Background . Ergogenic nutritional supplementation is sought by professional athletes for improving physical performance; nevertheless, scientific evidence to support the chronic use of L-Arginine among water polo players is missing. Methods . Seventeen male professional water polo players were randomly assigned to assume 5 grams per day of L-Arginine ( ) or placebo ( ) for 4 weeks. The players’ fitness level was assessed in the maximal speed swimming test. Ear lobe blood samples taken before and after the effort for serum lactate content were analyzed. A speed-to-lactate ratio was generated at the baseline and after 4 weeks of treatment. We also tested the effects of L-Arginine in vitro , measuring NO production, mitochondrial respiration, and gene expression in human fibroblasts. Results . L-Arginine did not modify BMI, muscle strength, and maximal speed at 200 meters after 4 weeks. However, L-Arginine ameliorated oxidative metabolism to exercise as suggested by the statistically significant lower lactate-to-speed ratio, which was not observed in placebo-treated controls. In vitro , L-Arginine induced the expression of a key regulator of mitochondrial biogenesis (PGC1 α ) and genes encoding for complex I and increased the production of nitric oxide and the maximal oxygen consumption rate. Conclusions . Chronic L-Arginine is safe and effective in ameliorating the oxidative metabolism of professional water polo players, through a mechanism of enhanced mitochondrial function.
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