Beetroot juice supplementation speeds O2uptake kinetics and improves exercise tolerance during severe-intensity exercise initiated from an elevated metabolic rate

Oct 4, 2013American journal of physiology. Regulatory, integrative and comparative physiology

Beetroot juice helps the body use oxygen faster and improves exercise endurance during intense activity starting from a high metabolic state

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Abstract

Dietary supplementation with NO3(-)-rich beetroot juice results in a 22% greater time-to-task failure during severe-intensity exercise.

NO3(-)-rich beetroot juice increased resting plasma nitrite concentration significantly compared to placebo.
Supplementation reduced the VO2 kinetics during transitions from moderate to severe-intensity exercise.
Faster VO2 kinetics were associated with quicker muscle oxygen utilization, as indicated by muscle [deoxyhemoglobin] kinetics.
The improvement in exercise tolerance was observed when starting from an elevated metabolic rate.

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Recent research has suggested that dietary nitrate (NO3(-)) supplementation might alter the physiological responses to exercise via specific effects on type II muscle. Severe-intensity exercise initiated from an elevated metabolic rate would be expected to enhance the proportional activation of higher-order (type II) muscle fibers. The purpose of this study was, therefore, to test the hypothesis that, compared with placebo (PL), NO3(-)-rich beetroot juice (BR) supplementation would speed the phase II VO2 kinetics (τ(p)) and enhance exercise tolerance during severe-intensity exercise initiated from a baseline of moderate-intensity exercise. Nine healthy, physically active subjects were assigned in a randomized, double-blind, crossover design to receive BR (140 ml/day, containing ~8 mmol of NO3(-)) and PL (140 ml/day, containing ~0.003 mmol of NO3(-)) for 6 days. On days 4, 5, and 6 of the supplementation periods, subjects completed a double-step exercise protocol that included transitions from unloaded to moderate-intensity exercise (U→M) followed immediately by moderate to severe-intensity exercise (M→S). Compared with PL, BR elevated resting plasma nitrite concentration (PL: 65 ± 32 vs. BR: 348 ± 170 nM, P < 0.01) and reduced the VO2 τ(p) in M→S (PL: 46 ± 13 vs. BR: 36 ± 10 s, P < 0.05) but not U→M (PL: 25 ± 4 vs. BR: 27 ± 6 s, P > 0.05). During M→S exercise, the faster VO2 kinetics coincided with faster near-infrared spectroscopy-derived muscle [deoxyhemoglobin] kinetics (τ; PL: 20 ± 9 vs. BR: 10 ± 3 s, P < 0.05) and a 22% greater time-to-task failure (PL: 521 ± 158 vs. BR: 635 ± 258 s, P < 0.05). Dietary supplementation with NO3(-)-rich BR juice speeds VO2 kinetics and enhances exercise tolerance during severe-intensity exercise when initiated from an elevated metabolic rate.

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Beetroot juice supplementation speeds O2uptake kinetics and improves exercise tolerance during severe-intensity exercise initiated from an elevated metabolic rate

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