Song R, Tong KY, Hu XL. Evaluation of velocity-dependent performance of the spastic elbow during voluntary movements. Objective: To evaluate quantitatively, using a voluntary elbow-tracking experiment, the performance at different angular velocities of unaffected elbow compared with spastic elbow after stroke. Design: Poststroke subjects were recruited to perform voluntary movements of elbow flexion and extension by following sinusoidal trajectories from 30° to 90° at peak angular velocities of 15.7°, 31.4°, 47.1°, 62.8°, 78.5°, and 94.2°/s in a horizontal plane. The actual elbow angle and the target position were displayed as real-time visual feedback. Setting: Rehabilitation center research laboratory. Participants: Nine hemiplegic chronic stroke patients. Interventions: Not applicable. Main Outcome Measures: Root mean square error (RMSE) between actual elbow angle and target angle, root mean square jerk (RMSJ), and Modified Ashworth Scale (MAS). Jerk is the rate of change of acceleration, which is the third derivative of the actual angle. A smooth motion has less jerk. Results: The RMSE and RMSJ had a good reliability. The RMSE and RMSJ increased in both affected and unaffected arms with increasing tracking velocity. The RMSE and RMSJ of the unaffected arms were significantly lower than those of the affected arms at all the velocities. There was significant correlation between the RMSJ and MAS at the peak velocities of 15.7°, 31.4°, 47.1°, 62.8°, and 94.2°/s (correlation coefficient range, .67-.83). Conclusions: The parameters reflected motion quality, which has potential for use in quantitatively evaluating the deficiencies of sensorimotor control of spastic elbow in persons after stroke during voluntary movements. ; Department of Health Technology and Informatics