Objective: This study examined the effects of a single and chronic oral intake of L-arginine supplementation on blood ammonia concentration and exercise performance. Methods: Sixteen healthy young men (mean ± standard deviation, 23 ± 3 years) participated in a randomised, double-blind, cross-over, placebo-controlled study. For the acute trials, the participants consumed 200 mL of water containing either L-arginine (5 g) or placebo (dextrin; 5.5 g) and performed cycling exercise at 75% of heart rate reserve for 60 min, followed by a 15-min cycling performance test. For the chronic trials, the participants continued to consume each designated supplement twice a day for another 13 days, and then repeated the same protocol as the acute trials at day 15. After a 14-day washout period, the participants changed the supplement and repeated the same protocol as above. Results: Plasma ammonia concentrations were lower in the chronic arginine trial than those in both acute placebo (mean difference - 4.5 μmol/L) and acute arginine (mean difference - 5.1 μmol/L) trials (p < 0.05). There was no difference in plasma ammonia concentration between the chronic arginine and chronic placebo trials (mean difference - 1.2 μmol/L). No differences were found in mean power output during the performance test between the chronic arginine and chronic placebo trials (mean difference 0.5 W) or between the acute arginine and acute placebo trials (mean difference 0.0 W). Conclusions: An acute and chronic oral intake of L-arginine supplementation did not attenuate exercise-induced increases in ammonia accumulation or had no significant impact on cycling performance.
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