The Tracking of Internal and External Training Loads with Next-Day Player-Reported Fatigue at Different Times of the Season in Elite Soccer Players

The aim was to assess factor structure of player-reported fatigue and quantify within-subjects association between changes in training load measures and next day player-reported fatigue at different time points of an elite football season. Using longitudinal research design, twenty-four professional footballers, mean (SD) age of 25.7 (3.4) years, were monitored during their competitive season, including preseason. Player-reported fatigue data and session ratings of perceived exertion (session-RPE) were collected via a mobile application. Player’s Heart rate (HR) and global positioning system (GPS) data were collected daily in field sessions. Principal component analysis (PCA) indicated three components with Eigenvalues above 1.0; “soreness”, “mood, and “hydration”. Within-player correlations between training load values and next day player-reported fatigue values were trivial to moderate (r ≈ -0.42 to -0.04). In-season we observed large correlations between Total Distance (TD) and PlayerLoad with Soreness (r=-0.55, 95% CI: -0.62 to -0.46; r=-.054, 95% CI: -0.62 to -0.46), but during pre-season, correlations were small (r=-0.15, 95% CI: -0.28 to -0.01; r=-0.13, 95% CI: -0.26 to 0.01). The HR TRIMP, TD and session-RPE measures each showed trivial to moderate correlations (r ≈ -0.41 to -0.08) with next day “mood”. Our in-house player-reported fatigue questionnaire was sensitive to the multi-dimensional nature of fatigue, identifying physiological (soreness), psychological (mood and stress) and nutritional (hydration and nutrition) components. We found the in-season correlations with training load to be greater than previously reported in the literature, specifically with next day player-reported “soreness”. Nevertheless, the items of our scale were not associated with pre-season training load.