Moritani T, Muro M, Kijima A, Gaffney F A, Parsons D
Exp Neurol. 1985 Jun;88(3):484-99. doi: 10.1016/0014-4886(85)90065-2.
Changes in the electrical activity of the human gastrocnemius and soleus muscles during fatiguing maximal plantar flexions were studied with computer-aided EMG frequency power spectral analysis and intramuscular spike amplitude-frequency histogram analysis. In some experiments, brief supramaximal nerve stimulations of 80 Hz were given at 15-s intervals during sustained maximal voluntary contractions (MVCs). Multiple muscle biopsy samples were also obtained from the gastrocnemius muscle for fiber type determination. The surface EMG frequency spectral analysis showed a highly significant reduction in mean power frequency and root mean square EMG amplitude during sustained MVCs. The intramuscular spike amplitude-frequency histograms showed that the gastrocnemius muscle had a progressive reduction in the motor unit discharge frequency, particularly those with a relatively high amplitude, whereas the soleus muscle hardly showed a reduction in motor unit activity. Reduction in motor unit activity was also found to be more pronounced in gastrocnemius muscles with higher proportions of type II fibers. Brief maximal tetanic stimulations initially matching the MVC failed to increase the contraction force. Similarly, the evoked compound mass action potentials showed little change in the amplitude in subjects with different muscle fiber compositions. Results of this study suggest that during sustained MVCs, force fatigue could not be attributed to a failure of muscle membrane electrical propagation; a progressive reduction in motor unit activation does not result in a functional disadvantage, but may optimize excitation-contraction coupling by avoiding a muscle electrical conduction failure; and the extent of the reduction in motor unit activation seems to be muscle-fiber-type-dependent which may account for the reduction in amplitude and frequency of the surface EMG.
采用计算机辅助肌电图频率功率谱分析和肌内锋电位幅度 - 频率直方图分析，研究了人类腓肠肌和比目鱼肌在疲劳性最大跖屈过程中的电活动变化。在一些实验中，在持续最大自主收缩（MVC）期间，每隔15秒给予80Hz的短暂超强神经刺激。还从腓肠肌获取多个肌肉活检样本以确定纤维类型。表面肌电图频谱分析显示，在持续MVC期间，平均功率频率和肌电图均方根幅度显著降低。肌内锋电位幅度 - 频率直方图显示，腓肠肌运动单位放电频率逐渐降低，尤其是那些幅度相对较高的运动单位，而比目鱼肌的运动单位活动几乎没有降低。在II型纤维比例较高的腓肠肌中，运动单位活动的降低也更为明显。最初与MVC匹配的短暂最大强直刺激未能增加收缩力。同样，在不同肌肉纤维组成的受试者中，诱发的复合肌肉动作电位幅度几乎没有变化。本研究结果表明，在持续MVC期间，力量疲劳不能归因于肌膜电传导失败；运动单位激活的逐渐减少不会导致功能劣势，但可能通过避免肌肉电传导失败来优化兴奋 - 收缩偶联；并且运动单位激活减少的程度似乎取决于肌纤维类型，这可能解释了表面肌电图幅度和频率的降低。
