Some authors suggest that habitual barefoot running could prevent impact-related injuries.1–3 Some studies pointed that humans had been made to run barefoot, and this running style can minimize impact peaks and provides increased proprioception and foot strength, also is hypothesized that can help avoid injury.4 In order to reduce the risk of injury, the runner's body produces changes in lower limb kinematics. Some authors have measured the risk of injury in runners’ feet before and after a training period transitioning from traditional to minimalist running shoes, participants in the training group showed significant increases in bone marrow edema in at least one bone after the training running period.5,6 Furthermore, barefoot running is also associated with a shorter stride a higher stride cadence both low and high running speed,7,8 reducing stride length decreased the probability of stress fracture by 3–6%.5

Previous studies of barefoot running specify even more the kinematic changes such as: shorter step length and larger step frequency, shorter landing phase, shorter contact time, shorter flight time and shorter step time.7–11 Barefoot running is also related with a higher stride cadence both low and high running speed.7,8 In addition, barefoot running reduces flight time and causes a lower peak force and higher pre-activation of the sural triceps than shod running.12

A recent study pointed that an intervention of six weeks of barefoot training simulation using Vibram Five-fingers shoes, is associated with a significant decrease in the loading rates and impact forces.13 Other study question about the process in which biomechanical adaptations happen and if these can be learned by everyone.14 It remains to be seen how training based on barefoot running can modify the kinematics of traditionally shod running. There are many aspects concerning the manner in which the athletes adapt kinematics variables to run after specific barefoot training but there is already no evidence for long term effects of barefoot running regarding biomechanics or health outcomes.15 This insight could be enhanced by studying the difference in kinematics after a sufficiently long controlled barefoot training program (BTP).

Considering the above information, we hypothesized that neuromuscular adaptations to BTP might be responsible for the change in kinematic variables in shod condition post-intervention. Therefore, the purpose of this study is to determine if after the 12-week barefoot intervention the pointed variables will be modified even when running shoes are put on.

This experimental study was conducted in adherence to the standards of the Declaration of Helsinki (2013 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 Jaen (Spain).

Participants

Thirty-nine trained shod runners from southeast of Spain participated voluntarily in this study and were randomly allocated by simple random sampling in the experimental group (EG), and control group (CG). The main characteristics of the participants were age=35.64±11.67-years-old (mean±standard deviation); body mass index=22.93±2.43kg/m2; km per week=60.18±20.41; sessions per week=5.47±1.29; and competitions per year=13.08±10.50. Only two athletes in the EG left the program because of illness. In the CG six people did not finish, because of illness during the intervention (n=1) or did not perform the post-test (n=3) or the data were corrupt or illegible (n=2). All the data from lost athletes were excluded (Fig. 1).

Figure 1.

Flowchart progress through the study participants.

(0.35MB).

The inclusion criteria were: (i) participants were all habitually shod runners (cushioned shoes); (ii) no significant injuries in the last three months and no damage or pain that could interfere with the proper monitoring of the training protocol without shoes; (iii) verifiable minimum sport level (have been able to participate in regional or national athletics championships in the last four years). Each participant signed an informed consent to participate in this research.

There are no significant differences between groups in relation to comfortable speed (EG=11.21±1.28km/h vs. CG=10.97±1.20km/h, p=0.611) and competition speed (EG=15.56±2.08km/h vs. CG=15.45±1.67km/h, p=0.873).

The results of BTP are presented in Table 2. At pre-test, no significant between-group differences were found in any variable. At post-test, only the duration of landing phase at high speed showed significant difference, the EG achieved shorter time than CG after the BTP (0.032±0.007s vs. 0.038±0.006s). In relation to within-group differences, CG showed an increase of stance phase at low speed (Δ=0.014s, p=0.024) and a reduction of flight time at high speed (Δ=−0.014s, p=0.034). Moreover, EG achieved a reduction of landing phase at high speed (Δ=−0.008s, p=0.004). No other significant differences were showed after BTP.

The purpose of this study was to determine the effects of a 12-week BTP on kinematic variables in long-distance runners. The main finding of this study showed that 12-week BTP does not alter significantly kinematic variables in long-distance runners. Only EG achieved a reduction of landing phase at high speed; no other significant differences were showed after BTP. Other studies found no changes in strength and proprioception after 8 weeks of a progressive BTP on a grass surface21 or changes in biomechanics after an 8-week, progressively introduced barefoot running program.22 Likewise, other studies showed that no biomechanical changes were found in the intervention group after 8 weeks of a progressive BTP.14 However, there was indicated that a 12-week intervention of controlled simulated barefoot running training was sufficient to elicit significant changes in lower limb kinematics not only during barefoot running, but also during running in regular cushioned running shoes.23 These controversial results indicate that future studies should be performed to clarify doubts about the effect of BTP on kinematic variables.

The authors suggest that the lack of significant effects in the current study may be due to several points: (i) shoes annul this effect; (ii) the insufficient duration of BTP; (iii) the insufficient load of the training program; (iv) the effect of training surface. When athletes run unshod, the hardness of the surface where they are running causes an alteration on foot strike pattern. In previous studies only the 20% of the participants ran with a midfoot or forefoot pattern on the soft surface whereas 65% of the participants ran with a midfoot or forefoot patterns on hard surface.24 Surface used in this study was grass, which may be a significant factor in causing no alteration in runner's kinematics pattern.

An unexplored area of the theory of barefoot running is the process by which biomechanical adaptations occur and if these are universally learned.14 Thus, the associated kinematic barefoot running can be a trainable ability, and requires adaptive training with changes in the neuromuscular activation of calf muscles to facilitate plantar flexion before ground impact. In this sense, when sufficient unshod steps in relation to shod steps, are made, this produces higher triceps sural muscles previous activation, which can lead to a reduction in the peak of impact and the subsequent reduction in mechanical stress during running.12,13

In contrast to recent studies in which numerous problems related to greater incidence of bone marrow edema due to barefoot training protocols and uncontrolled loads, a positive finding of this study may be the non-detection of physical problems or injuries occurring in athletes associated with designed barefoot training program.6 On balance a sufficient workload to cause changes in lower limb kinematics and a training protocol design which does not cause harm is needed. Referring to the correct progression from shod to barefoot condition, a prior step for adaptation to barefoot running could be minimalist footwear.

Finally, some limitations need to be considered such as 2D techniques in the video analysis. Moreover, it is very difficult to know how much barefoot training and at what intensity each subject has performed. It would be necessary to standardize training with caution to control the progress and problems of each athlete, as each runner progresses differently. Additionally, force measures does not has been included that would also be interesting to evaluate given their relationship to injury risk. However, the strengths of our study are that it provides new information about protocols for transitioning from shod to barefoot running and provides new insight into the already open debate about barefoot running with a protocol only based on running unshod without other interventions like plyometrics or neuromuscular workout. To the best of our knowledge, there is limited information about barefoot transition programs and this study will help to increase knowledge about this growing trend.

Despite no athlete suffered any harm during the study intervention, 12-week BTP based on the addition of barefoot running time at the end of daily training was not sufficient to cause chronic changes in lower limb kinematics shod, only in landing phase at high speed (that was lower). The authors suggest that running shoes may reduce the chronic effects of barefoot running. On the other hand, increasing the volume of workload or running on harder surfaces may be required to produce more chronic changes.

Authors declare that they don’t have any conflict of interests.