Wood S A, Morgan D L, Proske U
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Am J Physiol. 1993 Sep;265(3 Pt 1):C792-800. doi: 10.1152/ajpcell.1993.265.3.C792.
It has been proposed that lengthening of active muscle at long lengths is nonuniformly distributed between sarcomeres, with a few being stretched beyond overlap and most hardly being stretched at all. A small fraction of the overstretched sarcomeres may fail to reinterdigitate on subsequent relaxation, leading to progressive changes in the muscle's mechanical properties. Sartorius muscles of the toad Bufo marinus were subjected to repeated lengthening (eccentric) contractions at long lengths, while controls were passively stretched and then contracted isometrically or stretched at short lengths. The muscles undergoing eccentric contractions showed a progressive shift to the right of the length-tension curve, a fall in the yield point during stretch, an increase in slope of the tension response during stretch, and a fall in isometric tension. In control muscles, changes, if any, were significantly less. In electron micrographs, muscle fibers that had been subjected to a series of eccentric contractions showed sarcomeres with A bands displaced toward one half-sarcomere, leaving no overlap in the other half. Adjacent regions often looked normal. These results are all in agreement with the predictions of the nonuniform stretch of sarcomeres hypothesis.
有人提出，在长长度下主动肌的拉长在肌节之间分布不均匀，少数肌节被拉伸超过重叠范围，而大多数肌节几乎未被拉伸。一小部分过度拉伸的肌节在随后的松弛过程中可能无法重新交错，导致肌肉力学性能的逐渐变化。对海蟾蜍（Bufo marinus）的缝匠肌进行长长度下的重复拉长（离心）收缩，而对照组则进行被动拉伸，然后进行等长收缩或短长度拉伸。经历离心收缩的肌肉在长度-张力曲线上逐渐向右移动，拉伸过程中的屈服点下降，拉伸过程中张力反应的斜率增加，等长张力下降。在对照肌肉中，即使有变化也明显较小。在电子显微镜照片中，经历一系列离心收缩的肌纤维显示肌节的A带向一个半肌节移位，另一半没有重叠。相邻区域通常看起来正常。这些结果都与肌节不均匀拉伸假说的预测一致。
