Seasonal changes in physical fitness and body composition and their associations with external match load in elite youth football players

Abstract

Purpose: To compare seasonal changes in body composition and physical fitness and examine their associations with external match load in elite youth football players. Methods: Twenty-nine players from the U18 (n = 14) and U21 (n = 15) squads were assessed during two competitive periods (First and Second Phase). Body composition included muscle mass (%MM), fat mass (%FM), and the sum of 6 skinfolds (6skf). Physical fitness assessments comprised countermovement jump (CMJ), 10-m (T10) and 30-m sprint time (T30), change-of-direction ability (COD), kicking velocity (KV), and maximal oxygen uptake (VO2max). External match load was quantified using GPS technology. Results: Both categories showed significant improvements in body composition, with higher %MM and lower %FM and 6skf (p < .05). CMJ, T30, and KV also improved significantly, whereas VO2max remained unchanged. Correlation analyses identified significant associations between physical fitness, body composition, and external match load, with more relationships observed in U18 than U21 players. Conclusions: Elite youth football players improved primarily in neuromuscular performance and body composition across the season. The greater number of associations observed in U18 players represents an exploratory pattern and should not be interpreted as evidence of stronger relationships between physical qualities and match performance compared with U21 players.