Serum Creatine Kinase Activity and Its Relationship With Renal Function Indices in Professional Cyclists During the Giro dʼItalia 3-Week Stage Race

OBJECTIVE: : To analyze the behavior of total creatine kinase (CK) and other muscular damage markers and to compare CK activity and renal function indices in professional cyclists during a 3-week stage race. DESIGN: : Prospective, noncomparative, interventional. SETTING: : The athletes were recruited during the 2011 Giro d'Italia. PARTICIPANTS: : Nine professional road cyclists from the Liquigas-Cannondale team and competing in the race. ASSESSMENT OF RISK FACTORS: : Blood samples were collected on the day before the start of the race, on day 12, and on the final day (day 22) of the race. MAIN OUTCOME MEASURES: : Creatinine and cystatin C concentrations, CK, lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) activities were measured. The estimated glomerular filtration rate was calculated according to equations based on creatinine, cystatin C, or both. RESULTS: : Creatine kinase and AST activity increased during the second part of the race, and LDH activity progressively increased during the entire course of the race. There was a negative correlation between CK activity and the delta prerace-day 12 of glomerular filtration rate, as obtained with simple cystatin C or with Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine and cystatin C equations. CONCLUSIONS: : The effect of prolonged strenuous muscular effort on biochemical laboratory parameters in professional road cyclists was confirmed. The correlation observed between renal function and CK activity underscores that measurement of cystatin C is more accurate than creatinine alone in the evaluation of renal function and that it is unaffected by response to physical stress-induced muscular damage.