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The effect of beetroot juice on exercise performance in normoxia and moderate hypoxia MacLeod, Kristin Elizabeth


Beetroot juice (BR) has been shown to lower the oxygen cost of exercise in normoxia, and may also be beneficial to performance in hypoxia. We investigated the effect of BR on steady state economy and 10-km time trial (TT) performance in normoxia and in hypoxia (simulated altitude of 2500 m). Twelve trained male cyclists (VO₂max ≥ 60 ml·kg-¹·min-¹) completed four exercise trials. Two hours prior to exercise, subjects consumed 70 mL BR (~6 mmol nitrate) or 70 mL placebo (nitrate-depleted BR) in a randomized, double-blind manner. Subjects then completed a 15-min self-selected cycling warm-up followed by a 15-min steady-state exercise bout at 50% of maximum power output and a 10-km time trial (TT) in either normoxia (~21% O₂) or hypoxia (~16% O₂). Environmental conditions were randomized and single blind. Economy at 50% power output was similar in hypoxic and normoxic conditions (p > 0.05), but subjects had a significantly higher mean power output in the normoxic TT relative to the hypoxic TT (p < 0.05). BR did not affect economy, mean power output, or time to complete the 10-km TT relative to placebo in normoxia (p > 0.05 in all comparisons). Similarly, in hypoxia, BR did not affect economy, steady state SpO₂, mean power output or time to complete the 10-km TT relative to placebo (p > 0.05 in all comparisons). BR supplementation resulted in a significantly greater fraction of expired nitric oxide relative to PL (28 [12] vs. 22 [9] ppb). In a small sample of well-trained male cyclists, BR did not improve exercise performance in normoxia or hypoxia. This finding is possibly related to BR dosage, although it is congruent with previous evidence showing that BR may be less effective in trained populations in normoxia. The lack of an effect in hypoxia was contrary to our hypothesis.

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