Pethick Jamie, Winter Samantha L, Burnley Mark
Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, Canterbury, United Kingdom.
Physiol Rep. 2019 Sep;7(18):e14240. doi: 10.14814/phy2.14240.
To test the hypothesis that a system's metabolic rate and the complexity of fluctuations in the output of that system are related, thirteen healthy participants performed intermittent isometric knee extensor contractions at intensities where a rise in metabolic rate would (40% maximal voluntary contraction, MVC) and would not (20% MVC) be expected. The contractions had a 60% duty factor (6 sec contraction, 4 sec rest) and were performed until task failure or for 30 min, whichever occurred sooner. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) α scaling exponent. Muscle metabolic rate was determined using near-infrared spectroscopy. At 40% MVC, task failure occurred after (mean ± SD) 11.5 ± 5.2 min, whereas all participants completed 30 min of contractions at 20% MVC. Muscle metabolic rate increased significantly after 2 min at 40% MVC (2.70 ± 1.48 to 4.04 ± 1.23 %·s , P < 0.001), but not at 20% MVC. Similarly, complexity decreased significantly at 40% MVC (ApEn, 0.53 ± 0.19 to 0.15 ± 0.09; DFA α, 1.37 ± 0.08 to 1.60 ± 0.09; both P < 0.001), but not at 20% MVC. The rates of change of torque complexity and muscle metabolic rate at 40% MVC were significantly correlated (ApEn, ρ = -0.63, P = 0.022; DFA, ρ = 0.58, P = 0.037). This study demonstrated that an inverse relationship exists between muscle torque complexity and metabolic rate during high-intensity contractions.
为了验证一个系统的代谢率与该系统输出波动的复杂性相关这一假设，13名健康参与者在预期代谢率会上升（40%最大自主收缩，MVC）和不会上升（20%MVC）的强度下进行间歇性等长伸膝收缩。收缩的占空比为60%（收缩6秒，休息4秒），持续进行直至任务失败或持续30分钟，以先发生者为准。连续采集扭矩和表面肌电图信号。使用近似熵（ApEn）和去趋势波动分析（DFA）α标度指数对扭矩的复杂性和分形标度进行量化。使用近红外光谱法测定肌肉代谢率。在40%MVC时，（平均±标准差）11.5±5.2分钟后出现任务失败，而所有参与者在20%MVC时均完成了30分钟的收缩。在40%MVC时，2分钟后肌肉代谢率显著增加（从2.70±1.48至4.04±1.23%·秒，P<0.001），但在20%MVC时未增加。同样，在40%MVC时复杂性显著降低（ApEn，从0.53±0.19降至0.15±0.09；DFAα，从1.37±0.08降至1.60±0.09；两者P<0.001），但在20%MVC时未降低。40%MVC时扭矩复杂性和肌肉代谢率的变化率显著相关（ApEn，ρ=-0.63，P=0.022；DFA，ρ=0.58，P=0.037）。本研究表明，在高强度收缩期间，肌肉扭矩复杂性与代谢率之间存在负相关关系。
