Pethick Jamie, Winter Samantha L, Burnley Mark
Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, United Kingdom.
Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, United Kingdom
Am J Physiol Regul Integr Comp Physiol. 2016 Jun 1;310(11):R1144-53. doi: 10.1152/ajpregu.00019.2016. Epub 2016 Apr 13.
The complexity of knee extensor torque time series decreases during fatiguing isometric muscle contractions. We hypothesized that because of peripheral fatigue, this loss of torque complexity would occur exclusively during contractions above the critical torque (CT). Nine healthy participants performed isometric knee extension exercise (6 s of contraction, 4 s of rest) on six occasions for 30 min or to task failure, whichever occurred sooner. Four trials were performed above CT (trials S1-S4, S1 being the lowest intensity), and two were performed below CT (at 50% and 90% of CT). Global, central, and peripheral fatigue were quantified using maximal voluntary contractions (MVCs) with femoral nerve stimulation. The complexity of torque output was determined using approximate entropy (ApEn) and the detrended fluctuation analysis-α scaling exponent (DFA-α). The MVC torque was reduced in trials below CT [by 19 ± 4% (means ± SE) in 90%CT], but complexity did not decrease [ApEn for 90%CT: from 0.82 ± 0.03 to 0.75 ± 0.06, 95% paired-samples confidence intervals (CIs), 95% CI = -0.23, 0.10; DFA-α from 1.36 ± 0.01 to 1.32 ± 0.03, 95% CI -0.12, 0.04]. Above CT, substantial reductions in MVC torque occurred (of 49 ± 8% in S1), and torque complexity was reduced (ApEn for S1: from 0.67 ± 0.06 to 0.14 ± 0.01, 95% CI = -0.72, -0.33; DFA-α from 1.38 ± 0.03 to 1.58 ± 0.01, 95% CI 0.12, 0.29). Thus, in these experiments, the fatigue-induced loss of torque complexity occurred exclusively during contractions performed above the CT.
在疲劳性等长肌肉收缩过程中，膝伸肌扭矩时间序列的复杂性降低。我们假设，由于外周疲劳，扭矩复杂性的这种降低仅会在高于临界扭矩（CT）的收缩过程中发生。九名健康参与者进行了六次等长膝关节伸展运动（收缩6秒，休息4秒），持续30分钟或直至任务失败，以先发生者为准。四次试验在CT之上进行（试验S1 - S4，S1强度最低），两次在CT之下进行（分别为CT的50%和90%）。通过股神经刺激的最大自主收缩（MVC）来量化整体、中枢和外周疲劳。使用近似熵（ApEn）和去趋势波动分析-α标度指数（DFA-α）来确定扭矩输出的复杂性。在低于CT的试验中，MVC扭矩降低[在90%CT时降低了19±4%（均值±标准误）]，但复杂性并未降低[90%CT时的ApEn：从0.82±0.03降至0.75±0.06，95%配对样本置信区间（CIs），95%CI = -0.23，0.10；DFA-α从1.36±0.01降至1.32±0.03，95%CI -0.12，0.04]。在CT之上，MVC扭矩大幅降低（S1中降低了49±8%），且扭矩复杂性降低（S1的ApEn：从0.67±0.06降至0.14±0.01，95%CI = -0.72，-0.33；DFA-α从1.38±0.03降至1.58±0.01，95%CI 0.12，0.29）。因此，在这些实验中，疲劳诱导的扭矩复杂性降低仅发生在高于CT的收缩过程中。
