Background Knee valgus during landing and cutting situations has been described as the main biomechanical risk factor for anterior cruciate ligament (ACL) injuries. Evidence support the influence of hip strength and biomechanics on knee valgus in female athletes. To develop specific preventive measures for males, it is important to understand biomechanical and musculoskeletal variables associated with this mechanism during activities that mimic ACL injuries.

Objective To test the correlation between peak knee valgus during a single-leg vertical jump-landing task, and biomechanical and musculoskeletal variables in male soccer professional athletes.

Design Cross-sectional study.

Setting Biomechanics laboratory.

Participants Twenty-four healthy male professional soccer players.

Interventions Participants performed a vertical jump-landing task during the pre-season. Kinematic data were collected using an 8 high-speed cameras motion analysis system (Vicon, Oxford, UK) with a sample rate of 250 Hz. Maximal isometric hip strength was tested using a hand-held dynamometer and ankle dorsiflexion range of motion was measured using a digital inclinometer.

Main Outcome Measurements Predictor variables were lateral trunk lean, hip adduction and internal rotation, hip extensors, abductor and external rotator isometric strength, and ankle dorsiflexion range of motion. Interest variables were peak knee valgus during the landing task. Association between predictors and interest variables were tested using Pearson Correlation Coefficient (alpha = 0.05).

Results Lateral trunk lean (r =0.43, p=0.04) and hip internal rotation (r =-0.68, p<0.01) showed significant correlation with peak knee valgus during the vertical landing task.

Conclusions Trunk position seems to influence the ACL mechanism, possibly by increasing knee abduction moment related to the lateral displacement of centre of mass during lateral trunk lean. The negative correlation between hip internal rotation and knee valgus in males is opposite to the results usually described for females, and may be related to the different influence of hip on ACL injury mechanism between sexes.