Influence of the trunk position on knee kinematics during the single-leg landing: implications for injury prevention.

The purpose of the present study was to investigate the influence of the trunk position during the single-leg landing on the knee angle and muscle activity. Forty healthy university students (20 men and 20 women) performed right single-leg landings from a 40 cm-high platform with the trunk in neutral, flexion, extension, and right and left lateral flexion. Knee flexion and valgus angles were determined by two-dimensional video analysis, and rectus femoris (RF) and biceps femoris (BF) muscle activities were assessed. The knee flexion angle was significantly higher in the trunk-flexion position than in the other trunk positions. The knee valgus angle was significantly lower in the trunk-neutral and trunk-flexion positions than in the trunk-extension, trunk-right-lateral-flexion, and trunk-left-lateral flexion positions. Muscle activity of the RF was significantly lower in the trunk-flexion position than in the trunk-extension position and that of the BF was significantly higher in the trunk-flexion position than in the trunk-neutral, trunk-extension, and trunk-right-lateral-flexion positions. Single (right)-leg landing with the trunk in flexion may confer a low risk of anterior cruciate ligament injury compared to that with the trunk in extension or right lateral flexion.