Abstract
Human arm movements display characteristic patterns in their trajectories, the torques at the joints and in the EMG patterns in the various muscles. The relationship between the torques and the kinematics is described by physics but the relationship between these properties and the activation of the muscles that produce both is complex and far from well understood. The paper discusses some of the motor control theories that help us understand why we perform our movements in the way we do and how the central nervous system activates the muscles towards those ends. This paper argues that in spite of the well known regularities that are found in simple movement kinematics, an understanding of how muscles are activated will emerge from studying the regularities of the joint torques. However, because of the complex anatomical relations by which muscle forces are converted into joint torques, a full understanding of how the patterns of muscle activation are created may emerge only from the study of the EMG patterns themselves.
