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.
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 ( O ₂ ), O ₂ kinetics, and changes in vastus lateralis local O ₂ saturation (SmO ₂ ) 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 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.
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.