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

https://doi.org/10.1016/j.apmr.2007.05.006Get rights and content

Abstract

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<.05), associated with the significant decrease (P<.05) in the MAS score. The overall electromyographic activation level of the anterior deltoid also decreased significantly from the 8th to 20th sessions (P<.05). Significant decreases in the cocontractions of all muscle pairs were observed in all subjects and also in the overall cocontraction index (P<.05). The cocontraction between the biceps and triceps significantly decreased when the overall electromyographic levels of the 2 muscles were stable from the 10th to 20th sessions (P<.05). Significant improvements (P<.05) on the FMA and MSS score were also found by the pre- and postassessments.

Conclusions

In the 20-session robot-assisted training, the excessive muscle activations reduced mainly in the first half of the training course, which could be related to the learning process of the tracking skill and also to the reduction in muscle spasticity. The muscle coordination for achieving elbow tracking improved significantly in the latter sessions of the training, represented as decreased cocontraction indexes between the muscle pairs.

Section snippets

Methods

After obtaining approval from the Human Subjects Ethics Sub-Committee of the Hong Kong Polytechnic University, we recruited 7 hemiplegic subjects after stroke for the study. All of the subjects were in the chronic stage (at least 1y postonset of stroke; 6 men, 1 woman; age, 51.1±9.7y). All subjects received a robot-assisted elbow training program consisting of 20 sessions, with at least 3 sessions a week and at most 5 sessions a week, and finished in 7 consecutive weeks. Each training session

Results

Table 1 shows the clinical scales used for the impairment evaluation before and after the 20-session training. It was found that the mean values of scores for FMA and MSS had increased significantly (t tests, P<.05) and the mean value of MAS decreased significantly (t tests, P<.05) after the training. For each subject, the clinical scales indicated improvements in at least 2 items.

Figure 3 shows the variation of the overall RMSE of the elbow angle during the tracking training. The overall RMSE

Discussion

After the 20 sessions of robot training of the elbow extension/flexion, motor improvements could be observed in all subjects, associated with the improved clinical scores, and decreases in the RMSE, cocontraction indexes, and electromyographic activation levels. The decrease in the clinical score of MAS suggested a reduction in spasticity of the impaired upper limb of the subjects. Increases in the FMA score and MSS implied improved motor functions of the paretic upper limb during prescribed

Conclusions

In this study, significant motor improvements assessed by MAS, FMA, and MSS were observed after the 20-session training on elbow tracking task actively assisted by a rehabilitation robot. The muscle coactivation patterns during the interactive robot-assisted training on elbow flexion and extension were analyzed by the electromyographic activation level of individual muscles and the electromyographic cocontraction index of the muscle pairs. The electromyographic activation levels of the major

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    Supported by the Research Grants Council of the Hong Kong Special Administrative Region, China (grant no. PolyU 5271/05E) and The Hong Kong Polytechnic University (grant nos. G-U056, G-YX65).

    No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.

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