Fig. 4. Vertical ground reaction forces (GRF) versus time over one step, measured during walking with arcs of different radius and in normal shoes. Larger arc radii resulted in smoother collisions during the step-to-step transition. Small arc radii resulted in very large initial peaks in ground reaction force. With larger arcs this peak decreased to below its magnitude in normal walking, but it always occurred earlier in the step. Walking on arcs resulted in shorter double-support times, decreasing with smaller radii. Arc radius had little effect on the second peak in vertical force. Data shown are averaged over all subjects and plotted over the mean step period. A step begins at heelstrike and ends at opposite heelstrike, with double support occurring over the first 0.10–0.15 s. BW, body weight. Blue and green traces indicate forces under the trailing and leading legs, respectively.