Effects of Time-Varying Hip Abductor Vibration on Mediolateral Sway.

The control of mediolateral standing balance is disrupted in many clinical populations, likely due in part to altered sensation. Contributions of specific feedback sources to balance control can be investigated using sensory perturbations, as can be evoked with musculotendon vibration. The purpose of this study was to determine whether hip abductor vibration can elicit mediolateral sway at frequencies below 1 Hz, which dominate standing posture. Participants (n = 12) without neurological or orthopedic conditions performed a series of randomized standing trials on a force plate in which either hip abductor vibration was delivered or the standing surface translated mediolaterally. Vibration was delivered bilaterally in an out-of-phase pattern, with time-varying intensity following sum-of-sine trajectories with frequency content from 0.1 to 0.9 Hz. Surface translations followed similar sinusoidal trajectories, with the goal of increasing the likelihood that trials with vibration would be interpreted as reflecting true mediolateral sway. Participants were not instructed how to respond to the stimuli, and center of pressure location was calculated using recorded ground reaction forces and moments from the force plate. Vibration caused significant increases in mediolateral sway only at the specific frequencies targeted by each trajectory, suggesting that appropriately delivered hip vibration could shape mediolateral sway patterns through sensory augmentation.