Analysis of Skip Motion as a Recovery Strategy after an Induced Trip

Falls are one of the main causes of decreased quality of life and activities of daily living among the elderly individuals. Because tripping is the most common cause of falls, some types of recovery motions have been reported after tripping induced by a flat plate or block. Common recovery strategies observed under these conditions included elevating and lowering strategies. Especially, in case that the swinging leg contacts an obstacle at its early phase, the elevating strategy has been considered as a typical recovery motion. In this study, we performed a tripping experiment using a crossbar in the early and middle of swing phase. As a result, a new recovery strategy, which differed from those previously reported, was observed. In the new strategy, referred to as the skip strategy, the subjects lifted and moved the standing leg forward after tripping. The subjects utilized this strategy to recover from an early phase trip. The participants had to exert enough knee flexion and ankle plantar flexion torques of recovery leg with the skip strategy and enough knee extension, hip extension, and ankle plantar flexion torques of recovery leg with the lowering strategy. Especially for the elderly who cannot perform large joint torques, gait assistant devices such as physical assistant robots are required to compensate such joint torques in order to perform these recovery motions.