Injury Risk, Pain Perception in Minimalist Footwear Runners
Injury Risk, Pain Perception in Minimalist Footwear Runners
This study is the first to longitudinally examine the epidemiological effects of two different models of minimalist footwear. The participants in this study were recreational habitual runners without previous experience running barefoot or with other minimalist footwear models preparing for a 10 km event. The overall injury rate of 23.2% is low compared with other similar exposure times to running in the literature that speculatively may be a function of the running programme or our selection criteria (ie, being injury-free for the preceding 6 months).
On the basis of clinical data from this study our hypotheses were supported. The first hypothesis was supported with respect to minimalist footwear modifying injury risk. Injury event analysis showed there was a higher likelihood of experiencing an injury with minimalist footwear compared with a conventional neutral shoe model, with the partial minimalist condition having a particularly higher risk. The outcomes from the overall VAS for pain and FADI scores support our second hypothesis. Both minimalist shoes resulted in changes to reported pain and foot/ankle function at the shin/calf, knee, hip and lower back.
Compared with conventional neutral-supported shoes, wearing minimalist footwear appears to place the unfamiliar runner at an overall greater risk of experiencing an injury that stops running or experiencing running-related pain. This apparent injury risk was not equal across the minimalist conditions. Runners in the partial minimalist condition experienced three-times as many injury events as the neutral group, and five more injuries than the FMF group. Runners in the full minimalist condition reported greater shin and calf pain.
There is limited, and conflicting, experimental data on the biomechanical effects of wearing partial minimalist running footwear. Previously, it has been shown that use of a similar model of Nike Free (V.5.0) for routine activities three times per week modify neuromotor activation and increase muscle cross-sectional area for the long and intrinsic toe flexor group. The therapeutic effect of the Nike Free V.5.0 for treating chronic plantar fasciopathy may have been a result of such neuromuscular changes. Specifically use of the Nike Free V.5.0 could have resulted in an increase in foot flexor strength secondary to the greater flexibility of this shoe's forefoot. In contrast, a recent biomechanical analysis of the same model of Nike Free used in the present study (V.3.0) did not report any substantial difference in biomechanics between the Nike Free compared to otherwise conventional running footwear. Considering the effect of the Nike Free is thought to have a sizable effect on intrinsic foot motion and strength, we encourage future studies on this shoe (and other minimalist designs) to examine this footwear category's effect on rearfoot–forefoot motion and dynamics. We speculate that the larger injury rate in the group wearing the Nike Free, in comparison to the group wearing the 5-Fingers, may indeed be a function of the partial reduction of the Nike Free's sole. By only partially reducing midsole materials, the Nike Free might compromise the shock attenuation and stability properties of the full neutral shoe, yet maintain enough cushion to blunt the senosory-motor drive to modify gait possibly seen in runners wearing the 5-Fingers. Importantly, no study has longitudinally assessed the biomechanical and neuromuscular effects of persistent minimalist footwear use; therefore, it remains difficult to account mechanistically for the injury rates across footwear conditions seen in the present study.
It is noteworthy that runners in full minimalist footwear condition reported greater calf and shin pain throughout the 12-week period. This finding was not unexpected given the likelihood that some of the runners in the full minimalist footwear condition adopted a forefoot strike pattern that could have resulted in greater (and unaccustomed) loading of the Achilles tendon and triceps surae musculature secondary to a larger ankle dorsiflexion moment immediately following touchdown. The greater heel height in the partial minimalist footwear likely mitigated this loading on the shank. Preliminary clinical evidence suggests that runners may experience an increased risk of stress fractures to the foot and injury to the plantar fascia after transitioning from conventional running footwear to a full minimalist footwear condition, yet there was no increase in foot pain reported in the participants in the full minimalist footwear group. It is advisable that an appropriate period of transition to a minimalist footwear category based on individualised criteria should be established for each runner. Currently, however, there is no consensus on how such a progression should be made.
There are important limitations when interpreting outcomes from the present study. A diagnosis for the participants who did report injuries was not available and as a result there is some loss in the precision and accuracy of the injury data in this study. However, validated outcome measures for assessing pain, as well as ankle and foot disability were administered concurrent to the injury status for thorough reporting of a runner's 'clinical status'. The observation period in this study is relatively short at 12 weeks; the long-term clinical effects of habitual minimalist footwear use remain unknown. Participants were not blinded to their group allocation, a process that would be difficult to achieve in the context of studies on footwear minimalism. Additional data regarding concurrent sport participation was not recorded and may have influenced the outcomes. Strengths of this study are a random allocation of footwear condition (including the control or neutral footwear condition), similar training exposure, good participant study adherence and denominator-based reporting of injury incidence.
In conclusion, running in minimalist footwear appears to increase the likelihood of experiencing an injury and running-related pain in runners otherwise new to this footwear category while training for a 10 km event. Furthermore, it remains unknown to what extent, if any, a preparatory strengthening or conditioning programme would have at mitigating the injury risk associated with minimalist footwear. It is recommended that clinicians exercise caution when recommending minimalist footwear to runners without prior experience using this type of footwear.
