Kent-Braun J A
UCSF/VA Medical Center, Magnetic Resonance Unit, University of California, San Francisco 94121, USA.
Eur J Appl Physiol Occup Physiol. 1999 Jun;80(1):57-63. doi: 10.1007/s004210050558.
The purpose of this study was to estimate the relative contributions of central and peripheral factors to the development of human muscle fatigue. Nine healthy subjects [five male, four female; age = 30 (2) years, mean (SE)] sustained a maximum voluntary isometric contraction (MVC) of the ankle dorsiflexor muscles for 4 min. Fatigue was quantitated as the fall in MVC. Three measures of central activation and one measure of peripheral activation (compound muscle action potential, CMAP) were made using electromyography (EMG) and electrical stimulation. Measures of intramuscular metabolism were made using magnetic resonance spectroscopy. After exercise, MVC and electrically stimulated tetanic contraction (50 Hz, 500 ms) forces were 22.2 (3.7)% and 37.3 (7.1)% of pre-exercise values, respectively. The measures of central activation suggested some central fatigue during exercise: (1) the central activation ratio [MVC/(MVC + superimposed tetanic force)] fell from 0.94 (0.03) to 0.78 (0.09), (2) the MVC/tetanic force ratio fell from 2.3 (0.7) to 1.3 (0.7), and (3) the integral of the EMG (iEMG) signal decreased to 72.6 (9.1)% of the initial value, while the CMAP amplitude was unchanged. Intramuscular pH was associated by regression with the decline in MVC force (and therefore fatigue) and iEMG. The results indicate that central factors, which were not associated with altered peripheral excitability, contributed approximately 20% to the muscle fatigue developed, with the remainder being attributable to intramuscular (i.e., metabolic) factors. The association between pH and iEMG is consistent with proton concentration as a feedback mechanism for central motor drive during maximal effort.
本研究的目的是评估中枢和外周因素对人类肌肉疲劳发展的相对贡献。九名健康受试者[五名男性，四名女性；年龄 = 30（2）岁，平均值（标准误）]对踝背屈肌进行了4分钟的最大自主等长收缩（MVC）。疲劳程度通过MVC的下降来量化。使用肌电图（EMG）和电刺激进行了三项中枢激活测量和一项外周激活测量（复合肌肉动作电位，CMAP）。使用磁共振波谱法进行了肌肉内代谢测量。运动后，MVC和电刺激强直收缩（50Hz，500ms）力分别为运动前值的22.2（3.7）%和37.3（7.1）%。中枢激活测量表明运动期间存在一些中枢疲劳：（1）中枢激活率[MVC/（MVC + 叠加强直力）]从0.94（0.03）降至0.78（0.09），（2）MVC/强直力比值从2.3（0.7）降至1.3（0.7），（3）EMG（iEMG）信号积分降至初始值的72.6（9.1）%，而CMAP振幅未改变。肌肉内pH值与MVC力的下降（以及因此的疲劳）和iEMG通过回归相关。结果表明，与外周兴奋性改变无关的中枢因素对所产生的肌肉疲劳贡献约20%，其余归因于肌肉内（即代谢）因素。pH值与iEMG之间的关联与质子浓度作为最大努力期间中枢运动驱动的反馈机制一致。
