Effects of nitrate supplementation on aerobic performance in subjects with different fitness level

Introduction Dietary supplementation with either sodium nitrate or nitrate-rich beetroot juice has been consistently shown to reduce the oxygen demand of submaximal exercise (1) and improve time to exhaustion during high-intensity exercise (3,5). However, the ergogenic effect of nitrate supplementation in well-trained endurance athletes remains uncertain (2,4). Aim of this study was to evaluate the effects of short-term nitrate [NO3-] supplementation on aerobic performance in subjects with different fitness level. Material and Methods Twenty-one subjects (22.7±1.8 years, mean±SD) with different fitness level were involved in a randomized double-blind crossover study. Subjects were tested after 6 days of supplementation with either 0.5 l per day of nitrate-containing (5.0 mmol) water (NITR) or nitrate-free water (PLA). Participants performed an incremental running test in order to assess their peak oxygen uptake (V’O2peak). Several repetitions of sub-maximal (about 60% V’O2peak) constant load exercises on a motorized treadmill and a 3-km running time trial on the field were also performed. Results V’O2peak value ranged from 34 to 63 ml*kg-1*min-1. Plasma [NO3-] was 13.4±5.7 μM and 83.5±37.7μM in PLA and NITR respectively. During constant-load exercise, V’O2 at steady-state was significantly lower in NITR (1.90 ± 0.4 L*min-1) compared with PLA (2.05 ± 0.4 L*min-1). There was a significant negative correlation between the V’O2peak value and the change in [NO3-] following NITR (R2 = 0.71, p<0.001) and between the V’O2peak value and the change in VO2 at steady state (R2 = 0.69, p<0.001). As for 3-km Time Trial, no significant differences were observed between PLA (766.5±140.8 sec) and NITR (766.4±135.6 sec). However, if only subjects with a low fitness level (<50 ml*kg-1*min-1) were considered, the 3-km running performance significantly improved after NITR. Conclusion The results of the present study suggest that individual fitness level affects the ergogenic benefits induced by [NO3-] supplementation. Discrepancy results in literature may be explained by different source and/or duration of nitrate supplementation. Further studies are needed to clarify the molecular mechanism underlying this process. References 1. Bailey SJ, Winyard P, Vanhatalo A, et al. J Appl Physiol 2009 2. Bescòs R, Ferrer-Roca V, Galilea PA, et al. Med Sci Sports Exerc 2012 3. Cermak NM, Gibala MJ, van Loon LJ. Int J Sport Nutr Exerc Metab 2012 4. Christensen PM, Nyberg M, Bangsbo J. Scand J Med Sci Sports 2013 5. Lansley KE, Winyard PG, Bailey SJ, et al. Med Sci Sports Exerc 2011