Strategies underlying the control of disordered movement. The purpose of this article is fourfold. First, a theory of motor control--the dual-strategy hypothesis--is outlined. Second, the methodologies and theoretical framework that are used to develop this theory are examined. Third, motor dysfunction is discussed in the context of this theory. In particular, Down syndrome, Parkinson's disease, cardiovascular accidents, and spasticity are discussed. Finally, potential applications of the theory to physical therapy are considered. 