Differences in Sprinting-Related Force–Velocity Mechanical Variables Between Under-19 and Senior Players: Physical Performance Readiness in Elite Youth Soccer

Objectives: This study compares linear sprint force–velocity (F–v) mechanical variables between elite Under-19 (U19) academy players and senior professional players. Methods: Thirty-eight senior players (SP; mean age 24.5 ± 4.3 y) and 214 U19 academy players (YP; mean age 17.4 ± 0.5 y) from 14 first-division club academies were tested during October 2023 using a motorized resistance device (1080 Motion). The following F–v variables were assessed: maximal theoretical force (F0, N·kg−1), maximal theoretical velocity (v0, m·s−1), maximal ratio of horizontal-to-resultant force (RFmax, %), and decrease in the ratio of forces (DRF, %). Between-group comparisons were performed using the t-test, and Cohen’s d effect sizes were reported. Results: Senior players outperformed U19 players across all F–v variables. F0 exhibited a mean difference = 0.220 N·kg−1, with a 95% confidence interval (CI) 0.056, 0.384, p = 0.0166, and d = 0.46. v0 exhibited a mean difference = 0.560 m·s−1, with a 95% CI 0.410, 0.710, p < 0.0001, and d = 1.07. RFmax exhibited a mean difference = 1.470%, with 95% CI 0.830, 2.110, p = 0.0003, and d = 0.69. DRF exhibited a mean difference = 0.260%, with a 95% CI 0.103, 0.417, p = 0.0013, and d = 0.53. Conclusions: U19 players demonstrated lower F0, lower v0, and reduced mechanical effectiveness compared with senior players. Regular monitoring of F–v profiles and individualized training interventions (force- or velocity-targeted) may be useful for training and monitoring strategies aimed at supporting physical preparation during the transition to senior soccer.