Effect of oral nitrate supplementation on pulmonary hemodynamics during exercise and time trial performance in normoxia and hypoxia: a randomized controlled trial

Abstract

Background: Hypoxia-induced pulmonary vasoconstriction increases pulmonary arterial pressure (PAP) and may impede right heart function and exercise performance. This study examined the effects of oral nitrate supplementation on right heart function and performance during exercise in normoxia and hypoxia. We tested the hypothesis that nitrate supplementation would attenuate the increase in PAP at rest and during exercise in hypoxia, thereby improving exercise performance.Methods: Twelve trained male cyclists [age: 31 ± 7 year (mean ± SD)] performed 15 km time-trial cycling (TT) and steady-state submaximal cycling (50, 100, and 150 W) in normoxia and hypoxia (11% inspired O2) following 3-day oral supplementation with either placebo or sodium nitrate (0.1 mmol/kg/day). We measured TT time-to-completion, muscle tissue oxygenation during TT and systolic right ventricle to right atrium pressure gradient (RV-RA gradient: index of PAP) during steady state cycling.Results: During steady state exercise, hypoxia elevated RV-RA gradient (p > 0.05), while oral nitrate supplementation did not alter RV-RA gradient (p > 0.05). During 15 km TT, hypoxia lowered muscle tissue oxygenation (p < 0.05). Nitrate supplementation further decreased muscle tissue oxygenation during 15 km TT in hypoxia (p < 0.05). Hypoxia impaired time-to-completion during TT (p < 0.05), while no improvements were observed with nitrate supplementation in normoxia or hypoxia (p > 0.05).Conclusion: Our findings indicate that oral nitrate supplementation does not attenuate acute hypoxic pulmonary vasoconstriction nor improve performance during time trial cycling in normoxia and hypoxia.

Dietary nitrate supplementation enhances high-intensity running performance in moderate normobaric hypoxia, independent of aerobic fitness

“…Therefore, the high nitrate dose administered in this study relative to investigations which have not observed an effect of nitrate supplementation (~ 5 -7 mmol) [38][39][40] may have also contributed towards the consistent ergogenic effect observed here.…”

“…This is supported by the findings of a recent study, in which nitrate supplementation improved tolerance to severe intensity cycling in hypoxia (FIO2 13.1 %) but not normoxia [36]. However, in other studies, nitrate supplementation has been shown both to improve [8,22,37] and have no effect [38][39][40] on hypoxic exercise performance. These equivocal findings may be attributed to differences in the training status of participants, exercise protocol, supplementation protocol, and hypoxic stimuli applied, and warrant further exploration.…”

“…It is therefore possible that nitrate supplementation is more effective during shorter more high-intensity exercise, during which these muscle fibres are more heavily recruited [9,[43][44][45]64], or else in individuals with greater distribution of type II muscle fibres [43]. The time-trial duration employed in this study (< 6 minutes) was considerably less than other investigations (~ 17 -48 minutes) which have not observed an ergogenic effect of nitrate supplementation in hypoxia [38][39][40], and may be important. Thus, the combination of a hypoxic exercise environment and high-intensity TT may have maximised the effects of nitrate supplementation.…”

“…Conversely, studies in well-trained individuals exercising in hypoxia have typically found no effect of nitrate supplementation [38][39][40]. Well-trained individuals exhibit increased presence and activity of the NOS enzymes [31]; possess higher baseline nitrate/nitrite concentration [29]; may habitually consume high levels of nitrate as a consequence of their large daily energy intake [30]; and experience lower tissue acidosis and hypoxia [20] relative to the untrained.…”

Effects of Dietary Nitrate Supplementation on Physiological Responses, Cognitive Function, and Exercise Performance at Moderate and Very-High Simulated Altitude

“…In contrast to previous studies which have employed high-intensity leg-extension (Vanhatalo et al, 2011), cycle ergometry (Masschelein et al, 2012; Kelly et al, 2014; Muggeridge et al, 2014; Bourdillon et al, 2015; MacLeod et al, 2015), or treadmill running (Arnold et al, 2015; Shannon et al, 2016) exercise protocols at simulated altitude, we evaluated the effects of ${\text{NO}}_3^{-}$ supplementation using a protocol which more closely replicates the demands of altitude hiking. For this purpose, our participants were required to complete a 3 km uphill (10% gradient) treadmill test whilst carrying a weighted (10 kg) backpack.…”