Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, Kansas.
J Neurophysiol. 2021 Jun 1;125(6):2094-2106. doi: 10.1152/jn.00034.2021. Epub 2021 Apr 28.
The primary purpose of the present study is to determine if an organized control scheme exists for the antagonist muscle during steady isometric torque. A secondary focus is to better understand how firing rates of the antagonist muscle change from a moderate- to higher-contraction intensity. Fourteen subjects performed two submaximal isometric trapezoid muscle actions of the forearm flexors that included a linearly increasing, steady force at both 40% and 70% maximum voluntary contraction, and linearly decreasing segments. Surface electromyographic signals of the biceps and triceps brachii were collected and decomposed into constituent motor unit action potential trains. Motor unit firing rate versus recruitment threshold, motor unit action potential amplitude versus recruitment threshold, and motor unit firing rate versus action potential amplitude relationships of the biceps brachii (agonist) and triceps brachii (antagonist) muscles were analyzed. Moderate- to-strong relationships (|| ≥ 0.69) were present for the agonist and antagonist muscles for each relationship with no differences between muscles ( = 0.716, 0.428, 0.182). The -intercepts of the motor unit firing rate versus recruitment threshold relationship of the antagonist did not increase from 40% to 70% maximal voluntary contractions ( = 0.96), unlike for the agonist ( = 0.009). The antagonist muscle exhibits a similar motor unit control scheme to the agonist. Unlike the agonist, however, the firing rates of the antagonist did not increase with increasing intensity. Future research should investigate how antagonist firing rates adapt to resistance training and changes in antagonist firing rates in the absence of peripheral feedback. This is the first study to explore a potential motor unit control scheme and quantify changes in firing rates with increasing intensity of an antagonist muscle during isometric contractions. We demonstrate that the antagonist muscle possesses an organized motor unit firing rate and recruitment scheme similar to the agonist muscle during isometric forearm flexion, but unlike the agonist muscle, there was no significant increase in firing rates from a moderate- to higher-intensity isometric contraction.
本研究的主要目的是确定在稳定等长扭矩期间，拮抗肌是否存在有组织的控制方案。次要重点是更好地了解拮抗肌的放电率如何从中等收缩强度变为更高的收缩强度。 14 名受试者进行了两次前臂屈肌的次最大等距梯形肌肉动作，包括在 40%和 70%最大随意收缩以及线性减小的段上的线性增加的稳定力。肱二头肌和肱三头肌的表面肌电图信号被收集并分解成组成运动单位动作电位的列车。分析肱二头肌（主动肌）和肱三头肌（拮抗肌）肌肉的运动单位放电率与募集阈值、运动单位动作电位幅度与募集阈值以及运动单位放电率与动作电位幅度的关系。在每个关系中，对于主动肌和拮抗肌，都存在中度到强的关系（||≥0.69），并且肌肉之间没有差异（=0.716、0.428、0.182）。与主动肌不同，拮抗肌的运动单位放电率与募集阈值关系的-截距从 40%到 70%最大随意收缩没有增加（=0.96）。拮抗肌的放电率随着强度的增加而增加。未来的研究应该调查拮抗肌的放电率如何适应抗阻训练以及在没有外周反馈的情况下拮抗肌放电率的变化。这是第一项研究，旨在探索一种潜在的运动单位控制方案，并量化在等长收缩期间拮抗肌强度增加时放电率的变化。我们证明，在等距前臂屈曲期间，拮抗肌具有与主动肌相似的有组织的运动单位放电率和募集方案，但与主动肌不同，从中等到高强度等长收缩时，放电率没有显著增加。
