Szubski Christoph, Burtscher Martin, Löscher Wolfgang N
1Department of Sports Science, University of Innsbruck, Innsbruck, Austria.
Med Sci Sports Exerc. 2007 Jun;39(6):948-54. doi: 10.1249/mss.0b013e3180479918.
Hypoxia is known to change neuronal activity in vitro and to impair performance in vivo. The present study was designed to study neuromuscular fatigue in acute hypoxia, and we hypothesized that hypoxia results in additional fatigue during sustained contractions, presumably because of increased central fatigue.
Twelve healthy subjects participated in a normoxic (NX) and hypoxic (HX) experiment performed on separate days. Hypoxia was induced by breathing an HX air mixture containing 12% oxygen. Before, during, and after a 90-s sustained voluntary maximal contraction (MVC) of the first dorsal interosseus muscle, we measured force, voluntary activation (VA), and parameters of motor cortical excitability (motor-evoked potentials (MEP) and silent periods (SP)). Measures of peripheral nerve and muscle function, compound motor action potential (M-wave), and muscle twitch forces were also taken.
During the MVC, force declined similarly during both HX and NX. VA decreased throughout the contraction in HX, but, surprisingly, this decrease in VA in HX did not exceed that observed in NX. Also, motor cortical excitability changed to a similar degree in HX and NX; that is, MEP amplitude and SP duration increased. M-wave amplitude decreased significantly during the sustained MVC in NX and HX. The only difference observed between NX and HX was the quicker recovery of the muscle twitch in HX, which was even potentiated after 5 min of recovery.
The present results show that peripheral and central neuromuscular adaptations during a sustained fatiguing contraction are similar in NX and HX. The quicker recovery and potentiation of twitch forces in HX suggest alterations in myosin phosphorylation, which may enhance contractile force.
已知缺氧会在体外改变神经元活动，并在体内损害运动表现。本研究旨在探究急性缺氧状态下的神经肌肉疲劳，我们假设缺氧会在持续收缩过程中导致额外的疲劳，可能是由于中枢疲劳增加所致。
12名健康受试者分别在不同日期参与了常氧（NX）和缺氧（HX）实验。通过呼吸含12%氧气的HX混合气体诱导缺氧状态。在第一背侧骨间肌进行90秒持续自愿最大收缩（MVC）之前、期间和之后，我们测量了力量、自愿激活（VA）以及运动皮层兴奋性参数（运动诱发电位（MEP）和静息期（SP））。还测量了外周神经和肌肉功能指标、复合运动动作电位（M波）以及肌肉抽搐力量。
在MVC期间，HX和NX状态下力量下降情况相似。在HX状态下，VA在整个收缩过程中均下降，但令人惊讶的是，HX状态下VA的下降幅度并未超过NX状态下观察到的下降幅度。此外，HX和NX状态下运动皮层兴奋性变化程度相似，即MEP波幅和SP时长均增加。在NX和HX状态下，持续MVC期间M波幅均显著下降。NX和HX之间观察到的唯一差异是HX状态下肌肉抽搐恢复更快，且在恢复5分钟后甚至增强。
目前的结果表明，在持续疲劳性收缩过程中，NX和HX状态下外周和中枢神经肌肉适应性相似。HX状态下抽搐力量恢复更快且增强，提示肌球蛋白磷酸化发生改变，这可能增强收缩力。
