Walking in Minimalist Shoes Is Effective for Strengthening Foot Muscles

Sarah T. Ridge; Mark T. Olsen; Dustin A. Bruening; Kevin Jurgensmeier; David Griffin; Irene S. Davis; A. Wayne Johnson


Med Sci Sports Exerc. 2019;51(1):104-113. 

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There are a few limitations to this study that should be noted. First, we did not monitor the footwear subjects wore daily for activities other than running (with the obvious exception of the MSW walking group during their assigned number of minimalist footwear walking steps). Additionally, it is difficult to completely isolate intrinsic foot muscles for strength testing. Our testing methods were designed to try to minimize extrinsic activity and researchers watched subjects closely during testing to observe any unwanted movement indicative of extrinsic activation. There were, however, some difficulties with the strength testing equipment. Repeated testing relied on similar positioning of the subject's foot during each testing session. Although we had multiple researchers involved in data collection, each subject was assigned one researcher to follow them through the study. This helped ensure greater reliability of measurements.[27] Some subjects reported difficulty gripping the carabiner attached to the dynamometer for toe flexion testing. Doming was a new movement for many subjects, so it is possible that there was a learning effect. However, we taught subjects the movement when they first visited the laboratory to complete the paperwork and asked them to practice the movement for the subsequent days (no more than 3) before coming in for their baseline testing. We believe that this helped decrease any potential learning effect.

Although the strength testing procedures were designed to be functional and provide information about activation, rather than just hypertrophy, they also did not target all of the muscles that were measured via ultrasound. That may also account for some differences in the timing of strength and size gains throughout the study. It also should be noted that after the 8-wk interventions, the sizes of four of the seven measured muscles (ABDH, FHB, TA, and FDL) were similar in all groups. In these muscles, the C group had larger muscle sizes than the intervention groups at week 0. It is possible that there is a ceiling effect and these muscle sizes could not change in the C group. It is more likely, however, that the lack of increase in muscle size in the C group should be attributed to the lack of participation in a strengthening intervention.

Last, as with any training study, we relied on the subjects to honestly report their participation in the interventions. Although the number of steps taken in minimalist footwear was relatively objective (though the accuracy did rely on the subjects wearing the pedometer correctly and only when wearing the minimalist footwear), compliance with the exercise intervention is harder to quantify. Subjects completed training logs which indicated that they did the exercises, but there was no indication of how well they performed them or if they just went through the motions.