Abstract

This study investigated seasonal changes in anthropometric characteristics, vertical and horizontal jump performance, 30 m sprint performance, estimated maximal aerobic capacity, and repeated-sprint ability in competitive youth soccer players across the preparation, mid-season, and end-season phases. A longitudinal repeated-measures design was employed over one competitive season. Anthropometric variables, vertical and horizontal jump performance, 30 m sprint performance, estimated VO2max derived from the Vam-Eval field test, and repeated-sprint sets (2 × 5 × 20 m with 15 s recovery between sprints and 1 min between sets) were assessed at three time points. Significant seasonal changes were observed in anthropometric characteristics, with body mass and height increasing progressively and body fat percentage decreasing throughout the competitive season (F ≥ 12.0, p < 0.001, ηp2 ≥ 0.32). Body mass increased from 64.1 ± 6.7 to 66.7 ± 6.8 kg, height from 1.69 ± 0.07 to 1.72 ± 0.07 m, and body fat percentage decreased from 11.3 ± 2.0% to 9.4 ± 1.8%. Peak height velocity (PHV) significantly influenced changes in body mass and height but not body fat percentage. Seasonal improvements were observed in several physical performance measures. Squat jump, standing long jump, 15 s repeated jump performance, 10- and 30 m sprint performance, estimated maximal aerobic speed, estimated VO2max, and repeated-sprint performance changed significantly across the season (F ≥ 3.28, p ≤ 0.046, ηp2 ≥ 0.11), whereas countermovement jump, five-jump test, and flying 20 m sprint performance remained unchanged. Estimated VO2max and maximal aerobic speed improved from preparation to mid-season and were subsequently maintained. Repeated-sprint performance exhibited set-dependent seasonal adaptations, with significant Time × Set interactions indicating progressive improvements during the second repeated-sprint set, whereas the first set showed only transient improvements at mid-season. Significant PHV and Time × PHV effects were also observed for aerobic capacity and repeated-sprint performance. In conclusion, these seasonal variations likely reflect the combined influence of biological maturation, training exposure, and competitive demands rather than training effects alone.

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