A shoe insole delivering subsensory vibratory noise improves balance and gait in healthy elderly people

Objectives: To test whether subsensory vibratory noise applied to the sole of the foot using a novel piezoelectric vibratory insole can significantly improve sensation, enhance balance, and reduce gait variability in elderly people, as well as to determine the optimal level of vibratory noise and whether the therapeutic effect would endure and the user's sensory threshold would remain constant during the course of a day.

Design: A randomized, single-blind, crossover study of 3 subsensory noise stimulation levels on 3 days.

Setting: Balance and gait laboratory.

Participants: Healthy community-dwelling elderly volunteers (N=12; age, 65-90y) who could feel the maximum insole vibration.

Interventions: A urethane foam insole with the piezoelectric actuators delivering subsensory vibratory noise stimulation to the soles of the feet.

Main outcome measures: Balance, gait, and timed Up and Go (TUG) test.

Results: The vibratory insoles significantly improved performance on the TUG test, reduced the area of postural sway, and reduced the temporal variability of walking at both 70% and 85% of the sensory threshold and during the course of a day. Vibratory sensation thresholds remained relatively stable within and across study days.

Conclusions: This study provides proof of concept that the application of the principle of stochastic resonance to the foot sole sensory system using a new low-voltage piezoelectric technology can improve measures of balance and gait that are associated with falls. Effective vibratory noise amplitudes range from 70% to 85% of the sensory threshold and can be set once daily.