Chronic high-dose beetroot juice supplementation improves time trial performance of well-trained cyclists in normoxia and hypoxia.

Dietary nitrate (NO ₃ ^- ) supplementation via beetroot juice (BR) is known to improve endurance performance in untrained and moderately trained individuals. However, conflicting results exist in well-trained individuals. Evidence suggests that the effects of NO ₃ ^- are augmented during conditions of reduced oxygen availability (e.g., hypoxia), thereby increasing the probability of performance improvements for well-trained athletes in hypoxia vs. normoxia. This randomized, double-blinded, counterbalanced-crossover study examined the effects of 7 days of BR supplementation with 12.4 mmol NO ₃ ^- per day on 10-km cycling time trial (TT) performance in 12 well-trained cyclists in normoxia (N) and normobaric hypoxia (H). Linear mixed models for repeated measures revealed increases in plasma NO ₃ ^- and NO ₂ ^- after supplementation with BR (both p < 0.001). Further, TT performance increased with BR supplementation (∼1.6%, p < 0.05), with no difference between normoxia and hypoxia (p = 0.92). For respiratory variables there were significant effects of supplementation on VO ₂ (p < 0.05) and VE (p < 0.05) such that average VO ₂ and VE during the TT increased with BR, with no difference between normoxia and hypoxia (p ≥ 0.86). We found no effect of supplementation on heart rate, oxygen saturation or muscle oxygenation during the TT. Our results provide new evidence that chronic high-dose NO ₃ ^- supplementation improves cycling performance of well-trained cyclists in both normoxia and hypoxia.
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