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Influence of shod/unshod condition and running speed on foot-strike patterns, inversion/eversion, and vertical foot rotation in endurance runners a
a
b
M. Muñoz-Jimenez , P.A. Latorre-Román , V.M. Soto-Hermoso & F. García-Pinillos a
a
Department of Didactics of Corporal Expression, University of Jaén, Spain
b
Faculty of Sport Sciences, University of Granada, Spain Published online: 27 Mar 2015.
Click for updates To cite this article: M. Muñoz-Jimenez, P.A. Latorre-Román, V.M. Soto-Hermoso & F. García-Pinillos (2015): Influence of shod/ unshod condition and running speed on foot-strike patterns, inversion/eversion, and vertical foot rotation in endurance runners, Journal of Sports Sciences, DOI: 10.1080/02640414.2015.1026377 To link to this article: http://dx.doi.org/10.1080/02640414.2015.1026377
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Journal of Sports Sciences, 2015 http://dx.doi.org/10.1080/02640414.2015.1026377
Influence of shod/unshod condition and running speed on foot-strike patterns, inversion/eversion, and vertical foot rotation in endurance runners
M. MUÑOZ-JIMENEZ1, P.A. LATORRE-ROMÁN1, V.M. SOTO-HERMOSO2 & F. GARCÍA-PINILLOS1 1
Department of Didactics of Corporal Expression, University of Jaén, Spain and 2Faculty of Sport Sciences, University of Granada, Spain
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(Accepted 2 March 2015)
Abstract The aim of this study was to determine the influence of barefoot running on foot-strike patterns, eversion–inversion, running speed and vertical foot rotation in endurance runners. Eighty healthy recreational runners (age = 34.11 ± 12.95 years old, body mass index = 22.56 ± 2.65 kg · m−2) performed trials in shod/unshod running conditions on a treadmill at comfortable and competitive self-selected speeds. Data were collected by systematic observation of lateral and back recordings at 240 Hz. McNemar’s test indicated significant differences between shod/unshod conditions and foot strike at comfortable and competitive speeds (P < 0.001). Speed was related to vertical foot rotation type for shod (P < 0.01) and unshod conditions (P < 0.05). Significant differences were found between shod/unshod conditions in foot rotation at comfortable running speeds (P < 0.001) and competitive running speeds (P < 0.01). No significant difference was found in inversion or eversion (P ≥ 0.05). In conclusion, the results suggest that running kinematics, in terms of foot-strike patterns and vertical foot rotation, differ between shod/unshod conditions, while the inversion or eversion degree remains unchanged. Keywords: barefoot, running, kinematics, asymmetry, long distance
Introduction The effect of foot-strike patterns on the economy, performance and injury rates in endurance runners (and its relationship with footwear) has been widely discussed in recent literature (De Wit, De Clercq, & Aerts, 2000; Larson et al., 2011; Lieberman et al., 2010; Squadrone & Gallozzi, 2009). Possible causes of injury may include abrupt collision force (Hart & Smith, 2008; Lieberman et al., 2010), limited proprioception (Robbins & Gouw, 1991) and excessive foot pronation at heel strike (Clarke, Frederick, & Cooper, 1983; Stacoff, Denoth, Kaelin, & Stuessi, 1988). It has been suggested that the model of running shoes could be a key risk factor leading to injury (van Gent et al., 2007), and some authors suggest that habitual barefoot running could prevent impact related injuries (Lieberman et al., 2010; Stacoff, Nigg, Reinschmidt, van den Bogert, & Lundberg, 2000). Some studies have focused on the foot strike of runners and on how changes in running speed and high performance can change the type or the level of
strikes (Hasegawa, Yamauchi, & Kraemer, 2007; Larson et al., 2011). Larson et al. (2011) evaluated 286 sub-elite marathon runners, concluding that between 87.8% and 93.0% of them were rearfoot strikers. Yet, among the fastest runners, the midfoot strike was the most common strike pattern. Thus, it seems that running speed is related to strike pattern. Furthermore, Lieberman et al. (2010) found that 83% of usually shod runners keep a rearfoot strike when running barefoot in acute conditions. That study also mentions that unshod rearfoot strikes resulted in impact force and loading rates significantly higher than in the shod condition. These high magnitudes of impact forces in rearfoot striking, together with the stress by the high number of strikes in endurance training, could be harmful and could put runners at high risk of overuse injuries (Milner, Hamill, & Davis, 2007; Pohl, Hamill, & Davis, 2009). Thus, the risk of injury can be diminished by reducing the magnitude of impact forces, which can be achieved by adopting midfoot or forefoot strikes (Davis, Bowser, & Mullineaux, 2010). Moreover, changing rearfoot to
Correspondence: Marcos Muñoz Jimenez, Department of Didactics of Corporal Expression, University of Jaén, Campus de Las Lagunillas s/n. Building D2, office. 142. 23071, Jaén, Spain. E-mail: [email protected] © 2015 Taylor & Francis
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forefoot strikes may also reduce patella femoral pain (Cheung & Davis, 2011) and pain associated with chronic compartment syndrome of effort (Diebal, Gregory, Alitz, & Gerber, 2012). Furthermore, midfoot strike in barefoot running reduces flight time and causes a lower peak force and higher pre-activation of the sural triceps than shod running (Divert, Mornieux, Baur, Mayer, & Belli, 2005). Finally, Eslami, Begon, Farahpour, and Allard (2007) found significant variations in forefoot adduction/abduction and rearfoot eversion patterns. Eversion and inversion coupling could have little effect on the amount of tibial internal rotation. However, significant variations in the forefoot adduction/abduction and rearfoot eversion or inversion coupling patterns could have more effect on the amount of tibial internal rotations. It remains to be determined whether changes in the frontal plane forefoot–rearfoot coupling patterns influence the tibia kinematics for different shoes (Eslami et al., 2007; Hunt, Smith, Torode, & Keenan, 2001). Furthermore, rearfoot eversion is associated with injury (Pohl & Buckley, 2008), an association characteristic of shod runners (Murphy, Curry, & Matzkin, 2013). On their part, Sinclair, Hobbs, Currigan, Giannandrea, and Taylor (2014) found that barefoot running and minimalist running increased eversion and tibial internal rotation. Misalignments in the lower limb and excessive coronal and transverse plane motion of the ankle and tibia are linked to the development of a number of chronic injuries (Murphy et al., 2013; Sinclair et al., 2014). Considering the above information, the main objective of this study was to determine the influence of barefoot running (running speed included) in these variables in endurance runners.
Methods Participants Eighty healthy recreational runners (59 men and 21 women) from three Spanish athletics clubs volunteered as participants for this study (age = 34.11 ± 12.95 years old; body mass index [BMI] = 22.56 ± 2.65 kg · m−2). Each participant signed an informed consent form to participate in this study. The study was conducted in adherence to the standards of the Declaration of Helsinki (World Medical Association, 2008 version) and followed the European Community’s guidelines for Good Clinical Practice (111/3976/88 of July 1990), as well as the Spanish legal framework for clinical research on humans (Royal Decree 561/1993 on clinical trials). The informed consent and the study were approved by the Bioethics Committee of the University of Jaén (Spain).
Table I. Demographic characteristics and training background of the participants (mean ± s). Mean (s) N = 80 Age Height (cm) Weight (kg) BMI (kg · m−2) km per week Sessions per week Competitions per year
34.11 171.79 66.07 22.56 60.18 5.47 13.08
± ± ± ± ± ± ±
12.95 8.44 10.53 2.65 20.41 1.29 10.50
Note: BMI, Body Mass Index; s, standard deviation.
