Supplementation with beetroot juice (BR), which is rich in inorganic nitrate (NO3-), has received considerable attention due to its beneficial effects on several physiological functions. For example, BR has led to lowered resting blood pressure (BP) and a reduced oxygen (O2) cost during moderate-intensity exercise in healthy individuals, as well as improved maximal performance (1). Similar beneficial effects in athletes are less clear (2). The anaerobic reduction of NO3- to nitrite (NO2-) in the oral cavity increases the bioavailability of nitric oxide (NO), which is thought to explain the ergogenic effect of BR. Since NO is generally produced endogenously using O2 and multiple cofactors (3), any reduction in O2 availability would attenuate this NO-pathway. Therefore, BR supplementation is believed to have a more pronounced effect in hypoxia (H). The aim of the present study was to investigate the effects of BR supplementation in competitive cross-country skiers exercising in normoxia (N) and H.
Using a randomised crossover design, eight competitive cross-country skiers (5 males: age 22 +/- 3 y, body mass 74 +/- 8 kg, VO2max 5.2 +/- 0.4 L/min; 3 females: age 21 +/- 1 y, body mass 63 +/- 6 kg, VO2max 3.7 +/- 0.5 L/min;) supplemented with a single dose of NO3- (ca 13 mmol) or placebo (PL) performed two, 6-min submaximal exercise bouts and a 1000-m time-trial (TT) in N and H (16.8% O2). All tests were conducted on roller skis at a 6-degree incline using the diagonal-stride technique. Resting BP, blood O2 saturation (SpO2), VO2, respiratory exchange ratio (RER), heart rate (HR), rating of perceived exertion (RPE), blood lactate (La-) and time to complete the 1000-m TT (TTtime) were measured.
Plasma NO3- and NO2- levels were significantly higher following BR compared to PL (p < 0.001). However, resting BP, submaximal exercise variables and TTtime were unaffected by supplementation (p > 0.05). The VO2max obtained during the TT was significantly lower with BR in N (p < 0.05, small effect size d < 0.2), but not H.
Previous studies have shown beneficial effects of NO3- supplementation among well-trained athletes (4). In addition, individuals showing no effects of NO3- supplementation in N have nevertheless shown improved exercise tolerance in H (5). These findings were not reproduced in the current study, with no improvements in submaximal VO2 or TTtime following BR supplementation in N or H.
BR supplementation does not improve submaximal exercise economy or 1000-m TT performance in competitive cross-country skiers exercising in normoxic or hypoxic conditions.
1. Vanhatalo et al. 2010. Am J Physiol Regul Integr Comp Physiol. 299:R1121-31
2. Peacock et al. 2012. Med Sci Sports Exerc. 44:2213-19
3. Lundberg et al. 2015. Nat Rev Drug Discov. 14:623-41
4. Lansley et al. 2011. Med Sci Sports Exerc. 43:1125-31
5. Kelly et al. 2014. Am J Physiol Regul Integr Comp Physiol. 307:R920-30