Comparison of physical fitness and body composition by age categories in young professional football players in Chile

Introduction: physical and morphological development in youth football depends on age, maturation, and training loads. understanding these variations is key to planning the developmental process. Objective: to compare body composition and physical condition of young professional football players in Chile across different age categories. Method: 223 players from a professional club participated. body composition was assessed through fat mass, muscle mass, and the sum of six skinfolds. physical performance included countermovement jump, 10- and 30-meter sprints, change of direction test, one-repetition maximum squat, yo-yo intermittent recovery test, and kicking ability. a univariate anova was applied to compare variables between categories. Results: significant differences were found in all variables (p < 0.05; ηp2 > 0.14). post hoc analyses showed that older players had greater muscle mass, lower fat mass, and superior performance in strength and endurance tests, while younger categories presented lower values in these indicators. Discussion: findings confirm that maturation and training promote progressive improvements in physical and morphological capacities. variability across categories highlights the importance of considering both age and biological maturation. Conclusions: a clear physical and morphological progression was observed in youth footballers according to category, influenced by maturation and training. integrating biological factors into planning is essential to optimize performance and prevent injuries.