Jones D A
Ciba Found Symp. 1981;82:178-96. doi: 10.1002/9780470715420.ch11.
A number of changes in function occur beyond the neuromuscular junction during activity; three main types are described. (a) During high frequency stimulation there is a rapid loss of force accompanied by a slowing of the action potential waveform and an increase in the excitation threshold of the muscle. It is suggested that accumulation of K+ in the extracellular spaces of the muscle may be responsible for these changes. (b) Slowing of relaxation is a feature of fatigued muscle. The slowing allows a reduction in activation frequency (minimizing high frequency fatigue) without resulting in an appreciable loss of force. (c) Changes in shape and amplitude of the twitch have considerable effects on the force generated by low frequencies of stimulation. After a brief tetanus there is a reduction in the width of the twitch which increases the fusion frequency of the muscle and may account for the "sag' seen at the start of low frequency contractions. After a prolonged series of contractions the twitch amplitude is reduced and remains so for several hours. This may be the result of some structural damage to the sarcoplasmic reticulum or transverse tubular system.
在活动期间，神经肌肉接头之外会发生许多功能变化；本文描述了三种主要类型。(a) 在高频刺激期间，会迅速出现力量丧失，同时动作电位波形变缓，肌肉的兴奋阈值升高。有人认为，肌肉细胞外空间中钾离子的积累可能是这些变化的原因。(b) 放松减慢是疲劳肌肉的一个特征。这种减慢使得激活频率能够降低（将高频疲劳降至最低），而不会导致力量明显丧失。(c) 单收缩的形状和幅度变化对低频刺激产生的力量有相当大的影响。短暂强直收缩后，单收缩的宽度减小，这增加了肌肉的融合频率，可能是低频收缩开始时出现“下垂”的原因。经过长时间的一系列收缩后，单收缩幅度减小，并会持续数小时。这可能是肌浆网或横管系统受到某种结构损伤的结果。
