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The purpose of this study consisted in analyzing the alterations in samples of Creatine Kinase (CK), Creatine and Urea, in male swimmers under creatine supplementation. Seventeen athletes took part in a sequence of tests in a swimming pool (8 x 100 m freestyle) with progressive sets starting at 65 leading up to a 100% maximum capacity sets. The athletes were evaluated immediately before and after the tests (5 min), in order to obtain levels of CK, Creatine and Urea concentrations. After 6 days of supplementation with Creatine (20 g/ day) + maltodextrin (1 g/kg/day) or nothing but maltodextrin control (1 g/kg/day), new tests similar to the initials, were performed. The variables were analyzed by non-parametric tests of Wilcoxon (in the same group) and Mann-Whitney (between the groups). In statistical terms, a significant level was established: p<0.05. On CK it was observed, after supplementation, a statistically significant increase in the Creatine group at rest (172.83 mg/ul ± 2.43 to 326.42 mg/ul ± 13.69) and in the end of the tests (202.32 mg/ul ± 21.85 to 363.33 mg/ul ± 20.53). The same occurred with the creatine concentration at rest (1.05 mg/dl ± 0.12 to 1.27 mg/dl ± 0.20) and in the end of the tests (1.23 mg/ dl ± 0.23 to 1.53 mg/dl ± 0.26) with the only tendency of a significant comparison with the control group (p = 0.06). Significant differences in urea concentrations were not observed. Introduction Creatine and creatine kinase Creatine is a nitrogenous amine. A normal diet can provide approximately 1 g of creatine obtained with the consumption of meat, fish and other products of animal origin. The indication of daily intake to maintain optimum levels of creatine is 2 g. The other needed gram is obtained through an endogenous production of amino acids as glycine, arginine and methionine, from the kidneys, the pancreas and the liver. This occurs through a transaminase reaction that transfers the amino group of arginine to glycine, ornithine and guanidinoacetate. This reaction is reversible with the presence of the transaminase enzyme. Creatine is then formed by the transfer of a methyl group from S-adenosilmationina to guanidinoacetate through a methyltransferase [1]. When creatine is produced by the body or when it is ingested in diet is almost entirely absorbed by the muscles and at that same time the enzyme creatine kinase promotes phosphorylation of creatine. Creatine in the muscle tissue cannot be synthesized, therefore the use, in this case, of a creatine/sodium transporter [2]. Phosphocreatine is formed by the association of muscle creatine with the phosphate group. In a high-intensity activity, intramuscular phosphocreatine and ATP are limited and stocks last around 10 seconds [3]. As with phosphocreatine, the substance turns itself into a cyclic product, creatinine that is excreted in urine about 2 g/day [4]. Phosphocreatine is directly involved in the formation of Adenosine triphosphate (ATP), and this reaction is catalyzed by Creatine kinase (CK): PCr + ADP + H + ↔ ATP + Cr. By muscle biopsy, it is possible to determine that the total average amount of creatine is 124.4 mmol/kg of dry weight muscle, and of this, 49.0 mmol/kg is free creatine (39%) and 75.4 mmol/kg phosphocreatine (61%). The remaining 5% of body creatine content are mainly located in the brain and in the heart. This distribution of creatine in the body indicates that it is carried through the bloodstream, from the places of synthesis to the places of use [3]. The total creatine and its derivatives can be increased up to 30% by supplementation, the mechanism through which creatine supplementation may have potential ergogenic effects consists in an increase of creatine and phosphocreatine in muscle content, which allows an increase in speed resynthesis of ATP, a decrease in muscle fatigue and a better recovery during repeated highintensity exercises [5]. The effects of creatine supplementation have been quite completely studied in sedentary or moderately trained individuals, in laboratory conditions. However, we know very little about their possible influence on well-trained athletes participating in competitions. The athletes who were supplemented with creatine showed better results, especially in sports that require high-intensity activities [6]. Thus, creatine supplementation may be beneficial for high performance athletes, particularly in sports of high intensity, suchin the reduction of muscle fatigue during workouts, allowing the realization of training sessions at higher intensities [7].

Effects of Creatine Supplementation in the Concentrations of Creatine Kinase, Creatinine, Urea and Lactate on Male Swimmers