Research Center for Exercise and Health, Department of Biomedical Kinesiology, KU Leuven, Leuven, Belgium.
J Appl Physiol (1985). 2012 Sep 1;113(5):736-45. doi: 10.1152/japplphysiol.01253.2011. Epub 2012 Jul 5.
Exercise tolerance is impaired in hypoxia, and it has recently been shown that dietary nitrate supplementation can reduce the oxygen (O(2)) cost of muscle contractions. Therefore, we investigated the effect of dietary nitrate supplementation on arterial, muscle, and cerebral oxygenation status, symptoms of acute mountain sickness (AMS), and exercise tolerance at simulated 5,000 m altitude. Fifteen young, healthy volunteers participated in three experimental sessions according to a crossover study design. From 6 days prior to each session, subjects received either beetroot (BR) juice delivering 0.07 mmol nitrate/kg body wt/day or a control drink (CON). One session was in normoxia with CON (NOR(CON)); the two other sessions were in hypoxia (11% O(2)), with either CON (HYP(CON)) or BR (HYP(BR)). Subjects first cycled for 20 min at 45% of peak O(2) consumption (VO(2)peak; EX(45%)) and thereafter, performed a maximal incremental exercise test (EX(max)). Whole-body VO(2), arterial O(2) saturation (%SpO(2)) via pulsoximetry, and tissue oxygenation index of both muscle (TOI(M)) and cerebral (TOI(C)) tissue by near-infrared spectroscopy were measured. Hypoxia per se substantially reduced VO(2)peak, %SpO(2), TOI(M), and TOI(C) (NOR(CON) vs. HYP(CON), P < 0.05). Compared with HYP(CON), VO(2) at rest and during EX(45%) was lower in HYP(BR) (P < 0.05), whereas %SpO(2) was higher (P < 0.05). TOI(M) was ~4-5% higher in HYP(BR) than in HYP(CON) both at rest and during EX(45%) and EX(max) (P < 0.05). TOI(C) as well as the incidence of AMS symptoms were similar between HYP(CON) and HYP(BR) at any time. Hypoxia reduced time to exhaustion in EX(max) by 36% (P < 0.05), but this ergolytic effect was partly negated by BR (+5%, P < 0.05). Short-term dietary nitrate supplementation improves arterial and muscle oxygenation status but not cerebral oxygenation status during exercise in severe hypoxia. This is associated with improved exercise tolerance against the background of a similar incidence of AMS.
运动耐量在缺氧时会受到损害，最近有研究表明，膳食硝酸盐补充可以降低肌肉收缩的耗氧量。因此，我们研究了膳食硝酸盐补充对动脉、肌肉和脑氧合状态、急性高山病（AMS）症状以及在模拟海拔 5000 米时的运动耐量的影响。15 名年轻、健康的志愿者按照交叉研究设计参加了三个实验。从每个实验前 6 天开始，受试者分别接受含有 0.07 毫摩尔硝酸盐/公斤体重/天的甜菜根（BR）汁或对照饮料（CON）。一个实验在常氧下接受 CON（NOR（CON））；另外两个实验在缺氧（11%O2）下进行，接受 CON（HYP（CON））或 BR（HYP（BR））。受试者首先以 45%峰值摄氧量（VO2peak）进行 20 分钟的自行车运动（EX（45%）），然后进行最大增量运动试验（EX（max））。全身 VO2、动脉血氧饱和度（%SpO2）通过脉搏血氧仪测量，以及肌肉（TOI（M））和脑（TOI（C））组织的组织氧合指数通过近红外光谱测量。单纯缺氧显著降低 VO2peak、%SpO2、TOI（M）和 TOI（C）（NOR（CON）与 HYP（CON）相比，P < 0.05）。与 HYP（CON）相比，HYP（BR）在休息和 EX（45%）时的 VO2 更低（P < 0.05），而 %SpO2 更高（P < 0.05）。在休息和 EX（45%）和 EX（max）时，HYP（BR）的 TOI（M）比 HYP（CON）高约 4-5%（P < 0.05）。在任何时候，HYP（CON）和 HYP（BR）的 TOI（C）以及 AMS 症状的发生率都相似。缺氧使 EX（max）中的疲劳时间减少了 36%（P < 0.05），但 BR 部分抵消了这种疲劳效应（增加 5%，P < 0.05）。短期膳食硝酸盐补充可改善严重缺氧时运动中的动脉和肌肉氧合状态，但不能改善脑氧合状态。这与 AMS 发生率相似的情况下运动耐量的提高有关。
