Blood-borne fatigue markers during major international football tournaments – a retrospective analysis of data from the FIFA World Championships and UEFA European Championships 2006 – 2016

ABSTRACT Purpose:Monitoring of recovery needs is considered essential during international football tournaments, with blood-borne markers being an objective, well understood and conveniently measurable option. However, reference values from this level of play are largely lacking. Methods:We therefore report a retrospective analysis of the blood-borne fatigue markers creatine kinase (CK) and urea (U) from the German national football team during the FIFA World Championships and UEFA European Championships from 2006–2016. Values from 68 players could be analysed resulting in 1019 values for CK and 943 values for U. For 2014 and 2016, additional player tracking data were available. Results:Mean values (90% CI) for CK and U were 343.4 (333.3–353.6) U/l and 39.5 (39.0–39.9) mg/dl, respectively. Considerable between-subject variation was present accounting for 44% of random variability for logCK and 45% for logU. A significant decrease over time (p < 0.001) could be observed for both indicators. Total running distance and high-speed running were significantly correlated with CK levels 2 days after the match with a disproportionate CK response for overtime matches. Conclusion:Taken together, monitoring of recovery needs in elite football is likely to benefit from individualized reference values. When group-based reference ranges are used, they should be current and football-specific.