The inclusion criteria were as follows: (i) all participants were habitually shod runners with no experience in barefoot running; (ii) none of them had suffered any significant injury or pain in the three months prior to the study; (iii) all of them possessed a minimum verifiable performance level [i.e. all of them had participated in regional or national athletics championships]; (iv) athletes had been training for at least four years, five or six times a week, with at least 40 km completed each week. More information about the characteristics of the participants and their training backgrounds are presented in Table I.
Experimental procedure First of all, participants completed a form concerning socio-demographic information, and signed the informed consent. Then they performed the tests (just one attempt for each test). Regarding anthropometric parameters, weight was measured with a body composition analyser (Inbody R20, Biospace, Inc., Seoul, Korea) and height was measured with a stadiometer (Seca 217, Hamburg, Germany). BMI was calculated by dividing body mass (in kilograms) by the square of the height (in metres). The shod running test was performed with participants using their own running shoes, habitually used in their workouts. The order of conditions was randomised so that sometimes the athlete began with the shod tests and other times with the unshod tests. Videos were taken from a lateral and back view. In both cases, the camera was placed two metres away from the runner, perpendicularly to the treadmill at ground level, with no degree of inclination. The place where cameras were placed exactly was marked. Two camcorders with a rate of 240 Hz (Casio Exilim EXF1, Shibuya-ku, Tokyo 151–8543, Japan) were used. Video data were observed subsequently for obtaining data using a 2D video editor (VideoSpeed vs1.38, ErgoSport, Granada, Spain). In this experiment, the participants were asked to run consistently at their comfortable training speed (low speed = LS) and at their competitive speed (high
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Shod-unshod condition in endurance runners speed = HS), chosen by themselves. Before recording, participants had 8 min to warm-up and habituate to the treadmill (Salter E-Line PT-320, Salter International, Barcelona, Spain) and to the different speeds in each condition (shod/unshod/LS/HS). A period of 8 min was chosen because previous studies on human locomotion have shown that major changes for accommodation to a new condition occur within this time period (Divert, Baur, Mornieux, Mayer, & Belli, 2005; Schieb, 1986). The next minute after this warm up was recorded for collecting data. Four steps were analysed in each runner at all conditions (shod/ unshod; comfortable/competitive speed). Athletes were instructed to run (without stopping) at a stable speed in each condition. To make sure that the participants were selecting the speed based on perception, the speed display on the treadmill was covered from the participant’s field of view so that it was visible only to the researcher. Participants were allowed to adjust the speed up and down freely until they found a speed that matched their perceived overground speed. Once
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the runners had confirmed their speed, the researcher recorded the treadmill speed displayed on the screen. When the auto selected comfortable speed test was performed successfully, participants were allowed to increase the speed to their running competitive speed. Once the tests had finished and been recorded, the treadmill stopped and the participant changed to a shod or unshod condition, depending on what the runner had already done. Then the protocol started again, this time in the other condition. The following variables were observed (Lieberman, 2012): foot-strike patterns (first contact with the ground); forefoot strike (the ball of the foot lands before the heel); midfoot strike (heel and sole land simultaneously) and rearfoot strike (heel lands before the ball of the foot). Two other foot strikes were assessed to discriminate the severity of the strikes in rearfoot and forefoot: high rearfoot strike (landing with the second half of the heel, back of the heel) and high forefoot strike (the ball of the foot is the only part of the foot that contacts the ground, see Figure 1). Other
Figure 1. Examples of foot-strike patterns, tibial rotation and inversion or eversion of the foot. From top to bottom and left to the right. Foot-strike patterns: high forefoot strike, forefoot strike, midfoot strike, rearfoot strike and high rearfoot strike. Inversion, centred, eversion. Tibial rotation: over external rotation, external rotation, no rotation and internal rotation.
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variables studied were lateral inversion or eversion and external or internal vertical foot rotation in stance phase in shod/unshod conditions at LS and HS. Also, asymmetries were analysed in each of the above variables. Statistical analyses
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Descriptive statistics are represented as mean (s), frequency and percentage. To analyse the differences between the shod/unshod conditions and the effects of speed, McNemar’s test was used. Reliability intraobserver and interobserver was calculated using the Cohen’s Kappa coefficient. The level of significance was P < 0.05. Data analysis was performed using SPSS (version 21, SPSS Inc., Chicago, IL, USA).
proportion of agreement = 95%, value for inversion Kappa = 0.732, proportion of agreement = 85%, and the Kappa = 0.898 rotation, proportion of agreement = 90%, the average kappa value = 0.844 ± 0.09, considered a very good value (Landis & Koch, 1977). The interobserver reliability was obtained for foot strike Kappa = 0.801 ± 0.09 value, proportion of agreement = 90%, for inversion Kappa = 0.727 ± 0.11, proportion of agreement = 85% and 0.810 for Kappa = 0.08 ± rotation, proportion of agreement = 90%, the average kappa value = 0.780 ± 0.09, considered a good value (Landis & Koch, 1977). As for the sample size, some participants were lost in the analysis due to technical issues when editing and processing the video file (total sample in each analysed variable is showed in tables).
Results
Foot-strike patterns
Reliability intraobserver and interobserver was calculated using Kappa of Cohen. The intraobserver reliability was obtained for foot strike kappa = 0.904,
The frequencies and percentages related to the foot strikes listed in Table II indicate significant differences between shod/unshod conditions in
Table II. Foot strike patterns frequencies and percentages in shod/unshod conditions at low and high speeds and their relations. LSR Condition SLF
ULF
SRF
URF
Shod asymmetry Unshod asymmetry
HSR
FSP
Frequency
Percentage
Frequency
Percentage
P-value
High rearfoot Rearfoot Midfoot Forefoot High forefoot Total High rearfoot Rearfoot Midfoot Forefoot High forefoot Total P-value High rearfoot Rearfoot Midfoot Forefoot High forefoot Total High rearfoot Rearfoot Midfoot Forefoot High forefoot Total P-value Yes Non Yes Non P-value
39 27 5 5 2 78 10 26 20 19 3 78
50.0 34.6 6.4 6.4 2.6 100.0 12.8 33.3 25.6 24.4 3.8 100.0
39 25 7 4 2 77 10 25 27 15 2 79
50.6 32.5 9.1 5.2 2.6 100.0 12.7 31.6 34.2 19.0 2.5 100.0
0.675
51.3 30.8 9.0 6.4 2.6 100.0 17.5 26.3 31.3 21.3 3.8 100.0
39 21 10 5 2 77 12 25 25 15 2 79
50.6 27.3 13.0 6.5 2.6 100.0 15.2 31.6 31.6 19.0 2.5 100.0
0.392
3.9 96.1 6.4 93.6
6 69 9 68
8.0 92.0 11.7 88.3
0.250
< 0.001 40 24 7 5 2 78 14 21 25 17 3 80
< 0.001
< 0.001 3 73 7 73 1.000
0.181
0.298
< 0.001
0.219
0.375
Notes: FSP, foot-strike pattern; LSR, low speed running; HSR, high speed running; FSP, foot strike pattern; SLF, shod left foot; ULF, unshod left foot; SRF, shod right foot; URF, unshod right foot.
