Repeatability and effect of instruction of body sway.

The effect of instruction and repeatability of posturography measurement was studied in 24 healthy volunteers. In an instruction, "stable" (inverted pendular model) and "relaxed" (segmental oscillating model) positions were studied. In addition, the effect of habituation adaptation, and day-to-day variation were investigated. Sway velocity and average and maximum displacement during vibration perturbated stance were analysed. In individual responses, no statistically significant day-to-day variation could be observed and the individual variation was small. In the "relaxed" condition, the instability was greater when maximum displacement was analysed. No significant changes in sway velocity and average displacement were observed. The results demonstrated remarkable stability of normal postural control mechanism.