Posture, dynamic stability, and voluntary movement.

This paper addresses the question of why voluntary movement, which induces a perturbation to balance, is possible without falling down. It proceeds from a joint biomechanical and physiological approach, and consists of three parts. The first one introduces some basic concepts that constitute a theoretical framework for experimental studies. The second part considers the various categories of "postural adjustments" (PAs) and presents major data on "anticipatory postural adjustments" (APA). The last part explores the concept of "posturokinetic capacity" (PKC) and its possible applications.