Enoka R M, Rankin L L, Joyner M J, Stuart D G
Department of Physiology, University of Arizona, Tucson 85721.
Muscle Nerve. 1988 Nov;11(11):1123-32. doi: 10.1002/mus.880111104.
Brief repetitive trains of supramaximal nerve stimulation produce intermittent muscle activation and, in time, a progressive decline in force (i.e., neuromuscular fatigue) and depression of the electromyogram (EMG). These changes may include within-train reductions in EMG due to a failure of neuromuscular propagation. The aim of the present study was to investigate changes in EMG during a 360-second stimulus regimen designed to fatigue soleus and extensor digitorum longus muscles of anesthetized rats by activating the muscle with repetitive trains of 40 Hz stimuli. Measurements included peak force for each tetanus, variation of the within-train EMG (coefficient of variation for area), and magnitude of the first EMG waveform (area) of each train. Fatigue was characterized as the relative decline in force over the course of the test. The responses of the test muscles were categorized, based on an absolute scale of fatigability, into five groups: potentiated, nonfatigable, low fatigability, intermediate fatigability, and high fatigability. Fatigable muscles (low, intermediate, and high fatigability groups) demonstrated a decreased EMG magnitude and an increased EMG-area variation with repetitive activation. This increased variation, however, was nonmonotonically related to fatigability such that the least and most fatigable muscles had the smallest within-train EMG variation. We suggest that these data can be explained by considering the EMG (compound muscle action potential) as a stochastic process that represents a composite of single-fiber events (axonal to sarcolemmal transmission) with variable probabilities.
短暂重复的超强神经刺激序列会产生间歇性肌肉激活，并随着时间推移出现力量逐渐下降（即神经肌肉疲劳）以及肌电图（EMG）抑制。这些变化可能包括由于神经肌肉传导失败导致的刺激序列内EMG降低。本研究的目的是在一个360秒的刺激方案中，通过用40Hz的重复刺激序列激活肌肉，来研究麻醉大鼠比目鱼肌和趾长伸肌疲劳过程中EMG的变化。测量指标包括每个强直收缩峰力、刺激序列内EMG的变化（面积变异系数）以及每个刺激序列第一个EMG波形的幅度（面积）。疲劳被定义为测试过程中力量的相对下降。根据绝对疲劳程度量表，将测试肌肉的反应分为五组：增强型、不易疲劳型、低疲劳型、中度疲劳型和高疲劳型。易疲劳肌肉（低、中、高疲劳型组）在重复激活时表现出EMG幅度降低和EMG面积变异增加。然而，这种增加的变异与疲劳程度并非单调相关，使得最不易疲劳和最易疲劳的肌肉在刺激序列内的EMG变异最小。我们认为，这些数据可以通过将EMG（复合肌肉动作电位）视为一个随机过程来解释，该过程代表了具有可变概率的单纤维事件（轴突到肌膜传递）的复合。
