Effect of acute nitrate ingestion on V̇O₂ response at different exercise intensity domains

While nitrate supplementation influences oxygen uptake (V̇O₂) response to exercise, this effect may be intensity dependent. The purpose of this study was to investigate the effect of acute nitrate supplementation on V̇O₂ response during different exercise intensity domains in humans. Eleven men ingested 10 mg·kg^-1 body mass (8.76 ± 1.35 mmol) of sodium nitrate or sodium chloride (placebo) 2.5 h before cycling at moderate (90% of gas exchange threshold; GET), heavy (GET + 40% of the difference between GET and peak oxygen uptake (V̇O_2peak), Δ 40) or severe (GET + 80% of the difference between GET and V̇O_2peak, Δ 80) exercise intensities. Volunteers performed exercise for 10 min (moderate), 15 min (heavy) or until exhaustion (severe). Acute nitrate supplementation had no effect on any V̇O₂ response parameters during moderate and severe exercise intensities. However, the V̇O₂ slow amplitude (nitrate: 0.93 ± 0.36 L·min^-1 vs. placebo: 1.13 ± 0.59 L·min^-1, p = 0.04) and V̇O₂ slow gain (nitrate: 5.81 ± 2.37 mL·min^-1·W^-1 vs. placebo: 7.09 ± 3.67 mL·min^-1·W^-1, p = 0.04) were significantly lower in nitrate than in placebo during the heavy exercise intensity. There was no effect of nitrate on plasma lactate during any exercise intensity (p > 0.05). Time to exhaustion during the severe exercise intensity was also not affected by nitrate (p > 0.05). In conclusion, acute nitrate supplementation reduced the slow component of V̇O₂ only when performing heavy-intensity exercise, which might indicate an intensity-dependent effect of nitrate on V̇O₂ response.