Effects of light finger touch to the upper legs on postural sway and muscle activity during quiet standing

The purpose of the present study was to investigate the effects of light finger touch (LT) to one's own body on postural sway and ankle muscle activity during quiet standing. In the first part of the present study, 24 healthy men (19 +/- 1 years) stood upright with their eyes closed on a pneumatic balance disk under 3 different conditions. In the first condition, the participants kept their hands in loose fists, and contact between the fingers/palms and the legs was avoided. In the second condition, the participants touched the lateral sides of upper legs lightly (without applying force for mechanical support) with all fingers. In the third condition, the participants again held their hands in loose fists. Postural sway was significantly decreased during second condition compared to first condition. Further, it also tended to decrease in third condition (P = 0.08). The second part of the present study was designed to investigate the mechanisms underlying the association between postural sway and LT by analyzing electromyographic data. Data were obtained from 12 healthy men (20 +/- 1 years). During quiet stance on the stable surface, soleus activity did not significantly change by LT. However, tibialis-anterior activity significantly decreased with LT. These results suggest that LT to the upper part of one's own legs decreases postural sway (during and after touching) during a still stance by decreasing co-activation of the ankle muscles.