Effects of developmental stage and sex on lower extremity kinematics and vertical ground reaction forces during landing

Context: The presence or absence of biomechanical differences between the sexes before puberty may provide clues about the onset of adult landing pattern differences, which may help to explain the greater number of anterior cruciate ligament injuries in females than in males and provide the basis for interventions to reduce those injuries. Objective: To identify developmental sex-related and biomechanical differences during vertical jump landings. Design: A 2 X 2 developmental stage (prepubescent or postpubescent) X sex (male or female) between-subjects design. Setting: Controlled laboratory setting. Patients or Other Participants: Thirty prepubescent subjects (15 boys, age = 9.63 +/- 0.95 years; 15 girls, age = 9.19 +/- 1.00 years) and 28 postpubescent subjects (14 men, age 23.57 +/- 3.23 years; 14 women, age = 24.22 +/- 2.27 years). Intervention: Subjects performed a vertical jump to a target set at 50% of their maximum vertical jump height ability. Main Outcome Measure(s): Hip and knee kinematics of the dominant lower extremity and vertical ground reaction forces during impact were analyzed. Results: We found significant main effects for developmental stage. Children demonstrated greater knee valgus and less hip flexion at initial contact and at maximum vertical force, less knee flexion at maximum vertical force, greater maximum vertical force and impulse, and a shorter time to maximum vertical force than the adults. No sex differences were found among the biomechanical variables measured. Conclusions: The presence of significant biomechanical differences between children and adults suggests that physical development influences landing patterns. Sex does not appear to influence landing patterns during a 50% maximum vertical jump landing. These findings add to the body of knowledge regarding developmental and sex comparisons in a functional landing task.