Aim: The aim of the present study is to investigate Urinary creatine (URCR) and urinary creatinine (URCRN) response to CR supplementation in conjunction with exercise performance. Methods: Twenty-one sprint trained males were randomly divided into 3 groups. Each group followed a different CR dosage (10 g, 25 g and 35 g€day-1 for 4 days) and placebo (Pl) in the 1st and 2nd week, respectively. A double-blind design was used. Subjects' urine was collected every 24 hours during the entire period of supplementation (SP). All groups, at the end of each SP performed 3 times the Anaerobic Wingate Test (AWT) with 6 min active recovery (60 rpm) on a cycle ergometer. Results: Significantly (p<0.01) higher peak and mean power values were produced during the CR compared to Pl condition. A significant correlation (r=0.7, p<0.05) was also observed between peak power improvement (PPI) and URCR for the 3 groups. No such relationship was found between URCRN. Across all groups, URCR and URCRN increased significantly following ingestion compared with Pl (p<0.001). URCR post- supplementation presented a 7.4fold, 36fold and 21fold increase for 10 g, 25 g and 35 g dose respectively, whilst URCRN presented a mean 2.4fold increase for all different doses, which clearly shows the magnitude of sensitivity of these indices to CR supplementation. A strong correlation (r=0.95, p<0.01) observed between dose of CR ingestion and mean URCR (MRUCR) with prediction formula: CR = -0.936 + (5.613 x MRUCR) (SEE=3.5). Conclusion: 'URCR was an effective measure of each CR dosage administered as well as of the excretion pattern that each group followed throughout the SP. Furthermore the strong relationship of URCR and PPI could be particularly useful for monitoring and optimising CR loading in athletic populations.
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