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

Abstract

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 study investigated the effects of nitrate supplementation on muscle oxygenation profiles between active and inactive muscles. Nine healthy males performed 25 min 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 4 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 sec) was significantly longer than with PL (490 ± 39 sec, P < 0.05). In active muscles, BR suppressed the HHb increases at moderate work rates during EXmax compared to PL (P < 0.05). In addition, 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.

Limitation of Maximal Heart Rate in Hypoxia: Mechanisms and Clinical Importance

“…However, using the data presented in Figure 4 for 30–39 years age group, the overestimation increases by 1% in each example that has been provided. The overestimation calculated in relation to this particular case is consistent with those calculated from the data obtained in healthy subjects in previous studies (Friedmann et al, 2004 ; Horiuchi et al, 2017 ; Subudhi et al, 2011 ). Hence, depending on the calculation, a systematic overestimation of the intensity by 1–4% would be obtained in hypoxia.…”

“…Also, resting HR increases under hypoxia due to increase sympathetic and decrease parasympathetic activity (Windsor et al, 2010 ; Siebenmann and Lundby, 2015 ). This increase could reach 4-5 bpm (Friedmann et al, 2004 ; Subudhi et al, 2011 ; Horiuchi et al, 2017 ), even at low altitude (equivalent to only 1,650 m for (Subudhi et al, 2011 )). Knowing the resting HR of the author (55 bpm), the overestimation could have been 2 bpm (1.9%) for moderate (40% HRR) and 4 bpm (2.6%) for vigorous (85% HRR) intensity exercise at 2,500 m. The corresponding values would have been 2 bpm (2.4%) and 5 bpm (3.3%) at 3,500 m. Finally, by using the average decrement of 4.2 ± 3.9 bpm of HR max , the overestimation would have been 1 bpm (1.6%) and 3 bpm (2.2%) for moderate and vigorous intensity calculated from HRR.…”

A single dose of beetroot juice improves endothelial function but not tissue oxygenation in pregnant women: a randomised clinical trial

“…Although this study was unable to achieve the sample size of sixteen participants, the effect size was taken into account in order to determine the magnitude of the BJ ingestion effect on endothelial function and muscle StO 2 parameters (18) . In addition, previous studies have observed statistical difference in StO 2 parameters with ≤12 volunteers after beetroot supplementation (8,9,19) .…”

Pulmonary oxygen uptake on‐kinetics can predict acute physiological responses to resistance exercise training in healthy young men

“…On day one, a symptom‐limited cycle ergometer ramp test (25 W min −1 ) was performed at 60 revolutions min −1 until exhaustion (AEROBIKE75XLII; Konami Sports Club CO., Ltd, Tokyo, Japan) to determine the peak and AT. The test was terminated when participants met at least two of the following exhaustion criteria: (i) no increase in despite a further increase in work rate; (ii) HR reached 90% of the age‐predicted maximal value (220 − age); (iii) a Borg scale of perceived exertion rating of 19; or (iv) failure to pedal at 60 revolutions min −1 despite strong verbal encouragement (Horiuchi et al ., ). HR was monitored continuously via a three‐lead electrocardiogram (Bedside Monitor BSM 2400 series Life scope 1; Nihon Kohden, Tokyo, Japan).…”