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Shod-unshod condition in endurance runners foot-strike pattern at LS and HS for the left and the right foot (P < 0.001). High rearfoot strike is more frequent in the shod condition at LS and HS (LS: 50% shod left foot, 51.3% shod right foot; HS: 50.6% shod left foot, 50.6% shod right foot). Rearfoot strike is quite common in the shod condition (LS: 34.6% shod left foot, 30.8% shod right foot; HS: 32.5% shod left foot, 27.3% shod right foot). When athletes run unshod, the foot-strike pattern changes significantly, becoming closer to midfoot strikes (LS: from 6.4% shod left foot to 25.6% unshod left foot, from 9.0% shod right foot to 31.3% unshod right foot; HS: from 9.1% shod left foot to 34.2% unshod left foot, from 13% shod right foot to 31.6% unshod right foot) or forefoot strike (LS: from 6.4% shod left foot to 24.4% unshod left foot, from 6.4% shod right foot to 21.3% unshod right foot; HS: from 5.2% shod left foot to 19% unshod left foot, from 6.5% shod right foot to 19% unshod right foot). There was no significant difference (P ≥ 0.05) in shod/ unshod conditions at different speeds analysed (LS and HS). There were no significant differences in the frequency of asymmetries of foot-strike pattern between LS and HS or shod/unshod conditions (P ≥ 0.05).
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Vertical foot rotation Frequencies and percentages of vertical foot rotation in endurance runners are presented in Table III. External rotation was predominant in all conditions. The results show that speed is related to foot rotation type for the shod condition (P < 0.01). The unshod left foot, even with a lower value, also reached significant results (P < 0.05). Statistical tests indicated significant differences in shod/unshod conditions in the right foot for vertical foot rotation at LS and HS (P < 0.001). For the left foot, significant differences were also common at both speeds (LS: P < 0.001; HS: P < 0.01). There were no significant differences in the frequency of asymmetries of foot rotation between LS and HS or shod/ unshod conditions (P ≥ 0.05).
Inversion/eversion of the foot Inversion was observed in most of the cases studied (Table IV). In shod conditions at LS, inversion of the foot appeared in 67.6% of the shod left foot and 64.8% of the shod right foot. At HS, percentages increased (69% shod left foot, 69% shod right foot). For the unshod condition, percentages were similar (LS: 63.9% unshod left foot, 68.1% unshod right foot).
Table III. Influence of speed and race condition in foot vertical rotation. LSR Condition SLF
ULF
SRF
URF
Shod asymmetry Unshod asymmetry
VFR Over external rotation External rotation No rotation Internal rotation Total Over external rotation External rotation No rotation Internal rotation Total P-value Over external rotation External rotation No rotation Internal rotation Total Over external rotation External rotation No rotation Internal Total P-value Yes No Yes No P-value
Frequency
HSR Percentage
4 32 32 3 71 11 37 20 4 72
Frequency
5.6 45.1 45.1 4.2 100.0 15.3 51.4 27.8 5.6 100.0
9 34 25 3 71 15 37 15 4 71
7.0 69.0 21.1 2.8 100.0 30.6 55.6 13.9 0.00 100.0
12 47 11 1 71 25 38 8 0.00 71
< 0.001 5 49 15 2 71 22 40 10 0.00 72
12.7 47.9 35.2 4.2 100.0 21.1 52.1 21.1 5.6 100.0
0.002
16.9 66.2 15.5 1.4 100.0 35.2 53.5 11.3 0.00 100.0
0.009
33.3 66.7 40.6 59.4
0.581
0.018
0.223
< 0.001 37.7 62.3 41.4 58.6
1.000
P-value
0.007
< 0.001 26 43 29 41
Percentage
23 46 28 41
1.000
0.424
Notes: LSR, low speed running; HSR, high speed running; VFR, vertical foot rotation; SLF, shod left foot; ULF, unshod left foot; SRF, shod right foot; URF, unshod right foot.
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M. Muñoz-Jimenez et al. Table IV. Effects in inversion and eversion of the foot at different speeds and conditions. LSR
Condition
INV/EVE
Frequency
Percentage
Frequency
Percentage
P-value
SLF
Eversion Centred Inversion Total Eversion Centred Inversion Total P-value Eversion Centred Inversion Total Eversion Centred Inversion Total P-value Yes No Yes No P-value
1 22 48 71 1 25 46 72
1.4 31.0 67.6 100.0 1.4 34.7 63.9 100.0
1 21 49 71 1 18 52 71
1.4 29.6 69.0 100.0 1.4 25.4 73.2 100.0
0.564
1.4 33.8 64.8 100.0 1.4 30.6 68.1 100.0
1 21 49 71 1 20 50 71
5.8 94.2 17.1 82.9
6 63 12 57
ULF
SRF
URF
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HSR
Shod asymmetry Unshod asymmetry
0.491 1 24 46 71 1 22 49 72
0.439
0.467 4 65 12 58 0.065
0.160
1.4 29.6 69.0 100.0 1.4 28.2 70.4 100.0
0.830
0.500
0.637 8.7 91.3 17.4 82.6
0.625 1.000
0.180
Notes: LSR, low speed running; HSR, high speed running; INV/EVE, inversion or eversion of the foot; SLF, shod left foot; ULF, unshod left foot; SRF, shod right foot; URF, unshod right foot.
HS percentages were 73.2% of the unshod left foot and 70.4% of the unshod right foot. Significance was not found (P ≥ 0.05) between shod/unshod conditions and running speeds in inversion or eversion. Therefore, there were no significant differences in the frequency of asymmetries of inversion/eversion between LS and HS or shod/unshod conditions (P ≥ 0.05). Discussion Reliability intraobserver and interobserver were considered as very good results (Landis & Koch, 1977). The main aim of this study was to analyse kinematic changes in the running patterns of endurance runners, comparing both shod/unshod running conditions and LS/HS conditions. The results of this investigation showed and confirmed that barefoot running causes changes in foot-strike pattern from a rearfoot to a midfoot-strike pattern, which further causes alterations in other kinematic variables like vertical foot rotation. On the contrary, inversion/ eversion remains unchanged. Data obtained about foot-strike pattern at LS showed that in the shod condition most runners used high rearfoot or a rearfoot-strike pattern. Available published data from in-race studies conducted to date indicate that approximately 75–80% of runners are rearfoot strikers when initially contacting the ground (Hasegawa et al., 2007). The
prevalence of rearfoot strike is even greater according to other authors, such as Kasmer, Liu, Roberts, and Valadao (2013), who observed a 93.67% rearfoot strike prevalence in marathon runners. In the LS unshod condition, participants changed their foot-strike pattern to midfoot or forefoot strike, decreasing the percentage of the high rearfoot and rearfoot-strike pattern. When running at HS in shod conditions, most runners used high rearfoot or rearfoot strike. In the HS unshod condition, foot-strike pattern changed to midfoot or forefoot strike. Rearfoot striking had a prevalence of 31.6% in both feet. These findings confirm the conclusions of previous works (Altman & Davis, 2012; Gruber, Silvernail, Brueggemann, Rohr, & Hamill, 2013; Hamill, Russell, Gruber, & Miller, 2011; Lieberman et al., 2010), which note that the biggest difference between barefoot runners and shod runners occurs at the initial contact phase of gait; at that moment barefoot runners use forefoot or midfoot strike, whereas shod runners use rearfoot strike. Hence, as Hamill et al. (2011) indicated, runners will generally adopt a forefoot or midfoot footfall pattern when running barefoot on a firm surface, possibly to avoid heel contact on the hard surface. As for the vertical foot rotation, Eslami et al. (2007) concluded that forefoot–rearfoot strike coupling motion patterns could contribute to the amount of tibial rotation. In this sense, the main
