Hu X, Tong KY, Song R, Tsang VS, Leung PO, Li L. Variation of muscle coactivation patterns in chronic stroke during robot-assisted elbow training. Objective: To investigate the variation of muscle coactivation patterns during the course of robot-assisted rehabilitation on elbow flexion and extension for chronic stroke. Design: A detailed electromyographic analysis was conducted on muscle activation levels and muscle coactivation patterns, represented by a cocontraction index of a muscle pair, for the muscles of biceps brachii, triceps brachii, anterior deltoid, and posterior deltoid, during training of elbow extension and flexion, actively assisted by a robot, from 0° to 90° by tracking a target moving at a speed of 10°/s on the screen. Setting: Rehabilitation center research laboratory. Participants: Seven hemiplegic chronic stroke patients received elbow training. Interventions: Each subject received 20 sessions (1.5 hours/session) of the elbow training on his/her paretic side at an intensity of 3 to 5 times a week for a training period of 7 consecutive weeks. Main Outcome Measures: Muscle cocontraction index, muscle activation level, and Modified Ashworth Scale (MAS), Fugl-Meyer Assessment (FMA), and Motor Status Scale (MSS) scores. Results: The electromyographic activation levels of the biceps brachii, triceps brachii, and anterior deltoid of each subject decreased during the training. The overall electromyographic activation levels of the biceps and triceps, which, summarizing the performance of all subjects, decreased significantly in the middle sessions (from the 8th to 12th sessions) of the training (P