Landing from a jump is implicated in 50% of non-contact ACL injuries. Observation of filmed injuries suggests ACL failure is often associated with knee extension, tibial valgus and external rotation. If women land in this position excessively, their injury risk may increase. However, research conclusions regarding gender and landing knee angle have varied. In general, drop landing studies show women land with more extension, while functional landing studies show no differences in knee angle. An important issue in landing from a functional jump is that subjects achieve different absolute jump heights. This may affect the amount of impact-absorbing flexion used in a given landing.

PURPOSE: The purpose of this study was to identify differences in knee flexion angle, adjusted for jump height, between men and women landing from a vertical jump (VJ).

METHODS: Twenty-eight subjects provided informed consent and participated in this study (14 women, age=24.22+2.27; 14 men, age=23.57+3.23). Twenty-three reflective markers applied to each subject created an 8-segment linked model for 3D analysis. For each of four trials, subjects jumped for a ball set at 50% of their maximum VJ height, then landed on two feet, facing forward, with only their dominant foot on the force plate. Knee flexion angles at initial contact (IC), at peak vertical ground reaction force (Fz) and peak knee flexion (PKF) were normalized to kinetic energy (KE). Center of mass velocity in the frame before IC represented touchdown velocity. Data were analyzed using a paired T-test (a =0.05).

RESULTS: Gender comparison of knee angles in degrees revealed no differences. At IC women experienced 0.08+0.04 º/KE and men experienced 0.05+0.02°/KE (p =0.02). At Fz women experienced 0.54+0.11°/KE and men experienced 0.30 +0.08°/KE (p=0.00). For PKF, women experienced 0.26 +0.08°/KE and men experienced 0.14 +0.07°/KE (p=0.00).

CONCLUSIONS: When scaled by the kinetic energy generated during descent, women demonstrated more knee flexion than men. KE simultaneously considers mass and descent velocity, both of which may affect impact forces and the amount of flexion used to accommodate them. In attempting to determine the relative amount of flexion used in functional tasks, it may be necessary to account for differences in mass and landing force to insure appropriate comparisons.

Supported by NATAREF Grant #90166P008.

2004 Decoster LC, Swartz EE, Russell PJ, Croce RV: Gender Comparison of Vertical Jump Landing Knee Angles Normalized by Kinetic Energy (Abstract). MSSE, Volume 36:5 Suppl