This study focuses on the determination of the vagal threshold (T_va) during exercise with increasing intensity in normoxia and normobaric hypoxia. The experimental protocol was performed by 28 healthy men aged 20 to 30 years. It included three stages of exercise on a bicycle ergometer with a fraction of inspired oxygen (FiO₂) 20.9% (normoxia), 17.3% (simulated altitude ~1500 m), and 15.3% (~2500 m) at intensity associated with 20% to 70% of the maximal heart rate reserve (MHRR) set in normoxia. T_va level in normoxia was determined at exercise intensity corresponding with (M ± SD) 45.0 ± 5.6% of MHRR. Power output at T_va (PO_th), representing threshold exercise intensity, decreased with increasing degree of hypoxia (normoxia: 114 ± 29 W; FiO₂ = 17.3%: 110 ± 27 W; FiO₂ = 15.3%: 96 ± 32 W). Significant changes in PO_th were observed with FiO₂ = 15.3% compared to normoxia (p = 0.007) and FiO₂ = 17.3% (p = 0.001). Consequentially, normoxic %MHRR adjusted for hypoxia with FiO₂ = 15.3% was reduced to 39.9 ± 5.5%. Considering the convenient altitude for exercise in hypoxia, PO_th did not differ excessively between normoxic conditions and the simulated altitude of ~1500 m, while more substantial decline of PO_th occurred at the simulated altitude of ~2500 m compared to the other two conditions.

中文翻译：

---

常氧和常压低氧递增式逐步运动中的迷走阈阈值确定

这项研究的重点是确定运动过程中迷走神经阈值（T _va）随常氧和常压低氧强度的增加而增加。实验方案由年龄在20至30岁的28名健康男性进行。它包括在自行车测功机上进行的三个阶段的运动，其中一部分吸氧（FiO ₂）为20.9％（常氧），17.3％（模拟高度为〜1500 m）和15.3％（〜2500 m），强度分别为20％达到正常血氧中最大心率储备（MHRR）的70％。在运动强度对应于MHRR的（M±SD）45.0±5.6％的情况下确定常氧状态下的T _va水平。T _va上的功率输出（PO _th），代表阈值运动强度，随着缺氧程度的增加而降低（常氧：114±29 W; FiO ₂ = 17.3％：110±27 W; FiO ₂ = 15.3％：96±32 W）。与常氧（p = 0.007）和FiO ₂ = 17.3％（p = 0.001）相比，FiO ₂ = 15.3％时观察到PO _th的显着变化。因此，用FiO ₂ = 15.3％调整的低氧常氧％MHRR降至39.9±5.5％。考虑到锻炼缺氧方便高度，PO_日没有含氧量正常的条件和〜1500米高空模拟之间的过度差异，而PO的较大幅度的下滑_日 与其他两个条件相比，发生在〜2500 m的模拟高度上。