L-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans

The purpose of this study was to compare the effects of L-citrulline (Cit) and L-arginine (Arg) supplementation on nitric oxide (NO) biomarkers, pulmonary O-2 uptake ((V) over dot O-2) kinetics, and exercise performance. In a randomized, placebo (Pla)-controlled, crossover study, 10 healthy adult men completed moderate- and severe-intensity cycling exercise on days 6 and 7 of a 7-day supplementation period with Pla, Arg (6 g/day), and Cit (6 g/day). Compared with Pla, plasma Arg concentration was increased by a similar magnitude with Arg and Cit supplementation, but plasma Cit concentration was only increased (P < 0.001) with Cit supplementation. Plasma nitrite (NO2-) concentration was increased with Arg supplementation (P < 0.05) and tended to increase with Cit supplementation (P < 0.08) compared with Pla (83 +/- 25, 106 +/- 41, and 100 +/- 38 nM with Pla, Arg, and Cit, respectively); however, mean arterial blood pressure was only lower (P < 0.05) after Cit supplementation. The steady-state (V) over dot O-2 amplitude during moderateintensity cycle exercise was not significantly different between supplements, but Cit lowered the (V) over dot O-2 mean response time (59 +/- 8 and 53 +/- 5 s with Pla and Cit, respectively, P < 0.05) during severe-intensity exercise, improved tolerance to severe-intensity exercise (589 +/- 101 and 661 +/- 107 s with Pla and Cit, respectively), and increased the total amount of work completed in the exercise performance test (123 +/- 18 and 125 +/- 19 kJ with Pla and Cit, respectively, P < 0.05). These variables were not altered by Arg supplementation (P < 0.05). In conclusion, these results suggest that short-term Cit, but not Arg, supplementation can improve blood pressure, (V) over dot O-2 kinetics, and exercise performance in healthy adults.