Discussion
This study is the first to longitudinally examine the epidemiological effects of two different models of minimalist footwear. The participants in this study were recreational habitual runners without previous experience running barefoot or with other minimalist footwear models preparing for a 10 km event. The overall injury rate of 23.2% is low compared with other similar exposure times to running in the literature that speculatively may be a function of the running programme or our selection criteria (ie, being injury-free for the preceding 6 months).
On the basis of clinical data from this study our hypotheses were supported. The first hypothesis was supported with respect to minimalist footwear modifying injury risk. Injury event analysis showed there was a higher likelihood of experiencing an injury with minimalist footwear compared with a conventional neutral shoe model, with the partial minimalist condition having a particularly higher risk. The outcomes from the overall VAS for pain and FADI scores support our second hypothesis. Both minimalist shoes resulted in changes to reported pain and foot/ankle function at the shin/calf, knee, hip and lower back.
Compared with conventional neutral-supported shoes, wearing minimalist footwear appears to place the unfamiliar runner at an overall greater risk of experiencing an injury that stops running or experiencing running-related pain. This apparent injury risk was not equal across the minimalist conditions. Runners in the partial minimalist condition experienced three-times as many injury events as the neutral group, and five more injuries than the FMF group. Runners in the full minimalist condition reported greater shin and calf pain.
There is limited, and conflicting, experimental data on the biomechanical effects of wearing partial minimalist running footwear. Previously, it has been shown that use of a similar model of Nike Free (V.5.0) for routine activities three times per week modify neuromotor activation and increase muscle cross-sectional area for the long and intrinsic toe flexor group. The therapeutic effect of the Nike Free V.5.0 for treating chronic plantar fasciopathy may have been a result of such neuromuscular changes. Specifically use of the Nike Free V.5.0 could have resulted in an increase in foot flexor strength secondary to the greater flexibility of this shoe's forefoot. In contrast, a recent biomechanical analysis of the same model of Nike Free used in the present study (V.3.0) did not report any substantial difference in biomechanics between the Nike Free compared to otherwise conventional running footwear. Considering the effect of the Nike Free is thought to have a sizable effect on intrinsic foot motion and strength, we encourage future studies on this shoe (and other minimalist designs) to examine this footwear category's effect on rearfoot–forefoot motion and dynamics. We speculate that the larger injury rate in the group wearing the Nike Free, in comparison to the group wearing the 5-Fingers, may indeed be a function of the partial reduction of the Nike Free's sole. By only partially reducing midsole materials, the Nike Free might compromise the shock attenuation and stability properties of the full neutral shoe, yet maintain enough cushion to blunt the senosory-motor drive to modify gait possibly seen in runners wearing the 5-Fingers. Importantly, no study has longitudinally assessed the biomechanical and neuromuscular effects of persistent minimalist footwear use; therefore, it remains difficult to account mechanistically for the injury rates across footwear conditions seen in the present study.
It is noteworthy that runners in full minimalist footwear condition reported greater calf and shin pain throughout the 12-week period. This finding was not unexpected given the likelihood that some of the runners in the full minimalist footwear condition adopted a forefoot strike pattern that could have resulted in greater (and unaccustomed) loading of the Achilles tendon and triceps surae musculature secondary to a larger ankle dorsiflexion moment immediately following touchdown. The greater heel height in the partial minimalist footwear likely mitigated this loading on the shank. Preliminary clinical evidence suggests that runners may experience an increased risk of stress fractures to the foot and injury to the plantar fascia after transitioning from conventional running footwear to a full minimalist footwear condition, yet there was no increase in foot pain reported in the participants in the full minimalist footwear group. It is advisable that an appropriate period of transition to a minimalist footwear category based on individualised criteria should be established for each runner. Currently, however, there is no consensus on how such a progression should be made.
Strengths and Limitations
There are important limitations when interpreting outcomes from the present study. A diagnosis for the participants who did report injuries was not available and as a result there is some loss in the precision and accuracy of the injury data in this study. However, validated outcome measures for assessing pain, as well as ankle and foot disability were administered concurrent to the injury status for thorough reporting of a runner's 'clinical status'. The observation period in this study is relatively short at 12 weeks; the long-term clinical effects of habitual minimalist footwear use remain unknown. Participants were not blinded to their group allocation, a process that would be difficult to achieve in the context of studies on footwear minimalism. Additional data regarding concurrent sport participation was not recorded and may have influenced the outcomes. Strengths of this study are a random allocation of footwear condition (including the control or neutral footwear condition), similar training exposure, good participant study adherence and denominator-based reporting of injury incidence.
In conclusion, running in minimalist footwear appears to increase the likelihood of experiencing an injury and running-related pain in runners otherwise new to this footwear category while training for a 10 km event. Furthermore, it remains unknown to what extent, if any, a preparatory strengthening or conditioning programme would have at mitigating the injury risk associated with minimalist footwear. It is recommended that clinicians exercise caution when recommending minimalist footwear to runners without prior experience using this type of footwear.
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