Background After puberty female athletes are in 2–7 times higher risk of tearing the anterior cruciate ligament as compared to males.
Objective To compare following factors between 15 and 18 years boys and girls participating in soccer: 1) Vertical jump height. 2) Jump- and landing technique in drop jump. 3) EMG activity around the knee during jumping and landing.
Design Observational, cross-sectional study.
Setting National youth soccer teams in Iceland.
Participants 20 boys and 17 girls, 15–18 years, from three soccer teams and also participating in Icelandic national youth soccer teams were invited to participate. Of these, 10 boys and 10 girls accepted participation and showed up for testing.
Main outcome measurement (1) Jump height in counter movement jumps. (2) Degree of knee valgus during drop jumps. (3) EMG onset latency for five different muscles in each thigh during drop jumps.
Results Boys jumped significantly higher than girls in countermovement jump (30.3±2.6 cm vs 22.6±3.8 cm, p<0.001). In the drop jump, girls had significantly increased knee valgus compared to boys in three of five test points: when toes touch the floor (165.1±4.0° vs 168.7±4.1°, p=0.05), at 25% of the height from lowest position (163.3±6.4° vs 169.2±9.0°, p=0.013) and at toe off, when jumping up again (162.5±4.2° vs 167.2±4.4°, p=0.01). No difference was found for the lowest position or for 25% of the height from the lowest position to toe off. No gender difference was found for onset latencies of the leg muscles, except for right biceps femoris, where girls activated this muscle earlier before landing than boys (−0.31±0.39 vs −0.12±0.13, p<0.001).
Conclusion Boys jumped higher than girls. Girls had more knee valgus during landing, at 25% from the lowest position on the way down and, during toe off. No gender differences were found for muscle onset latencies except for one thigh muscle.