Dietary nitrate supplementation reduces the O₂cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans

Abstract

AM. Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. J Appl Physiol 107: 1144 -1155, 2009. First published August 6, 2009; doi:10.1152/japplphysiol.00722.2009.-Pharmacological sodium nitrate supplementation has been reported to reduce the O2 cost of submaximal exercise in humans. In this study, we hypothesized that dietary supplementation with inorganic nitrate in the form of beetroot juice (BR) would reduce the O 2 cost of submaximal exercise and enhance the tolerance to high-intensity exercise. In a double-blind, placebo (PL)-controlled, crossover study, eight men (aged 19 -38 yr) consumed 500 ml/day of either BR (containing 11.2 Ϯ 0.6 mM of nitrate) or blackcurrant cordial (as a PL, with negligible nitrate content) for 6 consecutive days and completed a series of "step" moderate-intensity and severe-intensity exercise tests on the last 3 days. On days 4 -6, plasma nitrite concentration was significantly greater following dietary nitrate supplementation compared with PL (BR: 273 Ϯ 44 vs. PL: 140 Ϯ 50 nM; P Ͻ 0.05), and systolic blood pressure was significantly reduced (BR: 124 Ϯ 2 vs. PL: 132 Ϯ 5 mmHg; P Ͻ 0.01). During moderate exercise, nitrate supplementation reduced muscle fractional O2 extraction (as estimated using nearinfrared spectroscopy). The gain of the increase in pulmonary O 2 uptake following the onset of moderate exercise was reduced by 19% in the BR condition (BR: 8.6 Ϯ 0.7 vs. PL: 10.8 Ϯ 1.6 ml ⅐ min Ϫ1 ⅐ W Ϫ1 ; P Ͻ 0.05). During severe exercise, the O 2 uptake slow component was reduced (BR: 0.57 Ϯ 0.20 vs. PL: 0.74 Ϯ 0.24 l/min; P Ͻ 0.05), and the time-to-exhaustion was extended (BR: 675 Ϯ 203 vs. PL: 583 Ϯ 145 s; P Ͻ 0.05). The reduced O2 cost of exercise following increased dietary nitrate intake has important implications for our understanding of the factors that regulate mitochondrial respiration and muscle contractile energetics in humans. exercise economy; muscle efficiency; O2 uptake; exercise performance; fatigue A FUNDAMENTAL TENET OF HUMAN exercise physiology is a predictable oxygen (O 2 ) cost for a given submaximal work rate. Upon the initiation of moderate-intensity exercise [i.e., exercise performed at work rates below the gas exchange threshold (GET)], pulmonary O 2 uptake (V O 2 ), which closely reflects O 2 consumption in the skeletal muscles (2, 29, 38), rises in an exponential fashion to attain a "steady state" within ϳ2-3 min in healthy humans (64). The steady-state increase in V O 2 is linearly related to the increase in external work rate; is essentially independent of factors such as age, health status or aerobic fitness; and approximates 10 ml O 2 ⅐min Ϫ1 ⅐W Ϫ1 of external power output during cycle ergometry (i.e., 10 ml ⅐min Ϫ1 ⅐W Ϫ1 ; Ref. 36). During supra-GET exercise, V O 2 dynamics become more complex, owing, in part, to the development of a delayed-onset V O 2 "slow component", which elevates the O 2 cost of exercise above 10 ml⅐min Ϫ1 ⅐W Ϫ1 (36, 64). Whereas it is known ...

Dietary nitrate supplementation enhances high-intensity running performance in moderate normobaric hypoxia, independent of aerobic fitness

“…These findings are in line with most previous investigations [4,5,22,37], and similar to the results of a recent meta-analysis [6]. The physiological mechanisms underlying the decreased V O2 subsequent to nitrate supplementation have not been fully elucidated, but may be accounted for by: a) an improvement in the efficiency of mitochondrial respiration [35] and/or b) enhanced efficiency of muscle force production [7].…”

“…Consistent with previous investigations, plasma nitrate and nitrite, and exhaled NO concentrations were significantly elevated following dietary nitrate supplementation [1,2,5,8,55,22,39,38], signifying an increase in the 'substrates' available for NO generation via the nitrate-nitrite-NO pathway [11]. Peak plasma nitrite concentration was 602 % higher in BRJ versus PLA, similar to Arnold et al [38] (775 %) (~ 7 mmol nitrate), but considerably greater than reported by Muggeridge et al [22] (134 %) (~ 5 mmol nitrate) and Vanhatalo et al [8] (150 %) (~ 9.3 mmol).…”

“…Increasing NO bioavailability via nitrate supplementation has been reported to improve exercise time to exhaustion (TTE) or time-trial (TT) performance in the majority [5,[16][17][18], but not all [23,24] previous investigations in untrained and moderately-trained individuals. Conversely, well-trained participants (V O2max > 60 ml·kg -1 ·min -1 ) are typically less responsive to dietary nitrate supplementation [17,[19][20][21][25][26][27], even when very high nitrate doses (~ 19.5 mmol) are administered [28].…”

“…These include, but are not restricted to: lower blood pressure [1][2][3], reduced O2 consumption (V O2) during steady-state exercise [4][5][6], attenuated muscle metabolic perturbations [7,8], and enhanced muscle force production [9,10]. These effects are not directly attributable to the nitrate anion, which is relatively inert [11].…”

Present and future pharmacotherapeutic agents in heart failure: an evolving paradigm

“…Our group and others have also investigated nitrite, which has been shown to be a hypoxic‐dependent vasodilator, significantly improving cardiac haemodynamics without causing symptomatic hypotension (Maher et al ., 2008). Nitrite has also been shown to exhibit additional benefits of metabolic modulation within skeletal muscle (Bailey et al , 2009), which may translate to cardiac muscle. Herein, we will review the significant evidence base behind the current medical treatments for HFrEF, the physiology of metabolic impairment in HF and discuss two promising novel agents, perhexiline and nitrite.…”