Ergogenic effects of beetroot juice supplementation during severe-intensity exercise in obese adolescents.

Previous studies showed a higher O2 cost of exercise, and therefore a reduced exercise tolerance, in obese patients during constant work rate (CWR) exercise compared to healthy subjects. Among the ergogenic effects of dietary nitrate (NO3-) supplementation in sedentary healthy subjects, a reduced O2 cost and enhanced exercise tolerance have often been demonstrated. The aim of this study was to evaluate the effects of beetroot juice supplementation, rich in NO3-, on physiological variables associated with exercise tolerance in obese adolescents. In a double-blind, randomized, crossover study, ten obese adolescents (8F, 2M; age=16{plus minus}1 yr; BMI=35.2{plus minus}5.0 kg.m-2) were tested after 6 days of supplementation with beetroot juice (5 mmol NO3- per day) (BR) or placebo (PLA). Following each supplementation period, patients carried out two repetitions of 6-min moderate-intensity CWR exercise and one severe-intensity CWR exercise until exhaustion. Plasma NO3- concentration was significantly higher in BR vs. PLA (108{plus minus}37 vs. 15{plus minus}5 ?M, P<0.0001). The O2 cost of moderate-intensity exercise was not different in BR vs. PLA (13.3{plus minus}1.7 vs. 12.9{plus minus}1.1 mL.min-1.W-1, P=0.517). During severe-intensity exercise, signs of a reduced amplitude of the O2 uptake slow component were observed in BR, in association with a significantly longer time to exhaustion (561{plus minus}198 s in BR vs. 457{plus minus}101 s in PLA, P=0.0143). In obese adolescents, short-term dietary NO3- supplementation is effective in improving exercise tolerance during severe-intensity exercise. This may prove to be useful in contrasting early fatigue and reduced physical activity in this at-risk population.