Acute <scp>l</scp>-arginine supplementation reduces the O₂ cost of moderate-intensity exercise and enhances high-intensity exercise tolerance

<jats:p> It has recently been reported that dietary nitrate (NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>) supplementation, which increases plasma nitrite (NO<jats:sub>2</jats:sub><jats:sup>−</jats:sup>) concentration, a biomarker of nitric oxide (NO) availability, improves exercise efficiency and exercise tolerance in healthy humans. We hypothesized that dietary supplementation with l-arginine, the substrate for NO synthase (NOS), would elicit similar responses. In a double-blind, crossover study, nine healthy men (aged 19–38 yr) consumed 500 ml of a beverage containing 6 g of l-arginine (Arg) or a placebo beverage (PL) and completed a series of “step” moderate- and severe-intensity exercise bouts 1 h after ingestion of the beverage. Plasma NO<jats:sub>2</jats:sub><jats:sup>−</jats:sup> concentration was significantly greater in the Arg than the PL group (331 ± 198 vs. 159 ± 102 nM, P &lt; 0.05) and systolic blood pressure was significantly reduced (123 ± 3 vs. 131 ± 5 mmHg, P &lt; 0.01). The steady-state O<jats:sub>2</jats:sub> uptake (V̇o<jats:sub>2</jats:sub>) during moderate-intensity exercise was reduced by 7% in the Arg group (1.48 ± 0.12 vs. 1.59 ± 0.14 l/min, P &lt; 0.05). During severe-intensity exercise, the V̇o<jats:sub>2</jats:sub> slow component amplitude was reduced (0.58 ± 0.23 and 0.76 ± 0.29 l/min in Arg and PL, respectively, P &lt; 0.05) and the time to exhaustion was extended (707 ± 232 and 562 ± 145 s in Arg and PL, respectively, P &lt; 0.05) following consumption of Arg. In conclusion, similar to the effects of increased dietary NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup> intake, elevating NO bioavailability through dietary l-Arg supplementation reduced the O<jats:sub>2</jats:sub> cost of moderate-intensity exercise and blunted the V̇o<jats:sub>2</jats:sub> slow component and extended the time to exhaustion during severe-intensity exercise. </jats:p>