Changes in postural sway as a function of prolonged walking.

For optimal balance, the postural system needs to quickly detect and respond to perturbations. The aim of this study was to investigate the immediate and long-term impact of walking at different speeds on standing balance and postural stability. Center of pressure (COP) motion was measured from 14 young individuals at discrete time intervals after they walked on a treadmill at three speeds (preferred walking speed (PWS), 120 %-PWS, 140 %-PWS). Results revealed that walking at a faster speed had the greatest impact on postural stability. This was reflected by increases in the amount (path length, range, 95 % ellipse), variability (standard deviation, SD), and structure (approximate entropy, ApEn) of COP motion and were most evident when compared to pre-walking assessments. In subsequent trials following pre-walking assessments there was a leveling-off for specific COP variables (range, variability, and ApEn) and a decline in path length. This plateau effect was observed even though measures of physical exertion (HR, RPE) continued to increase over the entire walking trial. Together, these results indicate that, despite the constant task demands induced by fast walking, the postural system was able to rapidly compensate and adjust appropriately.