Postural organisation during cascade juggling: influence of expertise.

The present study investigated how posture is organised during three-ball cascade juggling according to expertise. We hypothesized that the juggling task would place constraints on the postural organisation mode and that the posture-juggling coupling would be increased with expertise. Two groups, intermediates and experts, were asked to perform a postural-cascade juggling task. A three-dimensional motion recording system recorded the position of five light-reflecting markers for 30s to analyse the ball movements, the lateral oscillations of the sacrum and the flexion/extension of the right elbow. The spatial pattern of the cascade juggling showed no significant difference between groups. Moreover, both groups presented lateral oscillations of the sacrum during the task. The latencies between the maximal flexion/extension of the right elbow and the maximal lateral oscillations of the sacrum and their standard deviations were significantly lower for the experts than for the intermediates. We conclude that postural adaptations occur to facilitate the postural-suprapostural task and that experience modifies the posture-juggling coupling.