Sex-Based differences in isokinetic Force-Velocity profiles of the knee extensors and flexors in male and female football players: a Cross-Sectional study

Force-velocity (F-V) profiling is increasingly used to describe the mechanical capacities of the knee extensors and knee flexors in football, but almost all available reference data come from male players. It is not established whether male and female players differ in the parameters of the isokinetic force-velocity relationship, or whether any such differences persist once differences in body size are accounted for. This single-centre, cross-sectional observational study compared the isokinetic force-velocity profiles of the knee extensors and knee flexors between male and female competitive football players. Eligible participants were competitive players aged 18 to 35 years, training at least three times per week, free of current lower limb pain or injury and with no history of knee or hip surgery. During a single testing session, participants performed bilateral concentric isokinetic knee extension and flexion at five angular velocities (30, 60, 180, 240 and 300 degrees per second) on an isokinetic dynamometer, after a standardised warm-up, individual gravity correction and a familiarisation session. For each participant, limb and muscle group, peak torque was regressed against angular velocity to fit an individual linear torque-angular velocity relationship. The following parameters were derived: theoretical maximal torque (F0), theoretical maximal angular velocity (V0), the slope of the relationship, maximal theoretical power (Pmax), and torque and power at the extremes of the tested velocity range. The participant, defined as the mean of both limbs, was the unit of analysis. Male and female players were compared in absolute terms and after adjustment for body size, using ratio scaling to body mass, log-log allometric models and analysis of covariance with body mass and age as covariates. Secondary comparisons included the conventional hamstring-to-quadriceps ratio, inter-limb asymmetry and the orientation of the profile (F0/V0 ratio). The purpose of the study is to determine which sex differences in isokinetic force-velocity parameters are explained by body size and which persist after adjustment, in order to establish whether reference values obtained in male players can legitimately be applied to female players.