The effect of visual perturbation in planning landing from a jump in adult humans /

Prelanding EMG responses in uniarticular and biarticular flexors and extensors of the leg were assessed during landing from jump-downs at a constant height (0.45 m) or randomly varying heights (0.35, 0.45 and 0.55 meters) in normal humans under four visual conditions: normal, occluded, stabilized by a visual conflict dome, and disrupted by stroboscopic flash at 8 Hz. Pressure sensitive foot-switches and video recordings of each jump-down from a sagittal view allowed the expression of EMG in temporal relation to limb trajectories and foot-ground contact.Results from EMG analysis demonstrated a stable, global pattern of activation regardless of visual condition and independent of knowledge of the jump height. A generalized strategy of EMG activation was adequate for successful landing on stable height trials, but subjects developed a different default strategy for jumping at random height when inadequate visual update was provided. The prelanding EMG responses from the muscles recorded suggest that there are different roles for the muscles in preparing the body for ground impact. (Abstract shortened by UMI.