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

INTRODUCTION: 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(3)(−)) supplementation. METHODS: Thirty endurance-trained male participants were allocated to one of three groups: hypoxia (13% F(i)O(2)) + NO(3)(−); hypoxia + placebo; and normoxia (20.9% F(i)O(2)) + 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 (T(lim)) and a 3 min all-out test (3AOT) in hypoxia (F(i)O(2) = 13%) with pulmonary oxygen uptake ( [Formula: see text] O(2)), [Formula: see text] O(2) kinetics, and changes in vastus lateralis local O(2) saturation (SmO(2)) measured were completed by each participant before and after training. RESULTS: In all tests, performance improved to the same extent in hypoxia and normoxia, except for SmO(2) after T(lim) (p = 0.04, d = 0.82) and 3AOT (p = 0.03, d = 1.43) which were lower in the two hypoxic groups compared with the normoxic one. Dietary NO(3)(−) supplementation did not bring any additional benefits. CONCLUSION: 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(3)(−) supplementation was ineffective in further enhancing endurance performance at simulated altitude.