Bozler E
J Gen Physiol. 1977 Dec;70(6):697-705. doi: 10.1085/jgp.70.6.697.
The effect of shortening on contractile activity was studied in experiments in which shortening during the rising phase of an isotonic contraction was suddenly stopped. At the same muscle length and the same time after stimulation the rise in tension was much faster, if preceded by shortening, than during an isometric contraction, demonstrating an increase in contractile activity. In this experiment the rate of tension rise determined in various phases of contraction was proportional to the rate of isotonic shortening at the same time after stimulation. Therefore, the time course of the isotonic rising phase could be derived from the tension rise after shortening. The rate of isotonic shortening was found to be unrelated to the tension generated at various lengths and to correspond closely to the activation process induced by shortening. The length response explains differences between isotonic and isometric contractions with regard to energy release (Fenn effect) and time relations. These results extend previous work which showed that shortening during later phases of a twitch prolongs, while lengthening abbreviates contraction. Thus the length responses, which have been called shortening activation and lengthening deactivation, control activity throughout an isotonic twitch.
在等张收缩上升期缩短突然停止的实验中，研究了缩短对收缩活动的影响。在相同肌肉长度和刺激后相同时间，若之前有缩短，则张力上升比等长收缩时快得多，表明收缩活动增强。在该实验中，收缩各阶段测定的张力上升速率与刺激后相同时间的等张缩短速率成正比。因此，等张上升期的时间进程可从缩短后的张力上升推导得出。发现等张缩短速率与不同长度下产生的张力无关，且与缩短诱导的激活过程密切对应。长度反应解释了等张收缩和等长收缩在能量释放（芬恩效应）和时间关系方面的差异。这些结果扩展了先前的研究工作，即表明在单收缩后期缩短会延长收缩，而延长会缩短收缩。因此，被称为缩短激活和延长失活的长度反应控制着整个等张单收缩的活动。
