130 Influence of Joint Torques at Seat-Off on Rising Movements from a Chair

Abstract

We have already formulated the dynamics-switching three-link and three-joint (an upper body, two thighs, and two lower legs) optimal control model that reproduces human rising movements from a chair, and clarified its effectiveness and the existence of the optimal relation between two factors (input weight and dynamics-switching time) indispensable for sit-to-stand movements. This report clarifies theoretically how the knee- and ankle-joint torques at the seat-off time affect the subsequent rising movement, and examines the possibility to predict the risk of falling caused by miscalculation of these torques. Consequently, the following results are shown: (1) as for the knee- and ankle-joint torques at the seat-off time, there exist effective ranges necessary for the optimal control model to rise successfully from a chair, and the range of the knee-joint torque is smaller than that of the ankle-joint torque; (2) a shortage of the ankle-joint torque at the seat-off time makes the model pratfall; (3) a shortage of the knee-joint torque at the seat-off time makes the model fall forward to its knees, and an overage of the same torque makes the model pratfall. These results suggest that the knee- and ankle-joint torques at the seat-off time can be important factors controlling the success or failure of rising movements from a chair, and that the optimal control model is effective in simulating falling movements as well.