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

Disclosures

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

In This Article

Discussion

The purpose of this study was to measure the changes in foot muscle size and strength following an exercise or MSW intervention. Our results suggest that either intervention provides sufficient stimulus to increase muscle strength significantly. While it was expected that direct exercise would result in increased muscle size and strength, it was encouraging to find that the MSW resulted in similar improvements. We theorized that if a MSW intervention was as effective for strengthening, it could be easier to implement and have a higher compliance rate than a progressive resisted exercise protocol.

Minimalist shoe walking may be effective because it may require more muscle activation to support the foot, due to the decreased cushion and support of minimalist shoes. The current study shows that this is sufficient stimulus to induce hypertrophy and strength changes within the lower leg and foot. In MSW, this stimulus is stress that is placed on the intrinsic and extrinsic foot muscles throughout the stance phase, causing the muscles to adapt and increase strength and size. In addition, increasing the load by decreasing the cushioning may initiate the release of growth factors, resulting in increased protein synthesis and muscle hypertrophy.[29,30] Previous research showing that intrinsic foot muscle activity is lower in runners when running barefoot than shod presents conflicting evidence to the current study and others showing increases in intrinsic foot muscle size after running in minimalist footwear.[20–22,31] It is possible that, in the current study, requiring the foot to go through a greater range of motion (heel to toe walking, rather than midfoot striking during running) allows the intrinsic foot muscles to activate more to control the movement of the arch.

Previous research has shown that the intrinsic foot muscles are active under a variety of loading conditions. Though there is little to no intrinsic foot muscle activity during an unshod, unweighted condition, controlled loading studies have shown that as loading of the medial longitudinal arch increases, intrinsic foot muscle activity increases.[32,33] Kelly et al.[34] showed intrinsic foot muscle activity during barefoot quiet stance (body weight loading) in 10 healthy males. Other research has shown that the intrinsic musculature of the foot is active during barefoot walking, particularly during terminal stance,[7,35] and that as speed increased from walking to slow running to fast running, intrinsic foot muscle (specifically the ABDH, FDB, and QP) activity also increased.[7] Although barefoot walking may differ from minimalist footwear walking, the general lack of external support seems to have similar effects on the foot.

Little research has been conducted on populations that walk in minimalist footwear. One recent study showed that there are differences in ground reaction forces between walking barefoot and in minimalist footwear.[36] Another compared intrinsic foot muscle size in Tarahumara men who habitually wear minimalist footwear to American men who habitually wear supportive shoes.[37] The ABDH and abductor digiti minimi were larger in the Tarahumara, whereas the FDB was not significantly different in size.[37]

The literature on habitually unshod populations suggests that there is increased foot muscle activity due to increased forces placed on the intrinsic muscles when weight-bearing.[38] We are unaware of any studies that have reported foot muscle size in habitually barefoot subjects, though Aibast et al.[39] compared toe flexion and foot shortening (doming) muscle strength in habitually shod and habitually barefoot adolescent populations in Kenya. The habitually barefoot group was significantly stronger when performing GT flexion and doming strength tests, similar to our findings after 8 wk of foot strengthening exercise or MSW.

Although all muscles increased in size in both intervention groups in the current study, the FHB, QP, and FDB increased significantly more in the exercise group than the walking group. The specificity of some of the exercises included in the exercise protocol (e.g., the towel curl and doming) likely required more flexor muscle activity than walking. However, the greater increase in flexor muscle sizes after exercise should not detract from the benefits of the increases caused by walking, as walking still resulted in significant size and strength increases and is a more functional activity. Because most people spend a good portion of the day walking, this may be a more efficient intervention than a set of exercises that require additional time and energy to perform (though it should be noted that we had good compliance in both MSW and FS groups in the current study).

The length of our intervention (8 wk) was chosen based on previous research on strength training that show hypertrophy between 6 and 8 wk.[40] Typically, we would expect to see strength gains due to neural adaptation before size gains due to hypertrophy.[40] Our 8-wk intervention was sufficient to elicit both strength and size increases in both MSW and FS. We also saw some increases by 4 wk, which suggests that shorter interventions may have some success. It was noted that those in the FS group showed increased size earlier than those in the MSW group. In addition to the previous point regarding more directed stimulation of the measured muscle via exercise, it is also possible that the starting step count of the MSW group did not provide similar muscle stress as did the exercises in the FS group until the step count was increased at weeks 3 and 5. It is also possible that greater strength improvements could be made if participants combined the exercise and MSW interventions.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....