Influence of light finger touch on postural stability during upright stance with cold-induced plantar hypoesthesia.

The present study investigated the influence of light finger touch on postural stability during an upright stance with or without cold-induced plantar hypoesthesia. Participants were 21 healthy right-handed men (20-33 years), randomly assigned to a normal temperature group (NML-group; n = 11) or cold-induced plantar hypoesthesia group (COLD-group; n = 10). Participants performed two standing tasks with their eyes closed: 1) stand upright with the feet comfortably apart (normal standing); and 2) with the feet together in a side-by-side stance (Romberg standing). The order of the tasks was randomized across participants. After a rest period, they were asked to perform each standing task and let their right index finger lightly touch the fixed surface. Before the each task, participants in the COLD group were conducted a plantar intermediate hypothermic exposure. Postural sway was decreased by providing additional haptic sensory input through the light touching regardless of standing task difficulty with a normal plantar temperature. Although postural sway under plantar hypoesthesia is decreased by light touching, the effect was greater during the difficult posture task. These results suggest that, when the sensory information from the plantar surface is decreased, additional haptic input from the hand or finger might provide supplementary information about the relative changes in one's own body orientation. Therefore, sensory information provided by touching became relatively more important to maintaining postural control during the relatively difficult postural task performed under the reduced plantar sensitivity condition.