Does Preseason Training Load Shape Body Composition? External Load, Internal Load, and Fatigue in Semi-Professional...

Background: Monitoring athletes' responses to training is essential for optimizing performance and player management in football. Although training load is considered an important component of physiological adaptations, its relationship with body composition changes during preseason remains unclear. Objectives: This study aimed to (i) examine changes in body composition, training load, and fatigue throughout the preseason and (ii) determine whether accumulated training load and fatigue were associated with body composition changes in semi-professional football players. Methods: Twenty semi-professional male football players from the same team were monitored during a six-week preseason that included 28 training sessions and seven friendly matches. Body composition was assessed using bioelectrical impedance analysis at the beginning (Testing Session 1, TS1), middle (Testing Session 2, TS2), and end (Testing Session 3, TS3) of the preseason. External load and heart rate (HR) were quantified using Global Positioning System (GPS) devices, while internal load was assessed through session rating of perceived exertion (RPE), and fatigue was assessed using wellness questionnaires. Results: Significant changes in body composition were observed across the preseason. Fat mass increased, whereas fat-free mass, lean mass, and skeletal muscle mass decreased by TS3 (all p < 0.01; large, standardized effect sizes). No significant associations were found between accumulated external load, internal load, HR exposure, fatigue indicators, and body composition changes after baseline adjustment and multiple comparisons. Conclusions: Significant alterations in body composition were observed over the preseason period. Given the observational design and absence of a non-training control group, the observed changes cannot be attributed solely to the preseason training stimulus.