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Shod-unshod condition in endurance runners finding about vertical foot rotation was the increase in the unshod condition in the percentage of over external rotation and external rotation in both the left foot and the right foot at LS and HS. However, Eslami et al. (2007) found no significant differences in the tibial internal rotation excursion between shod/unshod conditions, results similar to those obtained by Stacoff et al. (2000), who compared normal shod/unshod running via the direct measurement of markers fixed on bones. Excessive coronal and transverse plane motions of the ankle and tibia are linked to the development of a number of chronic injuries (Murphy et al., 2013; Sinclair et al., 2014). To date, foot rotation of barefoot running has not been documented in the literature. Available literature on this topic is scarce and more research is needed to assess the effect of barefoot running on vertical foot rotation. Concerning the degree of inversion/eversion, the results obtained demonstrate that a high percentage of runners showed inversion when running in both conditions and speeds. This data obtained on the treadmill can be compared with previous findings obtained in race, such as those by Hasegawa et al. (2007), who got a lower prevalence (42%). Yet, the most important finding of this investigation was that no significant difference in the degree of inversion/ eversion was found between shod/unshod running conditions. Schutte, Miles, Venter, and Van Niekerk (2013) found no significant difference in ankle inversion/adduction between the barefoot and shod conditions. However, rearfoot eversion is characteristic in shod runners (Murphy et al., 2013). For their part, Sinclair et al. (2014) found that barefoot running and minimalist running increased eversion and tibial internal rotation. Nonetheless, Stacoff et al. (2000) maintained that participants tended to show less inversion on average, compared to shod in barefoot running conditions The second major aim of this study was to analyse the influence of running speed in both shod/unshod conditions in the controlled variables (foot-strike pattern, vertical foot rotation and inversion/eversion). In this sense, the main finding was that an increase of the running speed (from LS to HS) did not cause significant changes in foot strikes or inversion/eversion in any of both the shod/unshod conditions. Nevertheless, several studies suggest that footstrike pattern depends, at least in part, upon running speed (Hatala, Dingwall, Wunderlich, & Richmond, 2013; Keller et al., 1996). In this study, the increase of running speed entails significant alterations in vertical foot rotation in both shod and unshod conditions. Specifically, the results showed that an increase of running speed is associated with an increase in the percentage of over external rotation. The literature about this is scanty and more research
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is needed to assess the effect of speed on foot rotation. Finally, numerous studies have documented gait asymmetry in runners, particularly as it relates to injury risk (Zifchock, Davis, & Hamill, 2006; Zifchock, Davis, Higginson, McCaw, & Royer, 2008). However, to our knowledge, there are only a few studies (Larson et al., 2011) focused on the effect of the shod condition on foot strikes, inversion/eversion and degree asymmetry in runners not accustomed to barefoot running. The data obtained in the present study showed that the shod/unshod condition is not decisive for the presence of asymmetry, since no significant difference was recorded in any of the variables analysed. Larson et al. (2011) found that asymmetrical runners show rearfoot striking more often on the left side and forefoot or midfoot striking on the right side. In most cases, asymmetries were relatively minor, with one foot landing on the midfoot and the other landing slightly more towards the heel. It is unclear whether these asymmetrical landing patterns were simply chance observations of a single unusual foot strike sequence or genuine gait asymmetries. A limitation of the study was the occurrence of certain problems when editing and processing the video file, which resulted in the damage and loss of video files. Moreover, the issue of accuracy in using 2D video analysis to determine analysed variables and, specifically vertical foot rotation, must be considered an important limitation. Summing up, the results of this study suggest that running kinematics, in terms of foot-strike pattern and vertical foot rotation differ between shod/unshod conditions, while the inversion/eversion degree remains unchanged. Moreover, running speed significantly influences lower limb kinematics in endurance runners, specifically vertical foot rotation, so that an increase in running speed is associated with a higher prevalence of external rotation, although running speed does not influence footfall pattern or inversion/eversion degree. More research is needed to clarify the effectiveness of barefoot training programmes on the foot-strike patterns of endurance runners.
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Davis, I. S., Bowser, B., & Mullineaux, D. (2010). Do impacts cause running injuries? A prospective investigation. ASB. Retrieved from http://www.asbweb.org/conferences/2010/ abstracts/472.pdf De Wit, B., De Clercq, D., & Aerts, P. (2000). Biomechanical analysis of the stance phase during barefoot and shod running. Journal of Biomechanics, 33, 269–278. Diebal, A. R., Gregory, R., Alitz, C., & Gerber, J. P. (2012). Forefoot running improves pain and disability associated with chronic exertional compartment syndrome. The American Journal of Sports Medicine, 40, 1060–1067. Divert, C., Baur, H., Mornieux, G., Mayer, F., & Belli, A. (2005). Stiffness adaptations in shod running. Journal of Applied Biomechanics, 21, 311. Divert, C., Mornieux, G., Baur, H., Mayer, F., & Belli, A. (2005). Mechanical comparison of barefoot and shod running. International Journal of Sports Medicine, 26, 593–598. Eslami, M., Begon, M., Farahpour, N., & Allard, P. (2007). Forefoot–rearfoot coupling patterns and tibial internal rotation during stance phase of barefoot versus shod running. Clinical Biomechanics, 22, 74–80. Gruber, A. H., Silvernail, J. F., Brueggemann, P., Rohr, E., & Hamill, J. (2013). Footfall patterns during barefoot running on harder and softer surfaces. Footwear Science, 5, 39–44. Hamill, J., Russell, E. M., Gruber, A. H., & Miller, R. (2011). Impact characteristics in shod and barefoot running. Footwear Science, 3, 33–40. Hart, P. M., & Smith, D. R. (2008). Preventing running injuries through barefoot activity. Journal of Physical Education, Recreation & Dance, 79, 50–53. Hasegawa, H., Yamauchi, T., & Kraemer, W. J. (2007). Foot strike patterns of runners at the 15-km point during an elitelevel half marathon. The Journal of Strength & Conditioning Research, 21, 888–893. Hatala, K. G., Dingwall, H. L., Wunderlich, R. E., & Richmond, B. G. (2013). Variation in foot strike patterns during running among habitually barefoot populations. PloSone, 8, e52548. Hunt, A. E., Smith, R. M., Torode, M., & Keenan, A.-M. (2001). Inter-segment foot motion and ground reaction forces over the stance phase of walking. Clinical Biomechanics, 16, 592–600. Kasmer, M. E., Liu, X. C., Roberts, K. G., & Valadao, J. M. (2013). Foot-strike pattern and performance in a marathon. International Journal of Sports and Physiology Performance, 8, 286–292. Keller, T. S., Weisberger, A. M., Ray, J. L., Hasan, S. S., Shiavi, R. G., & Spengler, D. M. (1996). Relationship between vertical ground reaction force and speed during walking, slow jogging, and running. Clinical Biomechanics, 11, 253–259. Landis, J. R., & Koch, G. G. (1977). The measurement of observer agreement for categorical data. Biometrics, 33, 159–174. Larson, P., Higgins, E., Kaminski, J., Decker, T., Preble, J., Lyons, D., … & Normile, A. (2011). Foot strike patterns of recreational and sub-elite runners in a long-distance road race. Journal of Sports Sciences, 29, 1665–1673. Lieberman, D. E. (2012). What we can learn about running from barefoot running: An evolutionary medical perspective. Exercise and Sport Sciences Reviews, 40, 63–72.
