Hight Robert E, Beck Travis W, Bemben Debra A, Black Christopher D
Department of Health and Exercise Science, University of Oklahoma, Norman, Oklahoma, United States of America.
PLoS One. 2017 Dec 7;12(12):e0189323. doi: 10.1371/journal.pone.0189323. eCollection 2017.
Eccentric exercise results in an adaptation which attenuates muscle damage from subsequent exercise-termed the "repeated-bout effect (RBE)."
Study examined antagonist co-activation and motor-unit recruitment strategy, assessed via dEMG, concomitant to the RBE.
Nine participants performed 5 sub-maximal isometric trapezoid (ramp-up, hold, ramp-down) contractions at force levels corresponding to 50% and 80% of maximal isometric strength (MVC). Surface EMG signals of the biceps brachii were decomposed into individual motor-unit action potential trains. The relationship between mean firing rate (MFR) of each motor-unit and its recruitment threshold (RT) was examined using linear regression. Eccentric exercise was then performed until biceps brachii MVC had decreased by ~40%. Surface EMG of the biceps and triceps were collected during eccentric exercise. MVC, range-of-motion (ROM), and delayed onset muscle soreness (DOMS) were measured 24-hours, 72-hours, and 1-week following eccentric exercise. Three weeks later all procedures were repeated.
Changes in MVC (-32±14% vs -25±10%; p = 0.034), ROM (-11% vs 6%; p = 0.01), and DOMS (31.0±19mm vs 19±12mm; p = 0.015) were attenuated following the second bout of exercise. Triceps EMG was reduced (16.8±9.5% vs. 12.6±7.2%; p = 0.03) during the second bout of eccentric exercise. The slope (-0.60±0.13 vs -0.70±0.18; p = 0.029) and y-intercept (46.5±8.3 vs 53.3±8.8; p = 0.020) of the MFR vs. RT relationship was altered during contractions at 80% of MVC prior to the second bout of eccentric exercise. No changes were observed at 50% of MVC.
A reduction in antagonist co-activation during the second bout of eccentric exercise suggests less total force was required to move an identical external load. This finding is supported by the increased negative slope coefficient and an increased y-intercept of the linear relationship between RT and MFR.
离心运动可导致一种适应性变化，该变化可减轻后续运动引起的肌肉损伤，即“重复运动效应（RBE）”。
本研究通过动态肌电图（dEMG）检测与RBE相关的拮抗肌共同激活和运动单位募集策略。
9名参与者以相当于最大等长收缩力量（MVC）50%和80%的力量水平进行5次亚最大等长梯形（上升、保持、下降）收缩。肱二头肌的表面肌电图信号被分解为单个运动单位动作电位序列。使用线性回归分析每个运动单位的平均放电率（MFR）与其募集阈值（RT）之间的关系。然后进行离心运动，直到肱二头肌MVC下降约40%。在离心运动过程中收集肱二头肌和肱三头肌的表面肌电图。在离心运动后24小时、72小时和1周测量MVC、关节活动范围（ROM）和延迟性肌肉酸痛（DOMS）。三周后重复所有程序。
第二次运动后，MVC（-32±14%对-25±10%；p = 0.034）、ROM（-11%对6%；p = 0.01）和DOMS（31.0±19mm对19±12mm；p = 0.015）的变化有所减轻。在第二次离心运动期间，肱三头肌肌电图降低（16.8±9.5%对12.6±7.2%；p = 0.03）。在第二次离心运动前，80%MVC收缩期间，MFR与RT关系的斜率（-0.60±0.13对-0.70±0.18；p = 0.029）和y轴截距（46.5±8.3对53.3±8.8；p = 0.020）发生了改变。在50%MVC时未观察到变化。
第二次离心运动期间拮抗肌共同激活的减少表明，移动相同的外部负荷所需的总力量较小。RT与MFR之间线性关系的负斜率系数增加和y轴截距增加支持了这一发现。
