Ettema G J
Department of Anatomical Sciences, University of Queensland, Australia.
Exp Physiol. 1997 Jan;82(1):107-19. doi: 10.1113/expphysiol.1997.sp004001.
The effects of muscle fatigue on the mechanical efficiency of muscle work performance were studied in situ, in stretch-shortening cycles that resembled physiological conditions. The experiments were performed on the medial gastrocnemius muscles of seven rats. To calculate efficiency, a simple Hill-type model was used, consisting of the contractile component (CC) and the series elastic component (SEC). Mechanical efficiency was defined as the external work done by the muscle-tendon complex divided by the external work done upon the muscle-tendon complex plus work done by the CC. The fatiguing protocol consisted of a l Hz stretch-shortening cycle with a 0.3 duty factor (i.e. the muscle was stimulated for 300 ms in each cycle). In total, 240 cycles were imposed. The mechanical performance (work, force and mechanical efficiency) was determined throughout the fatiguing process. Fatigue reduced muscle power and force production to approximately 17 and 30%, respectively. SEC stiffness increased, but did not have any effect on muscle performance and probably reflects altered cross-bridge characteristics. Mechanical efficiency was enhanced during the imposed stretch-shortening cycles from 0.74 to 0.83. As a result of the lower peak forces, proportionally less series elastic energy was wasted during the relaxation period of each strength-shortening cycle in the fully fatigued muscles. These results indicate that, in vivo, the timing of muscle contractions in the fresh and the fatigued state may be different in order to perform muscle work efficiently. After a period of 30 min recovery, the condition of the muscles had (partially) returned to the fresh state in all aspects.
在类似于生理条件的拉伸-缩短循环中，对肌肉疲劳对肌肉工作表现机械效率的影响进行了原位研究。实验在7只大鼠的内侧腓肠肌上进行。为了计算效率，使用了一个简单的希尔型模型，该模型由收缩成分（CC）和串联弹性成分（SEC）组成。机械效率定义为肌腱复合体所做的外部功除以作用于肌腱复合体的外部功加上CC所做的功。疲劳方案包括1Hz的拉伸-缩短循环，占空比为0.3（即每个循环中肌肉被刺激300毫秒）。总共施加240个循环。在整个疲劳过程中测定机械性能（功、力和机械效率）。疲劳使肌肉功率和力的产生分别降低到约17%和30%。SEC刚度增加，但对肌肉性能没有任何影响，可能反映了横桥特性的改变。在施加的拉伸-缩短循环中，机械效率从0.74提高到0.83。由于峰值力较低，在完全疲劳的肌肉中，每个强度-缩短循环的松弛期浪费的串联弹性能量成比例减少。这些结果表明，在体内，新鲜和疲劳状态下肌肉收缩的时机可能不同，以便有效地进行肌肉工作。经过30分钟的恢复后，肌肉状况在各方面（部分）恢复到新鲜状态。
