We tested the hypothesis that acute supplementation with nitrate (NO3-)-rich beetroot juice (BR) would improve quadriceps muscle oxygenation, pulmonary oxygen uptake (V˙O2) kinetics and exercise tolerance (Tlim) in normoxia and that these improvements would be augmented in hypoxia and attenuated in hyperoxia. In a randomised, double-blind, cross-over study, ten healthy males completed two-step cycle tests to Tlim following acute consumption of 210 mL BR (18.6 mmol NO3-) or NO3--depleted beetroot juice placebo (PL; 0.12 mmol NO3-). These tests were completed in normobaric normoxia [fraction of inspired oxygen (FIO2): 21%], hypoxia (FIO2: 15%) and hyperoxia (FIO2: 40%). Pulmonary V˙O2 and quadriceps tissue oxygenation index (TOI), derived from multi-channel near-infrared spectroscopy, were measured during all trials. Plasma [nitrite] was higher in all BR compared to all PL trials (P < 0.05). Quadriceps TOI was higher in normoxia compared to hypoxia (P < 0.05) and higher in hyperoxia compared to hypoxia and normoxia (P < 0.05). Tlim was improved after BR compared to PL ingestion in the hypoxic trials (250 ± 44 vs. 231 ± 41 s; P = 0.006; d = 1.13), with the magnitude of improvement being negatively correlated with quadriceps TOI at Tlim (r = -0.78; P < 0.05). Tlim was not improved following BR ingestion in normoxia (BR: 364 ± 98 vs. PL: 344 ± 78 s; P = 0.087, d = 0.61) or hyperoxia (BR: 492 ± 212 vs. PL: 472 ± 196 s; P = 0.273, d = 0.37). BR ingestion increased peak V˙O2 in hypoxia (P < 0.05), but not normoxia or hyperoxia (P > 0.05). These findings indicate that BR supplementation is more likely to improve Tlim and peak V˙O2 in situations when skeletal muscle is more hypoxic.

中文翻译：

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肌肉氧合和富含硝酸盐的甜菜根汁补充对O2吸收动力学和运动耐量的影响。

我们检验了以下假设：在常氧状态下，急性补充富含硝酸盐（NO3-）的甜菜根汁（BR）可以改善股四头肌的氧合，肺部摄氧（V˙O2）动力学和运动耐力（Tlim），并且这些改善将得到增强在低氧状态下减弱，在高氧状态下减弱。在一项随机，双盲，交叉研究中，急性摄入210 mL BR（18.6 mmol NO3-）或消耗了NO3的甜菜根汁安慰剂（PL; 0.12 mmol）后，十名健康男性完成了对Tlim的两步循环测试NO3-）。这些测试是在常压常氧[吸入氧（FIO2）的分数：21％]，低氧（FIO2：15％）和高氧（FIO2：40％）中完成的。在所有试验中均测量了源自多通道近红外光谱的肺部V˙O2和股四头肌组织氧合指数（TOI）。与所有PL试验相比，所有BR中的血浆[亚硝酸盐]都更高（P <0.05）。股四头肌TOI在正常氧状态下高于缺氧（P <0.05），在高氧状态下则高于缺氧和正常氧（P <0.05）。在低氧试验中，BR摄入后与PL摄入相比，Tlim有所改善（250±44 vs. 231±41 s； P = 0.006； d = 1.13），改善幅度与Tlim时的股四头肌TOI呈负相关（r =- 0.78; P <0.05）。正常摄入BR（BR：364±98 vs. PL：344±78 s; P = 0.087，d = 0.61）或高氧血症（BR：492±212 vs. PL：472±196 s; P）后，Tlim没有改善= 0.273，d = 0.37）。BR摄入增加缺氧时的峰值V˙O2（P <0.05），但不增加常氧或高氧（P> 0.05）。