Controlling stability of a complex movement system. Human movement systems have frequently been treated as one-dimensional, single-axis, rigid bodies in order to simplify the gathering, analysis, and interpretation of data. The problem with this approach is that the results of such assumptions often lead to conclusions about the production and control of movement that do not relate to the control demands placed on the central nervous system. In order to truly understand how the central nervous system plans and produces movements to match environmental demands, we must take into account the many variations available within the body. The purpose of this article is to examine two movement systems that have the potential to act in multiple spatial dimensions with variable muscle action patterns when performing a stabilizing task. Methods of analyzing how the systems operate under differing task constraints and results of the experiments will be presented. Hypothetical models that have been proposed to explain how complex movement systems operate will also be discussed. 