Sprint speed and explosive power in under-13 academy football players: A 5-month longitudinal analysis
Danail Ivanov, Petar PeevAbstract
Study aim
To assess changes in selected motor abilities and inter-limb isokinetic force asymmetry in male under-13 academy football players across 5 months of the competitive season.
Material and methods
Twenty-three players (height, 154.7 ± 6.8 cm; mass, 40.8 ± 4.7 kg) were assessed in January and May 2025. Sprint times over 5, 10, and 20 m were recorded using photocell gates; squat jump (SqJ) and countermovement jump (CMJ) heights were recorded using an optical system; and unilateral isokinetic peak force of the knee extensors and flexors was measured at 60°/s, from which asymmetry was derived. Players followed the standard academy programme without dedicated sprint or resistance training. Paired t -tests and Cohen’s d were used. Paired data were available for 23 players (sprint), 22 (jump), 15 (extension), and 14 (flexion).
Results
Acceleration declined: sprint times increased over 5 m (from 1.23 to 1.27 s; p = 0.034; d = 0.47) and 10 m (from 2.06 to 2.11 s; p = 0.015; d = 0.55), whereas 20 m was unchanged ( p = 0.697). Explosive power improved: SqJ height increased from 26.9 to 27.9 cm ( p = 0.047; d = 0.45) and CMJ from 27.6 to 28.5 cm ( p = 0.036; d = 0.48). Asymmetry decreased for the knee extensors (from 14.7 ± 13.1% to 9.4 ± 6.4%) and increased for the flexors (from 7.1 ± 5.6% to 13.5 ± 13.3%).
Conclusions
Explosive power improved while acceleration declined, suggesting that a technical–tactical in-season programme may maintain lower-limb power without stimulating speed development. Opposing asymmetry trends indicate that inter-limb balance is task-specific. Maturity status was not assessed.