Sex differences in isokinetic strength and power of knee muscles in 10–12 year old swimmers

The aim of the study was to determine knee muscles absolute and relative strength and power, as well as flexor/extensor (F/E) ratios, in prepubescent male and female swimmers, during concentric isokinetic testing. Twenty boys and 20 girls, aged 10-12 years, participated in this study. Gravity corrected concentric isokinetic peak torque (strength) and average power (power) were measured by a Cybex Norm dynamometer at the angular velocities of 60, 120 and 180 ◦ /s, during unilateral knee extensions and flexions. The relative values of strength and power were expressed per kilogram of lean body mass. Knee extensors strength and power do not differ significantly between boys and girls at the angular velocities of 60 and 120 ◦ /s. In contrast, at the higher angular velocity of 180 ◦ /s boys exerted greater values than girls ( p< 0.01). With respect to the knee flexors, boys exerted greater values than girls only at the angular velocities of 120 and 180 ◦ /s ( p< 0.01). When relative strength and relative power were calculated, no significant differences existed between boys and girls for both muscle groups. Moreover, the shapes of strength-velocity and power-velocity curves, as well as knee F/E ratios, were similar for both groups.