Season-long changes in COD performance, jump, and flexibility in elite youth soccer players

TL;DR

Elite youth soccer players improved in change-of-direction performance, jump, and flexibility over a season, with explosive strength linked to better agility.

Contribution

Empirical evidence on the co-occurrence of physical qualities in elite youth soccer players across a competitive season.

Findings

Players showed significant improvements in flexibility, explosive strength, and COD performance over the season.

Explosive strength (SBJ) was moderately associated with better COD performance at season end.

Flexibility (sit-and-reach) was not significantly related to COD performance.

Abstract

In elite youth soccer, the interplay between the development of key physical qualities, change-of-direction (COD) performance, explosive strength, and flexibility, remains poorly understood. Conventional training often assumes transfer effects, yet empirical evidence on how these qualities co-occur within elite youth cohorts across a competitive season remains limited. We tested the hypothesis that flexibility and explosive strength would be positively associated with COD performance at end-season (T2).

Forty-five elite male youth players (Serie A academy; U12–U14) were monitored across one competitive season. COD performance (T-Test completion time), flexibility (sit-and-reach), and explosive strength (standing broad jump, SBJ) were assessed at the season's start (T0; September 1, 2024) and end (T2; May 1, 2025). Primary analyses used paired t-tests with Cohen's d_z and 95% confidence intervals (CI). Pearson correlations (with 95% CI) were computed cross-sectionally at T2.

Significant season-long improvements were observed in flexibility [Δsit-and-reach = + 1.83 ± 1.42 cm; 95% CI (1.40, 2.26); p = 4.87 × 10−11; d_z = 1.29], explosive strength [SBJ Δ =  + 12.8 ± 3.8 cm; 95% CI (11.66, 13.94); p < 1 × 10−20; d_z = 3.37], and COD performance [ΔT-Test = −1.16 ± 0.87 s; 95% CI (−1.42, −0.90); p = 1.86 × 10−11; d_z = −1.33]. At T2, SBJ was moderately associated with COD performance [SBJ vs. T-Test: r = −0.41, p = 0.005; 95% CI (−0.63, −0.13)] and with flexibility [SBJ vs. sit-and-reach: r = 0.32, p = 0.032; 95% CI (0.03, 0.56)], whereas sit-and-reach was not significantly related to T-Test time (r = −0.15, p = 0.31).

Elite youth players improved COD performance, flexibility, and horizontal power across the season. Cross-sectionally, higher SBJ performance co-occurred with faster COD performance at end-season, while sit-and-reach flexibility did not. These findings support multi-domain monitoring and targeted training prescriptions, while highlighting the need for maturation-informed designs to test longitudinal coupling of individual adaptations.