Effect of vibration stimuli on postural response in humans standing on stable and unstable supports

The purpose of this study was to analyze the effects of somatosensory inputs on the postural control in human standing. To study these effects, the center of pressure (COP) was closely observed while subjects were standing on a stable and an unstable support in turn with simultaneous or separate mechanical vibratory stimulations to flexor ankle muscles (tibialis anterior, triceps surae) and two plantar zones on both feet while standing on a stable and an unstable support. The simultaneous vibratory stimulations cleared influenced postural stability and the effects of vibrations were higher with the unstable support. In separate vibratory stimulations, the extent of the COP sway reduced when the direction of the vibratory stimulations and that of the inclination of body coincided for flexor ankle muscle stimulations. In the contrary, the extent of the COP sway increased when the direction of the stimulations and that of body inclination coincided for plantar zone stimulations. These findings can be useful for the development of rehabilitation systems that utilizes somatosensory inputs for postural balance.