Büdingen H J, Freund H J
Pflugers Arch. 1976 Mar 11;362(1):61-7. doi: 10.1007/BF00588682.
The recruitment properties of single motor units from the human extensor indicis muscle were investigated during voluntary isometric contractions of different rate of rise but equal amplitude. Both the electrical and the contractile events associated with recruitment were analyzed. The threshold force of recruitment (measured as the total muscle force at firing onset) decreased with increasing rate of rise of isometric tension. This was consistently found for all units. Differences between low and high threshold units indicating a preferential tonic or phasic mode of activation were not observed. The contractile events associated with recruitment were analyzed analoguously to the electrical events. For this purpose, muscle force was measured at the time of the first twitch as it was measured at the time of the first spike. This separate measurement of the electrical and mechanical recruitment of a unit is necessary, because during a change of muscle force, force is different at firing onset and during the subsequent twitch contraction. Muscle tension at the time of the peak of the first twitch contraction was calculated from measurements of the twitch concentration time of the single motor units. In contrast to firing onset, the peak of the first twitch of a motor unit occurs at approximately the same muscle tension no matter how fast the contraction is performed. This is the consequence of the result that the average decrease of the threshold force of recruitment at successively faster contraction has the same value as the corresponding increase of total muscle force during the mean contraction time of the motor units. On the basis of this precise matching between these two changes, the mechanical recruitment of motor units occurs at approximately the same force level irrespective of the rate of rise of tension.
在等长收缩幅度相同但上升速率不同的随意收缩过程中，对人类示指伸肌单个运动单位的募集特性进行了研究。分析了与募集相关的电活动和收缩活动。募集的阈力（以放电开始时的总肌肉力来衡量）随着等长张力上升速率的增加而降低。所有运动单位均一致呈现这一现象。未观察到低阈值和高阈值运动单位之间存在差异，这表明不存在优先的紧张性或位相性激活模式。与募集相关的收缩活动与电活动类似地进行了分析。为此，在首次出现峰电位时测量肌肉力，就如同在首次出现单收缩时测量肌肉力一样。对一个运动单位的电募集和机械募集进行这种单独测量是必要的，因为在肌肉力变化期间，放电开始时和随后单收缩期间的力是不同的。根据单个运动单位单收缩的收缩持续时间测量值计算出首次单收缩峰值时的肌肉张力。与放电开始不同，无论收缩进行得有多快，运动单位首次单收缩的峰值都出现在大致相同的肌肉张力水平。这是以下结果的体现：在收缩速度相继加快时，募集阈力的平均降低值与运动单位平均收缩时间内总肌肉力的相应增加值相同。基于这两种变化之间的精确匹配，运动单位的机械募集发生在大致相同的力水平，而与张力的上升速率无关。
