Isometric knee torque, quadriceps-hamstrings ratio, and jumping parameters in Brazilian soccer players of different age categories

Purpose. This study assessed the isometric torque, hamstring-to-quadriceps ratio, and jump performance among three age groups of soccer players. Methods. 67 male players were divided by chronological age into the under-17 (U17: n = 29), under-20 (U20: n = 22), and above-20-year (PRO: n = 16) groups. They performed countermovement (CMJ) and squat (SJ) jumps. Also, maximal isometric contractions during knee flexion and extension for right (R-TOR) and left limb (L-TOR) torque were assessed. Hamstrings-quadriceps (H:Q) and CMJ:SJ ratios were determined. Results. Compared with U17 and U20, PRO showed higher CMJ ( = 20% and 14%; both p < 0.01) and SJ ( = 19% and 13%; p < 0.01 and p = 0.02, respectively), and higher absolute R-TOR and L-TOR during knee extension ( = 40% and 58%; both p < 0.01). PRO exhibited higher absolute L-TOR and R-TOR during knee flexion than U17 ( = 22% and 26%; p = 0.04 and p < 0.01, respectively). Between-group differences were not detected in normalized torque, except for knee extension R-TOR (PRO > U17; p = 0.04). Greater differences for quadriceps absolute torque (effect size: 1.37–1.46) were observed in the hamstrings (effect size: 0.30–0.92) between PRO and U17. No differences were found for any H:Q torque ratio, but moderate effect sizes (0.71–0.75) were verified between PRO and the other groups. No differences were found for CMJ:SJ ratio. Conclusions. PRO players are more powerful than U17 and U20. Differences in strength level between PRO and U17/U20 are muscle-dependent. The larger strength development of quadriceps over hamstrings can result in lower isometric H:Q torque ratio for PRO.