Lieberman, D. E., Venkadesan, M., Werbel, W. A., Daoud, A. I., D’Andrea, S., Davis, I. S., … & Pitsiladis, Y. (2010). Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature, 463, 531–535. Milner, C. E., Hamill, J., & Davis, I. (2007). Are knee mechanics during early stance related to tibial stress fracture in runners? Clinical Biomechanics, 22, 697–703. Murphy, K., Curry, E. J., & Matzkin, E. G. (2013). Barefoot running: Does it prevent injuries? Sports Medicine, 43, 1131–1138. Pohl, M. B., & Buckley, J. G. (2008). Changes in foot and shank coupling due to alterations in foot strike pattern during running. Clinical Biomechanics, 23, 334–341. Pohl, M. B., Hamill, J., & Davis, I. S. (2009). Biomechanical and anatomic factors associated with a history of plantar fasciitis in female runners. Clinical Journal of Sport Medicine, 19, 372–376. Robbins, S. E., & Gouw, G. J. (1991). Athletic footwear: Unsafe due to perceptual illusions. Medicine & Science in Sports & Exercise, 23, 217–224. Schieb, D. A. (1986). Kinematic accommodation of novice treadmill runners. Research Quarterly for Exercise and Sport, 57, 1–7. Schutte, K. H., Miles, K. C., Venter, R. E., & Van Niekerk, S. M. (2013). Barefoot running causes acute changes in lower limb kinematics in habitually shod male runners. South African Journal for Research in Sport, Physical Education and Recreation, 35(1), 153–164. Sinclair, J., Hobbs, S. J., Currigan, G., Giannandrea, M., & Taylor, P. J. (2014). Tibiocalcaneal kinematics during barefoot and in barefoot inspired shoes in comparison to conventional running footwear. Movement & Sport Sciences, 1, 67–75. Squadrone, R., & Gallozzi, C. (2009). Biomechanical and physiological comparison of barefoot and two shod conditions in experienced barefoot runners. Journal of Sports Medicine and Physical Fitness, 49, 6–13. Stacoff, A., Denoth, J., Kaelin, X., & Stuessi, E. (1988). Running injuries and shoe construction: Some possible relationships. International Journal of Sport Biomechanics, 4, 342–357. Stacoff, A., Nigg, B. M., Reinschmidt, C., van den Bogert, A. J., & Lundberg, A. (2000). Tibiocalcaneal kinematics of barefoot versus shod running. Journal of Biomechanics, 33(11), 1387–1395. Van Gent, R. N., Siem, D., van Middelkoop, M., Van Os, A. G., Bierma-Zeinstra, S. M. A., & Koes, B. W. (2007). Incidence and determinants of lower extremity running injuries in longdistance runners: A systematic review. British Journal of Sports Medicine, 41, 469–480. World Medical Association. (2008). Declaration of Helsinki. Ethical principles for medical research involving human subjects. Retrieved from http://www.wma.net/e/policy/b3.htm Zifchock, R. A., Davis, I., & Hamill, J. (2006). Kinetic asymmetry in female runners with and without retrospective tibial stress fractures. Journal of Biomechanics, 39, 2792–2797. Zifchock, R. A., Davis, I., Higginson, J., McCaw, S., & Royer, T. (2008). Side-to-side differences in overuse running injury susceptibility: A retrospective study. Human Movement Science, 27, 888–902.
Journal of Sports Sciences Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rjsp20
Influence of shod/unshod condition and running speed on foot-strike patterns, inversion/eversion, and vertical foot rotation in endurance runners a
a
b
M. Muñoz-Jimenez , P.A. Latorre-Román , V.M. Soto-Hermoso & F. García-Pinillos a
a
Department of Didactics of Corporal Expression, University of Jaén, Spain
b
Faculty of Sport Sciences, University of Granada, Spain Published online: 27 Mar 2015.
Click for updates To cite this article: M. Muñoz-Jimenez, P.A. Latorre-Román, V.M. Soto-Hermoso & F. García-Pinillos (2015): Influence of shod/ unshod condition and running speed on foot-strike patterns, inversion/eversion, and vertical foot rotation in endurance runners, Journal of Sports Sciences, DOI: 10.1080/02640414.2015.1026377 To link to this article: http://dx.doi.org/10.1080/02640414.2015.1026377
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Journal of Sports Sciences, 2015 http://dx.doi.org/10.1080/02640414.2015.1026377
Influence of shod/unshod condition and running speed on foot-strike patterns, inversion/eversion, and vertical foot rotation in endurance runners
M. MUÑOZ-JIMENEZ1, P.A. LATORRE-ROMÁN1, V.M. SOTO-HERMOSO2 & F. GARCÍA-PINILLOS1 1
Department of Didactics of Corporal Expression, University of Jaén, Spain and 2Faculty of Sport Sciences, University of Granada, Spain
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(Accepted 2 March 2015)
Abstract The aim of this study was to determine the influence of barefoot running on foot-strike patterns, eversion–inversion, running speed and vertical foot rotation in endurance runners. Eighty healthy recreational runners (age = 34.11 ± 12.95 years old, body mass index = 22.56 ± 2.65 kg · m−2) performed trials in shod/unshod running conditions on a treadmill at comfortable and competitive self-selected speeds. Data were collected by systematic observation of lateral and back recordings at 240 Hz. McNemar’s test indicated significant differences between shod/unshod conditions and foot strike at comfortable and competitive speeds (P < 0.001). Speed was related to vertical foot rotation type for shod (P < 0.01) and unshod conditions (P < 0.05). Significant differences were found between shod/unshod conditions in foot rotation at comfortable running speeds (P < 0.001) and competitive running speeds (P < 0.01). No significant difference was found in inversion or eversion (P ≥ 0.05). In conclusion, the results suggest that running kinematics, in terms of foot-strike patterns and vertical foot rotation, differ between shod/unshod conditions, while the inversion or eversion degree remains unchanged. Keywords: barefoot, running, kinematics, asymmetry, long distance
Introduction The effect of foot-strike patterns on the economy, performance and injury rates in endurance runners (and its relationship with footwear) has been widely discussed in recent literature (De Wit, De Clercq, & Aerts, 2000; Larson et al., 2011; Lieberman et al., 2010; Squadrone & Gallozzi, 2009). Possible causes of injury may include abrupt collision force (Hart & Smith, 2008; Lieberman et al., 2010), limited proprioception (Robbins & Gouw, 1991) and excessive foot pronation at heel strike (Clarke, Frederick, & Cooper, 1983; Stacoff, Denoth, Kaelin, & Stuessi, 1988). It has been suggested that the model of running shoes could be a key risk factor leading to injury (van Gent et al., 2007), and some authors suggest that habitual barefoot running could prevent impact related injuries (Lieberman et al., 2010; Stacoff, Nigg, Reinschmidt, van den Bogert, & Lundberg, 2000). Some studies have focused on the foot strike of runners and on how changes in running speed and high performance can change the type or the level of
strikes (Hasegawa, Yamauchi, & Kraemer, 2007; Larson et al., 2011). Larson et al. (2011) evaluated 286 sub-elite marathon runners, concluding that between 87.8% and 93.0% of them were rearfoot strikers. Yet, among the fastest runners, the midfoot strike was the most common strike pattern. Thus, it seems that running speed is related to strike pattern. Furthermore, Lieberman et al. (2010) found that 83% of usually shod runners keep a rearfoot strike when running barefoot in acute conditions. That study also mentions that unshod rearfoot strikes resulted in impact force and loading rates significantly higher than in the shod condition. These high magnitudes of impact forces in rearfoot striking, together with the stress by the high number of strikes in endurance training, could be harmful and could put runners at high risk of overuse injuries (Milner, Hamill, & Davis, 2007; Pohl, Hamill, & Davis, 2009). Thus, the risk of injury can be diminished by reducing the magnitude of impact forces, which can be achieved by adopting midfoot or forefoot strikes (Davis, Bowser, & Mullineaux, 2010). Moreover, changing rearfoot to
