Leg Stiffness and Foot Orientations During Running

This study was done to determine whether leg stiffness (K _leg) during running was related to rearfoot-to-forefoot angle in standing (RFA_st) and running (RFA_run). Footprints obtained from 32 subjects were used to calculate RFA_ts, and RFA_run' defined as positive when forefoot axis was abducted from rearfoot axis. A spring-mass model was used to calculate K _leg in running from ground reaction forces, measured by a force platform. The K _leg of runners (13.0 ± 2.7 kN m⁻¹) was negatively correlated with RFA_st (−8.4° ± 6.4°) and RFA_run (−0.4° ± 7.2°). When runners were divided into opened foot (RFA_run > 0; N = 19) and closed foot (RFA_run < 0; N = 12) groups, the K _leg of opened foot runners was less than that of the closed runners. We suggest that foot structure is a factor responsible for the differences in leg stiffness observed in runners.