Abstract of Aaron Poliak’s 2015 undergraduate honors thesis
Our ancestors have been running barefoot for millions of years, and began wearing shoes only recently, perhaps 30kya. Because shoes influence the development of foot anatomy and foot function, biological anthropologists studying the biomechanics of ‘natural’ barefoot human running gaits have focused their research on modern habitually barefoot populations. These studies have had conflicting results, in that different barefoot populations seem to run in different ways. In some habitually barefoot groups, runners typically land on the balls of their feet (forefoot strike), not on their heels (heel strike), and researchers have suggested that this is a healthier and 'natural' way to run because it may reduce jarring impact forces. However, other studies found that certain habitually barefoot populations typically run with a heel strike, showing that there is not a stereotypical ‘healthy’ or ‘natural’ running gait that is used by all habitually barefoot people. The latter researchers hypothesized that factors such as running speed or the stiffness or compliance of the ground may influence foot strike patterns, so that people may alter their foot strike patterns under different sets of circumstances. This study explicitly tests the hypothesis that speed and/or ground compliance influences running foot strike patterns by collecting data on foot kinematics from 22 men and 11 women from the habitually barefoot Daasanach tribe in northern Kenya. These volunteers ran at several speeds on three different substrates: concrete, hard-packed natural ground, and artificially softened natural ground. Our results, from linear mixed effects modeling, indicate that the foot strike angles of the Daasanach are not significantly influenced by substrate compliance (p>0.5). However, speed does affect foot strike angles across all three surfaces (p<0.01). Our results indicate that speed, but not substrate, influences running form in the Daasanach, and shed important new light on debates over variations in running form among habitually barefoot people.