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.