A simple bipedal model for studying control of gait termination

We study the control of human gait termination with a simple bipedal locomotion model. Several control strategies have been proposed for gait termination. However, the relative importance of these strategies has not been evaluated in models of human gait. Here we extend the bipedal spring mass walking model in a least parameter fashion and study three explicit control strategies for gait termination, including the shortening of the final step, braking at the ankle, and extending the knee. Applying the strategies separately, we find that only braking at the ankle reduces the propulsive force enough to transition into quiet standing. In combination with the other two strategies, we observe that the range of control parameters suitable for gait termination increases, especially when the ankle control is applied intermittently by taking advantage of passive stabilizing dynamics. We further show the resulting model behavior is compatible with several experimental observations about the human center of mass dynamics and leg forces during gait termination, and discuss model improvements to correct mismatches. The proposed model may serve as a starting point for more advanced models that can provide a deeper understanding of human control strategies during gait termination.