Immediate After-Effects of Maintaining Light Touch using Electrical Muscle Stimulation to Index Finger Extensor Muscles on Postural Control *

In postural control, the light touch effect stabilizes posture by adding sensory cues when a part of the body, such as the fingertips, lightly touches a support surface. However, maintaining light touch can be difficult depending on individual characteristics and task difficulty. To address this challenge, we previously proposed a system that utilizes electrical muscle stimulation (EMS) on the index finger extensor muscle to maintain light touch. The present study aims to investigate the immediate after-effects of sustained light touch through the EMS-based system on postural control. Participants performed an eyes-closed single-leg stance without touch in the pre- and post-tests and performed the same task with their index finger lightly touching a handrail between the two tests (LT-test). During the LT test, the EMS group (n=10) lightly touched the handrail while EMS was administered, and the control group (n=10) performed the light touch without EMS. The postural sway parameters and electromyography were compared within each group between pre- and post-tests. The results showed a significant difference in the center of pressure sway in the EMS group, indicating decreased postural sway immediately after the LT test. This suggests that the sustained light touch with EMS enabled users to perceive more detailed sensory cues and facilitated the subsequent retention of postural control. Moreover, the postural stability was strongly associated with pelvic stability.