Effect of Assist Robot on Muscle Synergy during Sit-to-Stand Movement

Sit-to-Stand (STS) is an important movement in daily life and could be difficult for older people. Assist robot is expected to provide STS support. STS movement does not only require kinetic coordination, but also muscle coordination. Thus, understanding the muscle coordination during STS with robot assistance is a key issue of human-robot-interaction. The purpose of this study is to reveal the effect of assist robot on muscle coordination during STS through muscle synergy theory. Six subjects did self-performed and robot-assist STSs in total ten times. Surface electromyogram (EMG) of eight muscles was measured to extract muscle synergy using non-negative matrix factorization (NMF). As a result, two muscle synergies appeared in self-performed STS. There were three muscle synergies when STS was assisted by the robot. The spatial patterns of muscle synergies for lower limb muscles differed with and without robot assistance. Using the robot delayed the activation of muscle synergy at the temporal pattern.