Optimal Control in Virtual Walkway

A virtual walkway was developed to investigate the potential postural adaptation under simulated partial gravitational conditions. To track the simulated sinusoidal trajectory from the center of expansion of the optic flows, the looping gait was hypothesized based on an optimal control model (OCM). The dynamics of the plant were evaluated using the head movements and the ground reaction force profiles where a 2 order spring-damper-mass model was assumed. Bode plots were used to compare the predictions with the actual human tracking performance. The results show that the proposed model performs better than the crossover model within limited gait cycles. However, an unexpected step cycle skipping phenomenon was found among all subjects. The results suggest that the subjects might use both crossover and optimal control strategies during locomotion depending on their tracking performance. When the crossover control was robust, there were less feedback errors of the given system dynamics. In contrast, when the system became less reliable, OCM was evoked to recalibrate postural control for next step cycles. This unexpected gait cycle skipping should be considered in the future effort for partial gravity gait adaptation