AUTHOR=Sousa Ana , Viana João L. , Milheiro Jaime , Reis Vítor M. , Millet Grégoire P. 

TITLE=Dietary Nitrate Supplementation Is Not Helpful for Endurance Performance at Simulated Altitude Even When Combined With Intermittent Normobaric Hypoxic Training

JOURNAL=Frontiers in Physiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.839996

DOI=10.3389/fphys.2022.839996

ISSN=1664-042X

ABSTRACT=<sec><title>Introduction</title><p>Training intensity and nutrition may influence adaptations to training performed in hypoxia and consequently performance outcomes at altitude. This study investigates if performance at simulated altitude is improved to a larger extent when high-intensity interval training is performed in normobaric hypoxia and if this is potentiated when combined with chronic dietary nitrate (NO<sub>3</sub><sup>−</sup>) supplementation.</p></sec><sec><title>Methods</title><p>Thirty endurance-trained male participants were allocated to one of three groups: hypoxia (13% F<sub>i</sub>O<sub>2</sub>) + NO<sub>3</sub><sup>−</sup>; hypoxia + placebo; and normoxia (20.9% F<sub>i</sub>O<sub>2</sub>) + placebo. All performed 12 cycling sessions (eight sessions of 2*6 × 1 min at severe intensity with 1 min recovery and four sessions of 4*6*10 s all-out with 20 s recovery) during a 4-week period (three sessions/week) with supplementation administered 3–2.5 h before each session. An incremental exhaustion test, a severe intensity exercise bout to exhaustion (<italic>T</italic><sub>lim</sub>) and a 3 min all-out test (3AOT) in hypoxia (F<sub>i</sub>O<sub>2</sub> = 13%) with pulmonary oxygen uptake (<inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub>), <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> kinetics, and changes in <italic>vastus lateralis</italic> local O<sub>2</sub> saturation (SmO<sub>2</sub>) measured were completed by each participant before and after training.</p></sec><sec><title>Results</title><p>In all tests, performance improved to the same extent in hypoxia and normoxia, except for SmO<sub>2</sub> after <italic>T</italic><sub>lim</sub> (<italic>p</italic> = 0.04, <italic>d</italic> = 0.82) and 3AOT (<italic>p</italic> = 0.03, <italic>d</italic> = 1.43) which were lower in the two hypoxic groups compared with the normoxic one. Dietary NO<sub>3</sub><sup>−</sup> supplementation did not bring any additional benefits.</p></sec><sec><title>Conclusion</title><p>Performance at simulated altitude was not improved to a larger extent when high-intensity interval training was undertaken in normobaric hypoxic conditions, when compared with normoxic training. Additionally, dietary NO<sub>3</sub><sup>−</sup> supplementation was ineffective in further enhancing endurance performance at simulated altitude.</p></sec>