Rigidity is one of the cardinal symptoms in Parkinson's disease, along with Bradykinesia, tremor and postural instability. Rigidity in PD has been understudied, but its pathophysiological basis remains unclear. Various types of neurophysiological and biomechanical approach have been developed in order to investigate the neural control of muscle tone. A common approach is to observe the sensitivity of muscle resistance in response to stretch velocity or displacement [Kamper, Rea, He]. A recent study on elbow flexors in patients with spasticity and rigidity showed a velocity dependent increase in reactive torque in both groups [Lee H, et al). Even though this Study shows a correlation between elbow flexors and velocity, it doesn't discuss the role of elbow extensors. We studied the rigidity response in the elbow of both arms to different speed movements in 12 patients suffering from Parkinson's disease ON or OFF medication. The purpose of this study was to look at both elbow flexion and extension and show that quantitative measures of rigidity and movement disorders in subjects with Parkinson's disease correlate with the currently used clinical evaluations and also find the correlation between velocity and both elbow extension and flexion at the same time. Elbow was flexed and extended by means of a robotic arm,under four different speeds. The resistance to movement was recorded with a torque sensor and EMG of two elbow muscles; Biceps and Triceps; was recorded while the subjects were attempting to relax. The patients were also examined by physicians and their elbow rigidity and muscle tone and Parkinson's disease stage was evaluated and a Universal score in the categories of UPDRS, MMSE, and CAPIT was assigned for each arm of each individual. In the end we will argue that there is a very strong correlation between speed and elbow Extension and Flexion, muscle activity and the rigidity presented in each arm. We will also present the correlation between the robotic torque measurement and the clinical scores given to each subject.