Acute Administration of Inorganic Nitrate Reduces V˙O2peak in Endurance Athletes

Purpose: Humans can reduce inorganic nitrate (NO3-) to nitrite (NO2-), nitric oxide (NO), and other bioactive nitrogen oxides. The purpose of this study was to test the hypothesis that a single dose of inorganic nitrate before exercise might enhance the tolerance of endurance athletes to high intensity exercise. Methods: Eleven cyclists (age = 34.3 ± 4.8 yr, V·O2peak = 65.1 ± 6.2 mL·kg-1·min-1) participated in this randomized, double-blind, crossover study. Subjects received dietary supplementation with nitrate (NaNO3 10 mg·kg-1 of body mass) or a placebo (NaCl) 3 h before exercise. They then performed a cycle ergometer test that consisted of four 6-min submaximal workloads, corresponding to 2.0, 2.5, 3.0, and 3.5 W·kg-1 of body mass, interspersed with 3 min of passive recovery. After a 5-min recovery period, subjects performed one incremental exercise test until exhaustion. Results: Plasma nitrate and nitrite were significantly higher (P < 0.05) 3 h after supplementation (nitrate = 250 ± 80 µM, nitrite = 2313 ± 157 nM) than after the placebo (nitrate = 29 ± 8 µM, nitrite = 1998 ± 206 nM) at resting conditions. Nitrate supplementation significantly reduced V·O2peak (nitrate = 4.64 ± 0.35 L·min-1, placebo = 4.82 ± 0.33 L·min-1, P = 0.010) and the ratio between V·O2 and power at maximal intensity (nitrate = 11.2 ± 1.1 mL·min-1·W-1, placebo = 11.8 ± 1.1 mL·min-1·W-1, P = 0.031). This reduction of V·O2 occurred without changes in the time to exhaustion (nitrate = 416 ± 32 s, placebo = 409 ± 27 s) or in the maximal power (nitrate = 416 ± 29 W, placebo = 410 ± 28 W). Conclusions: A single oral dose of inorganic nitrate acutely reduces V·O2peak without compromising the maximal exercise performance