1Human Evolutionary Biology, Harvard University, 2Medical Physiology, Moi University Medical School
March 26, 2015 3:30, Grand Ballroom E/F/G
Most data on locomotor biomechanics derive from studies of habitually shod subjects, but cushioned, supportive shoes have become common only recently. Therefore, in order to evaluate hypotheses about the evolution of human locomotion, it is necessary to understand how shoes affect normative foot function during locomotion. We tested foot strength, foot stiffness, and lower extremity kinematics during walking and running gaits in a sample of 48 habitually barefoot and shod Kalenjin-speaking Kenyans and 23 Tarahumara Native Americans, who were habitually shod either in minimal sandals (huaraches) or conventional shoes. Sources and levels of variation in running form were experimentally manipulated, including speed, surface hardness, and stride rate. In both populations, conventionally shod individuals had approximately 50% less arch stiffness, and significantly less variation in arch height. In terms of kinematics, barefoot and shod individuals almost always rearfoot strike when walking, as do most runners in shoes with thick heels. However, strike types among habitual barefoot runners were significantly more variable. A general linear model indicates that foot strike angle was significantly affected by surface hardness, footwear history and running history, but not speed, with habitually barefoot individuals more likely to switch to mid- or forefoot strikes on harder surfaces. Strike type also covaries significantly with kinematics including trunk posture, preferred stride rate and degree of overstride. These results indicate that modern, habitually shod populations exhibit more variability in foot structure but less variation in gait kinematics, hence more variation in the forces acting on the lower extremity.
Funding provided by Harvard University.