Creatine kinase concentration on the second post-match day is not associated with risk of subsequent muscle injury in professional football players: a four-season cohort study.

Objective: The objective of this study was to examine the relationship between creatine kinase (CK) concentration following official matches and the risk of subsequent muscle injury in professional male football (soccer) players.

Methods: Blood samples were collected on the second post-match day for CK analysis over four consecutive seasons in a professional football club. Players were then followed for five days to observe any occurrence of indirect muscle injury (structural or functional in nature). Players exposed to at least 45 minutes in two consecutive matches within seven days were considered valid cases for analysis.

Results: Eighty players participated in the study, generating 1,656 cases eligible for analysis, of which 229 resulted in muscle injuries. The hamstrings were the most frequently injured muscle group (54%), followed by the adductor (21%), triceps surae (19%), quadriceps (5%), and psoas (1%). While CK concentration was higher in muscle injury cases [783 ± 507 U/L (95%CI, 717 to 849; min-max, 105-2,800)] compared with uninjured cases [688 ± 446 U/L (95%CI, 665 to 711; min-max, 100-2,950)], it was not an accurate predictor of subsequent muscle injury risk in professional football players (sensitivity = 56%; specificity = 55%; odds ratio = 1.00; area under curve = 0.557).

Conclusion: CK concentration on the second post-match day cannot be used to effectively screen subsequent muscle injury risk in professional male football players.