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 homogenous 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 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 a useful and hitherto unrecognised insight into skeletal muscle’s role in posture and movement.

人与动物既能自由活动，也需维持静止姿态。骨骼肌如何以节能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）具有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僵硬；而当肌肉开始运动时，这种僵硬会几乎瞬间得到缓解。本研究针对这一行为展开探究。我们同步监测肌肉的神经输入（本研究中以伸肌肌电图（extensor muscle EMG）作为测量指标）及其输出（以震颤——手指加速度——作为测量指标）。当受试者在姿势与运动之间平稳切换状态时，我们对这两种信号进行了连续分析。研究结果显示，震颤出现了显著变化：随着受试者运动速度加快，震颤幅度系统性增大，频率则相应降低。与之形成对比的是，肌电图信号变化微弱，其反映的是肌肉的肌力需求而非运动速度。这种震颤的变化，反映了肌肉行为中自然发生的触变性改变。我们的研究结果表明，生理性震颤可为我们理解骨骼肌在姿势维持与运动调控中的作用提供一项此前未被认知的、极具价值的视角。