Background The strength profile of the hamstrings is reported to be important to prevent strain and anterior cruciate ligament (ACL) injuries. There is little information about the functional state of muscles around the knee in young soccer players.

Objective To determine the differences in the characteristics of knee extensors and flexors in 11–16-year old, male soccer players.

Design Randomized cross-sectional study.

Setting Laboratory, youth sports.

Participants 60 randomly selected young male soccer players (11–16 years) – without lower extremity injury history – were assigned into 6 age groups: under 11, 12, 13, 14, 15 and U16 (10 players/group).

Main outcome measurements The peak torque of isometric hamstring (ICH) and quadriceps (ICQ) (70° of knee flexion), eccentric hamstring (ECH) and concentric quadriceps (CCQ) (60°/s, 10–90° knee flexion range of movement) for both lower extremities were measured on an isokinetic dynamometer (Multicont II). Hecc/Qcc and rate of torque development (RTD) H/Q ratio were calculated 50 ms after the onset of the contraction (RTD H/Q50).

Results ICH and ICQ significantly differed (P<.05) between U11 and U14 for both legs. There were no significant differences in ICH and in ECH between U13-U16 in the dominant leg, similarly between U14-U16 in the non-dominant leg (P>.05). Hecc/Qcc was significantly higher in the U11 group than in the U16 group (P<.05) in the dominant leg. There were no differences in RTD H/Q50 across age groups for both legs (P>.05).

Conclusions As eccentric and isometric hamstring peak torques did not differ between U14-U16, hamstring-emphasized strength training is advisable. RTD H/Q50 may have clinical relevance, as most ACL injuries occur 17–50 ms after initial contact. It did not differ between age groups, so the effects of intervention programs should be tested aiming to increase the RTD of the hamstrings.