Acute L-arginine supplementation reduces the O2 cost of moderate-intensity exercise and enhances high-intensity exercise tolerance

It has recently been reported that dietary nitrate (NO3-) supplementation, which increases plasma nitrite (NO2-) 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 NO2- concentration was significantly greater in the Arg than the PL group (331 +/- 198 vs. 159 +/- 102 nM, P < 0.05) and systolic blood pressure was significantly reduced (123 +/- 3 vs. 131 +/- 5 mmHg, P < 0.01). The steady-state O-2 uptake ((V) over dotO(2)) during moderate-intensity exercise was reduced by 7% in the Arg group (1.48 +/- 0.12 vs. 1.59 +/- 0.14 l/min, P < 0.05). During severe-intensity exercise, the (V) over dotO(2) slow component amplitude was reduced (0.58 +/- 0.23 and 0.76 +/- 0.29 l/min in Arg and PL, respectively, P < 0.05) and the time to exhaustion was extended (707 +/- 232 and 562 +/- 145 s in Arg and PL, respectively, P < 0.05) following consumption of Arg. In conclusion, similar to the effects of increased dietary NO3- intake, elevating NO bioavailability through dietary L-Arg supplementation reduced the O-2 cost of moderate-intensity exercise and blunted the (V) over dotO(2) slow component and extended the time to exhaustion during severe-intensity exercise.