TY - JOUR

T1 - Nitrate-rich beetroot juice ingestion reduces skeletal muscle O2 uptake and blood flow during exercise in sedentary men

AU - Nyberg, Michael

AU - Christensen, Peter Møller

AU - Blackwell, Jamie R

AU - Hostrup, Morten

AU - Jones, Andrew M

AU - Bangsbo, Jens

N1 - This article is protected by copyright. All rights reserved.

PY - 2021

Y1 - 2021

N2 - Dietary nitrate supplementation has been shown to reduce pulmonary O2 uptake during submaximal exercise and enhance exercise performance. However, the effects of nitrate supplementation on local metabolic and hemodynamic regulation in contracting human skeletal muscle remain unclear. To address this, eight healthy young male sedentary subjects were assigned in a randomized, double-blind, crossover design to receive nitrate-rich beetroot juice (NO3, 9 mmol) and placebo (PLA) 2.5 h prior to the completion of a double-step knee-extensor exercise protocol that included a transition from unloaded to moderate-intensity exercise (MOD) followed immediately by a transition to intense exercise (HIGH). Compared with PLA, NO3 increased plasma levels of nitrate and nitrite. During MOD, leg VO2 and leg blood flow (LBF) were reduced to a similar extent (∼9-15 %) in NO3. During HIGH, leg VO2 was reduced by ∼6-10 % and LBF by ∼5-9 % (did not reach significance) in NO3. Leg VO2 kinetics was markedly faster in the transition from passive to MOD compared with the transition from MOD to HIGH both in NO3 and PLA with no difference between PLA and NO3. In NO3, a reduction in nitrate and nitrite concentration was detected between arterial and venous samples. No difference in the time to exhaustion was observed between conditions. In conclusion, elevation of plasma nitrate and nitrate reduces leg skeletal muscle VO2 and blood flow during exercise. However, nitrate supplementation does not enhance muscle VO2 kinetics during exercise, nor does it improve time to exhaustion when exercising with a small muscle mass. 

AB - Dietary nitrate supplementation has been shown to reduce pulmonary O2 uptake during submaximal exercise and enhance exercise performance. However, the effects of nitrate supplementation on local metabolic and hemodynamic regulation in contracting human skeletal muscle remain unclear. To address this, eight healthy young male sedentary subjects were assigned in a randomized, double-blind, crossover design to receive nitrate-rich beetroot juice (NO3, 9 mmol) and placebo (PLA) 2.5 h prior to the completion of a double-step knee-extensor exercise protocol that included a transition from unloaded to moderate-intensity exercise (MOD) followed immediately by a transition to intense exercise (HIGH). Compared with PLA, NO3 increased plasma levels of nitrate and nitrite. During MOD, leg VO2 and leg blood flow (LBF) were reduced to a similar extent (∼9-15 %) in NO3. During HIGH, leg VO2 was reduced by ∼6-10 % and LBF by ∼5-9 % (did not reach significance) in NO3. Leg VO2 kinetics was markedly faster in the transition from passive to MOD compared with the transition from MOD to HIGH both in NO3 and PLA with no difference between PLA and NO3. In NO3, a reduction in nitrate and nitrite concentration was detected between arterial and venous samples. No difference in the time to exhaustion was observed between conditions. In conclusion, elevation of plasma nitrate and nitrate reduces leg skeletal muscle VO2 and blood flow during exercise. However, nitrate supplementation does not enhance muscle VO2 kinetics during exercise, nor does it improve time to exhaustion when exercising with a small muscle mass. 

KW - Faculty of Science

KW - O2 uptake kinetics

KW - Knee-extensor exercise

KW - Nitrite

U2 - 10.1113/JP281995

DO - 10.1113/JP281995

M3 - Journal article

C2 - 34587650

VL - 599

SP - 5203

EP - 5214

JO - The Journal of Physiology

JF - The Journal of Physiology

SN - 0022-3751

IS - 23

ER -