS, MFS and FFS runners.

The impact peak GRF was only compared betweenshoe conditions within the RFS runners because of itsabsence in FFS runners. The RFS runners in our studydid not yield different impact peak GRFs betweenfootwear conditions. These findings are consistent withprevious literature (De Clercq et al. 1994, De Wit et al.2000, Divert et al. 2008). Lieberman et al. (2010)showed that habitually shod RFS runners do not yielddifferent impact peaks in barefoot and shoes atunreported self-selected running speeds. However, theimpact peak has been shown to be smaller in barefootand MSH compared to shoes during a 6-min treadmillrunning bout at 3.33m/s in habitually barefoot runners(Squadrone and Gallozzi 2009). Foot strike patternwas not defined in their study but the FCAs (i.e.positive values) just before foot touchdown suggestthat RFS runners were tested. Divert et al. (2005) alsofound smaller impact peaks in barefoot compared toshod treadmill running during two 4-min bouts at3.33m/s. The same running speed was used in thesetwo previous studies and therefore methodologicaldifferences such as treadmill versus overground run-ning with an adaptation period (Divert et al. 2005,

Squadrone and Gallozzi 2009) may explain thedifferent findings for the impact peak. The sameimpact peak between footwear conditions suggeststhat running barefoot, in MSH or in shoes does notlead to acute changes in the impact peak.

In addition, a higher LR was found in barefoot andMSH compared to shoes within the RFS group. Thelower LR in shoes may be explained by the largeamount of cushioning found in the heel region of theshoes. During RFS barefoot running, the lack ofcushioning leads to high deformity of the heel padduring impact, reducing its shock attenuation proper-ties (De Clercq et al. 1994), which could be responsiblefor the higher LR in barefoot and MSH compared toshoes. This finding of a higher LR in RFS runnerswhen running barefoot compared to shoes is commonin the literature (De Wit et al. 2000, Lieberman et al.2010). Greater LRs have been associated with runnerswith a history of tibial stress fractures (Milner et al.2006, Kadpoor and Nikooyan 2011). A meta-analysisof 13 studies comparing GRF variables of healthyrunners and runners with a history of tibial stressfractures showed that a higher LR was significantlyassociated with tibial stress fractures (Kadpoor andNikooyan 2011). Lower extremity biomechanics datacombined with musculoskeletal simulation data haveshown that runners using shorter stride lengths couldreduce their probability of developing tibial stressfractures by 3% to 6% (Edwards et al. 2009).However, we only collected unilateral lower extremitybiomechanics data during the stance phase and there-fore step or stride length data are not available.

Peak plantarflexor moment and eccentric anklepower were greater in MSH than in running shoeswhile peak push-off GRF was the same in MSH andshoes but greater than barefoot. MSH yielded a greaterSI, indicating a more anterior foot strike that may leadto a greater GRF moment arm about the ankle jointcompared to shoes. The greater moment arm wouldincrease eccentric plantarflexor involvement in MSHcompared to shoes during weight acceptance. Impactand shock waves transmitted through the lowerextremity are attenuated by ankle, knee and hip flexion(Clarke et al. 1983) through eccentric muscle contrac-tions (Derrick et al. 1998). Thus, the greater plantar-flexor involvement in MSH may help to attenuate therapid GRF loading compared to shoes. However,greater load to the plantarflexors (i.e. gastrocnemius,soleus and Achilles tendon) may increase the risk ofmusculoskeletal injury development over time. A timehistory of lower extremity joint variables and verticalGRF may help in understanding the relationshipbetween joint moments and GRF peaks. The timingof joint variables and GRF peaks were not of primary

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16 M.R. Paquette et al.

importance in the current study but further studies are

needed to better understand the timing of lower

extremity joint variables during barefoot or MSH

running. Van Ginckel et al. (2009) found a smaller

anterior COP displacement in beginner runners who

developed Achilles tendinopathy after a 10-week bare-

foot running programme. The smaller anterior COP

displacement during the stance phase was hypothesized

to potentially reduce stance plantarflexor moment and

therefore greater Achilles tendon force generation

would be required to increase the plantarflexor

moment to maintain adequate push-off forces (Van

Ginckel et al. 2009). However, our findings of greater

early stance peak plantarflexor moment and eccentric

ankle power in MSH compared to shoes suggest that

MSH may involve greater elastic energy storage

through tendon stretch at the ankle, which may be

used to do mechanical work (McCrory et al. 1999, Hof

et al. 2002, Karamanidis and Arampatzis 2005) and

produce similar push-off force and concentric ankle

power compared to shoes in mid- to late stance.

