Postural challenge and adaptation to vibration-induced disturbances.

The described experiment investigated whether adaptation to successive Achilles tendon vibration depends on the postural challenge. In phase 1, thirty-six participants were divided into three groups, each with a different postural challenge. After being blindfolded, participants received 15 trials of Achilles tendon vibration (10 s-90 Hz) while standing upright in either a free-standing condition (FS group), a light finger touch condition (LFT group), or a restrained-standing condition (RS group) in which a dorsal stand prevented body displacement. In phase 2, all participants were freely standing and received 15 additional trials of vibration. Antero-posterior trunk tilt was measured at the level of the trunk (C7). Although there were limited postural readjustments in LFT, adaptation was observed in phase 1 in both FS and LFT groups. In phase 2, the evoked postural displacement was greater in the RS group than in the other two groups. We concluded that although the absence of any postural challenge concomitant to the sensory stimulation prevented adaptation to occur, a minimal challenge was sufficient.