Effects of Chronic Supplementation of L‐Arginine on Physical Fitness in Water Polo Players

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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 (n = 9) or placebo (n = 8) 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 (PGC1α) 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.