Chronic, But Not Acute, Oral L-Arginine Supplementation Attenuates Exercise-Induced Ammonia Accumulation in Healthy Young Men: A Randomised, Double-Blind, Cross-Over, Placebo-Controlled Trial

Background This study examined the effects of a single and continuous oral intake of L-arginine supplementation on blood metabolites 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 (L-arginine was replaced with dextrin) and performed cycling exercise at 75 % of heart rate reserve for 60 min, followed by a 15-min cycling performance test. The participants continued to consume each designated supplement twice a day for 13 days. For the chronic trials, the participants 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. The linear mixed model was used to examine between-trial differences over the 1-day or 2-week intervention for outcome variables. Results Plasma ammonia concentrations were lower in the chronic arginine (43.5 ± 27.6 µmol/L) trial than in both acute arginine (52.1 ± 36.3 µmol/L, 95% confidence interval − 15.907 to − 1.318 µmol/L, Effect size = 0.262) and placebo (51.1 ± 32.7 µmol/L, 95% confidence interval − 14.932 to − 0.343 µmol/L, Effect size = 0.249) trials (p < 0.05). No differences were found in mean power output during the performance test between the chronic arginine (169.3 ± 8.6 W) and placebo (168.8 ± 2.3 W) trials (p > 0.05). Conclusions These results indicate that a continuous oral intake of L-arginine supplementation attenuated ammonia accumulation, but this did not influence cycling performance.