Combat-related spine injuries from improvised explosive devices are attributed to vertical loading transmitted from the seat to the pelvis to the torso and head-neck regions. The presence of personal protective equipment (PPE) adds to the weight of the torso, influencing the load transmission within the vertebral column. In this study, a detailed mid-size male finite element model from the Global Human Body Models Consortium was used to investigate the effect of PPE on spine kinematics, forces, and moments along the vertebral column. The model was positioned on a rigid seat, such that the posture represented an upright seated soldier. Once positioned, the model was updated with PPE. The models, with and without PPE were simulated under two high acceleration vertical loading pulses and the spine accelerations, forces and moments were investigated. The PPE increased the spinal loads, with reduced time to peak. The presence of PPE increased forces in the cervical and thoracic spines up to 14% and 9%, while it decreased the lumbar spine forces up to 7%. PPE increased cervical spine extension moment up to 104%, thoracic spine flexion moment up to 14%, and decreased the lumbar spine flexion moment up to 11%. The increase in thoracic spine compressive forces and flexion moments due to PPE suggest increased risk of injury in compression-flexion, such as anterior or burst fractures of the thoracic vertebrae with or without the distraction of posterior elements/ligaments. Whereas, the PPE may be effective in reducing the injury in lumbar spine, with reduced forces and moments. The pulse variation showed that the seat velocity along with the acceleration influence the spine kinematics and further parametric studies are needed to understand the effectiveness of PPE for varying seat velocities/accelerations. Spinal accelerations peaked earlier with PPE; however, their peak and morphologies were unchanged. This study delineates the kinetics of the spine injury during underbody blast loading and the role of PPE on potential injuries and injury mechanisms based on forces and moments.

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