Very few studies have been performed that systematically examine the patterns of muscle activation that generate movement in patients with Parkinson's disease. As such, the long-term objective of the proposed research program is to understand how Parkinson's disease alters the way muscles are activated to perform movements. This laboratory has been instrumental in developing organizing principles for how muscles are activated to perform movements in neurologically normal individuals and has developed a model of motor control. This model is applicable for movements performed over different distances, in flexion and extension and generalizes to movements performed against inertial, viscous and elastic loads. This model also provides a framework with which to understand the motor deficits of Parkinson's disease. Aim 1 of the project is to test the prediction of this model that the motor deficits in performing movements over long distances common to Parkinson's disease are associated with an absence of the modulation of the duration and latency of electromyographic bursts. Aim 2 is to determine whether the durations and latencies of muscle activation for movements of different long distances are influenced by whether the agonist muscle is an elbow flexor or an elbow flexor or an elbow extensor and by whether patients with Parkinson's disease are making movements on or off medication. Aim 3 is to determine how patients with Parkinson's disease alter the durations and latencies of muscle activation to generate the appropriate forces required to perform movements against known inertial, viscous and elastic loads. The studies that have been devised to address these three aims will allow the investigation of how patients with Parkinson's disease perform movements whose force requirements are very different. The studies will determine whether the motor problems of Parkinson's disease are due to changes in agonist height and duration modulation, changes in antagonist timing, or muscle coactivation. The studies will also relate such factors as subject strength and the absence of medication to changes in muscle activation patterns. The experimental data will be useful in developing simple motor tasks that will provide insight into how patterns of muscle activation differ in patients with Parkinson's disease both on and off medication. These simple tasks also correlate with disease severity. Understanding how muscle activation patterns change to perform movements is important in evaluating pharmacological, neurosurgical as well as physical therapy interventions for patients with Parkinson's disease.