Cross-correlation analysis of the lateral hip strategy in unperturbed stance

Subjects standing heel-to-toe on either hard ground or soft support were instructed to stand upright keeping optimal balance. Lateral accelerometric measurements at head, hip and ankle levels were subjected to conjugate cross-correlations analysis in order to determine the co-ordinated movements or strategies. The results strongly suggest that there exists a hip lateral strategy which is very similar to the hip strategy previously described in fore-aft body oscillations. This lateral hip strategy was only observed when the greatest body oscillations were observed, namely on the soft supporting surface, and its descending sequence of co-ordinated movements is consistent with the idea of a top-down organization of postural control during movement or difficult stance conditions.