Females with patellofemoral pain have impaired impact absorption during a single-legged drop vertical jump

Background: Females with patellofemoral pain (PFP) have been reported to land with altered biomechanics in some, but not all studies. Kinematic alterations previously reported may indicate, and relate to potential impairments in absorbing impact. Research question: To compare vertical ground reaction force (vGRF) and lower limb kinematics during sing-lelegged drop vertical jumps in females with and without PFP; and establish the relationship between vGRF and kinematics during this task. Methods: Fifty-two physically active females (26 with PFP and 26 controls) participated in the present cross-sectional study. Peak of vGRF was evaluated during landing; and lower limb kinematics in the sagittal and frontal planes during deceleration (landing) and acceleration (take-off) phases were evaluated. Results: The PFP group had 11% greater vGRF (p < 0.01); and 13-24% lower hip, knee and ankle excursion in the sagittal plane during acceleration and deceleration phases (p < 0.02) compared to the control group. No significant between group differences (p > 0.05) for hip, knee and ankle excursion in the frontal plane were identified. Greater impact was significantly correlated with reduced knee (r = -0.56), hip (r = -0.50) and ankle (r = -0.41) excursion in the sagittal plane during the acceleration phase in the control group, but not in the PFP group. No significant correlations were found between vGRF and kinematics variables during the deceleration phase in either group. Significance: Impaired ability to absorb load and reduced lower limb movement in the sagittal plane during landing in females with PFP may provide separate treatment targets during rehabilitation.