Physiology: Foot calluses are good for your sole

Foot calluses protect the soles of barefoot walkers without compromising sensitivity or gait, reports a study published online in Nature this week. By contrast, cushion-soled shoes reduce sensitivity and alter the forces transmitted from our feet to our joints. Footwear with thin, stiff and uncushioned soles, such as moccasins or sandals, might offer protection and sensitivity that are more similar to that of thick calluses, the authors suggest.

Thick foot calluses develop naturally in people who habitually walk barefoot, offering protection on uncomfortable or slippery surfaces. Modern shoes offer similar protection, but reduce the ability to perceive tactile stimuli. It has been assumed that thick calluses might also reduce sensitivity; however, Daniel Lieberman and colleagues challenge this hypothesis by studying the feet of 81 Kenyan and 22 American adults.

As expected, they find that calluses tend to be thicker and harder in people who habitually walk barefoot than in people who regularly wear shoes. However, they also show that callus thickness does not alter the sensitivity of nerves on the soles of the feet. In addition, they show that footwear affects impact forces from the foot striking the ground, delivering more energy to the joints than seen in thick-callused individuals. The effect that this altered mechanical loading has on the skeleton is poorly understood and requires further study.

doi: 10.1038/s41586-019-1345-6

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