Journal
MUSCLE & NERVE
Volume 46, Issue 6, Pages 926-931Publisher
WILEY-BLACKWELL
DOI: 10.1002/mus.23427
Keywords
botulinum toxin; cocontraction; isometric effort; muscle overactivity; spastic paresis
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Funding
- Allergan, Inc.
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Introduction: In this study of spastic hemiparesis we evaluated cocontraction during sustained agonist/antagonist efforts, before and after botulinum toxin (BoNT) injection in 1 agonist. Methods: Nineteen hemiparetic subjects performed maximal isometric elbow flexion/extension efforts with the elbow at 100 degrees (extensors stretched). Using flexor and extensor surface electromyography we calculated agonist recruitment/cocontraction indices from 500-ms peak voluntary agonist recruitment, before and 1 month after onabotulinumtoxinA injection (160 U) into biceps brachii. Results: Before injection, agonist recruitment and cocontraction indices were higher in extensors than flexors [0.74 +/- 0.15 vs. 0.59 +/- 0.10 (P < 0.01) and 0.43 +/- 0.25 vs. 0.25 +/- 0.13 (P < 0.05), respectively]. Biceps injection decreased extensor cocontraction index (-35%, P < 0.05) while increasing flexor agonist recruitment and cocontraction indices. Conclusions: In spastic hemiparesis, stretch may facilitate agonist recruitment and spastic cocontraction. In the non-injected antagonist, cocontraction may be reduced by enhanced reciprocal inhibition from a more relaxed, and therefore stretched, agonist, or through decreased recurrent inhibition from the injected muscle. Muscle Nerve 46: 926-931, 2012
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