Dartnall Tamara J, Nordstrom Michael A, Semmler John G
Discipline of Physiology and Research Centre for Human Movement Control, School of Molecular and Biomedical Science, The University of Adelaide, Adelaide, Australia.
J Neurophysiol. 2008 Feb;99(2):1008-19. doi: 10.1152/jn.00686.2007. Epub 2008 Jan 2.
The purpose of this study was to determine the effect of eccentric exercise on correlated motor unit discharge (motor unit synchronization and coherence) during low-force contractions of the human biceps brachii muscle. Eight subjects (age, 25 +/- 7 yr) performed three tasks involving isometric contraction of elbow flexors while EMG (surface and intramuscular) records were obtained from biceps brachii. Tasks were 1) maximum voluntary contraction (MVC); 2) constant-force contraction at various submaximal targets; and 3) sustained discharge of pairs of concurrently active motor units for 2-5 min. These tasks were performed before, immediately after, and 24 h after fatiguing eccentric exercise. MVC force declined 46% immediately after eccentric exercise and remained depressed (31%) 24 h later, which is indicative of muscle damage. For the constant-force task, biceps brachii EMG ( approximately 100% greater) and force fluctuations ( approximately 75% greater) increased immediately after exercise, and both recovered by approximately 50% 24 h later. Motor unit synchronization, quantified by cross-correlation of motor unit pairs during low-force (1-26% MVC) contractions, was 30% greater immediately after (n = 105 pairs) and 24 h after exercise (n = 92 pairs) compared with before exercise (n = 99 pairs). Similarly, motor unit coherence at low (0-10 Hz) frequencies was 20% greater immediately after exercise and 34% greater 24 h later. These results indicate that the series of events leading to muscle damage from eccentric exercise alters the correlated behavior of human motor units in biceps brachii muscle for > or =24 h after the exercise.
本研究的目的是确定离心运动对人肱二头肌低强度收缩时相关运动单位放电（运动单位同步化和相关性）的影响。八名受试者（年龄25±7岁）进行了三项涉及肘部屈肌等长收缩的任务，同时从肱二头肌获取肌电图（表面和肌内）记录。任务包括：1）最大自主收缩（MVC）；2）在不同次最大目标下的恒力收缩；3）同时激活的运动单位对持续放电2 - 5分钟。这些任务在疲劳性离心运动前、运动后即刻以及运动后24小时进行。离心运动后即刻MVC力量下降了46%，24小时后仍维持在较低水平（下降31%），这表明存在肌肉损伤。对于恒力任务，运动后即刻肱二头肌肌电图（增加约100%）和力量波动（增加约75%）增大，24小时后两者均恢复了约50%。通过低强度（1 - 26%MVC）收缩时运动单位对的互相关量化的运动单位同步化，与运动前（n = 99对）相比，运动后即刻（n = 105对）和运动后24小时（n = 92对）分别增加了30%。同样，低频率（0 - 10Hz）下的运动单位相关性在运动后即刻增加了20%，24小时后增加了34%。这些结果表明，导致离心运动引起肌肉损伤的一系列事件在运动后≥24小时改变了肱二头肌中人类运动单位的相关行为。
