Footfall dynamics for racewalkers and runners barefoot on compliant surfaces.

The main purpose of this study is to investigate the role of footfall surface compliance on the physical parameters affecting barefoot racewalkers and runners. These parameters are identified using a new inverted pendulum body model with a forward moving foot pivot. Model correlations of footfall loads measured for four compliant surface mats showed leg-foot compression stiffness for both gaits were in the range of 10.8-12.9 kN/m, with the initial stiffness spikes in the range of 6.5-52 kN/m. The average leg damping factor was about 0.6% for racewalkers and 6% for runners. For both gaits there was negative leg damping just prior to foot lift-off. Compared to the peak reactions for the rigid surface, a mat of intermediate compliance (1020 kN/m) was effective in reducing the runners' peak reaction spikes by as much as 17%.