Stepping Back to Minimal Footwear

Applications Across the Lifespan

Irene S. Davis; Karsten Hollander; Daniel E. Lieberman; Sarah T. Ridge; Isabel C.N. Sacco; Scott C. Wearing

Disclosures

Exerc Sport Sci Rev. 2021;49(4):228-243. 

In This Article

In the Beginning

Most mammals walk and run on their toes, but humans evolved from African great apes that have plantigrade feet that are well adapted for climbing trees. African great apes have long, curved toes, an abducted hallux, a relatively short and flexible midfoot that lacks an arch, and a less developed calcaneus with a mobile ankle joint. However, over the 7 million years since the human and chimpanzee lineages diverged, hominin feet evolved substantially. This first occurred to facilitate bipedal walking and then later running over longer distances than apes.[2] For example, human feet have adapted to include an enlarged calcaneus. This helped stabilize the rearfoot and bear repeated, higher stresses during the impact phase of walking considerably longer distances on two versus four legs.[3] In addition, they developed an elongated midfoot that is stiffened by transverse and medial longitudinal arches[4,5] and a thicker plantar fascia.[6] The hallux became elongated, and the toes became shorter and straighter with dorsally oriented metatarsophalangeal joints[7] (Figure 1). Together, these adaptations compromise our ability to climb trees. However, they optimized the human foot for both walking and running.[2]

Figure 1.

Comparison of the structure of the chimpanzee and human foot. Note the higher arch, more aligned hallux, and greater plantarflexion at push-off in the human foot. [Reprinted with permission from.2 Copyright © 2018 The Company of Biologists Ltd. All permission requests for this image should be made to the copyright holder.]

For most of the last 7 million years, humans also walked and ran barefoot. They did this over a variety of surfaces from soft grasslands to hardpacked savannah. As such, humans have evolved with the ability to adjust their overall leg stiffness to the hardness of the substrate they negotiate to maintain a constant stiffness of the system. For example, they increase their leg stiffness when encountering soft surfaces and reduce their leg stiffness when encountering hard surfaces. This has been demonstrated in a number of modern studies[8–10] and underscores that humans are equipped to walk and run on a wide variety of surface stiffnesses.

Until about 600 generations ago, all humans were hunter-gatherers who walked on average 9–15 km·d−1, approximately 10–15,0000 steps, either barefoot or in minimal footwear.[11] The oldest preserved sandals are about 10,000 yr old,[12] and the oldest shoes are from about 6000 yr ago from Armenia.[13] However, it is reasonable to hypothesize that footwear was available by at least 40,000 yr ago when needles and other tailoring technologies first appear in the archeological record.[14] Around this time, there also is some evidence for a reduction in metatarsal robusticity (cross-sectional thickness relative to bone length). This indirectly suggests that the use of footwear such as sandals decreases bending forces on the midfoot during propulsion.[15]

For most of human evolutionary history, shoes probably were used only occasionally. In addition, until recently, almost all footwear were minimal such as sandals or moccasin-like shoes. Features common in modern shoes such as toe springs, stiffened midsoles, elevated heels, and arch supports are generally quite recent. Ethylene-vinyl acetate-cushioned shoes have been available since only the 1970s.[16] Features in these shoes provide some benefits, notably protection and comfort. However, these structured shoes potentially contribute to several hypothesized evolutionary mismatches. Evolutionary mismatches are conditions that are more prevalent or severe because bodies are inadequately or imperfectly adapted for novel environmental conditions.[17] Put differently, although shoes provide some advantages, they may also have some drawbacks for which we are not well adapted.

Evolutionary mismatches related to footwear fall into three categories. First, cushioned (elastic) soles slow the rate of loading at impact and decrease sensory perception.[18,19] As a result, people who habitually wear cushioned shoes experience higher ground reaction force impulses when walking,[19] and they are more likely to rearfoot strike (RFS) when running.[20] This results in an abrupt impact transient of the vertical ground reaction force not seen with forefoot striking[21] (Figure 2). Second, these supportive shoes reduce the demand on the foot muscles, which can result in weaker feet, as evidenced from smaller muscle cross-sectional areas.[22] Finally, structured shoes alter our foot mechanics. The added sole flares increase the external torques to the foot, creating abnormal loading to the foot and lower extremity.[23] In addition, the arch support in structured shoes reduces the longitudinal and transverse arch compression during midstance,[24] which is important for elastic energy storage. All of these changes potentially lead to mismatches between the way the foot was adapted to function and how it functions in structured shoes, which can lead to dysfunction and injury.

Figure 2.

Relation between footwear history and footstrike angle in Kenyan runners. Note that as footwear usage decreased, runners adopted a more FFS pattern. (Reprinted from.20 CC BY 4.0.)

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