The effect of an inclined landing surface on biomechanical variables during a jumping task

Background Professional dancers sustain a high number of injuries. Epidemiological studies have suggested that performing on inclined “raked” stages increases the likelihood of injury. However, no studies have examined if biomechanical differences exist between inclined and flat surfaces during functional tasks, such as landing from a jump. Such differences may provide a biomechanical rationale for differences in injury risk for raked stages. Methods Eight professional dancers performed drop jumps from a 40 cm platform on flat and inclined surfaces while forces, lower extremity kinematics, and electromyographic activity were collected in a controlled laboratory environment. Findings Dancers landed on the laterally inclined surface with significantly higher knee valgus (4°), peak knee flexion (9°), and medial–lateral ground reaction force (GRF) (13.4% body weight) compared to the flat condition. The posterior GRF was higher in the anterior inclined condition compared to the flat condition. In the anterior inclined condition, subjects landed with 1.4° higher knee valgus, 4° more plantarflexion at initial contact, and 3° less dorsiflexion at the end of landing. Interpretation Biomechanical variables that have been suggested to contribute to injury in previous studies are increased in the inclined floor conditions. These findings provide a preliminary biomechanical rationale for differences in injury rates found in observational studies of raked stages.