236 Health, Sports & Rehabilitation Medicine Vol. 22, no. 4, October-December 2021, 236–241 Should Creatine Kinase be tested at baseline in athletes? Bianca Jurjiu 1 , Marc Damian 2 , Cezar Login 3 , Simona Grad 4 , Adina Chiș 5,6 , Maria-Magdalena Tămaș 7 , Laura Muntean 7 , Ileana Filipescu 7 , Siao-Pin Simon 7 , Romana Vulturar 5,6 1 Department of Rheumatology, Emergency Clinical County Hospital Cluj, Discipline of Rheumatology, “Iuliu Hațieganu” University of Medicine and Pharmacy Cluj-Napoca, Romania 2 Student 5 th year, Faculty of Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy Cluj- Napoca, Romania 3 Department of Physiology, “Iuliu Hatieganu” University of Medicine and Pharmacy Cluj-Napoca, Romania 4 2 nd Department of Internal Medicine, Emergency Clinical County Hospital Cluj, “Iuliu Hațieganu” University of Medicine and Pharmacy Cluj-Napoca, Romania 5 Department of Molecular Sciences, “Iuliu Hațieganu” University of Medicine and Pharmacy Cluj-Napoca, Romania 6 Cognitive Neuroscience Laboratory, Babeș-Bolyai University Cluj-Napoca, Romania 7 Department of Rheumatology, Emergency Clinical County Hospital Cluj, Centre for Rare Autoimmune and Autoinfammatory Diseases (ERN-ReCONNET); Discipline of Rheumatology, “Iuliu Hațieganu” University of Medicine and Pharmacy Cluj-Napoca, Romania Abstract Creatine kinase (CK) level depends on muscle mass, age, race, physical activity and various pathologies involving the muscles or the heart. Resistance training elicits the greatest release of CK, and is the best way to attain muscle hypertrophy. The highest post-exercise serum enzyme level is found after prolonged exercise such as ultradistance marathon running or weight-bearing exercises and downhill running, which produce eccentric muscular contractions. Persistently elevated CK levels in apparently healthy subjects may indicate a late-onset underlying condition. The decrease in the serum enzyme level depends on the period of rest after exercise, as short-term physical inactivity may reduce the lymphatic transport of CK and the release of the enzyme from the muscle fbres. We discuss the source and level of CK in various situations, the diferent CK isoenzymes and also when to test for an underlying myopathy or other pathologies which may impact the long-term athletic performance. It is likely safe for athletes with suspected myopathy to continue physical activity at a lower intensity to prevent muscle damage, and allow appropriate rest to favour recovery. Thyroid dysfunctions and drug-induced myopathies should be ruled out. History and clinical examination could help clarify whether other muscle-directed investigations are required. Keywords: creatine kinase, athlete, physical training, rhabdomyolysis, myopathy, statins Copyright © 2010 by “Iuliu Haţieganu” University of Medicine and Pharmacy Publishing Received: 2021, September 2; Accepted for publication: 2021, September 13 Address for correspondence: “Iuliu Haţieganu” University of Medicine and Pharmacy Cluj-Napoca, 6, Pasteur Street, PC 400349, Cluj- Napoca, Romania E-mail: marctudordamian@yahoo.com Corresponding author: Damian Marc, marctudordamian@yahoo.com https://doi.org/10.26659/pm3.2021.22.4.236 Creatine kinase - biological functions Creatine kinase (CK) is a crucial enzyme in the metabolism of creatine, catalyzing the formation of creatine phosphate and ADP from creatine and ATP (Fig. 1). Creatine (Cr), or N-aminoiminomethyl-N- methylglycine, is mainly but not exclusively synthesized in the pancreas and in the kidney, which have high AGAT (L-arginine:glycine amidinotransferase) activity, as well as in the cells of the liver, where high concentrations of GAMT (S-adenosyl-L-methionine: N-guanidinoacetate methyltransferase) can be found. From the organs of synthesis, creatine is transported via the bloodstream to the tissues which use creatine (mainly the brain and muscles), where both the endogenously synthesized creatine and the creatine derived from dietary sources is taken up by a creatine transporter (CRTR, or SLC6A8), a sodium dependent system enhanced by insulin (Stockler- Ipsiroglu et al., 2016; Lange at al., 2020).