Human Performance Laboratory, University of Calgary, Calgary, AB, CANADA.
LIBM, Inter-University Laboratory of Human Movement Science, University Savoie Mont Blanc, Chambery, FRANCE.
Med Sci Sports Exerc. 2020 Sep;52(9):1888-1899. doi: 10.1249/MSS.0000000000002331.
The understanding of fatigue in hypoxia is limited due to: lack of control in arterial saturation, different exercise intensities and hypoxia levels, lag time between exercise cessation and fatigue evaluation. We aimed at evaluating fatigue during cycling and immediately after exhaustion (EXH) in normoxia, moderate and severe hypoxia at relative and absolute intensities.
Thirteen subjects completed three sessions in normoxia, moderate, and severe hypoxia with intensity based on percentage of normoxic maximal power output (NOR, MODABS, SEVABS) plus two sessions where intensity was based on the corresponding environmental condition (MODREL, SEVREL). Arterial saturation was clamped at 85% and 70% in moderate and severe hypoxia, respectively. Before, during cycling, and at EXH, maximum voluntary contraction (MVC), peripheral fatigue (high-frequency doublet [Db100], twitch [Pt]), and central fatigue (cortical voluntary activation [VATMS]) were evaluated without delay using an innovative ergometer.
Time to EXH declined not only with hypoxia level at absolute but also relative intensities compared to NOR. At isotime, MVC, Pt, and Db100 were similarly depreciated in NOR, MODREL, and SEVREL. At EXH, there was a similar reduction among conditions in MVC (-26% to -31%), Db100 (-25% to -35%) and VATMS (-9% to -13%). However, Pt was less decreased in SEVREL compared with NOR (-33% ± 17% vs -46% ± 16%).
The shorter time to EXH in relative hypoxia and yet lower peripheral fatigue and similar central fatigue compared with normoxia suggests that hypoxia per se may affect brain areas not directly implicated in quadriceps motor function.
由于动脉饱和度缺乏控制、运动强度和缺氧水平不同、运动停止和疲劳评估之间存在滞后时间，因此对缺氧条件下疲劳的理解有限。我们的目的是评估常氧、中氧和高氧环境下，以相对和绝对强度进行的踏车运动中和运动后即刻（EXH）的疲劳。
13 名受试者在常氧、中氧和高氧三种环境下分别完成了基于常氧最大输出功率百分比的强度（NOR、MODABS、SEVABS）的 3 次测试，以及基于相应环境条件的强度（MODREL、SEVREL）的 2 次测试。中氧和高氧时，动脉饱和度分别被夹在 85%和 70%。在踏车前、踏车中和 EXH 时，使用创新的测力计无延迟地评估最大自主收缩（MVC）、外周疲劳（高频双脉冲[Db100]、单次收缩[Pt]）和中枢疲劳（皮质自愿激活[VATMS]）。
与常氧相比，不仅在绝对强度，而且在相对强度下，EXH 的时间随着缺氧水平的增加而缩短。在等时相，NOR、MODREL 和 SEVREL 中的 MVC、Pt 和 Db100 都有类似的下降。在 EXH 时，所有条件下的 MVC（-26%至-31%）、Db100（-25%至-35%）和 VATMS（-9%至-13%）都有类似的降低。然而，与常氧相比，SEVREL 中 Pt 的降低幅度较小（-33%±17%比-46%±16%）。
与常氧相比，相对缺氧时 EXH 时间更短，外周疲劳更低，中枢疲劳相似，这表明缺氧本身可能会影响与股四头肌运动功能不直接相关的大脑区域。
