Introduction: L-arginine is a semi-essential amino acid that can affect some physiological responses, including protein synthesis and carbohydrate and fat metabolism. This study aimed to investigate the acute effect of L-arginine supplementation on fat and carbohydrate metabolism before, during, and after endurance exercise of athletes.
Methods: The present study was a single-blind crossover design with one group which were 16 to 20-year-old male football players from Shahrood city. This research was the time series model (including two time series of L-arginine or placebo consumption with an interval of two weeks) with repeated measurements In this way, on the testing day and after measuring the weight and height, the first stage of blood sampling was performed and the gas analyzer test was performed at rest, then the subjects consumed six grams of L-arginine or a placebo along with 400 ml of water. After 45 minutes, the second stage of blood sampling was done and the Bruce test was performed on a treadmill. Immediately after the test, the third stage of blood sampling was done and after 30 minutes of rest, the subjects participated in the last stage of blood sampling. blood samples’ and respiratory gases’ data were analyzed using an analysis of variance with repeated measures and Bonferroni correction.  
Results: Acute consumption of L-arginine supplement decreased maximal fat oxidation and increased maximal carbohydrate oxidation and respiratory exchange ratio after progressive physical activities (P=0.001). In addition, acute L-arginine supplementation increased blood glucose (P=0.001) and glycerol concentrations (P=0.02).
Conclusion: Based on the findings of this study, acute consumption of L-arginine supplement lead to an increase in endurance performance and changes in metabolism during exercise in athletes.