# Influence of Sex and Acute Beetroot Juice Supplementation on 2 KM Running Performance
## 1 Introduction  
Consumption of dietary supplements is a common pre-competition strategy for athletes competing in a variety of sports at different competitive standards in an attempt to enhance performance [1, 2, 3, 4, 5, 6]. Although not unequivocal, there is evidence to suggest that dietary supplementation with inorganic nitrate (NO3\({}^{-}\)) can enhance exercise performance in a variety of settings [7, 8]. After ingestion, NO3\({}^{-}\) undergoes a stepwise reduction to nitrite (NO2\({}^{-}\)) and then nitric oxide (NO), with the latter step augmented in conditions of acidosis and hypoxia, and believed to be responsible for the ergogenic effects of NO3\({}^{-}\) supplementation [7, 9]. NO is a potent signalling molecule that elicits biological effects on numerous tissues and is involved in an array of physiological processes including, but not limited to, vasodilation, calcium handling, mitochondrial respiration, and neurotransmission [9]. Most of the research assessing the ergogenic potential of NO3\({}^{-}\) supplementation to date has been conducted in males completing cycling exercise [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27]. This experimental approach has limited wider understanding of the settings in which NO3\({}^{-}\) supplementation is more and less likely to be ergogenic. In studies assessing the effect of NO3\({}^{-}\) supplementation on running exercise responses, improved economy has been reported in recreationally active and moderately trained subjects, but not highly trained subjects [28, 29, 30, 31, 32, 33], whereas improved time to exhaustion has beenreported in both recreationally active [29] and highly trained [28] subjects. During running time trial (TT) performance tests in well trained endurance athletes, most studies [30; 32; 33; 34; 35] have observed no change in performance over distances spanning 1.5-10 km after NO3\({}^{-}\) supplementation, but improved performance appears more likely over a shorter distance (1.5 km) compared to a longer distance (10 km) in this population after acute NO3\({}^{-}\) supplementation [36]. The effect of NO3\({}^{-}\) supplementation on running TT performance is less clear in recreationally active and moderately trained subjects with improvements in 3 km [32] and 5 km [37] performance having been observed in some studies, and no improvement in 5 km [36] and 10 km [38] performance having been observed in other studies. Therefore, further research is required to address the effect of NO3\({}^{-}\) supplementation on middle distance (<5 km) running TT performance in moderately trained subjects. Moreover, since NO3\({}^{-}\) supplementation has been reported to improve performance over the first half, but not the second half, of a 10 km TT [38], and to improve 5 km performance by mostly enhancing performance in the latter stages on the TT [36], further research is required to address which phases of TT performance are most likely to be enhanced by NO3\({}^{-}\) supplementation. To date, the majority of studies assessing the effect of NO3\({}^{-}\) supplementation on running performance have either used exclusively male subjects [32; 33; 34; 38], or not reported data for each sex to allow potential sex-specific effects of NO3\({}^{-}\) supplementation on running TT performance to be understood [30; 36; 37]. There is some evidence that, relative to males, females exhibit a greater increase in plasma [NO2\({}^{-}\)] [39] and greater improvements in muscle contractile function [40] after NO3\({}^{-}\) supplementation. However, females present with a more oxidative skeletal muscle phenotype compared to males [41], which could blunt NO2\({}^{-}\) reduction to NO and the improvement in performance after NO3\({}^{-}\) supplementation. Although [PERSON] et al. [42] reported no effect of acute NO3\({}^{-}\) supplementation on 3 km running TT performance in untrained women, the NO3\({}^{-}\) supplement was ingested 30 min prior to exercise such that plasma [NO2\({}^{-}\)] would not have peaked until after the TT had been completed [43].