Impact of limited hamstring flexibility on vertical jump, kicking speed, sprint, and agility in young football players

This study aims to analyse the impact of limited hamstring flexibility (HF) on specific football skills, such as sprinting and jumping ability, agility, and kicking speed in young football players. Forty-three male football players (aged 14-18) from a semi-professional football academy participated voluntarily in this study. Data about anthropometric measurements, HF (unilateral passive straight-leg raise test: PSLR), vertical jumping ability (countermovement jump: CMJ), sprinting ability (5, 10, 20 m: S5 m, S10 m, S20 m), agility (Balsom agility test: BAT), and kicking speed in terms of ball speed (dominant and non-dominant leg: KSdom and KSnon-dom) were collected. Cluster analysis grouped according to HF, dividing participants into a flexible group (FG, n = 24) and a non-flexible group (NFG, n = 19) in relation to performances on the PSLR test. Despite finding no significant differences between groups in body composition and age, the FG performed better in terms of sprint scores (S5 m: 6.12%, S10 m: 4.09%, S20 m: 3.29%), BAT score (4.11%), CMJ score (10.49%), and scores for KSdom (6.86%) and KSnon-dom (8%) than the NFG. The results suggest that HF is a key factor for performing football-specific skills, such as sprinting, jumping, agility, and kicking in young football players. These results support the rationale that muscle flexibility must be specifically trained in football players beginning at early ages.