Correspondence: Marcos Muñoz Jimenez, Department of Didactics of Corporal Expression, University of Jaén, Campus de Las Lagunillas s/n. Building D2, office. 142. 23071, Jaén, Spain. E-mail: [email protected] © 2015 Taylor & Francis
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forefoot strikes may also reduce patella femoral pain (Cheung & Davis, 2011) and pain associated with chronic compartment syndrome of effort (Diebal, Gregory, Alitz, & Gerber, 2012). Furthermore, midfoot strike in barefoot running reduces flight time and causes a lower peak force and higher pre-activation of the sural triceps than shod running (Divert, Mornieux, Baur, Mayer, & Belli, 2005). Finally, Eslami, Begon, Farahpour, and Allard (2007) found significant variations in forefoot adduction/abduction and rearfoot eversion patterns. Eversion and inversion coupling could have little effect on the amount of tibial internal rotation. However, significant variations in the forefoot adduction/abduction and rearfoot eversion or inversion coupling patterns could have more effect on the amount of tibial internal rotations. It remains to be determined whether changes in the frontal plane forefoot–rearfoot coupling patterns influence the tibia kinematics for different shoes (Eslami et al., 2007; Hunt, Smith, Torode, & Keenan, 2001). Furthermore, rearfoot eversion is associated with injury (Pohl & Buckley, 2008), an association characteristic of shod runners (Murphy, Curry, & Matzkin, 2013). On their part, Sinclair, Hobbs, Currigan, Giannandrea, and Taylor (2014) found that barefoot running and minimalist running increased eversion and tibial internal rotation. Misalignments in the lower limb and excessive coronal and transverse plane motion of the ankle and tibia are linked to the development of a number of chronic injuries (Murphy et al., 2013; Sinclair et al., 2014). Considering the above information, the main objective of this study was to determine the influence of barefoot running (running speed included) in these variables in endurance runners.
Methods Participants Eighty healthy recreational runners (59 men and 21 women) from three Spanish athletics clubs volunteered as participants for this study (age = 34.11 ± 12.95 years old; body mass index [BMI] = 22.56 ± 2.65 kg · m−2). Each participant signed an informed consent form to participate in this study. The study was conducted in adherence to the standards of the Declaration of Helsinki (World Medical Association, 2008 version) and followed the European Community’s guidelines for Good Clinical Practice (111/3976/88 of July 1990), as well as the Spanish legal framework for clinical research on humans (Royal Decree 561/1993 on clinical trials). The informed consent and the study were approved by the Bioethics Committee of the University of Jaén (Spain).
Table I. Demographic characteristics and training background of the participants (mean ± s). Mean (s) N = 80 Age Height (cm) Weight (kg) BMI (kg · m−2) km per week Sessions per week Competitions per year
34.11 171.79 66.07 22.56 60.18 5.47 13.08
± ± ± ± ± ± ±
12.95 8.44 10.53 2.65 20.41 1.29 10.50
Note: BMI, Body Mass Index; s, standard deviation.
The inclusion criteria were as follows: (i) all participants were habitually shod runners with no experience in barefoot running; (ii) none of them had suffered any significant injury or pain in the three months prior to the study; (iii) all of them possessed a minimum verifiable performance level [i.e. all of them had participated in regional or national athletics championships]; (iv) athletes had been training for at least four years, five or six times a week, with at least 40 km completed each week. More information about the characteristics of the participants and their training backgrounds are presented in Table I.
Experimental procedure First of all, participants completed a form concerning socio-demographic information, and signed the informed consent. Then they performed the tests (just one attempt for each test). Regarding anthropometric parameters, weight was measured with a body composition analyser (Inbody R20, Biospace, Inc., Seoul, Korea) and height was measured with a stadiometer (Seca 217, Hamburg, Germany). BMI was calculated by dividing body mass (in kilograms) by the square of the height (in metres). The shod running test was performed with participants using their own running shoes, habitually used in their workouts. The order of conditions was randomised so that sometimes the athlete began with the shod tests and other times with the unshod tests. Videos were taken from a lateral and back view. In both cases, the camera was placed two metres away from the runner, perpendicularly to the treadmill at ground level, with no degree of inclination. The place where cameras were placed exactly was marked. Two camcorders with a rate of 240 Hz (Casio Exilim EXF1, Shibuya-ku, Tokyo 151–8543, Japan) were used. Video data were observed subsequently for obtaining data using a 2D video editor (VideoSpeed vs1.38, ErgoSport, Granada, Spain). In this experiment, the participants were asked to run consistently at their comfortable training speed (low speed = LS) and at their competitive speed (high
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Shod-unshod condition in endurance runners speed = HS), chosen by themselves. Before recording, participants had 8 min to warm-up and habituate to the treadmill (Salter E-Line PT-320, Salter International, Barcelona, Spain) and to the different speeds in each condition (shod/unshod/LS/HS). A period of 8 min was chosen because previous studies on human locomotion have shown that major changes for accommodation to a new condition occur within this time period (Divert, Baur, Mornieux, Mayer, & Belli, 2005; Schieb, 1986). The next minute after this warm up was recorded for collecting data. Four steps were analysed in each runner at all conditions (shod/ unshod; comfortable/competitive speed). Athletes were instructed to run (without stopping) at a stable speed in each condition. To make sure that the participants were selecting the speed based on perception, the speed display on the treadmill was covered from the participant’s field of view so that it was visible only to the researcher. Participants were allowed to adjust the speed up and down freely until they found a speed that matched their perceived overground speed. Once
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the runners had confirmed their speed, the researcher recorded the treadmill speed displayed on the screen. When the auto selected comfortable speed test was performed successfully, participants were allowed to increase the speed to their running competitive speed. Once the tests had finished and been recorded, the treadmill stopped and the participant changed to a shod or unshod condition, depending on what the runner had already done. Then the protocol started again, this time in the other condition. The following variables were observed (Lieberman, 2012): foot-strike patterns (first contact with the ground); forefoot strike (the ball of the foot lands before the heel); midfoot strike (heel and sole land simultaneously) and rearfoot strike (heel lands before the ball of the foot). Two other foot strikes were assessed to discriminate the severity of the strikes in rearfoot and forefoot: high rearfoot strike (landing with the second half of the heel, back of the heel) and high forefoot strike (the ball of the foot is the only part of the foot that contacts the ground, see Figure 1). Other
Figure 1. Examples of foot-strike patterns, tibial rotation and inversion or eversion of the foot. From top to bottom and left to the right. Foot-strike patterns: high forefoot strike, forefoot strike, midfoot strike, rearfoot strike and high rearfoot strike. Inversion, centred, eversion. Tibial rotation: over external rotation, external rotation, no rotation and internal rotation.
