van Bolhuis B M, Medendorp W P, Gielen C C
Department of Medical Physics and Biophysics, University of Nijmegen, The Netherlands.
Exp Brain Res. 1997 Oct;117(1):120-30. doi: 10.1007/s002210050205.
Simultaneous recordings of action potentials (APs) of multiple single motor units (MUs) were obtained in brachialis and biceps (caput breve) muscles during sinusoidally modulated isometric contractions of elbow flexor muscles and during sinusoidal flexion/extension movements in the elbow against a preload in the extension direction. The results show that MUs typically fire in one short burst for each sinusoidal cycle. The mean phase lead of the bursts of APs relative to a sinusoidally modulated isometric torque in the elbow joint or relative to sinusoidal movements in the elbow increases gradually with frequency. The increase of the mean phase lead during isometric contractions was very similar for all MUs and could be explained well by modeling the force production of MUs with a second-order linear low-pass system. For sinusoidal flexion/extension movements each MU reveals a specific, reproducible phase lead as a function of frequency. However, there is a large variability in phase behavior between MUs. Also, the modulation of the firing rate for sinusoidal isometric contractions versus sinusoidal movements appeared to be different for various MUs. In simultaneous recordings some MUs clearly revealed a larger firing rate in each burst for movements relative to isometric contractions, whereas other MUs revealed a smaller firing rate. This suggests that some MUs are preferentially activated during movements whereas others are preferably activated during isometric contractions. The results demonstrate task-dependent changes in the relative activation of MUs within a single muscle for sinusoidal isometric contractions and movements.
在肘关节屈肌进行正弦调制等长收缩期间以及在肘关节对抗伸展方向预负荷进行正弦屈伸运动期间，同时记录了肱肌和肱二头肌（短头）中多个单运动单位（MU）的动作电位（AP）。结果表明，每个正弦周期中，运动单位通常会在一次短脉冲串中放电。动作电位脉冲串相对于肘关节中正弦调制等长扭矩或相对于肘关节正弦运动的平均相位超前随频率逐渐增加。在等长收缩期间，所有运动单位的平均相位超前增加非常相似，并且通过用二阶线性低通系统对运动单位的力产生进行建模可以很好地解释这一现象。对于正弦屈伸运动，每个运动单位都显示出特定的、可重复的相位超前作为频率的函数。然而，不同运动单位之间的相位行为存在很大差异。此外，对于不同的运动单位，正弦等长收缩与正弦运动时放电频率的调制似乎也有所不同。在同步记录中，一些运动单位在运动时每次脉冲串中的放电频率明显高于等长收缩时，而其他运动单位则显示出较低的放电频率。这表明一些运动单位在运动期间优先被激活，而其他运动单位在等长收缩期间优先被激活。结果表明，在正弦等长收缩和运动过程中，单个肌肉内运动单位的相对激活存在任务依赖性变化。
