Creatine Kinase (CK) is an enzyme widely used as a marker of muscle damage and overtraining in professional football. Its release into the bloodstream occurs when muscle cells suffer microlesions, a common condition in high-intensity sports such as football. However, its interpretation must be done with caution, as multiple factors can influence its levels, including the type of exercise, match frequency, player position, and recovery between sessions.
In the study by Lazarim et al. (2007), conducted during the Brazilian National Championship, CK levels were analyzed in 128 professional football players, determining that CK values were significantly higher than those reported in the general population. The upper percentiles of 97.5 and 90 were set at 1,338 U/L and 975 U/L, respectively. This reflects that elite footballers, due to the intensity and frequency of matches, naturally present elevated CK levels. However, these values are not always indicative of structural muscle damage, but may reflect an adaptive process.
The study showed that, at the beginning of the championship, CK values were higher and less homogeneous, indicating greater muscle stress. As the season progressed, these values decreased and stabilized, suggesting a positive muscular adaptation. To control the risk of overtraining, players who exceeded the 90th percentile limit (975 U/L) underwent a reduction in their training load for one week. As a result, their CK levels decreased significantly, indicating that this strategy was effective in preventing progressive muscle damage.
A specific documented case was that of a player with a CK value of 1,800 U/L one day before the match, who participated in the game and suffered an injury. This incident reinforces the utility of CK as a risk marker for injury. The ability to objectify these values allows coaches and medical teams to make data-driven decisions to protect players.
For effective management, it is essential to establish personalized analysis protocols that allow training loads to be adjusted and appropriate recovery strategies to be planned. Reference values should be adjusted to the specific profile of the team and the phase of the season, as newly incorporated players or those in preseason may have higher values due to lack of adaptation.
The study by Lazarim et al. also highlights the importance of conducting standardized measurements, preferably under relative rest conditions (48 hours after the last physical effort), and that the use of automatic analyzers and portable devices could facilitate real-time monitoring, enabling immediate decisions during competitions.
In conclusion, CK is a valuable tool for diagnosing and monitoring muscle damage and overtraining in professional football, and the implementation of a continuous analysis system allows for maximizing sports performance and minimizing injury risk.
