An analysis of leg joint synergy during backward walking.

Grasso et al. (1998) proposed the hypothesis that motor commands for the backward walking is designed so as to reproduce the reversal motion of forward walking. In this study, we analyzed the leg joint synergy in backward walking by the UCM analysis and compared the results with the time reversal profile of the synergy in forward walking. Some similarities between them were observed, e.g., the body posture is controlled by utilizing joint synergy during double support phase. However, differences were also observed during swing phase, e.g., at touch down at the end of swing phase the joint synergy is utilized to adjust the foot position in backward walking, contrary in forward walking the synergy is not utilized but the variance of joint angles are suppressed. The results indicate that the backward walking is not a reversal motion of forward walking, but planned independently of forward walking.