Coordination of multi-joint movements: An introduction to emerging views

Abstract

In this introductory paper, an overview is provided of the topics addressed in this special issue. These topics center around what is often referred to as Bernstein's problem. The first two topics both offer partial solutions to the indeterminacy problem. The first by identification of constraints acting on the neuro-musculo-skeletal system, in its interaction with the environment; the second by expanding the number of variables that are to be controlled. Regarding the first, it is argued that a distinction should be made between holonomic and nonholonomic constraints. Regarding the second, the necessity of independent control of in particular stiffness is a recurrent theme. The third and fourth topics concern choices to be made when modelling motor behavior. In particular, the level of detail at which the neuro-musculo-skeletal system is to be modelled in studies of coordination, and the merits of descriptive models offered by nonlinear dynamics are discussed. Apart from refining our models of the nervous system, the models of which are currently identified as a weak link, a major challenge for the coming years is concluded to lie in linking neuro-musculo-skeletal models to the behavioral models generated by nonlinear dynamics.