Departments of Kinesiology and Physical Education, Physics and Physiology, McGill University, Montreal (PQ), Canada.
Proc Biol Sci. 2012 Jul 22;279(1739):2705-13. doi: 10.1098/rspb.2012.0467. Epub 2012 Apr 25.
When activated skeletal muscles are stretched, the force increases significantly. After the stretch, the force decreases and reaches a steady-state level that is higher than the force produced at the corresponding length during purely isometric contractions. This phenomenon, referred to as residual force enhancement, has been observed for more than 50 years, but the mechanism remains elusive, generating considerable debate in the literature. This paper reviews studies performed with single muscle fibres, myofibrils and sarcomeres to investigate the mechanisms of the stretch-induced force enhancement. First, the paper summarizes the characteristics of force enhancement and early hypotheses associated with non-uniformity of sarcomere length. Then, it reviews new evidence suggesting that force enhancement can also be associated with sarcomeric structures. Finally, this paper proposes that force enhancement is caused by: (i) half-sarcomere non-uniformities that will affect the levels of passive forces and overlap between myosin and actin filaments, and (ii) a Ca(2+)-induced stiffness of titin molecules. These mechanisms are compatible with most observations in the literature, and can be tested directly with emerging technologies in the near future.
当激活的骨骼肌被拉伸时，力会显著增加。拉伸后，力会下降并达到一个稳定状态水平，高于在纯等长收缩时相应长度产生的力。这种现象被称为残余力增强，已经观察了 50 多年，但机制仍然难以捉摸，在文献中引发了相当大的争论。本文综述了用单个肌纤维、肌原纤维和肌节进行的研究，以探讨拉伸引起的力增强的机制。首先，本文总结了力增强的特征和早期与肌节长度不均匀性相关的假说。然后，它回顾了新的证据表明力增强也可以与肌节结构有关。最后，本文提出力增强是由：（i）半肌节的不均匀性，这将影响被动力的水平和肌球蛋白和肌动蛋白丝之间的重叠，以及（ii）肌联蛋白分子的 Ca(2+)诱导的刚性。这些机制与文献中的大多数观察结果一致，并可以在不久的将来通过新兴技术直接进行测试。
