This project continues our study of the compliant behavior at the human elbow, ankle and wrist produced by muscle and neural control mechanisms. We will apply controlled changes or torque to resisting or relaxed limbs and measure the resultant motion and electromyographic responses. We are interested in more completely describing the behavior of the limb under such perturbations in terms of its visco-elastic and plastic behaviors. By carefully studying the temporal variation in these behaviors, we hope to separate purely muscular mechanism from more variable neural control mechanisms. The parametric descriptions that are measured experimentally will be used to build non-linear computer models of the limb and the muscles. Such models have a dual purpose. They are directly useful in biomechanical studies such as predicting head motion following sudden impacts to the body or head. In our own lab, the model will be used to help interpret the electromyographic controlling signals that are observed in muscles during voluntary movements.