Meeting Abstract
Habitually barefoot humans possess thick plantar calluses that develop in response to frictional stresses during walking and running. Because all humans were barefoot until relatively recently, plantar calluses should be viewed as a normal feature of human anatomy, yet we know surprisingly little about them. In this study we tested the common assumption that thick calluses tradeoff protection with a loss of sensory perception. We collected data from a large sample of adults from a Kalenjin-speaking population in western Kenya, including 35 habitually barefoot individuals and 46 habitually shod individuals. We used ultrasound to measure plantar skin thickness at the heel and first metatarsal head and found that habitually barefoot individuals have thicker epidermal skin than habitually shod individuals at both locations (p<0.001). We also measured skin hardness using a Shore durometer and found that hardness correlates with epidermal thickness across subjects at both the heel (r=0.64, p<0.001) and metatarsal head (r=0.56, p<0.001), with habitually barefoot individuals having harder skin (p<0.001). Finally, we tested the sensitivity of fast-adapting mechanoreceptors (types 1 and 2) at these locations using a standard vibration stimulus protocol. We found no relationship between plantar sensitivity and epidermal thickness at either location across subjects, even after controlling for age, sex and footwear use. This finding indicates that unlike footwear, calluses provide protection without loss of dynamic plantar sensitivity, making them a remarkable example of evolutionary engineering that allow us to walk and run barefoot safely.
