Introduction: Large variability has been reported for indicators of exercise induced physical fatigue (1,2). This obviously impedes on their diagnostic accuracy. However, despite the practical importance of monitoring fatigue, not much data about the sources of this variability is currently available. Therefore, this study aims to analyse the inter- and intra-individual variabilities in indicators of physical fatigue during in-season training phases in football players. Methods: 41 male football players (4th League Germany, 26.5 ± 4.2 y) participated in the study. Within a period of 3 months in the regular football season venous blood samples (analysed for CK and UREA) and counter movement jump (CMJ) performances were collected repeatedly in `fatigued` and `recovered` states. Players were defined as fatigued after performing >2 training sessions within 48h and as recovered when they had at least 1 day off. Training load was documented throughout data collection. A minimum of 3 observations per fatigue status was necessary to be included for analysis (n = 35 included). Standard error of measurement expressed as a percentage of the groups mean score (coefficients of variation (CV)) for CK, UREA and CMJ was calculated. Variability was analysed using a mixed effects model (fixed factor: fatigue status, random factor: subject ID and fatigue statusby-subject ID interaction). Results: CV for fatigued values was: CK: 52.3%, UREA: 14.6%, CMJ: 4.3%; and for recovered values: CK: 45.2%, UREA: 14.0%, CMJ: 4.5%. The fixed effect of fatigue status was highly significant for CK and UREA (p < 0.001) but not significant for CMJ (p = 0.49). The proportion of total variability attributable to subject ID was 37.9% for CK, 54.7% for UREA and 64.8% for CMJ. Fatigue statusby-subject ID interaction accounted for only 1.1% of total variability for CK and 0.5% for UREA. Discussion: The current analysis indicates a high inter- as well as intra-individual variation in fatigue induced changes of CK, UREA and CMJ. By contrast status-by-subject ID interaction (`individual response`) is negligible. Regarding the large between subject variability individualised interpretation using baseline measurements might lead to greater accuracy in the monitoring of the fatigue status in footballers.
© Copyright 2016 21st Annual Congress of the European College of Sport Science (ECSS), Vienna, 6. -9. July 2016. Veröffentlicht von University of Vienna. Alle Rechte vorbehalten.