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(Tremor Group): 1. At least 40 years of age, and no more than 90 years of age. 2. Meet UK Parkinson's disease brain bank diagnostic criteria 3. Have clinical evidence of rest tremor of one or both upper extremities defined as involuntary, rhythmic oscillations about any joint within the upper extremities 4. Tremor amplitude must be at minimum 1 cm as determined by expert opinion by a movement disorders specialist. 5. Due to the nature of measurements occurring during a grasp maneuver, the tremor must be deemed to become re-emergent with a fixed posture. This shall be defined by development of postural tremor that does not begin immediately upon grasping the vertical object, but instead with a delay in development of oscillatory movement of at least half a second as timed by a stopwatch, and that may grow in amplitude over seconds to maximum amplitude without changing the force of the grasp at first. Note that within-individual intermittency and variability of tremor can be influenced by anxiety, stress, cold temperature, and fatigue. In an effort to reduce this variability, we will have subjects perform tasks in a comfortable area, providing up to 20 minutes to allow them to relax in a temperature-neutral location, and reduce anxiety

(Tremor Group): 1. Muscle weakness as determined by Medical Research Council grade less than 5/5 on direct testing in the upper limb afflicted with rest tremor 2. Infection at the upper limb at time of assessment 3. Pre-existing, concomitant neuromuscular or cerebellar disorders 4. Use of medications that can alter the function of the neuromuscular junction. 5. Those with concomitant essential tremor as determined by history or confirmed by movement disorders specialist prior to assessments. Inclusion Criteria (Able Body): Subjects will fall under the able body category if they exhibit no movement disorders and can perform grasping motion with no inhibition.