The effect of a sensory perturbation on step direction or length while crossing an obstacle from quiet stance

Background and aims: The purpose of this study was to investigate the effect of a sensory perturbation on step length and direction while crossing an obstacle from quiet stance. Methods: Nine healthy adults were asked to step over an obstacle to land on a primary target (normal stepping condition). Following a light signal subjects had to respond as quickly as possible by stepping to secondary targets either forward or diagonal to the primary target. Results: Distinct changes in the slope of the anterior-posterior (Fx) and medial-lateral (Fy) ground reaction forces occurred 176 ms following the light signal. For diagonal stepping stance limb tibialis anterior (TA) and bilateral gluteus medius (GM) were responsible for directing the swing limb to the target. An increase in step length towards the long target was achieved primarily by activation of bilateral GM. Conclusions: Both EMG and force plate changes suggest that diagonal stepping is a more complex and challenging task than long stepping. (C) 2009 Published by Elsevier B.V.