Beetroot juice supplementation speeds O2 uptake kinetics and improves exercise tolerance during severe-intensity exercise initiated from an elevated baseline.
ABSTRACT 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 to placebo (PL), NO3--rich beetroot juice (BR) supplementation would speed the phase II vo2 kinetics (τp) 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 to PL, BR elevated resting plasma nitrite concentration (PL: 65 ± 32 vs. BR: 348 ± 170 nM, P<0.01) and reduced the vo2 τp 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 NIRS-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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ABSTRACT: • Dietary nitrate consumption increases plasma nitrate and nitrite levels in chronic obstructive disease (COPD) patients.• Dietary nitrate consumption increases submaximal exercise capacity in COPD patients.• Dietary nitrate consumption decreases resting systolic blood pressure in COPD patients.• Dietary nitrate consumption decreases exercise diastolic blood pressure in COPD patients.Nitric Oxide 10/2014; DOI:10.1016/j.niox.2014.10.007 · 3.18 Impact Factor
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ABSTRACT: Nitrate (NO3−) supplementation via beetroot juice (BR) preferentially improves vascular conductance and O2 delivery to contracting skeletal muscles comprised predominantly of type IIb + d/x (i.e. highly glycolytic) fibers following its reduction to nitrite and nitric oxide (NO). To address the mechanistic basis for NO3− to improve metabolic control we tested the hypothesis that increased NO bioavailability via BR supplementation would elevate microvascular PO2 (PO2mv) in fast twitch but not slow twitch muscle. Twelve young adult male Sprague–Dawley rats were administered BR ([NO3−] 1 mmol/kg/day, n = 6) or water (control, n = 6) for 5 days. PO2mv (phosphorescence quenching) was measured at rest and during 180 s of electrically induced 1-Hz twitch contractions (6–8 V) of the soleus (9% type IIb +d/x) and mixed portion of the gastrocnemius (MG, 91% type IIb + d/x) muscles. In the MG, but not the soleus, BR elevated contracting steady state PO2mv by ~43% (control: 13.7 ± 0.5, BR: 19 ± 1.6 mmHg (P < 0.05)). This higher PO2mv represents a greater blood–myocyte O2 driving force during muscle contractions thus providing a potential mechanism by which NO3− supplementation via BR improves metabolic control in fast twitch muscle. Recruitment of higher order type II muscle fibers is thought to play a role in the development of the VO2 slow component which is inextricably linked to the fatigue process. These data therefore provide a putative mechanism for the BR-induced improvements in high-intensity exercise performance seen in humans.Nitric Oxide 09/2014; DOI:10.1016/j.niox.2014.09.157 · 3.18 Impact Factor
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ABSTRACT: Dietary nitrate supplementation, usually in the form of beetroot juice, has been heralded as a possible new ergogenic aid for sport and exercise performance. Early studies in recreationally active participants indicated that nitrate ingestion significantly reduces the O2 cost of submaximal exercise and improves performance during high-intensity endurance exercise. Subsequent studies have begun to address the physiological mechanisms underpinning these observations and to investigate the human populations in whom, and the exercise conditions (high- vs. low-intensity, long- vs. short-duration, continuous vs. intermittent, normoxic vs. hypoxic) under which, nitrate supplementation may be beneficial. Moreover, the optimal nitrate loading regimen in terms of nitrate dose and duration of supplementation has been explored. Depending on these factors, nitrate supplementation has been shown to exert physiological effects that could be conducive to exercise performance enhancement, at least in recreationally active or sub-élite athletes. This article provides a "state-of-the-art" review of the literature pertinent to the evaluation of the efficacy of nitrate supplementation in altering the physiological determinants of sport and exercise performance.Applied Physiology Nutrition and Metabolism 04/2014; 39(9):1-10. DOI:10.1139/apnm-2014-0036 · 2.23 Impact Factor