# Influence of Sex and Acute Beetroot Juice Supplementation on 2 KM Running Performance
## 4 Discussion
Therefore, BJ supplementation might boost middle distance running performance by attenuating fatigue development over the latter stages of the race. Supplementation with BJ resulted in a comparable improvement in 2 km running TT performance in the present study in males (0.9%) and females (1%). Although the effects of NO3- supplementation on running TT performance in males has been addressed in several studies [32; 33; 34; 35; 38], and while some previous studies have assessed running performance in female subjects [30; 36; 37], independent effects in males and females were not reported in the latter group of studies, which has thwarted understanding of potential sex-specific effects of NO3- supplementation on performance. Moreover, the only study to assess the effects of BJ supplementation on performance in recreational female runners did not observe an improvement in 3 km TT performance [42]. However, the interpretation of this finding is confounded by the fact that the authors administered an acute BJ dose 30 min prior to the TT, which was insufficient time to allow plasma [NO2-] to peak after NO3- ingestion [43]. In spite of previous reports that plasma [NO2-] is increased more after BJ supplementation in females than males [39] and that males might present with a preferential phenotype to aid the reduction of NO2- to NO [41], comparable improvements in 2 km running performance after BJ supplementation were observed across sexes in the present study. Therefore, an important novel contribution of the current study is that BJ supplementation appears similarly ergogenic in male and female recreational runners completing a 2 km TT. Previous studies have linked the ergogenic effects of NO3- supplementation to improvements in skeletal muscle perfusion, metabolic control and contractility [7]. In the present study, RPEgeneral was lower after the 2 km TT in the BJ compared to the PL condition in both the male and female subjects. A lower RPE has been observed in some studies that report improved running performance after BJ supplementation [28; 36]. However, there are also studies reporting improved running performance in the absence of changes of RPE [32; 35; 38]. The lowering in RPEgeneral after BJ supplementation might be a function of an increase in brain perfusion [55] or a lowering in muscle metabolite accumulation [56], which would subsequently attenuate activation of type III/IV muscle afferent feedback to the central nervous system and the potential for central fatigue development [57]. Further research is required to resolve the underlying mechanisms for improved performance following BJ supplementation. It is acknowledged that a limitation of the current study is that we did not assess plasma [NO2-] to ascertain whether this was increased to a greater extent in females compared to males, as reported previously [39]. In addition, the menstrual cycle of female subjects was not controlled in the current study. Dietary supplementation with BJ has emerged as a nutritional strategy to enhance exercise performance under certain experimental conditions [7]. However, much of the existing understanding of the ergogenic potential of BJ supplementation is derived from studies conducted exclusively on male subjects. This is a limitation not just of the NO3- supplementation literature, but is emblematic of sport science research more generally [58]. Therefore, further research is required to elucidate whether males and females exhibit similar or divergent responses to various interventions with the potential to enhance exercise performance. Such information is vital to administer bespoke, evidence-based ergogenic interventions for males and females prior to competition. With regard to potential sex-specific effects of NO3- supplementation, it has been reported that females present with an oral microbiome that is more conducive to oral NO3- reduction and results in a plasma [NO2-] after NO3- supplementation [39]. On the other hand, males might present with a phenotype that favors NO2- reduction to NO during exercise [41].