Barclay C J
Department of Physiology, University of Auckland, New Zealand.
Am J Physiol. 1992 Nov;263(5 Pt 1):C1065-72. doi: 10.1152/ajpcell.1992.263.5.C1065.
Changes in the rate of isometric force development with fatigue were measured in vitro (25 degrees C) using mouse soleus and extensor digitorum longus (EDL) muscles. Muscles were fatigued using 30 tetanic contractions. Rate of force development was determined from the rate constant of an exponential curve fitted to the rising force phase of a tetanus. For both muscles, when the intertetanus interval was 3 s, maximum isometric force and relaxation rate were significantly reduced in the final tetanus relative to the values in the first tetanus. Rate of force development in soleus muscles transiently increased and then decreased a small amount. The final rate was 92.7 +/- 3.3% (n = 4) of the initial rate. In contrast, the rate of force development in EDL muscles increased to 133.7 +/- 3.3% (n = 4) of the initial rate. This increased rate was evident from the second tetanus of the series, was fully established after 5 tetani, and the magnitude of the increase in rate was inversely proportional to intertetanus interval and was independent of presumed energy expenditure. The enhanced rate decayed with a time constant of 14.3 +/- 2.0 s and was independent of presumed energy expenditure. Most of these observations can be explained by the effects of P(i) on cross bridge kinetics. Other possible mechanisms, involving more rapid activation, are also suggested.
在体外（25摄氏度），使用小鼠比目鱼肌和趾长伸肌（EDL）测量等长力发展速率随疲劳的变化。通过30次强直收缩使肌肉疲劳。力发展速率由拟合强直上升力阶段的指数曲线的速率常数确定。对于这两种肌肉，当强直间隔为3秒时，相对于第一次强直的值，最后一次强直中的最大等长力和松弛速率显著降低。比目鱼肌中的力发展速率短暂增加，然后略有下降。最终速率为初始速率的92.7±3.3%（n = 4）。相比之下，EDL肌肉中的力发展速率增加到初始速率的133.7±3.3%（n = 4）。这种增加的速率从该系列的第二次强直开始明显，在5次强直后完全确立，并且速率增加的幅度与强直间隔成反比，并且与假定的能量消耗无关。增强的速率以14.3±2.0秒的时间常数衰减，并且与假定的能量消耗无关。这些观察结果大多可以用无机磷酸（P(i)）对横桥动力学的影响来解释。还提出了其他可能的机制，涉及更快的激活。
