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.

An analysis of leg joint synergy during bipedal walking in Japanese macaques.

We analyzed bipedal locomotion of Japanese macaques from the view point of leg joint synergy by the UCM (Uncontrolled manifold) analysis in order to examine how and when hip, knee and ankle joints cooperate so as to suppress the variances of the toe position relative to the hip position. Our results showed that joint synergy is exploited at some moments during walking. For instance, the variance of the vertical toe position was suppressed by joint synergy when the tip of the finger passes its lowest position from the ground. Some characteristics of the synergy pattern of macaques have been also reported in human walking, on the other hand, some differences between humans and macaques were found. For instance, high degree of joint synergy that suppresses the variance of hip height was observed around the end of stance phase in human walking, but such synergy was weak in macaques. The results suggest that different control strategies are used in bipedal walking of macaques and humans.