Full length articleIs symmetry of loading improved for injured runners during novice barefoot running?
Introduction
Walking and running, are considered relatively symmetric activities. When movement patterns become asymmetric, they can disrupt the natural rhythm of the gait. Examples of this include walking with uneven step lengths or with a lateral trunk lean. In theory, these asymmetries can lead to overloading certain musculoskeletal structures, increasing their risk for injury. When ground reaction forces (GRF) become asymmetric, one limb becomes more loaded than the other which can also be associated with injury. For example, Zifchock et al. [1] have shown that the injured limb of runners is associated with the side with the highest impact loading during running. It has been noted that some degree of asymmetry is normal in running [2]. However, when gait asymmetry is above expected differences, the goal of many interventions is to improve the symmetry to reduce injury risk [[3], [4], [5]].
In terms of running, impact loading, specifically GFR loadrates, have been associated with injury in both retrospective [[6], [7]] and prospective [[8], [9]] studies. This impact loading is strongly influenced by footstrike patterns. Runners who land with a forefoot strike (FFS) have significantly lower vertical loadrates compared to those who land with a rearfoot strike (RFS), especially when footwear cushioning is minimized [[10], [11]]. This impact reduction is in part due to the eccentric action of the calf musculature during a FFS landing [12].
Impact loading is also reduced when running barefoot compared with running in cushioned shoes [13]. This has been attributed to two factors. First, barefoot runners are more likely to run with a FFS pattern [14]. This is because the heel pad does not adequately attenuate the impact loads of running and becomes painful when loads exceed those of walking [15]. Additionally, depending on the surface hardness, the sensory input from the plantar surface of the foot influences stiffness of the leg during landing [[16], [17]]. When landing on a hard surface, leg stiffness is reduced and when landing on a soft surface, leg stiffness is increased.
Unfortunately, cushioned footwear may disrupt this important sensory input, likely resulting in altered landing mechanics including dynamic stability [18]. For example, an injured runner may have an associated harder landing on their affected side. The cushioned shoes may make it more difficult to sense this difference in landing. However, landing this hard when barefoot may be very painful. Thus, it is possible that the runner will adapt their mechanics to land softer on that side resulting in less asymmetry. If this is the case, running barefoot may be a way to retrain the symmetry of loading.
Therefore, the purpose of this study was to examine differences in asymmetry of loading between shod and novice barefoot conditions. We hypothesize that impact loading will be reduced in both feet in the barefoot conditions. We also expect that the asymmetry of loading variables will be reduced when running barefoot compared to shod.
Section snippets
Methods
Subjects in this study were a subset of runners seeking evaluation at a running injury clinic. Force data from the injured RFS runners who were habitually shod were collected as standard of care as part of a running clinic evaluation, and therefore a waiver of informed consent was granted.
Results
The study group was comprised of 67 runners (34 female, 33 male, average age 37.2 yrs) meeting the inclusion criteria. Runners presented with a variety of running related injuries. Data on demographics and information on recent injury was available on 66 of 67 runners. Thirty-nine of the runners had unilateral injuries and 33 runners localized one or more recent injury to a joint (hip, knee or ankle). All runners completed both condition with nearly no pain. (NPRS = 0.15 ± 0.52). Only 6 of the
Discussion
The purpose of this investigation was to compare symmetry of loadrates between shod and barefoot conditions. We hypothesized that asymmetry would be reduced when additional sensory input was provided. However, we only found this to be true only for runners with the highest degree of asymmetry in their shod condition.
Contrary to our hypotheses, loading symmetry did not improve when sensory input was increased in the BF condition across subjects. When assessing the shod symmetry data by
Conclusions
In summary, the additional sensory input of running barefoot did not improve the average loading symmetry across all runners. However, in the case of the highest degree of shod asymmetry, this was significantly improved when running barefoot. This suggests that training in a barefoot condition may be help in more extreme cases of loading asymmetry.
Conflict of interest statement
No funding was received to support this investigation. Authors have no conflicts of interest to disclose related to this work.
Acknowledgements
We are grateful to all of our patients for inspiring our investigation and providing data that we can use to both treat their ailments and further our understanding of running injuries. No funding was received to support this investigation. Authors have no conflicts of interest to disclose related to this work. AST, MCR, STJ, and ISD were responsible for conception and design of the study, acquisition of data, analysis and interpretation of data. PPS contributed to acquisition of data, analysis
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