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

Previous studies showed a higher O-2 cost of exercise, and therefore, a reduced exercise tolerance in patients with obesity during constant work rate (CWR) exercise compared with healthy subjects. Among the ergogenic effects of dietary nitrate (NO3-) supplementation in sedentary healthy subjects, a reduced O-2 cost and enhanced exercise tolerance have often been demonstrated. The aim of this study was to evaluate the effects of beetroot juice (BR) supplementation, rich in NO3-, on physiological variables associated with exercise tolerance in adolescents with obesity. In a double-blind, randomized crossover study, 10 adolescents with obesity (8 girls, 2 boys; age = 16 +/- 1 yr; body mass index = 35.2 +/- 5.0 kg/m(2)) were tested after 6 days of supplementation with BR (5 mmol NO3- per day) 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 versus PLA (108 +/- 37 vs. 15 5 mu M, P < 0.0001). The O-2 cost of moderate-intensity exercise was not different in BR versus PLA (13.3 +/- 1.7 vs. 12.9 +/- 1.1 ml.min(-1).W-1, P = 0.517). During severe-intensity exercise, signs of a reduced amplitude of the O-2 uptake slow component were observed in BR, in association with a significantly longer time to exhaustion (561 +/- 198 s in BR vs. 457 +/- 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 counteracting early fatigue and reduced physical activity in this at-risk population.