Acute Ingestion of Dietary Nitrate Does Not Enhance Running Performance in Highly-Trained Endurance Athletes

Dietary nitrate supplementation has been shown to reduce the oxygen cost of submaximal exercise and improve tolerance of high-intensity exercise in man. Limited data are available regarding the effects of nitrate ingestion during simulated competition, and it remains to be determined whether nitrate supplementation has performance-enhancing effects in highly-trained athletes. The present study examined the effects of acute dietary nitrate supplementation on the oxygen cost of submaximal exercise and endurance running time-trial performance in highly-trained athletes. Ten Norwegian male junior-elite cross-country skiers (maximum oxygen uptake ≈70 mL/kg/min) each completed two trials in a randomised, double-blind, cross-over design. Participants received dietary supplementation with potassium nitrate (614 mg nitrate) or a nitrate-free placebo 2.5 h before performing two 5-min submaximal exercise tests on a treadmill at 10 km/h (≈55% of maximum oxygen uptake) and 14 km/h (≈75% of maximum oxygen uptake), followed by a 5-km running time-trial on an indoor track. Ozone-based chemiluminescence was employed for plasma detection of nitric oxide metabolites. A paired two-tailed t-test was used to identify difference between means and a two-way general linear model for repeated measures (treatment x time) was used to identify differences over time. Data are means ± standard deviation and statistical significance was set at the 0.05 level. Plasma nitrite concentrations were higher after nitrate supplementation (325 ± 95 nmol/L) compared with placebo (143 ± 59 nmol/L, p<0.001). There was no significant difference in 5-km time-trial performance between nitrate (1005 ± 53 s) and placebo treatments (996 ± 49 s, p=0.124). The oxygen cost of submaximal running was not significantly different between placebo and nitrate trials at 10 km/h (both 2.84 ± 0.34 L/min) and 14 km/h (3.89 ± 0.39 L/min versus 3.77 ± 0.62 L/min). These results suggest that acute ingestion of dietary nitrate may not represent an effective strategy for reducing the oxygen cost of submaximal exercise or for enhancing endurance running performance compared to a nitrate-free placebo in this group of highly trained athletes.