Effects of nitrate supplementation on repeated sprint performance in healthy subjects

Introduction: Several studies have shown that short term (3-6 days) of either pharmacological (NaNO3- and KNO3-) or dietary nitrate (NO3-) supplementation reduces the whole body oxygen cost during continuous moderate-intensity exercise, improving eendurance exercise tolerance. Furthermore, The nitrate supplementation appears to be particularly effective in enhancing performance in hypoxia (Kenjale et al. 2011; Vanhatalo et al. 2011; Masschelein et al. 2012) and it may specifically improve O2 delivery and force production in type II muscle fibres (Hernandez et al.2012, Ferguson et al. 2013). During high-intensity intermittent exercise, type II muscle fibres are heavily recruited. Thus, an impaired O2delivery/O2uptake may result in the development of muscle hypoxia, as well as low muscle pH and disturbances of ionic balance. The aim of this study was to examine in vivo the effects of nitrate supplementation (by spinach juice) on intermittent high-intensity performance. Methods: Seven healthy male subjects (age: 25 ± 2 years) participated in a randomized double-blind placebo-controlled cross-over study. They were tested after 6 days of supplementation of either 0.5 l per day of spinach juice (5.5 mol/day nitrate) (SPINACH) or placebo (PLACEBO). Subjects performed a Repeated Sprint Ability test (RSA), which consisted in five “all out” 6 seconds sprints on a cycloergometer (894E, Monark, Sweden) separated by 24 seconds of inactive recovery. Results: After PLACEBO, plasma [NO3-] and [NO2-] were 11 ± 2 µM and 0.3 ± 0.04 µM, respectively. After SPINACH, plasma [NO3-] significantly increased to 127 ± 24 µM, whereas [NO2-] was not significantly different from PLACEBO (0.3 ± 0.04 µM). As for RSA, there was no difference in absolute peak power output of the first two sprints between SPINACH (701.9 ± 8.1 and 703.9 ± 8.0 W) and PLACEBO (684.4 ± 6.7 and 690.3 ± 7.1 W). In contrast, the peak power output of the 3rd, 4th and 5th sprint were significantly higher in SPINACH (695.9 ± 8.3, 682.5 ± 7.6 and 666.1 ± 7.1 W, respectively) than in PLACEBO (663.9 ± 6.5, 641.2 ± 7.2 and 622.1 ± 7.2 W, respectively). Conclusion: This study has shown that short term dietary nitrate supplementation can improve repeated sprint performance in healthy subjects. This finding suggestconfirmed that NO3- may be an effective ergogenic aid not only for endurance-typeaerobic activitiesperformance but also for team sport or racquet players.