Effect of Heading a Soccer Ball as an External Focus During a Drop Vertical Jump Task

Abstract

Background: Research has demonstrated that performing a secondary task during a drop vertical jump (DVJ) may affect landing kinetics and kinematics. Purpose: To examine the differences in the trunk and lower extremity biomechanics associated with anterior cruciate ligament (ACL) injury risk factors between a standard DVJ and a DVJ while heading a soccer ball (header DVJ). Study Design: Descriptive laboratory study. Methods: Participants comprised 24 college-level soccer players (18 female and 6 male; mean ± SD age, 20.04 ± 1.12 years; height, 165.75 ± 7.25 cm; weight, 60.95 ± 8.47 kg). Each participant completed a standard DVJ and a header DVJ, and biomechanics were recorded using an electromagnetic tracking system and force plate. The difference (Δ) in 3-dimensional trunk, hip, knee, and ankle biomechanics between the tasks was analyzed. In addition, for each biomechanical variable, the correlation between the data from the 2 tasks was calculated. Results: Compared to the standard DVJ, performing the header DVJ led to significantly reduced peak knee flexion angle (Δ = 5.35°; P =.002), knee flexion displacement (Δ = 3.89°; P =.015), hip flexion angle at initial contact (Δ = −2.84°; P =.001), peak trunk flexion angle (Δ = 13.11°; P =.006), and center of mass vertical displacement (Δ = −0.02m; P =.010), and increased peak anterior tibial shear force (Δ = −0.72 N/kg; P =.020), trunk lateral flexion angle at initial contact (Δ = 1.55°; P