The purpose of the present study was to investigate gender-based differences in knee and hip kinetics and kinematics during a single-leg landing with a lateral trunk obliquity. The results of this study showed that female subjects demonstrated larger hip adduction moment at the time of peak VGRF than male subjects whereas female subjects landed with smaller peak VGRF compared with male subjects. In addition, female subjects showed larger hip external rotation angle at IC than male subjects. However, we failed to find any gender-based differences in knee kinetics and kinematics including knee abduction moment.
In the present study, the angle of the laterally inclined trunk was set at 15° before dropping off the box to investigate gender-based differences in knee and hip kinetics and kinematics during a landing with lateral trunk obliquity. Female and male subjects showed 14.8° and 16.1° of lateral trunk obliquity at IC and there were no gender-based differences in the angle of laterally inclined trunk at IC or peak VGRF. Therefore, the landing task with lateral trunk obliquity was properly conducted to compare knee and hip kinetics and kinematics between female and male subjects.
It was hypothesized that female subjects would show larger knee abduction angle and moment compared to male subjects during landing with lateral trunk obliquity. This was motivated by the fact that larger knee abduction angle and moment increased by the lateral trunk obliquity was a proposed female specific ACL injury mechanism [13, 17, 25]. However, we failed to find gender-based differences in knee kinetic or kinematics. Instead, female subjects showed larger hip external rotation angle at IC than male subjects as similar to previous studies [26, 27]. Since hip internal rotation is a part of dynamic knee valgus motion and associated with larger knee abduction moment [4, 28], increased hip external rotation would diminish dynamic knee valgus motion and knee abduction moment. Therefore, female subjects might attempt to reduce knee abduction moment and dynamic knee valgus motion by a increasing hip external rotation angle.
In the present study, female subjects showed larger hip adduction moment at the time of peak VGRF compared with male subjects. Larger hip adduction moment would be associated with higher activity of hip abductor muscles and smaller co-contraction with hip adductor muscles [13, 14, 29]. A recent study has shown that larger hip abductor force was associated with smaller knee abduction moment during landing . Therefore, there is a possibility that female subjects might adapt to reduce knee abduction moment during landing with lateral trunk obliquity by increasing hip external rotation angle and hip adduction moment. Large VGRF is also one of the risk factors of ACL injury and it is associated with large knee abduction moment during a landing, especially with lateral trunk obliquity toward a landing leg [3, 13, 23, 30]. Therefore, female subjects might adapt to reduce the peak VGRF during landing with lateral trunk obliquity by decrease in the peak VGRF as well as hip joint adaptations.
Concerning clinical relevance, the findings of the present study indicated that female athletes are considered to avoid excessive knee abduction moment during landing with lateral trunk obliquity by kinematic and kinetic changes in their hip joint. Therefore, sports-medicine specialists should take more notice of strength and motions around the hip joint in order to prevent noncontact ACL injuries for female athletes.
Some limitations should be acknowledged. First, the lateral trunk obliquity in the present study was intentional, and the landing was conducted in a well-controlled condition. In actual sports situations, the effect of lateral trunk obliquity on knee kinetics and kinematics may be different between female and male athletes. Second, we did not measure any muscle activities although we expected that the hip abductor activity would be larger in the female subjects than the male subjects based on the gender difference in the hip adduction moment. Future study should be conducted to evaluate gender differences in muscle activities to reveal the mechanism of hip adaptation. Third, the ACL strain or the load was not measured in the present study. In addition, it is unclear whether gender differences in hip kinetics and kinematics are related to the decrease or increase of the risk of ACL injury because the present study was a cross-sectional design.