Dataset for: Muscle oxygenation profiles between active and inactive muscles with nitrate supplementation under hypoxic exercise

Whether dietary nitrate supplementation improves exercise performance or not is still controversial. While redistribution of sufficient oxygen from inactive to active muscles is essential for optimal exercise performance, no studies was investigated effects of nitrate supplementation on muscle oxygenation profiles between active and inactive muscles. Nine healthy males performed 25 minutes of submaximal (heart rate ~ 140 bpm; EXsub) and incremental cycling (EXmax) until exhaustion under three conditions: (a) normoxia without drink; (b) hypoxia (FiO2 = 13.95%) with placebo (PL); and (c) hypoxia with beetroot juice (BR). PL and BR were provided for four days. Oxygenated and deoxygenated hemoglobin (HbO2 and HHb) were measured in vastus lateralis (active) and biceps brachii (inactive) muscles, and the oxygen saturation of skeletal muscle (StO2; HbO2/total Hb) were calculated. During EXsub, BR suppressed the HHb increases in active muscles during the last 5 min of exercise. During EXmax, time to exhaustion with BR (513 ± 24 s) was significantly longer than with PL (490 ± 39 s, P < 0.05). In active muscles, BR suppressed the HHb increases at moderate work rates during EXmax compared to PL (P < 0.05). Additionally, BR supplementation was associated with greater reductions in HbO2 and StO2 at higher work rates in inactive muscles during EXmax. Collectively, these findings indicate that short-term dietary nitrate supplementation improved hypoxic exercise tolerance, perhaps due to suppressed increases in HHb in active muscles at moderate work rates. Moreover, nitrate supplementation caused greater reductions in oxygenation in inactive muscle at higher work rates during hypoxic exercise.

膳食硝酸盐补充剂是否可改善运动表现，目前仍存在争议。尽管将充足氧气从非活动肌肉重新分配至活动肌肉是实现最佳运动表现的必要条件，但尚无研究探讨硝酸盐补充剂对活动与非活动肌肉间肌肉氧合特征的影响。本研究纳入9名健康男性受试者，在三种实验条件下完成运动测试：（a）常氧无饮水组；（b）低氧（吸入氧分数（Fraction of Inspired Oxygen, FiO2）=13.95%）安慰剂（PL）组；（c）低氧甜菜根汁（BR）组。其中亚极量骑行运动（EXsub）为持续25分钟的运动，目标心率约140次/分钟；递增负荷骑行运动（EXmax）则持续至受试者力竭。受试者需连续4天服用PL或BR补剂。研究人员分别对活动肌股外侧肌与非活动肌肱二头肌的氧合血红蛋白（oxygenated hemoglobin, HbO2）和去氧血红蛋白（deoxygenated hemoglobin, HHb）进行测量，并计算骨骼肌氧饱和度（skeletal muscle oxygen saturation, StO2；即HbO2/总Hb）。在亚极量运动（EXsub）期间，甜菜根汁组在运动最后5分钟时可抑制活动肌中HHb的升高。在递增负荷力竭运动（EXmax）期间，甜菜根汁组的力竭时间（513±24秒）显著长于安慰剂组（490±39秒，P<0.05）。与安慰剂组相比，甜菜根汁组在递增负荷运动的中等工作强度阶段可抑制活动肌中HHb的升高（P<0.05）。此外，在递增负荷运动的高工作强度阶段，甜菜根汁补剂会使非活动肌的HbO2与StO2出现更为显著的下降。综合来看，本研究结果表明，短期膳食硝酸盐补充可提升低氧环境下的运动耐受力，其潜在机制可能为中等工作强度下活动肌HHb升高受到抑制。此外，在低氧运动的高工作强度阶段，硝酸盐补充会使非活动肌的氧合水平出现更为显著的下降。