Dietary nitrate (NO3-) is converted to nitrite (NO2-) and can be further reduced to the vasodilator nitric oxide (NO) amid a low Oenvironment. Accordingly, dietary NO3- increases hind limb blood flow in rats during treadmill exercise; however, the evidence of such an effect in humans is unclear. We tested the hypothesis that acute dietary NO3- (via beetroot [BR] juice) increases forearm blood flow (FBF) via local vasodilation during handgrip exercise in young adults (n = 11; 25 ± 2 years). FBF (Doppler ultrasound) and blood pressure (Finapres) were measured at rest and during graded handgrip exercise at 5%, 15%, and 25% maximal voluntary contraction (MVC) lasting 4 min each. At the highest workload (25% MVC), systemic hypoxia (80% SaO) was induced and exercise continued for three additional minutes. Subjects ingested concentrated BR (12.6 mmol nitrate (n = 5) or 16.8 mmol nitrate (n = 6) and repeated the exercise bout either 2 (12.6 mmol) or 3 h (16.8 mmol) postconsumption. Compared to control, BR significantly increased FBF at 15% MVC (184 ± 15 vs. 164 ± 15 mL/min), 25% MVC (323 ± 27 vs. 286 ± 28 mL/min), and25% + hypoxia (373 ± 39 vs. 343 ± 32 mL/min) and this was due to increases in vascular conductance (i.e., vasodilation). The effect of BR on hemodynamics was not different between the two doses of BR ingested. Forearm VOwas also elevated during exercise at 15% and 25% MVC. We conclude that acute increases in circulating NO3- and NO2- via BR increases muscle blood flow during moderate- to high-intensity handgrip exercise via local vasodilation. These findings may have important implications for aging and diseased populations that demonstrate impaired muscle perfusion and exercise intolerance.

PURPOSE:This study investigated whether reported improvements in blood flow distribution, and the possible related effects on thermoregulation during exercise following supplementation with beetroot juice (BR), a rich source of dietary nitrate (NO), are mitigated in the heat.

METHODS:12 male endurance-trained cyclists (age 27 ± 6 years, VO68.6 ± 8.1 ml kg min) completed two 60 min submaximal cycling trials at 60% of VOpower output. Trials were performed in hot environmental conditions (33.3 ± 0.4 °C, 48.8 ± 3.0% RH) following 3 days of supplementation with either NO-rich BR (6.5 mmol NOfor 2 days and 13 mmol NOon the final day) or NO-depleted placebo (PLA). Salivary NOand nitrite (NO) were measured before and after the supplementation period. During exercise, cutaneous blood flow, blood pressure (MAP), core temperature (T), mean skin temperature (T), indices of muscle oxygenation and oxygen (O) consumption were measured.

RESULTS:Salivary NOand NOincreased significantly following BR by 680 and 890%, respectively. There were no significant differences observed for cutaneous blood flow, MAP, T, T, muscle oxygenation, or Oconsumption between BR and PLA.

CONCLUSION:This investigation shows that the ergogenic effects and health benefits of BR supplementation, such as augmented cutaneous blood flow, reduced MAP, increased muscle oxygenation, and improved aerobic efficiency may be attenuated when exercise is performed in hot conditions.

This article provides an overview of the current literature relating to the efficacy of dietary nitrate (NO) ingestion in altering aspects of cardiovascular and metabolic health and exercise capacity in healthy and diseased individuals. The consumption of NO-rich vegetables, such as spinach and beetroot, have been variously shown to promote nitric oxide bioavailability, reduce systemic blood pressure, enhance tissue blood flow, modulate muscle Outilisation and improve exercise tolerance both in normoxia and in hypoxia, as is commonly observed in a number of disease states. NOingestion may, therefore, act as a natural means for augmenting performance and attenuating complications associated with limited Oavailability or transport, hypertension and the metabolic syndrome. Recent studies indicate that dietary NOmight also augment intrinsic skeletal muscle contractility and improve the speed and power of muscle contraction. Moreover, several investigations suggest that NOsupplementation may improve aspects of cognitive performance both at rest and during exercise. Collectively, these observations position NOas more than a putative ergogenic aid and suggest that increasing natural dietary NOintake may act as a prophylactic in countering the predations of senescence and certain cardiovascular-metabolic diseases.

This study investigated the influence of dietary inorganic nitrate (NO) supplementation on pulmonary Ouptake (V˙O) and muscle deoxyhemoglobin/myoglobin (i.e. deoxy [Hb + Mb]) kinetics during submaximal cycling exercise. In a randomized, placebo-controlled, cross-over study, eight healthy and physically active male subjects completed two step cycle tests at a work rate equivalent to 50% of the difference between the gas exchange threshold and peak V˙Oover separate 4-day supplementation periods with NO-rich (BR; providing 8.4 mmol NO∙day) and NO-depleted (placebo; PLA) beetroot juice. Pulmonary V˙Owas measured breath-by-breath and time-resolved near-infrared spectroscopy was utilized to quantify absolute deoxy [Hb + Mb] and total [Hb + Mb] within the,, andThere were no significant differences (>0.05) in the primary deoxy [Hb + Mb] mean response time or amplitude between the PLA and BR trials at each muscle site. BR significantly increased the mean (three-site) end-exercise deoxy [Hb + Mb] (PLA: 91 ± 9 vs. BR: 95 ± 12 mol/L,<0.05), with a tendency to increase the mean (three-site) area under the curve for total [Hb + Mb] responses (PLA: 3650 ± 1188 vs. BR: 4467 ± 1315 mol/L sec,=0.08). The V˙Oslow component reduction after BR supplementation (PLA: 0.27 ± 0.07 vs. BR: 0.23 ± 0.08 L min,=0.07) correlated inversely with the mean increases in deoxy [Hb + Mb] and total [Hb + Mb] across the three muscle regions ( = 0.62 and 0.66,<0.05). Dietary NOsupplementation increased Odiffusive conductance across locomotor muscles in association with improved V˙Odynamics during heavy-intensity cycling transitions.