Dartnall Tamara J, Rogasch Nigel C, 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, South Australia 5005, Australia.
J Neurophysiol. 2009 Jul;102(1):413-23. doi: 10.1152/jn.91285.2008. Epub 2009 May 6.
The purpose of this study was to determine the effect of eccentric muscle damage on recruitment threshold force and repetitive discharge properties of low-threshold motor units. Ten subjects performed four tasks involving isometric contraction of elbow flexors while electromyographic (EMG) data were recorded from human biceps brachii and brachialis muscles. Tasks were 1) maximum voluntary contraction (MVC); 2) constant-force contraction at various submaximal targets; 3) motor unit recruitment threshold task; and 4) minimum motor unit discharge rate task. These tasks were performed on three separate days before, immediately after, and 24 h after eccentric exercise of elbow flexor muscles. MVC force declined (42%) immediately after exercise and remained depressed (29%) 24 h later, indicative of muscle damage. Mean motor unit recruitment threshold for biceps brachii was 8.4+/-4.2% MVC, (n=34) before eccentric exercise, and was reduced by 41% (5.0+/-3.0% MVC, n=34) immediately after and by 39% (5.2+/-2.5% MVC, n=34) 24 h after exercise. No significant changes in motor unit recruitment threshold were observed in the brachialis muscle. However, for the minimum tonic discharge rate task, motor units in both muscles discharged 11% faster (10.8+/-2.0 vs. 9.7+/-1.7 Hz) immediately after (n=29) exercise compared with that before (n=32). The minimum discharge rate variability was greater in brachialis muscle immediately after exercise (13.8+/-3.1%) compared with that before (11.9+/-3.1%) and 24 h after exercise (11.7+/-2.4%). No significant changes in minimum discharge rate variability were observed in the biceps brachii motor units after exercise. These results indicate that muscle damage from eccentric exercise alters motor unit recruitment thresholds for >or=24 h, but the effect is not the same in the different elbow flexor muscles.
本研究的目的是确定离心性肌肉损伤对低阈值运动单位的募集阈力和重复放电特性的影响。10名受试者进行了四项涉及肘屈肌等长收缩的任务，同时记录肱二头肌和肱肌的肌电图（EMG）数据。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）运动单位募集阈任务；4）最小运动单位放电率任务。这些任务在肘屈肌离心运动前、运动后即刻和运动后24小时这三个不同的日子进行。运动后即刻MVC力下降（42%），24小时后仍处于较低水平（29%），表明存在肌肉损伤。肱二头肌运动单位的平均募集阈在离心运动前为8.4±4.2%MVC（n = 34），运动后即刻降低了41%（5.0±3.0%MVC，n = 34），运动后24小时降低了39%（5.2±2.5%MVC，n = 34）。肱肌运动单位的募集阈未观察到显著变化。然而，对于最小强直放电率任务，与运动前（n = 32）相比，运动后即刻（n = 29）两块肌肉的运动单位放电速度均加快了11%（10.8±2.0对9.7±1.7Hz）。运动后即刻肱肌的最小放电率变异性（13.8±3.1%）高于运动前（11.9±3.1%）和运动后24小时（11.7±2.4%）。肱二头肌运动单位运动后的最小放电率变异性未观察到显著变化。这些结果表明，离心运动导致的肌肉损伤会在≥24小时内改变运动单位的募集阈，但不同肘屈肌的影响并不相同。
