Fig. 9.
Initial stance phase knee angle determines limb posture and the work balance among the joints. The knee angle is the only joint angle that differs significantly at the onset of ground contact among the U response modes. If the knee is extended at contact (left silhouette) the limb has a lower initial angle and longer initial length. This extended posture is associated with larger decelerating forces, greater energy absorption by the ankle and TMP, and net energy absorption by the limb. If the knee is flexed at contact (right silhouette), the limb has a higher initial angle and shorter initial length. This flexed posture is associated with lower decelerating forces, spring-like function of the ankle and TMP, and net energy production by the limb. In cases with an extremely flexed knee, the distal limb simply collapses without supporting substantial weight (KEv mode, silhouette not shown). Values are mean ± s.e.m. (N=10, 7, 9, 3, for the respective categories).