Introduction Most studies focusing on differences between males and females in children through to adulthood are cross-sectional in nature. The aim of this study was to prospectively examine kinematics during a drop jump (DJ) performance in male and female athletes, focusing on the knee at initial contact (IC).

Materials and Methods Athletes from local sports clubs (n=293, age 9–12 years), participated in a data collection where they performed a bilateral DJ (ten trials) while marker-based 3D motion capture was used to obtain kinematic data of each lower limb. Over a third of them (n=105) returned after five years and repeated the procedure. A mixed-model analysis of variance (ANOVA) for repeated measures was used for statistical analysis of knee angles in the sagittal plane at IC, using limb (right vs. left) and time (child vs. teen) as within subject factors and sex for groups. Alpha was set at 0.05 for significance.

Results Males increased the knee flexion angle at IC over time, while females leaned towards greater extension (interaction; p<0.001). Moreover, a significant 3-way interaction showed that while both sexes demonstrated inter-limb symmetry for knee flexion angles at IC as children, females increased asymmetry over time, while males did not (interaction; p<0.001).

Conclusion This prospective study demonstrates that age influences DJ performance and that changes for females, not males, generally move towards a more extended knee and greater asymmetry between limbs. This may have implications for knee injury and may be a target for intervention to lower injury risk.