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variables studied were lateral inversion or eversion and external or internal vertical foot rotation in stance phase in shod/unshod conditions at LS and HS. Also, asymmetries were analysed in each of the above variables. Statistical analyses
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Descriptive statistics are represented as mean (s), frequency and percentage. To analyse the differences between the shod/unshod conditions and the effects of speed, McNemar’s test was used. Reliability intraobserver and interobserver was calculated using the Cohen’s Kappa coefficient. The level of significance was P < 0.05. Data analysis was performed using SPSS (version 21, SPSS Inc., Chicago, IL, USA).
proportion of agreement = 95%, value for inversion Kappa = 0.732, proportion of agreement = 85%, and the Kappa = 0.898 rotation, proportion of agreement = 90%, the average kappa value = 0.844 ± 0.09, considered a very good value (Landis & Koch, 1977). The interobserver reliability was obtained for foot strike Kappa = 0.801 ± 0.09 value, proportion of agreement = 90%, for inversion Kappa = 0.727 ± 0.11, proportion of agreement = 85% and 0.810 for Kappa = 0.08 ± rotation, proportion of agreement = 90%, the average kappa value = 0.780 ± 0.09, considered a good value (Landis & Koch, 1977). As for the sample size, some participants were lost in the analysis due to technical issues when editing and processing the video file (total sample in each analysed variable is showed in tables).
Results
Foot-strike patterns
Reliability intraobserver and interobserver was calculated using Kappa of Cohen. The intraobserver reliability was obtained for foot strike kappa = 0.904,
The frequencies and percentages related to the foot strikes listed in Table II indicate significant differences between shod/unshod conditions in
Table II. Foot strike patterns frequencies and percentages in shod/unshod conditions at low and high speeds and their relations. LSR Condition SLF
ULF
SRF
URF
Shod asymmetry Unshod asymmetry
HSR
FSP
Frequency
Percentage
Frequency
Percentage
P-value
High rearfoot Rearfoot Midfoot Forefoot High forefoot Total High rearfoot Rearfoot Midfoot Forefoot High forefoot Total P-value High rearfoot Rearfoot Midfoot Forefoot High forefoot Total High rearfoot Rearfoot Midfoot Forefoot High forefoot Total P-value Yes Non Yes Non P-value
39 27 5 5 2 78 10 26 20 19 3 78
50.0 34.6 6.4 6.4 2.6 100.0 12.8 33.3 25.6 24.4 3.8 100.0
39 25 7 4 2 77 10 25 27 15 2 79
50.6 32.5 9.1 5.2 2.6 100.0 12.7 31.6 34.2 19.0 2.5 100.0
0.675
51.3 30.8 9.0 6.4 2.6 100.0 17.5 26.3 31.3 21.3 3.8 100.0
39 21 10 5 2 77 12 25 25 15 2 79
50.6 27.3 13.0 6.5 2.6 100.0 15.2 31.6 31.6 19.0 2.5 100.0
0.392
3.9 96.1 6.4 93.6
6 69 9 68
8.0 92.0 11.7 88.3
0.250
< 0.001 40 24 7 5 2 78 14 21 25 17 3 80
< 0.001
< 0.001 3 73 7 73 1.000
0.181
0.298
< 0.001
0.219
0.375
Notes: FSP, foot-strike pattern; LSR, low speed running; HSR, high speed running; FSP, foot strike pattern; SLF, shod left foot; ULF, unshod left foot; SRF, shod right foot; URF, unshod right foot.
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Shod-unshod condition in endurance runners foot-strike pattern at LS and HS for the left and the right foot (P < 0.001). High rearfoot strike is more frequent in the shod condition at LS and HS (LS: 50% shod left foot, 51.3% shod right foot; HS: 50.6% shod left foot, 50.6% shod right foot). Rearfoot strike is quite common in the shod condition (LS: 34.6% shod left foot, 30.8% shod right foot; HS: 32.5% shod left foot, 27.3% shod right foot). When athletes run unshod, the foot-strike pattern changes significantly, becoming closer to midfoot strikes (LS: from 6.4% shod left foot to 25.6% unshod left foot, from 9.0% shod right foot to 31.3% unshod right foot; HS: from 9.1% shod left foot to 34.2% unshod left foot, from 13% shod right foot to 31.6% unshod right foot) or forefoot strike (LS: from 6.4% shod left foot to 24.4% unshod left foot, from 6.4% shod right foot to 21.3% unshod right foot; HS: from 5.2% shod left foot to 19% unshod left foot, from 6.5% shod right foot to 19% unshod right foot). There was no significant difference (P ≥ 0.05) in shod/ unshod conditions at different speeds analysed (LS and HS). There were no significant differences in the frequency of asymmetries of foot-strike pattern between LS and HS or shod/unshod conditions (P ≥ 0.05).
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Vertical foot rotation Frequencies and percentages of vertical foot rotation in endurance runners are presented in Table III. External rotation was predominant in all conditions. The results show that speed is related to foot rotation type for the shod condition (P < 0.01). The unshod left foot, even with a lower value, also reached significant results (P < 0.05). Statistical tests indicated significant differences in shod/unshod conditions in the right foot for vertical foot rotation at LS and HS (P < 0.001). For the left foot, significant differences were also common at both speeds (LS: P < 0.001; HS: P < 0.01). There were no significant differences in the frequency of asymmetries of foot rotation between LS and HS or shod/ unshod conditions (P ≥ 0.05).
Inversion/eversion of the foot Inversion was observed in most of the cases studied (Table IV). In shod conditions at LS, inversion of the foot appeared in 67.6% of the shod left foot and 64.8% of the shod right foot. At HS, percentages increased (69% shod left foot, 69% shod right foot). For the unshod condition, percentages were similar (LS: 63.9% unshod left foot, 68.1% unshod right foot).
Table III. Influence of speed and race condition in foot vertical rotation. LSR Condition SLF
ULF
SRF
URF
Shod asymmetry Unshod asymmetry
VFR Over external rotation External rotation No rotation Internal rotation Total Over external rotation External rotation No rotation Internal rotation Total P-value Over external rotation External rotation No rotation Internal rotation Total Over external rotation External rotation No rotation Internal Total P-value Yes No Yes No P-value
Frequency
HSR Percentage
4 32 32 3 71 11 37 20 4 72
Frequency
5.6 45.1 45.1 4.2 100.0 15.3 51.4 27.8 5.6 100.0
9 34 25 3 71 15 37 15 4 71
7.0 69.0 21.1 2.8 100.0 30.6 55.6 13.9 0.00 100.0
12 47 11 1 71 25 38 8 0.00 71
< 0.001 5 49 15 2 71 22 40 10 0.00 72
12.7 47.9 35.2 4.2 100.0 21.1 52.1 21.1 5.6 100.0
0.002
16.9 66.2 15.5 1.4 100.0 35.2 53.5 11.3 0.00 100.0
0.009
33.3 66.7 40.6 59.4
0.581
0.018
0.223
< 0.001 37.7 62.3 41.4 58.6
1.000
P-value
0.007
< 0.001 26 43 29 41
Percentage
23 46 28 41
1.000
0.424
Notes: LSR, low speed running; HSR, high speed running; VFR, vertical foot rotation; SLF, shod left foot; ULF, unshod left foot; SRF, shod right foot; URF, unshod right foot.
