School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Crawley, WA, Australia.
Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
Eur J Appl Physiol. 2021 Jan;121(1):95-107. doi: 10.1007/s00421-020-04495-2. Epub 2020 Sep 29.
To compare the effects of different hypoxia severities on exercise capacity, cardio-respiratory, tissue oxygenation and neuromuscular fatigue characteristics in response to exhaustive intermittent cycling.
Eleven well-trained cyclists, repeated supra-maximal cycling efforts of 15 s (30% of anaerobic power reserve, 609 ± 23 W), interspersed with 45 s of passive rest until task failure. The exercise was performed on separate days in normoxia (SL; simulated altitude/end-exercise arterial oxygen saturation = 0 m/~ 96%), moderate (MH; 2200 m/~ 90%) and severe (SH; 4200 m/~ 79%) hypoxia in a cross-over design. Neuromuscular tests, including brief (5 s) and sustained (30 s) maximal isometric voluntary contractions of the knee extensors, were performed at baseline and exhaustion.
Exercise capacity decreased with hypoxia severity (23 ± 9, 16 ± 6 and 9 ± 3 cycle efforts in SL, MH and SH, respectively; P < 0.001; η = 0.72). Both cerebral (P < 0.001; η = 0.86) and muscle (P < 0.01; η = 0.54) oxygenation decreased throughout the exercise, independent of condition (P ≥ 0.45; η ≥ 0.14). Compared to SL, muscle oxygenation was globally lower in MH and SH (P = 0.011; η = 0.36). Cardiovascular solicitation neared maximal values at exhaustion in all conditions. Peak twitch amplitude with single and paired electrical stimuli (P < 0.001; η ≥ 0.87), maximal torque (P < 0.001; η ≥ 0.48) and voluntary activation measured using transcranial magnetic stimulation (P ≤ 0.034; η ≥ 0.31) during brief and sustained MVCs were all reduced at exhaustion, independent of condition (P ≥ 0.196; η ≥ 0.15).
Despite reduced exercise capacity with increasing severity of hypoxia during exhaustive intermittent cycling, neuromuscular fatigue characteristics were not different at task failure and cardiovascular solicitation neared maximum values.
比较不同缺氧严重程度对衰竭性间歇性循环运动中运动能力、心肺功能、组织氧合和神经肌肉疲劳特征的影响。
11 名训练有素的自行车运动员，在模拟海拔/运动结束时动脉血氧饱和度为 0 米/96%的常氧（SL）、2200 米/90%的中度（MH）和 4200 米/~79%的严重（SH）缺氧下，分别进行 15 秒的超最大循环努力（无氧功率储备的 30%，609±23 W），然后进行 45 秒的被动休息，直到任务失败。在交叉设计中，在不同的日子里进行神经肌肉测试，包括短暂（5 s）和持续（30 s）的最大等长膝关节伸肌自愿收缩。
随着缺氧严重程度的增加，运动能力下降（SL、MH 和 SH 分别为 23±9、16±6 和 9±3 个循环努力；P<0.001；η=0.72）。脑（P<0.001；η=0.86）和肌肉（P<0.01；η=0.54）氧合在整个运动过程中均降低，与条件无关（P≥0.45；η≥0.14）。与 SL 相比，MH 和 SH 时肌肉氧合全局较低（P=0.011；η=0.36）。在所有条件下，心血管刺激在运动结束时接近最大值。在所有条件下，单次和双次电刺激的峰值抽搐幅度（P<0.001；η≥0.87）、最大扭矩（P<0.001；η≥0.48）和经颅磁刺激测量的自愿激活（P≤0.034；η≥0.31）在短暂和持续 MVC 时，在运动结束时均降低，与条件无关（P≥0.196；η≥0.15）。
尽管在衰竭性间歇性循环运动中，随着缺氧严重程度的增加，运动能力下降，但在任务失败时，神经肌肉疲劳特征并无差异，心血管刺激接近最大值。
