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Co-contraction in the hemiparetic forearm: quantitative EMG evaluation.
M C Hammond1, S S Fitts, G H Kraft
1Department of Rehabilitation Medicine, University of Washington, Seattle 98195.
Archives of Physical Medicine and Rehabilitation
|May 1, 1988
Summary
Stroke survivors with hemiparesis show impaired muscle control. This study found reduced agonist muscle activation and increased antagonist muscle activity, indicating issues with both muscle recruitment and inhibition in the affected arm.
Area of Science:
- Neuroscience
- Clinical Neurology
- Rehabilitation Medicine
Background:
- Co-contraction of antagonist muscles is observed in patients after cerebrovascular accident (stroke).
- Existing literature shows conflicting findings regarding increased antagonist electromyography activity in hemiparesis.
Purpose of the Study:
- To investigate motor unit activity in wrist flexor and extensor muscles in stable stroke patients.
- To compare agonist and antagonist muscle activity during voluntary isometric contractions between patients and controls.
Main Methods:
- Developed a technique for simultaneous motor unit counting using monopolar needle electromyography.
- Tested stable stroke patients and age/sex-matched controls during maximal voluntary isometric wrist flexion and extension.
Main Results:
- Fewer agonist motor unit events were counted in paretic muscles compared to controls (p < 0.05).
- More antagonist motor unit events were observed in paretic muscles than in controls (p < 0.10).
- The co-contraction ratio (antagonist activity/total activity) was significantly higher in stroke patients (p < 0.01).
Conclusions:
- Agonist muscle recruitment is impaired in the hemiparetic arm following stroke.
- Antagonist muscle inhibition is also impaired, contributing to abnormal co-contraction.
- These findings suggest a dual deficit in motor control following cerebrovascular accident.