Vertical drop jump landing depth influences knee kinematics in female recreational athletes

Objectives

To examine whether different vertical drop jump (VDJ) landing depth (small versus deep) and stance width (wide versus narrow) may alter movement biomechanics in female recreational athletes. The purpose was also to identify whether leg muscle strength is a predictive factor for knee control during a VDJ.
Design

Cross-sectional.
Setting

Biomechanics laboratory. Participants: Eighteen women aged between 18 and 30 years.
Main outcome measures

Three VDJ tests were used for biomechanical analysis: 1) small “bounce” jump (BJ), 2) deep “countermovement” jump with wide (CMJW) and 3) narrow foot position (CMJN). Subjects also performed an isometric knee-extension strength test, dichotomized to ‘weak’ versus ‘strong’ subjects according to median and quartiles.
Results

There were greater knee valgus angles during landing for both the CMJW and CMJN test compared to the BJ test (p ≤ 0.05). Differences in knee valgus between weak and strong subjects were significant for the BJ test (p = 0.044) but not for any of the other tests.
Conclusions

VDJ landing depth influences knee kinematics in women. Landing depth may therefore be considered when screening athletes using the VDJ test. Also, muscle strength seems to influence the amount of knee valgus angles, but the difference was not statistically significant (except for the BJ test) in this small cohort.