However, barefoot running showed less early stance

eccentric ankle involvement and reduced push-off force

and late concentric ankle power compared to MSH

and shoes. A potential explanation for lower push-off

force through lower concentric ankle power in barefoot

compared to MSH and shoes could be related to the

greater sagittal plane knee joint power in late stance

indicating greater knee involvement in shoes and hence

reduced ankle involvement in barefoot. Squadrone and

Gallozzi (2009) reported no differences between bare-

foot, MSH and shoes for peak vertical push-off force

but their runners were habitually barefoot. Overall,

these findings suggest that the cutaneous protection in

MSH and shoes may allow greater propulsive GRF in

habitually shod runners. Therefore, these acute differ-

ences in propulsive GRF and ankle kinetics may

indicate that our runners are more cautious in barefoot

running by reducing ankle loading but appear to be

more aggressive in MSH using an ankle strategy

compared to shoes to attenuate a higher LR.In addition, smaller eversion ROM was found in

barefoot compared to MSH and may have also

contributed to force attenuation in MSH. However,

frontal plane ankle kinetic variables were not different

between the shoe groups. Reductions in frontal plane

foot motion leading to greater ankle eversion in stiff

shoe soles have been suggested to be a potential cause

for running injuries (Stacoff et al. 1989). Thus, it is

possible that greater eversion found in MSH could lead

to running-related injuries but our findings only

pertain to acute changes in joint motion. In addition,

ankle inversion moment was not different, indicating

similar frontal plane ankle involvement between shoeconditions.

Peak knee flexion and ROM, peak extensormoment, peak early stance eccentric and late stanceconcentric power were reduced in barefoot and MSHcompared to shoes. Lieberman et al. (2010) alsoshowed that barefoot runners produce smaller kneeflexion ROM compared to shod runners during theimpact phase of stance. However, Squadrone andGallozzi (2009) showed no difference in knee flexionROM between barefoot, MSH and shod but greatankle dorsiflexion ROM in habitual barefoot runnersduring treadmill running. The smaller peak kneeflexion and ROM in barefoot may be explained bythe greater ST in shoes compared to barefoot, whichwould provide more time to increase knee flexionduring stance. In shoes, the knee appears to be largelyinvolved in early stance energy storing in preparationfor greater force generation at push-off. However, itappears that MSH may play a greater role at the anklerather than the knee by making elastic energy stored inearly stance available in late stance. The greater LRcoupled with the lack of cushioning materials under thefeet may provide an explanation for the greater kineticankle involvement in MSH as a strategy to immedi-ately attenuate the rapid GRF loading transmittedproximally to the lower limb. However, the higher loadplaced on the plantarflexors in MSH may increased therisk of developing Achilles tendinopathy over time.

The primary focus of the study was to comparebarefoot, MSH and running shoes but we alsocompared foot strike patterns. Our results indicatethat RFS runners produced a higher LR compared toFFS runners, specifically within the MSH condition.By contrast, LR has been shown to be much higher inbarefoot RFS compared to barefoot FFS (Liebermanet al. 2010) and in habitual shod RFS asked to adoptan FFS during one testing session compared to RFS(Laughton et al. 2003). Researchers have attributedthis lower LR in FFS to the transfer of translationalenergy into rotational energy at the ankle in FFS(Lieberman et al. 2010). Longitudinal studies on theeffects of foot strike in MSH and barefoot running oninjury risk are warranted.

Finally, our finding that dorsiflexion ROM wasgreater in FFS compared to RFS runners is consistentwith previous research (Laughton et al. 2003, Arendseet al. 2004, Stackhouse et al. 2004, Lieberman et al.2010). The more anterior COP location and flatter footposition in FFS runners allow for greater ROM at theankle as the heel is lowered to the ground in mid-stance. Our results showed smaller knee flexion ROMand greater peak knee eccentric power in FFScompared to RFS runners. Other researchers have

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Footwear Science 17

importance in the current study but further studies are

needed to better understand the timing of lower

extremity joint variables during barefoot or MSH

running. Van Ginckel et al. (2009) found a smaller

anterior COP displacement in beginner runners who

developed Achilles tendinopathy after a 10-week bare-

foot running programme. The smaller anterior COP

displacement during the stance phase was hypothesized

to potentially reduce stance plantarflexor moment and

therefore greater Achilles tendon force generation

would be required to increase the plantarflexor

moment to maintain adequate push-off forces (Van

Ginckel et al. 2009). However, our findings of greater

early stance peak plantarflexor moment and eccentric

ankle power in MSH compared to shoes suggest that

MSH may involve greater elastic energy storage

through tendon stretch at the ankle, which may be

used to do mechanical work (McCrory et al. 1999, Hof

et al. 2002, Karamanidis and Arampatzis 2005) and

produce similar push-off force and concentric ankle

power compared to shoes in mid- to late stance.

However, barefoot running showed less early stance

eccentric ankle involvement and reduced push-off force

and late concentric ankle power compared to MSH

and shoes. A potential explanation for lower push-off

force through lower concentric ankle power in barefoot

compared to MSH and shoes could be related to the

greater sagittal plane knee joint power in late stance

indicating greater knee involvement in shoes and hence

reduced ankle involvement in barefoot. Squadrone and

Gallozzi (2009) reported no differences between bare-

foot, MSH and shoes for peak vertical push-off force

but their runners were habitually barefoot. Overall,

these findings suggest that the cutaneous protection in

MSH and shoes may allow greater propulsive GRF in

habitually shod runners. Therefore, these acute differ-

ences in propulsive GRF and ankle kinetics may

indicate that our runners are more cautious in barefoot

running by reducing ankle loading but appear to be

more aggressive in MSH using an ankle strategy

compared to shoes to attenuate a higher LR.In addition, smaller eversion ROM was found in

barefoot compared to MSH and may have also

contributed to force attenuation in MSH. However,

frontal plane ankle kinetic variables were not different

between the shoe groups. Reductions in frontal plane

foot motion leading to greater ankle eversion in stiff

shoe soles have been suggested to be a potential cause

for running injuries (Stacoff et al. 1989). Thus, it is

possible that greater eversion found in MSH could lead

to running-related injuries but our findings only

pertain to acute changes in joint motion. In addition,

ankle inversion moment was not different, indicating

similar frontal plane ankle involvement between shoeconditions.

