Multiple-day high-dose beetroot juice supplementation does not improve pulmonary or muscle deoxygenation kinetics of well-trained cyclists in normoxia and hypoxia

Apr 8, 2021Nitric oxide : biology and chemistry

Several days of high-dose beetroot juice do not improve lung or muscle oxygen use during exercise in well-trained cyclists at normal and low oxygen levels

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Abstract

High-dose beetroot juice supplementation (12.4 mmol NO per day) does not significantly change exercise efficiency or oxygen uptake kinetics in well-trained athletes.

Beetroot juice supplementation lowered the amplitude of the oxygen uptake response by 2.1%.
No significant changes were observed in the primary time constant for oxygen uptake or muscle deoxygenation during cycling.
Steady state oxygen uptake and exercise efficiency remained unchanged with supplementation.
Results indicate that multiple-day, high-dose beetroot juice does not enhance performance metrics in normoxia or hypoxia.

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Dietary nitrate (NO) supplementation via beetroot juice (BR) has been reported to lower oxygen cost (i.e., increased exercise efficiency) and speed up oxygen uptake (VO) kinetics in untrained and moderately trained individuals, particularly during conditions of low oxygen availability (i.e., hypoxia). However, the effects of multiple-day, high dose (12.4 mmol NOper day) BR supplementation on exercise efficiency and VOkinetics during normoxia and hypoxia in well-trained individuals are not resolved. In a double-blinded, randomized crossover study, 12 well-trained cyclists (66.4 ± 5.3 ml min∙kg) completed three transitions from rest to moderate-intensity (~70% of gas exchange threshold) cycling in hypoxia and normoxia with supplementation of BR or nitrate-depleted BR as placebo. Continuous measures of VOand muscle (vastus lateralis) deoxygenation (ΔHHb, using near-infrared spectroscopy) were acquired during all transitions. Kinetics of VOand deoxygenation (ΔHHb) were modeled using mono-exponential functions. Our results showed that BR supplementation did not alter the primary time constant for VOor ΔHHb during the transition from rest to moderate-intensity cycling. While BR supplementation lowered the amplitude of the VOresponse (2.1%, p = 0.038), BR did not alter steady state VOderived from the fit (p = 0.258), raw VOdata (p = 0.231), moderate intensity exercise efficiency (p = 0.333) nor steady state ΔHHb (p = 0.224). Altogether, these results demonstrate that multiple-day, high-dose BR supplementation does not alter exercise efficiency or oxygen uptake kinetics during normoxia and hypoxia in well-trained athletes. 3 2 3-2 2 2 2 2 2 2 --1 -1

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Multiple-day high-dose beetroot juice supplementation does not improve pulmonary or muscle deoxygenation kinetics of well-trained cyclists in normoxia and hypoxia

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