School of Sport and Exercise Sciences, University of Birmingham, Birmingham B15 2TT, UK.
J Physiol. 2012 May 15;590(10):2471-83. doi: 10.1113/jphysiol.2011.226449. Epub 2012 Mar 19.
Limb resonance imparts a characteristic spectrum to hand tremor. Movement will alter the resonance. We have examined the consequences of this change. Rectified forearm extensor muscle EMG and physiological hand tremor were recorded. In postural conditions the EMG spectrum is relatively flat whereas the acceleration spectrum is sharply peaked. Consequently, the gain between EMG and acceleration is maximal at the frequency where the tremor is largest (∼8 Hz). The shape of the gain curve implies mechanical resonance. Substantial alterations in posture do not significantly change the characteristics of the tremor or the shape or size of the gain curve. By contrast, slow or moderately paced voluntary wrist flexion–extension movements dramatically increase the hand tremor size and lower its peak frequency. These changes in size and frequency of the tremor cannot be attributed to changes in the EMG. Instead they reflect a very large change in the size and shape of the gain curve relating EMG to acceleration. The gain becomes larger and the peak moves to a lower frequency (∼6 Hz). We suggest that a movement-related (thixotropic) alteration in resonant properties of the wrist provides a simple explanation for these changes. The mechanism is illustrated by a model. Our new findings confirm that resonance plays a major role in wrist tremor. We also demonstrate that muscles operate very differently under postural and dynamic conditions. The different coupling between EMG and movement in posture and when moving must pose a considerable challenge for neural predictive control of skeletal muscles.
肢体共振赋予手部震颤特征性频谱。运动将改变共振。我们已经研究了这种变化的后果。记录了纠正后的前臂伸肌肌电图和生理性手部震颤。在姿势条件下，肌电图频谱相对平坦，而加速度频谱则急剧尖峰。因此，在震颤最大的频率（约 8 Hz）处，肌电图和加速度之间的增益最大。增益曲线的形状暗示了机械共振。姿势的大幅度改变不会显著改变震颤的特征或增益曲线的形状或大小。相比之下，缓慢或适度的自愿腕关节屈伸运动显著增加手部震颤的幅度并降低其峰值频率。震颤幅度和频率的这些变化不能归因于肌电图的变化。相反，它们反映了与肌电图相关的加速度的增益曲线的大小和形状发生了非常大的变化。增益变大，峰值移至较低频率（约 6 Hz）。我们认为，手腕共振特性的与运动相关的（触变）改变提供了对这些变化的简单解释。该机制通过模型来说明。我们的新发现证实，共振在腕部震颤中起着重要作用。我们还表明，肌肉在姿势和动态条件下的运作方式非常不同。姿势和运动时肌电图与运动之间的不同耦合，对骨骼肌肉的神经预测控制构成了相当大的挑战。
