Variation of Muscle Coactivation Patterns in Chronic Stroke During Robot-Assisted Elbow Training

The experimental setup used for elbow extension and flexion training. Subjects conducted elbow flexion and extension on the horizontal plane, by tracking a target cursor moving at 10° per second on the screen. Electromyography (EMG) electrode pairs were attached to the skin surface of the muscles biceps brachii (BIC), triceps brachii (TRI), anterior deltoid (AD), and posterior deltoid (PD). After preamplification and filtering, the electromyographic signals were digitized and stored along with the angle and torque signals. The electromyographic activity of triceps brachii was also used as a control signal to the electromyography-driven motor system for providing the supportive torque during the training. Abbreviation: A/D, analog to digital.

Representative signals captured in the training experiment. (A) The raw electromyographic signals from the triceps brachii and biceps brachii, and torque signals during IMVF and IMVE after the filtering; and the biceps brachii and triceps brachii electromyographic signals and the angle signals during a tracking trial. (B) Illustration of the calculation of cocontraction indexes (CI) (with the unit of %Max) of the muscle pairs during a tracking trial.

The variation of the mean RMSE values of individual subjects (from S1 to S7, represented by symbols shown in the legend); and the global RMSE summarizing the performance of all subjects during the tracking across the training sessions, represented by the values of mean and standard deviation (SD) (error bars).

The variations of electromyographic activation level for the biceps brachii, triceps brachii, anterior deltoid, and posterior deltoid muscles. The electromyographic activation levels from individual subjects (ie, S1 to S7) are represented by their respective symbols shown in the legend. The global electromyographic activation levels of the muscles, summarizing the performance of all subjects, are represented by values of mean and SD (error bar).

The variations in cocontraction index of the muscle pairs, triceps brachii and posterior deltoid, biceps brachii and triceps brachii, biceps brachii and anterior deltoid, anterior deltoid and posterior deltoid, triceps brachii and anterior deltoid, and biceps brachii and posterior deltoid. The cocontraction indexes of individual subjects are represented by symbols shown in the legend. The values of the global cocontraction indexes for a muscle pair summarizing the performance of all subjects are represented by the values of mean and SD (error bar).