Pethick Jamie, Whiteaway Katherine, Winter Samantha L, Burnley Mark
Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, UK.
Exp Physiol. 2019 Jan;104(1):100-111. doi: 10.1113/EP087295. Epub 2018 Nov 28.
What is the central question of this study? Does eccentric exercise leading to prolonged knee-extensor torque depression also result in a prolonged loss of knee-extensor torque complexity? What is the main finding and its importance? The recovery of the loss of torque complexity after eccentric exercise took 24 h, whereas after acute muscle fatigue it took 10 min. The depression of torque complexity after eccentric exercise was prolonged.
Neuromuscular fatigue reduces the temporal structure, or complexity, of muscle torque output. Exercise-induced muscle damage reduces muscle torque output for considerably longer than high-intensity fatiguing contractions. We hypothesized that muscle-damaging eccentric exercise would lead to a persistent decrease in torque complexity, whereas fatiguing exercise would not. Ten healthy participants performed five isometric contractions (6 s contraction, 4 s rest) at 50% maximal voluntary contraction (MVC) before, immediately after and 10, 30 and 60 min and 24 h after eccentric (muscle-damaging) and isometric (fatiguing) exercise. These contractions were also repeated 48 h and 1 week after eccentric exercise. Torque and surface EMG signals were sampled throughout each test. Complexity and fractal scaling were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis α exponent (DFA α). Global, central and peripheral perturbations were quantified using MVCs with femoral nerve stimulation. Complexity decreased after both eccentric [ApEn, mean (SD), from 0.39 (0.10) to 0.20 (0.12), P < 0.001] and isometric exercise [from 0.41 (0.13) to 0.09 (0.04); P < 0.001]. After eccentric exercise, ApEn and DFA α required 24 h to recover to baseline levels, but after isometric exercise they required only 10 min. The MVC torque remained reduced [from 233.6 (74.2) to 187.5 (64.7) N m] 48 h after eccentric exercise, with such changes evident only up to 60 min after isometric exercise [MVC torque, from 246.1 (77.2) to 217.9 (71.8) N m]. The prolonged depression in maximal muscle torque output is therefore accompanied by a prolonged reduction in torque complexity.
本研究的核心问题是什么？导致膝关节伸肌扭矩长时间下降的离心运动是否也会导致膝关节伸肌扭矩复杂性的长期丧失？主要发现及其重要性是什么？离心运动后扭矩复杂性丧失的恢复需要24小时，而急性肌肉疲劳后则需要10分钟。离心运动后扭矩复杂性的下降持续时间更长。
神经肌肉疲劳会降低肌肉扭矩输出的时间结构或复杂性。运动诱导的肌肉损伤使肌肉扭矩输出降低的时间比高强度疲劳收缩长得多。我们假设，造成肌肉损伤的离心运动会导致扭矩复杂性持续下降，而疲劳运动则不会。10名健康参与者在离心（造成肌肉损伤）和等长（疲劳）运动前、运动后立即以及运动后10、30和60分钟及24小时，以最大自主收缩（MVC）的50%进行了五次等长收缩（6秒收缩，4秒休息）。在离心运动后的48小时和1周也重复了这些收缩。在每个测试过程中对扭矩和表面肌电图信号进行采样。使用近似熵（ApEn）和去趋势波动分析α指数（DFAα）对复杂性和分形标度进行量化。使用股神经刺激下的MVC对整体、中枢和外周扰动进行量化。离心运动[ApEn，平均值（标准差），从0.39（0.10）降至0.20（0.12），P<0.001]和等长运动后[从0.41（0.13）降至0.09（0.04）；P<0.001]复杂性均降低。离心运动后，ApEn和DFAα需要24小时恢复到基线水平，但等长运动后仅需10分钟。离心运动后48小时，MVC扭矩仍降低[从233.6（74.2）降至187.5（64.7）N·m]，而等长运动后这种变化仅在60分钟内明显[MVC扭矩，从246.1（77.2）降至217.9（71.8）N·m]。因此，最大肌肉扭矩输出的长期下降伴随着扭矩复杂性的长期降低。
