Effects of dietary nitrate on the O2 cost of submaximal exercise: Accounting for “noise” in pulmonary gas exchange measurements

Abstract

ABSTRACT Dietary nitrate (NO3 –) supplementation can reduce the oxygen cost of submaximal exercise, but this has not been reported consistently. We hypothesised that the number of step transitions to moderate-intensity exercise, and corresponding effects on the signal-to-noise ratio for pulmonary O2, may be important in this regard. Twelve recreationally active participants were assigned in a randomised, double-blind, crossover design to supplement for 4 days in three conditions: 1) control (CON; water); 2); PL (NO3 –-depleted beetroot juice); and 3) BR (NO3 –-rich beetroot juice). On days 3 and 4, participants completed two 6-min step transitions to moderate-intensity cycle exercise. Breath-by-breath O2 data were collected and O2 kinetic responses were determined for a single transition and when the responses to 2, 3 and 4 transitions were ensemble-averaged. Steady-state O2 was not different between PL and BR when the O2 response to one-, two- or three-step transition was compared but was significantly lower in BR compared to PL when four-step transitions was considered (PL: 1.33 ± 0.34 vs. BR: 1.31 ± 0.34 L·min−1, P < 0.05). There were no differences in pulmonary O2 responses between CON and PL (P > 0.05). Multiple step transitions may be required to detect the influence of NO3 − supplementation on steady-state O2.