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 ¼ 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.