Unpowered Sensorimotor-Enhancing Suit Reduces Muscle Activation and Improves Force Perception

Studies suggest that the level of muscle activation may influence force reproduction. The purpose of this study was to develop a sensorimotor-enhancing suit (SEnS)—unpowered assistive clothing without actuators or electrical devices—and to examine its efficacy for reducing voluntary muscle activation and improving force reproduction in the upper limb in healthy young adults. The SEnS was made of elastic fabric and designed to produce assistive shoulder flexion moment that can partially mitigate the required activation of the user's shoulder flexor muscles. A series of human experiments were then conducted in healthy young adults. As a proof of concept, reduction in force reproduction performance of the shoulder moment was confirmed with mitigation of the shoulder moment by using an external string. To examine the efficacy of the SEnS, voluntary muscle activation and force reproduction performance was examined with and without using the SEnS, by comparing the amount of activation in the shoulder flexor muscles and the error in force reproduction in the upper limb. The results showed that wearing SEnS reduced muscle activation and force reproduction error. These results suggest that the accuracy of force reproduction can be improved substantially by partially mitigating the shoulder moment and associated voluntary muscle activation, using the SEnS.