MINIMUM ENERGY TRAJECTORIES OF THE SWING ANKLE WHEN STEPPING OVER OBSTACLES OF DIFFERENT HEIGHTS

This study was performed to test the hypothesis that the motion of the lower extremities when stepping over obstacles is governed by the cri terion of minimum mechanical energy. The trajectories of the swing ank le during level walking and when stepping over obstacles of 51, 102, 1 53, and 204 mm heights were predicted and measured for eight healthy y oung adults. The predictions were made with a planar, seven-link linka ge model based on the criterion of minimum mechanical energy using the method of dynamic programming. When stepping over obstacles, the pred icted trajectories of the swing ankle were just high enough for the sw ing toe to clear the obstacles. The clearances measured between the ob stacle and toe were significantly larger than those predicted. When st epping over obstacles the levels of work required to generate the meas ured trajectories were significantly larger (p less than or equal to 0 .002) than those required to produce the predicted trajectories. The a mount of work necessary to generate the measured or predicted trajecto ries increased linearly (significant at p less than or equal to 0.022) with obstacle height and, except when predicting the trajectory for t he lowest obstacle, was significantly greater than that required when walking on level ground (p < 0.02). Thus, conservation of energy was f ound to become a less dominant criterion for governing the motion of t he body when crossing obstacles than when walking on level ground. Cop yright (C) 1996 Published by Elsevier Science Ltd.