Postural coordination modes considered as emergent phenomena

The coordination of multiple body se,aments (torso and legs) in the control of standing posture during a suprapostural task was studied. The analysis was motivated by dynamical theories of motor Coordination. In 2 experiments it was found that multisegment postural coordination could be described by the relative phase of rotations around the hip and ankle joints. The effec tive length of the feet, the height of the center of mass, and the amplitud e of head motions in a visual tracking task were varied. Across these varia tions, 2 modes of hip-ankle coordination were observed: in-phase and anti-p hase. The emergence of these modes was influenced by constraints imposed by the suprapostural tracking task, supporting the idea that such tasks influ ence postural control in an adaptive manner. Results are interpreted in ter ms of a dynamical approach to coordination in which postural coordination m odes can be viewed as emergent phenomena.