CONTRACTILE SPEED AND EMG CHANGES DURING FATIGUE OF SUSTAINED MAXIMAL VOLUNTARY CONTRACTIONS
CONTRACTILE SPEED AND EMG CHANGES DURING FATIGUE OF SUSTAINED MAXIMAL VOLUNTARY CONTRACTIONS
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DOI：
10.1152/jn.1983.50.1.313
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发表时间：
1983-01-01
影响因子：
2.5
通讯作者：
WOODS, JJ
中科院分区：
文献类型：
--
作者：
BIGLANDRITCHIE, B;JOHANSSON, R;WOODS, JJ
在持续 60 秒的最大等长自主收缩之前、期间和之后，对人类拇内收肌的力量、收缩速度和肌电图活动 (EMG) 进行测量。通过使用单次电击或一系列电击进行最大神经刺激的简短测试期，可以在每次收缩过程中研究各种肌肉机械特性。在对表面电位进行整流和平滑后，并通过使用细线肌内电极计算运动单位群每单位时间的电位总数，测量电活动。在 60 秒的最大自主收缩期间，力量下降了 30-50%。在整个实验过程中，随意力与超最大强直神经刺激产生的力相匹配。这表明，通过充分的练习，可以通过自愿努力维持充分的肌肉激活。平滑、校正肌电图的幅度和尖峰计数率下降。由于没有发现神经肌肉阻滞的证据，肌电图和尖峰计数的下降归因于中枢神经系统的神经驱动逐渐减少，尽管仍保持最大努力。在长时间的随意收缩后，抽搐持续时间延长，主要是由于松弛速率减慢。未融合的破伤风抽搐总和增加。最大松弛率和力衰减时程均下降了 50-70%。在随意收缩和刺激测试期间也发现了类似的变化。通过这些参数测量的肌肉收缩速度的百分比变化大约等于同时测量的表面肌电图的百分比变化。在持续 60 秒的最大自主收缩期间，收缩速度逐渐减慢，从而导致产生最大力量所需的激励速率降低，肌电图的同时下降可能是由于运动神经元放电速率的持续下降，并且肌电图下降不一定会导致力量损失。
Measurements were made from the human adductor pollicis muscle of force, contractile speed and electromyographic activity (EMG) before, during and after maximal isometric voluntary contractions sustained for 60 s. The use of brief test periods of maximal nerve stimulation with single shocks or trains of shocks enabled various muscle mechanical properties to be studied throughout each contraction. Electrical activity was measured after rectification and smoothing of the surface potentials and also by counting the total number of potentials per unit time from a population of motor units using fine wire intramuscular electrodes. During a 60 s maximal voluntary contraction, the force fell by 30-50%. Throughout the experiment the voluntary force matched that produced by supramaximal tetanic nerve stimulation. This indicated that, with sufficient practice, full muscle activation could be maintained by voluntary effort. The amplitude of the smoothed, rectified EMG and the rate of spike counts declined. Since no evidence for neuromuscular block was found, the decline in EMG and spike counts was attributed to a progressive reduction of the neural drive from the central nervous system, despite maintained maximum effort. After the prolonged voluntary contractions twitch duration was prolonged, mainly as a result of slowing in relaxation rate. Twitch summation in unfused tetani increased. Both the maximum rate of relaxation and the time course of force decay declined by 50-70%. Similar changes were seen in both voluntary contractions and in test periods of stimulation. The percentage change in muscle contractile speed measured by these parameters approximately equaled the percentage change in the surface EMG measured simultaneously. During a 60 s sustained maximal voluntary contraction there is a progressive slowing of contraction speed such that the excitation rate required to give maximal force generation is reduced, the simultaneous decline in EMG may be due to a continuous reduction in motoneuron discharge rate, and the EMG decline may not necessarily contribute to force loss.