The Stretch-Shortening Cycle
The Stretch-Shortening Cycle
复制标题
拉伸-缩短周期
作者：
C. Nicol;J. Avela;P. Komi
神经肌肉疲劳传统上是用孤立形式的等距、同心或偏心动作来检查的。然而，这些动作都不是人类（或动物）在地面运动中自然发生的。基本的肌肉功能被定义为拉伸-缩短周期（SSC），其中预激活的肌肉首先被拉伸（偏心动作），然后是缩短（同心）动作。由于SSC对骨骼肌的机械作用非常强，它对反射激活的影响变得明显，与上面提到的孤立形式的肌肉活动非常不同。跑步、跳跃和跳跃等与地面接触的阶段是腿伸肌SSC的例子；类似的阶段也可以发现上半身的活动。因此，对SSC活动过程中的疲劳现象进行研究是正常的，也是预期的。重复SSC动作的疲劳反应是非常多样和复杂的，因为疲劳不仅仅取决于代谢负荷，而代谢负荷在肌肉动作中是不同的。许多神经力学参数的恢复模式很好地反映了SSC疲劳的复杂性。SSC疲劳反应的基本模式（例如，当使用跳跃或跳跃的完全疲劳模型时）是双峰型，表现为在运动期间表现立即下降，在1-2小时内迅速恢复，然后是二次下降，通常在运动后的第二天表现为最低值，此时肌肉酸痛/损伤的症状也最大。完全恢复可能需要4-8天，这取决于参数和运动的严重程度。每个受试者可能有自己的随时间变化的双峰曲线。根据回顾的文献，建议疲劳方案“完全”详尽，以减少疲劳反应中主体间变异性的重要影响。双峰概念在被动或主动条件下的拉伸反射反应中尤为明显。有趣的是，反射反应遵循一些纯机械参数的平行变化，例如在跑步或跳跃的初始地面接触时产生的制动力。SSC疲劳的机理，特别是性能退化和恢复的双峰响应往往难以解释。大多数测量参数在运动后立即下降，并在运动后1-2小时部分恢复，这主要是由于运动引起的代谢疲劳。这些参数的二次减少发生在肌肉酸痛最严重的时候。文献给出了几种可能的结构损伤，包括肌外纤维和肌内纤维的损伤。结构蛋白和肌肉-肌腱相互作用的暂时变化可能与疲劳引起的力减少有关。尽管本文引用的许多研究更多地强调了彻底的SSC疲劳对纺锤运动-肌纺锤体系统的影响，但椎上水平的神经调节自然是可行的。然而，为什么肌肉酸痛消失后，功能恢复会持续数天，这仍然令人困惑。不幸的是，这和许多其他可能的机制需要在动物模型中进行更彻底的测试，前提是SSC的动作可以真正地在正常的人类运动中表现出来。
Neuromuscular fatigue has traditionally been examined using isolated forms of either isometric, concentric or eccentric actions. However, none of these actions are naturally occurring in human (or animal) ground locomotion. The basic muscle function is defined as the stretch-shortening cycle (SSC), where the preactivated muscle is first stretched (eccentric action) and then followed by the shortening (concentric) action. As the SSC taxes the skeletal muscles very strongly mechanically, its influence on the reflex activation becomes apparent and very different from the isolated forms of muscle actions mentioned above. The ground contact phases of running, jumping and hopping etc. are examples of the SSC for leg extensor muscles; similar phases can also be found for the upper-body activities. Consequently, it is normal and expected that the fatigue phenomena should be explored during SSC activities.The fatigue responses of repeated SSC actions are very versatile and complex because the fatigue does not depend only on the metabolic loading, which is reportedly different among muscle actions. The complexity of SSC fatigue is well reflected by the recovery patterns of many neuromechanical parameters. The basic pattern of SSC fatigue response (e.g. when using the complete exhaustion model of hopping or jumping) is the bimodality showing an immediate reduction in performance during exercise, quick recovery within 1–2 hours, followed by a secondary reduction, which may often show the lowest values on the second day post-exercise when the symptoms of muscle soreness/damage are also greatest. The full recovery may take 4–8 days depending on the parameter and on the severity of exercise. Each subject may have their own time-dependent bimodality curve.Based on the reviewed literature, it is recommended that the fatigue protocol is ‘completely’ exhaustive to reduce the important influence of inter-subject variability in the fatigue responses. The bimodality concept is especially apparent for stretch reflex responses, measured either in passive or active conditions. Interestingly, the reflex responses follow parallel changes with some of the pure mechanical parameters, such as yielding of the braking force during an initial ground contact of running or hopping. The mechanism of SSC fatigue and especially the bimodal response of performance deterioration and its recovery are often difficult to explain. The immediate post-exercise reduction in most of the measured parameters and their partial recovery 1–2 hours post-exercise can be explained primarily to be due to metabolic fatigue induced by exercise. The secondary reduction in these parameters takes place when the muscle soreness is highest.The literature gives several suggestions including the possible structural damage of not only the extrafusal muscle fibres, but also the intrafusal ones. Temporary changes in structural proteins and muscle-tendon interaction may be related to the fatigue-induced force reduction. Neural adjustments in the supraspinal level could naturally be operative, although many studies quoted in this article emphasise more the influences of exhaustive SSC fatigue on the fusimotor-muscle spindle system. It is, however, still puzzling why the functional recovery lasts several days after the disappearance of muscle soreness. Unfortunately, this and many other possible mechanisms need more thorough testing in animal models provided that the SSC actions can be truly performed as they appear in normal human locomotion.
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影响因子：
4.1
作者：
Robert B. Armstrong
通讯作者：
Robert B. Armstrong
偏心收缩引起的肌肉损伤后细胞骨架破坏。
影响因子：
4.2
作者：
Lieber,RichardL;Shah,Sameer;Fridén,Jan
通讯作者：
Fridén,Jan
影响因子：
2.5
作者：
BIGLANDRITCHIE, B;JOHANSSON, R;WOODS, JJ
通讯作者：
WOODS, JJ
影响因子：
5.5
作者：
BIGLANDRITCHIE, BR;DAWSON, NJ;LIPPOLD, OCJ
通讯作者：
LIPPOLD, OCJ