SHORTENING OF MUSCLE-FIBERS DURING STRETCH OF THE ACTIVE CAT MEDIAL GASTROCNEMIUS-MUSCLE - THE ROLE OF TENDON COMPLIANCE
SHORTENING OF MUSCLE-FIBERS DURING STRETCH OF THE ACTIVE CAT MEDIAL GASTROCNEMIUS-MUSCLE - THE ROLE OF TENDON COMPLIANCE
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DOI：
10.1113/jphysiol.1991.sp018547
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发表时间：
1991-05-01
影响因子：
5.5
通讯作者：
GRIFFITHS, RI
中科院分区：
文献类型：
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作者：
GRIFFITHS, RI
1. 采用超声技术测量麻醉猫腓肠肌内侧（MG）肌肌纤维长度。在“等距”收缩过程中，肌纤维通过拉伸柔顺肌腱而缩短，直到肌纤维不再产生足够的力量来进一步拉伸肌腱。在最佳肌长（L(o)）时，肌纤维的最大缩短率为28%。当肌肉长度比L(o)长得多时，“等距”收缩会在拉伸肌腱时产生肌肉纤维的缓慢缩短，从而导致张力缓慢上升。这种现象，通常被称为“蠕变”，是由于长肌纤维长度的低功率。本研究表明，肌腱中的系列顺应性是猫MG肌“蠕变”的主要原因。当肌腱在收缩过程中拉伸时，肌节的平均长度变短，提供了更大的纤维重叠和增加的力量。在收缩开始后不久进行慢速到中速拉伸，就像猫在走路和小跑时发生的那样，在整个肌肉拉伸过程中，肌腱完全占据了肌肉纤维，肌肉纤维实际上缩短了。当在肌肉长度大于L(o)的地方进行早期拉伸时，肌肉的拉伸产生的峰值力比不进行拉伸时要小。对于长度小于L(o)的拉伸，情况正好相反。当达到峰值力后再进行拉伸时，力大大增强，肌纤维也得到拉伸。对一只自由行走的猫使用相同的技术，在198个连续的步进循环中，当肌肉被拉伸时，在步进循环的站立阶段，肌肉纤维缩短了1.0 +/- 0.3毫米。肌腱起着机械缓冲的作用，保护肌肉纤维在偏心收缩时不受损伤。由于MG肌的拉伸并没有忠实地施加到肌纤维上，运动过程中肌肉纺锤体功能的研究需要考虑肌腱顺应性的这些影响。主流观点认为，当脚在正常运动中着地时，肌肉纺锤体随着肌肉一起被拉伸，导致收缩力的反射增强。这项研究表明，在这种情况下，肌肉纤维不会拉伸，除非在高速运动时拉伸率也很高。
1. The length of muscle fibres in the medial gastrocnemius (MG) muscle of the anaesthetized cat was measured using ultrasound techniques. During the course of 'isometric' contractions, the muscle fibres shortened by stretching the compliant tendons, until the muscle fibres could no longer produce enough force to stretch the tendons further. At optimal muscle length (L(o)) the maximal shortening of muscle fibres was 28%.2. At muscle lengths much longer than L(o), 'isometric' contractions produced a slow shortening of the muscle fibres as the tendons were stretched and this resulted in a slow rise in tension. This phenomenon, usually referred to as 'creep', is due to low power at long muscle fibre length. This study shows that the series compliance present in the tendons is the major contributor to 'creep' in the cat MG muscle. As the tendons stretched during the course of the contraction, the average sarcomere length became shorter providing greater filament overlap and increasing power.3. Slow to medium speed stretches applied shortly after the onset of contraction, as occurs in cat MG during walking and trotting, were entirely taken up in the tendons and the muscle fibres actually shortened throughout the imposed muscle stretch.4. When early stretches were applied at muscle lengths longer than L(o), stretch of the muscle resulted in a peak force that was less than if the stretch had not been applied. This was the reverse of the situation for stretches at lengths less than L(o). When stretch was applied after attaining peak force, the force was greatly enhanced and the muscle fibres were also stretched.5. Using the same techniques in a freely walking cat, the muscle fibres shortened by 1.0 +/- 0.3 mm during the stance phase of the step-cycle when the muscle was being stretched, in 198 consecutive step-cycles.6. The tendons act as a mechanical buffer to protect muscle fibres from damage during eccentric contractions.7. Since stretches of the MG muscle are not faithfully imposed on the muscle fibres, studies of muscle spindle function during locomotion need to take into consideration these effects of tendon compliance. The dominant view, when the foot lands on the ground during normal locomotion, is that muscle spindles are stretched along with the muscle resulting in reflex enhancement of contractile force. This study shows that the muscle fibres do not stretch under these circumstances, except at high speeds of locomotion when the stretch rate is also high.