Peak knee flexion and ROM, peak extensormoment, peak early stance eccentric and late stanceconcentric power were reduced in barefoot and MSHcompared to shoes. Lieberman et al. (2010) alsoshowed that barefoot runners produce smaller kneeflexion ROM compared to shod runners during theimpact phase of stance. However, Squadrone andGallozzi (2009) showed no difference in knee flexionROM between barefoot, MSH and shod but greatankle dorsiflexion ROM in habitual barefoot runnersduring treadmill running. The smaller peak kneeflexion and ROM in barefoot may be explained bythe greater ST in shoes compared to barefoot, whichwould provide more time to increase knee flexionduring stance. In shoes, the knee appears to be largelyinvolved in early stance energy storing in preparationfor greater force generation at push-off. However, itappears that MSH may play a greater role at the anklerather than the knee by making elastic energy stored inearly stance available in late stance. The greater LRcoupled with the lack of cushioning materials under thefeet may provide an explanation for the greater kineticankle involvement in MSH as a strategy to immedi-ately attenuate the rapid GRF loading transmittedproximally to the lower limb. However, the higher loadplaced on the plantarflexors in MSH may increased therisk of developing Achilles tendinopathy over time.

The primary focus of the study was to comparebarefoot, MSH and running shoes but we alsocompared foot strike patterns. Our results indicatethat RFS runners produced a higher LR compared toFFS runners, specifically within the MSH condition.By contrast, LR has been shown to be much higher inbarefoot RFS compared to barefoot FFS (Liebermanet al. 2010) and in habitual shod RFS asked to adoptan FFS during one testing session compared to RFS(Laughton et al. 2003). Researchers have attributedthis lower LR in FFS to the transfer of translationalenergy into rotational energy at the ankle in FFS(Lieberman et al. 2010). Longitudinal studies on theeffects of foot strike in MSH and barefoot running oninjury risk are warranted.

Finally, our finding that dorsiflexion ROM wasgreater in FFS compared to RFS runners is consistentwith previous research (Laughton et al. 2003, Arendseet al. 2004, Stackhouse et al. 2004, Lieberman et al.2010). The more anterior COP location and flatter footposition in FFS runners allow for greater ROM at theankle as the heel is lowered to the ground in mid-stance. Our results showed smaller knee flexion ROMand greater peak knee eccentric power in FFScompared to RFS runners. Other researchers have

also found greater peak knee eccentric power in FFS

compared to RFS running (Laughton et al. 2003,

Stackhouse et al. 2004) and greater knee joint stiffness

(Laughton et al. 2003) has been reported in the

literature. In addition, greater knee flexion immedi-

ately before impact using a human pendulum device

has been shown to increase overall axial shock

attenuation (Lafortune et al. 1996). Thus, smaller

knee flexion ROM may indicate greater knee extensor

involvement during the loading phase of stance

associated with greater peak knee eccentric power,

which could also explain the smaller LR in FFS

compared to RFS runners.The FFS runner group may have contained MFS

and this may have introduced variability that pre-

vented significant differences being observed between

footwear or foot strike groups. In addition, only

unilateral biomechanical variables were analysed in

this study. Thus, it is possible that differences in

spatiotemporal variables of running gait such as step

length and frequency were overlooked and may have

altered lower limb biomechanics between runners.

Finally, differences in marker placement on the shoes

or foot may have introduced errors in foot and ankle

variable computations, although the same researcher

placed markers for each footwear condition.

5. Conclusions

Our findings indicate that LR was greater in barefoot

and MSH compared to shoes in RFS runners. This

may indicate that RFS runners may be susceptible to

greater lower limb loading during the impact phase of

running stance in barefoot and MSH. Because the LR

was reduced in FFS compared to RFS runners,

adopting an FFS may be beneficial for habitually

shod RFS runners. However, habitually shod RFS

runners should be cautious when running in barefoot

and MSH for the first time because of the greater LR

compared to shoes and the greater plantarflexor

moment found in MSH compared to barefoot and

shoes. MSH appear to increase eccentric ankle joint

plantarflexor involvement in the sagittal plane com-

pared to shoes, while shoes increase eccentric knee

joint extensor involvement in the sagittal plane in

habitually shod distance runners. This study focused

on the acute effects of different footwear and therefore

training interventions in MSH and barefoot are

warranted to further understand their adaptation

effects on lower limb biomechanics and running

performance after adaptation periods.

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