School of Kinesiology, The University of Western Ontario, London, Ontario, Canada.
Med Sci Sports Exerc. 2010 Sep;42(9):1651-9. doi: 10.1249/MSS.0b013e3181d6c5b5.
In addition to torque (force) loss during dynamic fatiguing contractions, an important aspect of fatigue is the reduction in shortening velocity. Relatively few reports have studied changes in shortening velocity in response to fatigue, and inconsistencies in the results might depend on the muscle tested. To better understand fatigue-related changes in shortening velocity in different muscles, we compared the fatigue response of two muscles in humans with different physiological properties using the same criterion for task failure.
During separate sessions for the triceps brachii and soleus, 10 young males performed repetitive shortening contractions with a moderate load (50% of maximum voluntary isometric contraction (MVC) torque) until they achieved a 50% reduction in loaded shortening velocity at task failure.
In the unfatigued condition, these muscles expressed different physiological features with similar power output but approximately 1.5 times slower shortening velocity, approximately 1.4 times slower normalized evoked 50-Hz maximum rate of relaxation, and approximately 47% lower postactivation potentiation in the soleus compared with the triceps brachii. During the fatiguing task, significantly less total work was performed in the soleus ( approximately 1986 J) compared with the triceps brachii ( approximately 3940 J), suggesting greater endurance in the triceps brachii. Despite similar relative reductions in shortening velocity in both muscles at task failure, the soleus had a smaller reduction in MVC torque than the triceps brachii at task failure. Furthermore, in both muscles, there was a greater reduction at task failure and a faster restoration of shortening velocity compared with MVC torque.
Our findings suggest that fatigue-related mechanisms that reduce torque are not the same as those that reduce shortening velocity.
除了动态疲劳收缩过程中的扭矩（力）损失外，疲劳的一个重要方面是缩短速度的降低。相对较少的报告研究了缩短速度对疲劳的反应，结果的不一致性可能取决于所测试的肌肉。为了更好地理解不同肌肉中与疲劳相关的缩短速度变化，我们使用相同的任务失败标准比较了两种具有不同生理特性的人类肌肉的疲劳反应。
在肱三头肌和比目鱼肌的单独测试中，10 名年轻男性用中等负荷（最大自主等长收缩（MVC）扭矩的 50%）进行重复缩短收缩，直到达到负荷缩短速度降低 50%时任务失败。
在未疲劳状态下，这些肌肉表现出不同的生理特征，具有相似的功率输出，但缩短速度约慢 1.5 倍，约慢 1.4 倍，标准化诱发 50-Hz 最大松弛速率约慢 47%，比目鱼肌的后激活增强作用比肱三头肌低 47%。在疲劳任务中，比目鱼肌完成的总工作量明显低于肱三头肌（约 1986 J），比目鱼肌的耐力更强。尽管在任务失败时两种肌肉的缩短速度都有相似的相对降低，但比目鱼肌的 MVC 扭矩降低幅度小于肱三头肌。此外，在两种肌肉中，与 MVC 扭矩相比，任务失败时的降低幅度更大，缩短速度的恢复速度更快。
我们的发现表明，降低扭矩的与疲劳相关的机制与降低缩短速度的机制不同。
