Background Overuse knee injuries, such as patellar tendinopathy, are one of the most prevalent and frequent injuries in volleyball with up to 50% of male indoor volleyball players sustaining this injury in their careers.

Objective The aim of this research was to examine the intrinsic and extrinsic risk factors associated with patellar tendinopathy including muscle flexibility, muscle strength, vertical jump, and their relationship to vertical ground reaction forces (vGRF) during cross-over block jump landings.

Design Structural alignment, lower limb flexibility, and muscle strength assessed were measured for each participant who then performed five trials of a cross-over step block. vGRF (vGRF: 1500 Hz; Kistler) were collected for takeoff and landing.

Setting A portable volleyball net was used to simulate a typical and realistic volleyball condition in a biomechanics laboratory. A standard volleyball was mounted on a post and used as a target.

Participants Elite male (EM) (N=10), sub-elite male (SEM) (N=10), and sub-elite female (N=10) volleyball players with no existing knee joint injury or history of lower limb surgery participated in this study.

Main outcome measurements Magnitudes of and correlations among risk factor measures and peak vGRF.

Results Gender differences were observed with SEM displaying significantly smaller Q-angle (p=0.04), greater strength (p=0.00), and maximal jump height (p=0.00) than SEF. EM displayed passive greater hip extension (p=0.01) and trunk flexion (p=0.05), and significantly greater strength in their non-dominant quadriceps (p=0.01) than SEM. SEM generated significantly higher vGRF compared to SEF. Significant negative correlations were found between vGRF and Q-angle and gastrocnemius flexibility for SEF but not SEM or EM.

Conclusions The results of this study may provide further insight why and which volleyball athletes may be prone to developing overuse knee injuries.