Data from: Physiological tremor reveals how thixotropy adapts skeletal muscle for posture and movement

People and animals can move freely, but they must also be able to stay still. How do skeletal muscles economically produce both movement and posture? Humans are well known to have motor units with relatively homogeneous mechanical properties. Thixotropic muscle properties can provide a solution by providing a temporary stiffening of all skeletal muscles in postural conditions. This stiffening is alleviated almost instantly when muscles start to move. In this paper, we probe this behaviour. We monitor both the neural input to a muscle, measured here as extensor muscle electromyography (EMG), and its output, measured as tremor (finger acceleration). Both signals were analysed continuously as the subject made smooth transitions between posture and movement. The results showed that there were marked changes in tremor which systematically increased in size and decreased in frequency as the subject moved faster. By contrast, the EMG changed little and reflected muscle force requirement rather than movement speed. The altered tremor reflects naturally occurring thixotropic changes in muscle behaviour. Our results suggest that physiological tremor provides useful and hitherto unrecognized insights into skeletal muscle's role in posture and movement.

人与动物既能自由活动，亦能维持静止姿态。那么骨骼肌如何以经济高效的方式同时实现运动与姿势维持？众所周知，人类的运动单位（motor units）具备相对均一的力学特性。触变性（thixotropic）肌肉特性可提供一种解决方案：在姿势维持状态下，使所有骨骼肌产生暂时性刚度增强；当肌肉启动运动时，该刚度增强效应可近乎瞬时解除。本研究针对该行为展开探究。我们同步监测了肌肉的神经输入（此处以伸肌肌电图（extensor muscle electromyography, EMG）作为量化指标）及其力学输出（以震颤即手指加速度作为量化指标）。当受试者在姿势维持与运动状态间平滑切换时，我们对两类信号进行了连续分析。结果显示，震颤存在显著变化：随着受试者运动速度提升，震颤幅度系统性增大，而频率则随之降低。与之形成鲜明对比的是，肌电图信号变化极小，其仅反映肌肉的肌力需求，而非运动速度。这种震颤的改变，反映了肌肉行为中自然发生的触变性变化。本研究结果表明，生理性震颤可为理解骨骼肌在姿势维持与运动中的作用提供此前未被认知的有效视角。