<scp>l</scp>-Citrulline supplementation improves O₂ uptake kinetics and high-intensity exercise performance in humans

<jats:p> 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<jats:sub>2</jats:sub> uptake (V̇o<jats:sub>2</jats:sub>) 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 &lt; 0.001) with Cit supplementation. Plasma nitrite (NO<jats:sub>2</jats:sub><jats:sup>−</jats:sup>) concentration was increased with Arg supplementation ( P &lt; 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 &lt; 0.05) after Cit supplementation. The steady-state V̇o<jats:sub>2</jats:sub> amplitude during moderate-intensity cycle exercise was not significantly different between supplements, but Cit lowered the V̇o<jats:sub>2</jats:sub> mean response time (59 ± 8 and 53 ± 5 s with Pla and Cit, respectively, P &lt; 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 &lt; 0.05). These variables were not altered by Arg supplementation ( P &gt; 0.05). In conclusion, these results suggest that short-term Cit, but not Arg, supplementation can improve blood pressure, V̇o<jats:sub>2</jats:sub> kinetics, and exercise performance in healthy adults. </jats:p>