Lakie Martin, Campbell Kenneth S
School of Sport, Exercise and Rehabilitation, University of Birmingham , Birmingham , United Kingdom.
Department of Physiology, College of Medicine, University of Kentucky , Lexington, Kentucky.
J Appl Physiol (1985). 2019 Jun 1;126(6):1790-1799. doi: 10.1152/japplphysiol.00788.2018. Epub 2019 May 9.
Relaxed skeletal muscle has an inbuilt resistance to movement. In particular, the resistance manifests itself as a substantial stiffness for small movements. The stiffness is impermanent, because it forms only when the muscle is stationary for some time and is reduced upon active or passive movement. Because the resistance to movement increases with time at rest and is reduced by movement, this behavior has become known as muscle thixotropy. In this short review, we describe the phenomenon of thixotropy and illustrate its significance in postural control with particular emphasis on human standing. We show how thixotropy came to be unambiguously associated with muscle mechanics and we review present knowledge of the molecular basis of thixotropic behavior. Specifically, we examine how recent knowledge about titin, and about the control of cross-bridge cycling, has impacted on the role of non-cross-bridge mechanisms and cross-bridge mechanisms in explaining thixotropy. We describe how thixotropic changes in muscle stiffness that occur during transitions from posture to movement can be tracked by analyzing physiological tremor. Finally, because skeletal muscle contains sensory receptors, and because some of these receptors are themselves thixotropic, we outline some of the consequences of muscle thixotropy for proprioception.
松弛的骨骼肌对运动具有内在阻力。具体而言，这种阻力表现为小幅度运动时的显著僵硬。这种僵硬是暂时的，因为它仅在肌肉静止一段时间后形成，并在主动或被动运动时减小。由于对运动的阻力在静止时随时间增加而在运动时减小，这种行为被称为肌肉触变性。在这篇简短的综述中，我们描述了触变性现象，并阐述了其在姿势控制中的意义，特别强调人体站立。我们展示了触变性如何明确地与肌肉力学相关联，并综述了目前关于触变性行为分子基础的知识。具体而言，我们研究了关于肌联蛋白以及横桥循环控制的最新知识如何影响非横桥机制和横桥机制在解释触变性中的作用。我们描述了如何通过分析生理性震颤来追踪从姿势到运动转变过程中肌肉僵硬的触变性变化。最后，由于骨骼肌含有感觉受体，并且其中一些受体本身具有触变性，我们概述了肌肉触变性对本体感觉的一些影响。
