Specific whole-body shifts induced by frequency-modulated vibrations of human plantar soles

This study sought to analyze the postural responses induced by separately or simultaneously vibrating with different frequencies the forefoot and rear foot zones of both soles in standing subjects. Stimulating each zone separately resulted in spatially oriented body tilts; their amplitude and velocity varied linearly according to the frequency, and their direction was always opposite to the plantar site vibrated. When the two zones were each co-stimulated at different frequencies, the parameters of the postural responses depended on the frequency difference. When this frequency difference was zero, no clearly oriented body tilts occurred. We concluded that the change in the relative pressures evoked by differently co-vibrating these zones gave rise to regulative postural adjustments able to cancel the simulated body deviation.