Bailey Stephen J, Varnham Richard L, DiMenna Fred J, Breese Brynmor C, Wylie Lee J, Jones Andrew M
Sport and Health Sciences, College of Life and Environmental Sciences, University of Exeter, Exeter, UK;
Sport and Health Sciences, Faculty of Health and Life Science, Oxford Brookes University, Oxford, UK;
J Appl Physiol (1985). 2015 Jun 1;118(11):1396-405. doi: 10.1152/japplphysiol.01141.2014. Epub 2015 Apr 9.
We tested the hypothesis that inorganic nitrate (NO3 (-)) supplementation would improve muscle oxygenation, pulmonary oxygen uptake (V̇o2) kinetics, and exercise tolerance (Tlim) to a greater extent when cycling at high compared with low pedal rates. In a randomized, placebo-controlled cross-over study, seven subjects (mean ± SD, age 21 ± 2 yr, body mass 86 ± 10 kg) completed severe-intensity step cycle tests at pedal cadences of 35 rpm and 115 rpm during separate nine-day supplementation periods with NO3 (-)-rich beetroot juice (BR) (providing 8.4 mmol NO3 (-)/day) and placebo (PLA). Compared with PLA, plasma nitrite concentration increased 178% with BR (P < 0.01). There were no significant differences in muscle oxyhemoglobin concentration ([O2Hb]), phase II V̇o2 kinetics, or Tlim between BR and PLA when cycling at 35 rpm (P > 0.05). However, when cycling at 115 rpm, muscle [O2Hb] was higher at baseline and throughout exercise, phase II V̇o2 kinetics was faster (47 ± 16 s vs. 61 ± 25 s; P < 0.05), and Tlim was greater (362 ± 137 s vs. 297 ± 79 s; P < 0.05) with BR compared with PLA. These results suggest that short-term BR supplementation can increase muscle oxygenation, expedite the adjustment of oxidative metabolism, and enhance exercise tolerance when cycling at a high, but not a low, pedal cadence in healthy recreationally active subjects. These findings support recent observations that NO3 (-) supplementation may be particularly effective at improving physiological and functional responses in type II muscle fibers.
与低踏频骑行相比，补充无机硝酸盐（NO3 (-)）在高踏频骑行时能更大程度地改善肌肉氧合、肺摄氧量（V̇o2）动力学和运动耐力（Tlim）。在一项随机、安慰剂对照的交叉研究中，7名受试者（平均±标准差，年龄21±2岁，体重86±10千克）在分别为期九天的补充富含NO3 (-)的甜菜根汁（BR）（每天提供8.4毫摩尔NO3 (-)）和安慰剂（PLA）的期间，以35转/分钟和115转/分钟的踏频完成了高强度阶梯式自行车测试。与PLA相比，BR使血浆亚硝酸盐浓度增加了178%（P < 0.01）。当以35转/分钟骑行时，BR和PLA之间的肌肉氧合血红蛋白浓度（[O2Hb]）、II期V̇o2动力学或Tlim没有显著差异（P > 0.05）。然而，当以115转/分钟骑行时，与PLA相比，BR组在基线和整个运动过程中的肌肉[O2Hb]更高，II期V̇o2动力学更快（47±16秒对61±25秒；P < 0.05），Tlim更长（362±137秒对297±79秒；P < 0.05）。这些结果表明，在健康的休闲活动受试者中，短期补充BR可增加肌肉氧合，加快氧化代谢的调整，并在高踏频而非低踏频骑行时增强运动耐力。这些发现支持了最近的观察结果，即补充NO3 (-)在改善II型肌纤维的生理和功能反应方面可能特别有效。
