Fukutani Atsuki, Isaka Tadao, Herzog Walter
Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan.
Department of Physiology and Pharmacology, Karolinska Institutet, Solna, Sweden.
Front Physiol. 2021 Jan 8;11:609553. doi: 10.3389/fphys.2020.609553. eCollection 2020.
Force attained during concentric contraction (active shortening) is transiently enhanced following eccentric contraction (active stretch) in skeletal muscle. This phenomenon is called stretch-shortening cycle (SSC) effect. Since many human movements contain combinations of eccentric and concentric contractions, a better understanding of the mechanisms underlying the SSC effect would be useful for improving physical performance, optimizing human movement efficiency, and providing an understanding of fundamental mechanism of muscle force control. Currently, the most common mechanisms proposed for the SSC effect are (i) stretch-reflex activation and (ii) storage of energy in tendons. However, abundant SSC effects have been observed in single fiber preparations where stretch-reflex activation is eliminated and storage of energy in tendons is minimal at best. Therefore, it seems prudent to hypothesize that factor(s) other than stretch-reflex activation and energy storage in tendons contribute to the SSC effect. In this brief review, we focus on possible candidate mechanisms for the SSC effect, that is, pre-activation, cross-bridge kinetics, and residual force enhancement (RFE) obtained in experimental preparations that exclude/control the influence of stretch-reflex activation and energy storage in tendons. Recent evidence supports the contribution of these factors to the mechanism of SSCs, and suggests that the extent of their contribution varies depending on the contractile conditions. Evidence for and against alternative mechanisms are introduced and discussed, and unresolved problems are mentioned for inspiring future studies in this field of research.
骨骼肌在离心收缩（主动拉伸）后，向心收缩（主动缩短）过程中所产生的力量会短暂增强。这种现象被称为拉长-缩短周期（SSC）效应。由于许多人体运动都包含离心收缩和向心收缩的组合，因此更好地理解SSC效应背后的机制，将有助于提高身体机能、优化人体运动效率，并深入了解肌肉力量控制的基本机制。目前，针对SSC效应提出的最常见机制是：（i）牵张反射激活；（ii）肌腱中的能量储存。然而，在消除牵张反射激活且肌腱中能量储存极少的单纤维标本中，也观察到了大量的SSC效应。因此，推测除牵张反射激活和肌腱中的能量储存之外，还有其他因素导致SSC效应，似乎是合理的。在这篇简短的综述中，我们重点关注SSC效应可能的候选机制，即在排除/控制牵张反射激活和肌腱中能量储存影响的实验标本中获得的预激活、横桥动力学和残余力增强（RFE）。最近的证据支持这些因素对SSC机制的作用，并表明其作用程度因收缩条件而异。文中介绍并讨论了支持和反对其他机制的证据，还提及了未解决的问题，以启发该领域未来的研究。