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M. Muñoz-Jimenez et al. Table IV. Effects in inversion and eversion of the foot at different speeds and conditions. LSR
Condition
INV/EVE
Frequency
Percentage
Frequency
Percentage
P-value
SLF
Eversion Centred Inversion Total Eversion Centred Inversion Total P-value Eversion Centred Inversion Total Eversion Centred Inversion Total P-value Yes No Yes No P-value
1 22 48 71 1 25 46 72
1.4 31.0 67.6 100.0 1.4 34.7 63.9 100.0
1 21 49 71 1 18 52 71
1.4 29.6 69.0 100.0 1.4 25.4 73.2 100.0
0.564
1.4 33.8 64.8 100.0 1.4 30.6 68.1 100.0
1 21 49 71 1 20 50 71
5.8 94.2 17.1 82.9
6 63 12 57
ULF
SRF
URF
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HSR
Shod asymmetry Unshod asymmetry
0.491 1 24 46 71 1 22 49 72
0.439
0.467 4 65 12 58 0.065
0.160
1.4 29.6 69.0 100.0 1.4 28.2 70.4 100.0
0.830
0.500
0.637 8.7 91.3 17.4 82.6
0.625 1.000
0.180
Notes: LSR, low speed running; HSR, high speed running; INV/EVE, inversion or eversion of the foot; SLF, shod left foot; ULF, unshod left foot; SRF, shod right foot; URF, unshod right foot.
HS percentages were 73.2% of the unshod left foot and 70.4% of the unshod right foot. Significance was not found (P ≥ 0.05) between shod/unshod conditions and running speeds in inversion or eversion. Therefore, there were no significant differences in the frequency of asymmetries of inversion/eversion between LS and HS or shod/unshod conditions (P ≥ 0.05). Discussion Reliability intraobserver and interobserver were considered as very good results (Landis & Koch, 1977). The main aim of this study was to analyse kinematic changes in the running patterns of endurance runners, comparing both shod/unshod running conditions and LS/HS conditions. The results of this investigation showed and confirmed that barefoot running causes changes in foot-strike pattern from a rearfoot to a midfoot-strike pattern, which further causes alterations in other kinematic variables like vertical foot rotation. On the contrary, inversion/ eversion remains unchanged. Data obtained about foot-strike pattern at LS showed that in the shod condition most runners used high rearfoot or a rearfoot-strike pattern. Available published data from in-race studies conducted to date indicate that approximately 75–80% of runners are rearfoot strikers when initially contacting the ground (Hasegawa et al., 2007). The
prevalence of rearfoot strike is even greater according to other authors, such as Kasmer, Liu, Roberts, and Valadao (2013), who observed a 93.67% rearfoot strike prevalence in marathon runners. In the LS unshod condition, participants changed their foot-strike pattern to midfoot or forefoot strike, decreasing the percentage of the high rearfoot and rearfoot-strike pattern. When running at HS in shod conditions, most runners used high rearfoot or rearfoot strike. In the HS unshod condition, foot-strike pattern changed to midfoot or forefoot strike. Rearfoot striking had a prevalence of 31.6% in both feet. These findings confirm the conclusions of previous works (Altman & Davis, 2012; Gruber, Silvernail, Brueggemann, Rohr, & Hamill, 2013; Hamill, Russell, Gruber, & Miller, 2011; Lieberman et al., 2010), which note that the biggest difference between barefoot runners and shod runners occurs at the initial contact phase of gait; at that moment barefoot runners use forefoot or midfoot strike, whereas shod runners use rearfoot strike. Hence, as Hamill et al. (2011) indicated, runners will generally adopt a forefoot or midfoot footfall pattern when running barefoot on a firm surface, possibly to avoid heel contact on the hard surface. As for the vertical foot rotation, Eslami et al. (2007) concluded that forefoot–rearfoot strike coupling motion patterns could contribute to the amount of tibial rotation. In this sense, the main
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Shod-unshod condition in endurance runners finding about vertical foot rotation was the increase in the unshod condition in the percentage of over external rotation and external rotation in both the left foot and the right foot at LS and HS. However, Eslami et al. (2007) found no significant differences in the tibial internal rotation excursion between shod/unshod conditions, results similar to those obtained by Stacoff et al. (2000), who compared normal shod/unshod running via the direct measurement of markers fixed on bones. Excessive coronal and transverse plane motions of the ankle and tibia are linked to the development of a number of chronic injuries (Murphy et al., 2013; Sinclair et al., 2014). To date, foot rotation of barefoot running has not been documented in the literature. Available literature on this topic is scarce and more research is needed to assess the effect of barefoot running on vertical foot rotation. Concerning the degree of inversion/eversion, the results obtained demonstrate that a high percentage of runners showed inversion when running in both conditions and speeds. This data obtained on the treadmill can be compared with previous findings obtained in race, such as those by Hasegawa et al. (2007), who got a lower prevalence (42%). Yet, the most important finding of this investigation was that no significant difference in the degree of inversion/ eversion was found between shod/unshod running conditions. Schutte, Miles, Venter, and Van Niekerk (2013) found no significant difference in ankle inversion/adduction between the barefoot and shod conditions. However, rearfoot eversion is characteristic in shod runners (Murphy et al., 2013). For their part, Sinclair et al. (2014) found that barefoot running and minimalist running increased eversion and tibial internal rotation. Nonetheless, Stacoff et al. (2000) maintained that participants tended to show less inversion on average, compared to shod in barefoot running conditions The second major aim of this study was to analyse the influence of running speed in both shod/unshod conditions in the controlled variables (foot-strike pattern, vertical foot rotation and inversion/eversion). In this sense, the main finding was that an increase of the running speed (from LS to HS) did not cause significant changes in foot strikes or inversion/eversion in any of both the shod/unshod conditions. Nevertheless, several studies suggest that footstrike pattern depends, at least in part, upon running speed (Hatala, Dingwall, Wunderlich, & Richmond, 2013; Keller et al., 1996). In this study, the increase of running speed entails significant alterations in vertical foot rotation in both shod and unshod conditions. Specifically, the results showed that an increase of running speed is associated with an increase in the percentage of over external rotation. The literature about this is scanty and more research
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is needed to assess the effect of speed on foot rotation. Finally, numerous studies have documented gait asymmetry in runners, particularly as it relates to injury risk (Zifchock, Davis, & Hamill, 2006; Zifchock, Davis, Higginson, McCaw, & Royer, 2008). However, to our knowledge, there are only a few studies (Larson et al., 2011) focused on the effect of the shod condition on foot strikes, inversion/eversion and degree asymmetry in runners not accustomed to barefoot running. The data obtained in the present study showed that the shod/unshod condition is not decisive for the presence of asymmetry, since no significant difference was recorded in any of the variables analysed. Larson et al. (2011) found that asymmetrical runners show rearfoot striking more often on the left side and forefoot or midfoot striking on the right side. In most cases, asymmetries were relatively minor, with one foot landing on the midfoot and the other landing slightly more towards the heel. It is unclear whether these asymmetrical landing patterns were simply chance observations of a single unusual foot strike sequence or genuine gait asymmetries. A limitation of the study was the occurrence of certain problems when editing and processing the video file, which resulted in the damage and loss of video files. Moreover, the issue of accuracy in using 2D video analysis to determine analysed variables and, specifically vertical foot rotation, must be considered an important limitation. Summing up, the results of this study suggest that running kinematics, in terms of foot-strike pattern and vertical foot rotation differ between shod/unshod conditions, while the inversion/eversion degree remains unchanged. Moreover, running speed significantly influences lower limb kinematics in endurance runners, specifically vertical foot rotation, so that an increase in running speed is associated with a higher prevalence of external rotation, although running speed does not influence footfall pattern or inversion/eversion degree. More research is needed to clarify the effectiveness of barefoot training programmes on the foot-strike patterns of endurance runners.
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