Abstract

It has been suggested that the supplementation of dietary inorganic nitrate (NO3 –) has a profound ability to improve muscle efficiency and endurance exercise tolerance (Bailey et al., 2009, Journal of Applied Physiology, 107, 1144-1155) in addition to modulating resting blood pressure and energy metabolism (Kapil et al., 2010, Hypertension, 56, 274-281). NO3 – has been reported to increase nitrate oxide (NO) bioavailability and the subsequent concentrations of plasma nitrate levels, leading to increased blood flow. Current literature has predominantly focused on the effects of NO3 – on cycling and rowing time trial performance, with limited research examining the effectiveness of NO3 – on high intensity intermittent sports performance within the female population. Therefore, the purpose of this study was to investigate the effects of NO3 – on performance of the Yo-Yo Intermittent Recovery Level 1 Test (YYIR1) with female university level athletes. This study adopted a randomised controlled crossover, repeated measures design with single-blind measures. Following institutional ethical approval, ten female participants volunteered for the study (mean age 21 ± 1.3 years, stature 165.6 ± 7.6 cm, body mass 60.89 ± 5.7 kg). Participants completed one familiarisation and two experimental trials, separated by seven days. In the experimental trials, participants consumed either 70cl of nitrate concentrated beetroot juice or a 70cl placebo of nitrate depleted beetroot juice 2.5 hours prior to completing the YYIR1. Participants were instructed to refrain from eating foods high in NO3 – during testing. Upon arrival, resting HR and blood lactate (BL) were measured. At the end of each stage interval (IV) (IV1 – 5.1km/h, IV2 – 9.1km/h, IV3 – 11.2km/h, IV4 – 12.3km/h) HR and rate of perceived exertion (RPE) were recorded using the Borg scale (6-20). Following exhaustion, BL and HR were recorded immediately post-test and at four and eight minutes during recovery. Total distance (m) achieved was used as a performance measure to estimate VO2max. Data was analysed using a paired-samples t-test and factorial repeated measures analysis of variance (ANOVA), with Bonferroni post-hoc tests implemented and statistical significance accepted at P<0.05. Based on previous empirical evidence, it is hypothesised that NO3 – supplementation would increase VO2max, extending total distance covered and thus time to exhaustion. It is also hypothesised that NO3 – would reduce BL accumulation during the YYIR1 and improve the efficiency of lactate dissipation during recovery. These findings contribute to the growing literature regarding NO and could be useful in the sports nutrition and performance industries.