Effect of hypoxia and nitrate supplementation on different high-intensity interval-training sessions

To test the hypothesis that interval-training (IHT) would be impaired by hypoxia to a larger extent than repeated-sprint training (RSH) and that dietary nitrate (NO₃^-) would mitigate the detrimental effect of hypoxia to a larger extent during IHT than RSH.

Thirty endurance-trained male participants performed IHT (6 × 1 min at 90%∆ with 1 min active recovery) and RSH (2 sets of 6 × 10 s "all-out" efforts with 20 s active recovery) on a cycle ergometer, allocated in one of three groups: normobaric hypoxia (~ 13% F_iO₂) + NO₃^- - HNO, n = 10; normobaric hypoxia + placebo - HPL, n = 10; normoxia (20.9% F_iO₂) + placebo - CON, n = 10. Submaximal oxygen uptake ([Formula: see text]O₂), time spent above 90% of maximal [Formula: see text]O₂ (≥ 90 [Formula: see text]O₂max) and heart rate (≥ 90 HRmax) were compared between IHT and RSH sessions and groups. Additionally, mean power output (MPO), decrement score and % of power associated with [Formula: see text]O_2max (%p[Formula: see text]O₂max) in RSH sessions were analyzed.

[Formula: see text]O₂ at sub-maximal intensities did not differ between training protocols and groups (~ 27 ml kg^-1 min^-1).  ≥ 90 HRmax was significantly higher in IHT compared to RSH session (39 ± 8 vs. 30 ± 8%, p = 0.03) but only in HNO group. MPO (range 360-490 W) and decrement score (10-13%) were similar between groups although %p[Formula: see text]O₂max was significantly higher (p = 0.04) in CON (166 ± 16 W) compared with both HPL (147 ± 15 W) and HNO (144 ± 10 W) groups.

IHT responses were neither more impaired by hypoxia than RSH ones. Moreover, dietary NO₃^- supplementation impacted equally IHT and RSH training responses' differences between hypoxia and normoxia.