Tax A A, Denier van der Gon J J, Erkelens C J
Department of Medical and Physiological Physics, University of Utrecht, The Netherlands.
Exp Brain Res. 1990;81(3):567-72. doi: 10.1007/BF02423505.
Motor-unit activity in m. biceps brachii, m. brachialis and m. brachioradialis during isometric contractions has been compared with motor-unit activity during slow voluntary (extension and flexion) movements made against external loads. During these slow movements the recruitment threshold of m. biceps motor units is considerably lower than it is during isometric contractions but the recruitment threshold of both m. brachialis and m. brachioradialis motor units is considerably higher. For all three elbow flexor muscles the motor-unit firing frequency seems to depend on the direction of movement: the firing frequency is higher during flexion movements (3 deg/s) and lower during extension movements (-3 deg/s) than during isometric contractions. The relative contribution of the biceps to the total exerted flexion torque during slow voluntary movements is estimated to increase from 36% to about 48% and that of the brachialis/brachioradialis is estimated to decrease from 57% to about 45% compared to the relative contribution of these muscles during isometric contractions. This difference in the relative contribution of the three major elbow flexor muscles is shown to be caused by differences in the central activation in force tasks and movement tasks.
已将肱二头肌、肱肌和肱桡肌在等长收缩期间的运动单位活动与在对抗外部负荷进行的缓慢随意（伸展和屈曲）运动期间的运动单位活动进行了比较。在这些缓慢运动期间，肱二头肌运动单位的募集阈值比在等长收缩期间低得多，但肱肌和肱桡肌运动单位的募集阈值则高得多。对于所有三块肘屈肌，运动单位的放电频率似乎取决于运动方向：在屈曲运动（3度/秒）期间的放电频率高于等长收缩期间，而在伸展运动（-3度/秒）期间的放电频率低于等长收缩期间。与这些肌肉在等长收缩期间的相对贡献相比，在缓慢随意运动期间肱二头肌对总施加的屈曲扭矩的相对贡献估计从36%增加到约48%，而肱肌/肱桡肌的相对贡献估计从57%减少到约45%。这三块主要肘屈肌相对贡献的差异表明是由力量任务和运动任务中的中枢激活差异所导致的。
