Dietary Nitrate Supplementation Is Not Helpful for Endurance Performance at Simulated Altitude Even When Combined...

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 (NO₃ ^-) supplementation.

Thirty endurance-trained male participants were allocated to one of three groups: hypoxia (13% F_iO₂) + NO₃ ^-; hypoxia + placebo; and normoxia (20.9% F_iO₂) + 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_iO₂ = 13%) with pulmonary oxygen uptake ( $$ O₂), $$ O₂ kinetics, and changes in vastus lateralis local O₂ saturation (SmO₂) measured were completed by each participant before and after training.

In all tests, performance improved to the same extent in hypoxia and normoxia, except for SmO₂ 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 NO₃ ^- supplementation did not bring any additional benefits.

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 NO₃ ^- supplementation was ineffective in further enhancing endurance performance at simulated altitude.