Task and Skill Level Constraints on the Generality of the Proximal–Distal Principle for Within-Limb Movement Coordination

This paper examines the influence of task and skill level constraints on the generality of proximal–distal control for within-limb movement coordination. Analysis and synthesis of the experimental findings leads to the proposition that proximal–distal is one of several within-limb patterns of coordination, including: the reverse distal–proximal sequence, simultaneous activation of segments, and other sequence variations of this. The probability of particular patterns occurring is induced by task constraints and skill level of the individual, together with their evolving biomechanical consequences, including: open/closed chain, absorption/ propulsion of force, magnitude of momentum, and accuracy/timing. We develop the theoretical perspective that classes of task constraints induce particular types of neuromechanical organization to within-arm or within-leg segment coordination. In this task constraint framework, proximal–distal within-limb organization is a particular rather than a general case for within-limb coordination. The limitations of anatomically-based accounts of directional change for within-limb organization are discussed with reference to a general functional degrees of freedom task constraint framework for movement coordination and control.