Effect of Water Immersion of Fingertip Somatic Sensation on Quiet Bipedal Stance: A Basic Study for Neurophysiological Effect of Water Exercise

Abstract

Studies have shown that a fingertip lightly touching a stable surface reduces postural sway, by providing additional tactile feedback information to the postural control system. In the present study, we examined whether or not water immersion of a fingertip enhances the postural control system during quiet standing. Eight young and nine elderly subjects maintained quiet standing for 40s with the index fingertip in the water （water touch, WT） or on the stable surface （light touch, LT）．The temperature of water in the WT condition was 20, 30, or 40℃ for young subjects and 30℃ for elderly subjects. In the control condition （CON），a no touch trial, the subject quietly stood on a force platform for 40s, with their arms by their sides. In the young subjects, eight trials were conducted for each condition; while the elderly subjects completed three trials for each condition. The results showed that, in the young subjects, the mean velocities of the foot center of pressure （CoP） in the anteroposterior （AP） direction was significantly reduced in the LT and WT at individual optimal temperature, compared to that in the CON condition （P<0.05）．On the other hand, in the elderly subjects, the power of low-frequency CoP sway （below 1Hz） in the AP direction significantly decreased at LT and WT conditions （P<0.05）．These results indicate that WT can enhance the postural control system, as well as the LT. This promises the neurophysiogical effect of water exercise on the postural control system.