School of Sport and Exercise Sciences, College of Life and Environmental Sciences, University of Birmingham, Birimingham B15 2TT, UK.
J Neurophysiol. 2010 Oct;104(4):2020-3. doi: 10.1152/jn.00513.2010. Epub 2010 Jul 21.
Active or passive movement causes a temporary reduction in muscle stiffness that gradually returns to baseline levels when the muscle remains still. This effect, termed muscle thixotropy, alters the mechanical properties of the joint around which the muscle acts, reducing its resonant frequency. Because physiological tremor is affected by joint mechanics, this suggests that prior movement may alter tremor independently of neural output. To address this possibility, vertical acceleration of the outstretched prone hand was recorded in eight healthy subjects, along with EMG activity of the extensor digitorum communis muscle. A series of voluntary wrist flexion/extension movements was performed every 20 s, interspersed by periods during which hand position was maintained. Time-dependent changes in the amplitude and frequency of acceleration and EMG were analyzed using a continuous wavelet transform. Immediately following movement, acceleration displayed a significant increase in wavelet power accompanied by a reduction in peak frequency. During the postmovement period, power declined by 63%, and frequency increased from 7.2 to 8.0 Hz. These changes occurred with an exponential time constant of 2-4 s, consistent with a thixotropic mechanism. In contrast to acceleration, EMG activity showed no significant changes despite being strongly related to acceleration during the movement itself. These results show that prior movement transiently increases the amplitude and reduces the frequency of physiological tremor, despite unchanging neural output. This effect is best explained by a reduction in joint stiffness caused by muscle thixotropy, highlighting the importance of mechanical factors in the genesis of physiological tremor.
主动或被动运动可暂时降低肌肉僵硬度，当肌肉静止时，僵硬度逐渐恢复到基线水平。这种效应被称为肌肉触变性，改变了肌肉作用的关节的力学特性，降低了其共振频率。由于生理震颤受关节力学的影响，这表明先前的运动可能会改变震颤，而与神经输出无关。为了研究这种可能性，记录了 8 名健康受试者伸展俯卧位手的垂直加速度，以及伸指总肌的肌电图活动。每 20 秒进行一次自愿的腕关节屈伸运动，期间手的位置保持不变。使用连续小波变换分析加速度和肌电图的振幅和频率随时间的变化。运动后，加速度的小波功率显著增加，同时峰值频率降低。在运动后的阶段，功率下降了 63%，频率从 7.2Hz 增加到 8.0Hz。这些变化的时间常数为 2-4 秒，与触变性机制一致。与加速度相反，尽管在运动过程中肌电图活动与加速度密切相关，但它并没有显示出显著的变化。这些结果表明，尽管神经输出不变，先前的运动仍会暂时增加生理震颤的幅度并降低其频率。肌肉触变性引起的关节刚度降低可最好地解释这种效应，这突出了机械因素在生理震颤产生中的重要性。
