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.
"Although the C2C12 experiments lack an appropriate NO − 3 - depleted beetroot juice control ( see above ) , increased coupling efficiency of oxidative phosphorylation agrees with data reported by Larsen et al . ( 2011 ) , who show that skeletal muscle mitochondria isolated from NO − 3 - supplemented subjects exhibit higher respiratory control and P / O ratios ( defined in Brand and Nicholls , 2011 ) than mitochondria from non - supplemented controls , and that increases in P / O ratio correlate with NO − 3 - induced decreases in whole - body O 2 uptake during exercise . This increased efficiency of ATP synthesis in isolated mitochondria , however , emerges from decreased respiration linked to mitochondrial proton leak , not from stimulated O 2 uptake coupled to phosphorylation ( Larsen et al . "
[Show abstract][Hide abstract] ABSTRACT: Inorganic nitrate is present at high levels in beetroot and celery, and in green leafy vegetables such as spinach and lettuce. Though long believed inert, nitrate can be reduced to nitrite in the human mouth and, further, under hypoxia and/or low pH, to nitric oxide. Dietary nitrate has thus been associated favorably with nitric-oxide-regulated processes including blood flow and energy metabolism. Indeed, the therapeutic potential of dietary nitrate in cardiovascular disease and metabolic syndrome-both aging-related medical disorders-has attracted considerable recent research interest. We and others have shown that dietary nitrate supplementation lowers the oxygen cost of human exercise, as less respiratory activity appears to be required for a set rate of skeletal muscle work. This striking observation predicts that nitrate benefits the energy metabolism of human muscle, increasing the efficiency of either mitochondrial ATP synthesis and/or of cellular ATP-consuming processes. In this mini-review, we evaluate experimental support for the dietary nitrate effects on muscle bioenergetics and we critically discuss the likelihood of nitric oxide as the molecular mediator of such effects.
Frontiers in Physiology 08/2015; 6:211. DOI:10.3389/fphys.2015.00211 · 3.53 Impact Factor
"Surprisingly, a more recent study by Shepherd et al. , involving thirteen patients with chronic obstructive pulmonary disease (COPD), showed that a 4-fold rise in plasma nitrate concentration induced by two days of nitrate supplementation did not reduce the oxygen cost of moderate intensity cycling, increase distance covered in the six-minute walk test, or lower blood pressure. The recent study suggests that the ergogenic effect of nitrate supplementation is mostly present in type II muscle fibers, which is why its effect should be more pronounced during exercise of high intensity . It should not be forgotten that NO can also have a potentially harmful effect on exercise capacity by inhibiting cytochrome c oxidase, as reported previously . "
"Recently, dietary nitrate (NO3 − ) has been shown to be a nutraceutical that can improve exercise capacity in young healthy individuals   . Dietary NO3 − supplementation has been shown to exert its effects as a result of its conversion to NO2 − and then to NO. NO is recognized as an endogenous effector molecule that has a role in a variety of physiological functions including vasoregulation, vascular homeostasis, neurotransmission, cellular metabolism and immune function  . "
[Show abstract][Hide abstract] ABSTRACT: Dietary nitrate (NO3-) supplementation via beetroot juice has been shown to increase the exercise capacity of younger and older adults. The purpose of this study was to investigate the effects of acute NO3- ingestion on the submaximal constant work rate exercise capacity of COPD patients. Fifteen patients were assigned in a randomized, single-blind, crossover design to receive one of two treatments (beetroot juice then placebo or placebo then beetroot juice). Submaximal constant work rate exercise time at 75% of the patient's maximal work capacity was the primary outcome. Secondary outcomes included plasma NO3- and nitrite (NO2-) levels, blood pressure, heart rate, oxygen consumption (VO2), dynamic hyperinflation, dyspnea and leg discomfort. Relative to placebo, beetroot ingestion increased plasma NO3- by 938% and NO2- by 379%. Median (+interquartile range) exercise time was significantly longer (p = 0.031) following the ingestion of beetroot versus placebo (375.0 + 257.0 vs. 346.2 + 148.0 s, respectively). Compared with placebo, beetroot ingestion significantly reduced iso-time (p = 0.001) and end exercise (p = 0.008) diastolic blood pressures by 6.4 and 5.6 mmHg, respectively. Resting systolic blood pressure was significantly reduced (p = 0.019) by 8.2 mmHg for the beetroot versus the placebo trial. No other variables were significantly different between the beetroot and placebo trials. These results indicate that acute dietary NO3- supplementation can elevate plasma NO3- and NO2- concentrations, improve exercise performance, and reduce blood pressure in COPD patients.
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