Objective: We aimed to explore the validity of applying current reference ranges of the enzyme creatine kinase (CK) when analysing the medical status of professional footballers and to offer a more functional CK reference range for professional footballers.
Methods: A sample of 27 professional male footballers competing in The Football League Championship was analysed. The single sample Wilcoxon signed-rank test was used to compare the CK distribution of the study group with that of a control group of military personnel reported in the literature.
Results: The median values for study group and the published control group were 284 U/L and 124 U/L, respectively (P<0.001) suggesting that the average CK activity of professional footballers is higher than that of the normal healthy military population.
Conclusion: Ethnicity, sex, age and physical exercise are factors that likely influence CK levels among various populations. From our analysis, we recommend a new 95% reference interval of 64.9 U/L to 1971.7 U/L for professional footballers.
Keywords: athlete; creatine; exercise; football; injury.