Vertical Stiffness, Pelvic Tilt Range and Jump Height during Vertical Jumping in Youth Soccer: Influence of Age, Sex and the Playing Position
(Rafael Martínez, Alejandro Sanz, Florentino Huertas, Paul J. Byrne, Javier Martínez-Gramage)

This study aimed to examine the influence of sex, age, and the playing position on vertical stiffness, pelvic tilt range, and jump height during vertical jumping in young soccer players. A total of 542 players (129 females, 413 males) aged 12 to 19 years from elite soccer academies participated. Players were divided into U14, U16, and U19 categories, and jump height, vertical stiffness, and pelvic tilt range were evaluated using the countermovement jump (CMJ) with an inertial sensor. Results revealed that vertical stiffness and jump height were significantly higher in males than females (p < 0.001) and significantly increased with age in males only from U14 to U16, U16 to U19 and U14 to U19 (p < 0.01 to p = 0.015). Pelvic tilt range was significantly greater in females only (p < 0.001), with forwards showing larger pelvic tilt range than midfielders (p = 0.023), though no differences were found by age. The analysis of the playing position showed no significant differences in vertical stiffness or jump height, suggesting that these variables were more influenced by biological and sex-related factors rather than positional roles during developmental stages. These findings provide normative data that can aid in the design of individualized training programs aimed at optimizing performance and reducing injury risk in youth soccer players.