Biomechanical differences between horizontal and vertical single-leg jumps: what could each one reveal about functional impairments?

Jumps are used to assess musculoskeletal health. This study investigates neuromechanical differences in single-leg jumps for maximum height and distance regarding propulsion and landing phases to identify joint- and muscle-specific deficits. Nineteen healthy women performed both jump types, with assessments including 3D kinematics, ground reaction forces, and electromyography (EMG). Joint kinematics and torques were calculated using OpenSim, and muscle synergies derived from EMG data using Non-Negative Matrix Factorization guided by Variability Accounted For (VAF) metrics. Statistical parametric mapping compared the centre of mass displacement, angular trajectories, joint moments, and neural commands between jump types. Maximal height jumps require greater hip joint effort and emphasise knee mechanics and pelvic misalignments in the frontal plane. During landing, height jumps impose higher demands on eccentric knee extension and pelvis list, whereas distance jumps necessitate increased lumbar extension torques. The reduced knee extension torque and increased knee, trunk, and hip flexion angles in distance jumps may protect the knee. Landing from height jumps promotes anterior pelvic tilt in the sagittal plane. The analysis shows that two muscle synergies reconstruct propulsion EMGs, while landing requires three, indicating increased complexity. These findings highlight the need for customised assessments targeting specific neuromuscular and biomechanical aspects of lower-limb function.