Characteristics of elbow movements to different amounts of surface electromyography-based assistive torque

This study investigated the characteristics of human responses to different amounts of SEMG-based assistive torque. A power assistive device provided proportional torque with respect to the estimated human torque using surface electromyography (SEMG). Seven participants performed self-paced elbow flexion tests under five conditions, each having the different proportion of the assistance. We computed the variability of the angle and angular velocity of the elbow joint to quantify relative stability of the assisted movements. Power spectral density of the angular acceleration of the joint was also computed to characterize the power and bandwidth of the movements in the frequency domain. From the experiments the variability gradually increased with the amount of the assistive torque and it indicated that the movements in response to increased assistive torque became relatively more unstable. In addition, the power and bandwidth of the movements were gradually increased although subject's physical efforts for the movements were decreased. This study can be used as a cornerstone to determine the amount of SEMG-based assistive torque for maintaining smooth and natural human movements.