Innervation zone distribution of the biceps brachii muscle examined using voluntary and electrically-evoked high-density
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(2019) 16:73
RESEARCH
Open Access
Innervation zone distribution of the biceps brachii muscle examined using voluntary and electrically-evoked high-density surface EMG Chengjun Huang1,2,3, Cliff S. Klein1, Zhaojian Meng1, Yingchun Zhang4, Sheng Li2,3 and Ping Zhou2,3*
Abstract Background: High density surface electromyography (EMG) can be used to estimate muscle innervation zones (IZ). The objective of this study was to compare the differences in the distribution of the biceps brachii (BB) IZ derived from voluntary contractions (VC) and electrical stimulation (ES) of the musculocutaneous nerve. Methods: Surface EMG signals were recorded from the medial and lateral BB with two 64-channel high density electrode matrices in eight healthy men. The surface EMG was recorded at different percentages of the maximal voluntary contraction (MVC) force (20–100% MVC) and at different percentages of the current needed to elicit a maximal M-wave (20–100% Imax). The IZs of the medial and lateral BB were identified from the EMG signals and expressed as a row number within a given medial-lateral column. Results: ES current intensity had no significant effect on the group mean IZ location (p > 0.05). However, The IZ during VC was located more proximally with increasing force (p < 0.05), likely due to muscle shortening. The position of the IZ varied slightly (by up to ~ 8 mm) in a medial-lateral direction under both contraction types, but this spatial effect was not significant. The IZ during ES and weak VC (20, 40% MVC) was similar (p > 0.05), but was more proximal in the latter than the former during 60–100% MVC (p < 0.05). Conclusion: ES can be used to detect spatial differences in IZ location free of the confounding effects of muscle shortening and recruitment order of different sized motor units. The method may prove beneficial for locating the IZ in patients who lack voluntary control of their musculature. Keywords: EMG, Innervation zone, High-density electrode matrices, Electrical stimulation, Voluntary contraction
Introduction Muscle spasticity often occurs in patients with neurological damage such as stroke and can have a negative impact on motor function [1]. It has been demonstrated that intramuscular injection of botulinum neurotoxins (BTX) is an effective and relatively safe treatment for spasticity [2, 3]. However, there are side effects including muscle weakness, blocking of autonomic nerves, and muscle atrophy, which may relate to the toxin dosage * Correspondence: [email protected] 2 Department of Physical Medicine and Rehabilitation, University of Texas Health Science Center at Houston, Houston, TX, USA 3 TIRR Memorial Hermann Research Center, 1333B Moursund St, TIRR Research Building, Suite 326, Houston, TX 77030, USA Full list of author information is available at the end of the article
[4]. The effectiveness of BTX treatment depends on the distance between the injection site and the location of the neuromuscular junctions [5, 6], which tend to cluster in a relatively narrow band termed the innervation z
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