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

Background 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). Methods 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 dᵦ and 95% confidence intervals (CI). Pearson correlations (with 95% CI) were computed cross-sectionally at T2. Results 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 ; dᵦ = 1. 29, explosive strength SBJ Δ = + 12. 8 ± 3. 8 cm; 95% CI (11. 66, 13. 94) ; p 1 × 10 −20 ; dᵦ = 3. 37, and COD performance Δ T -Test = −1. 16 ± 0. 87 s; 95% CI (−1. 42, −0. 90) ; p = 1. 86 × 10 −11 ; dᵦ = −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). Conclusions 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.