Smith Cory M, Salmon Owen F, Jenkins Jasmin R
Human & Environmental Physiology Laboratory, The University of Texas at El Paso, El Paso, TX, USA.
Interdisciplinary Health Sciences PhD Program, The University of Texas at El Paso, El Paso, TX, USA.
Curr Res Physiol. 2021 Nov 4;4:243-251. doi: 10.1016/j.crphys.2021.11.001. eCollection 2021.
The purpose of this study is to examine the effects of fatigue on muscular performance, oxygenation saturation, and cognition following acute hypoxic exposure at Normoxia, Moderate Hypoxia (MH), and Severe Hypoxia (SH).
Twelve males performed 3 sets of leg extensions to failure under Normoxia (FiO: 21%), MH (Fi0: 15.4%), and SH (Fi0: 12.9%). Heart rate, peripheral oxygenation saturation, total saturation index, psychomotor vigilance testing reaction time, psychomotor vigilance error rate, maximum strength, and repetitions to failure were measured throughout each visit.
The primary findings indicated that MH and SH resulted in significant decreases in psychomotor vigilance test performance (MH: 388.25-427.17 ms, 0.41-0.33 error rate; SH: 398.17-445.42 ms reaction time, 0.25-1.00 error rate), absolute muscle tissue oxygen saturation (Abs-StO) (MH:67.22% compared to SH:57.56%), but similar muscular strength, heart rate, and patterns of muscle tissue oxygen saturation responses (StO%) during fatigue when compared to Normoxia. There was an acute decrease in the ability to remain vigilant and/or respond correctly to visual stimuli as indicated by the worsened reaction time (PVT) during MH (FiO: 15.4%) and increased PVT and error rate (PVT) during SH (FiO: 12.9%) conditions.
Acute hypoxic exposure in the current study was not a sufficient stimuli to elicit hypoxic-related changes in HR, muscular strength (1-RM), or repetitions to failure. The SpO responses were hypoxic-level dependent with increasing levels of hypoxia resulting in greater and more sustained reductions in SpO. The combined SpO and StO responses at MH and SH suggested a balance between the muscles metabolic demand remaining lower than the muscle oxygen diffusion capacity. During the SH condition, Abs-StO suggested greater metabolic stress than Normoxia and MH conditions during the fatiguing leg extensions. The patterns of responses for StO% during the three sets of leg press to failure indicated that exercise is a more potent influencer to muscle oxygenation status than hypoxic conditions (FiO: 15.4 and 12.9%).
本研究旨在探讨常氧、中度缺氧（MH）和重度缺氧（SH）条件下急性缺氧暴露后疲劳对肌肉性能、氧饱和度和认知的影响。
12名男性在常氧（FiO₂：21%）、中度缺氧（FiO₂：15.4%）和重度缺氧（FiO₂：12.9%）条件下进行3组腿部伸展运动直至力竭。在每次检查过程中测量心率、外周血氧饱和度、总饱和度指数、心理运动警觉性测试反应时间、心理运动警觉性错误率、最大力量和力竭重复次数。
主要研究结果表明，中度缺氧和重度缺氧导致心理运动警觉性测试表现显著下降（中度缺氧：反应时间388.25 - 427.17毫秒，错误率0.41 - 0.33；重度缺氧：反应时间398.17 - 445.42毫秒，错误率0.25 - 1.00），绝对肌肉组织氧饱和度（Abs-StO）下降（中度缺氧：67.22%，重度缺氧：57.56%），但与常氧相比，疲劳期间肌肉力量、心率和肌肉组织氧饱和度反应模式（StO%）相似。如中度缺氧（FiO₂：l5.4%）期间反应时间（PVT）恶化以及重度缺氧（FiO₂：12.9%）期间PVT和错误率增加所示，保持警觉和/或对视觉刺激正确反应的能力急剧下降。
本研究中的急性缺氧暴露并非引发心率、肌肉力量（1-RM）或力竭重复次数出现缺氧相关变化的充分刺激因素。SpO₂反应取决于缺氧水平，缺氧程度增加会导致SpO₂更大且更持续的降低。中度缺氧和重度缺氧时SpO₂和StO%的综合反应表明，肌肉代谢需求保持低于肌肉氧扩散能力之间存在平衡。在重度缺氧条件下，Abs-StO表明在疲劳的腿部伸展运动中，代谢压力比常氧和中度缺氧条件下更大。三组腿部推举至力竭过程中StO%的反应模式表明，运动对肌肉氧合状态的影响比缺氧条件（FiO₂：15.4和12.9%）更强。
