Severities and types of under‐body blast lumbar injuries maybe associated with loading severity and amount of torso‐borne mass, such as personal protective equipment. The objective of this study was to delineate these effects using a high‐fidelity pelvis‐lumbar spine finite element model (FEM).

Geometries of the FEM was reconstructed from computed tomography scans and scaled to 50th percentile male. Hexagonal solid elements were used for majority of the FEM, except shell elements for cortical shells and endplates and nonlinear springs for ligaments. Material properties were obtained from in‐house high‐rate bulk and shear testing when available. Pelvis acceleration loadings were obtained from full‐body Hybrid‐III FEM. Simulations were conducted with high and low pelvis accelerations, with and without torso‐borne mass. Results found loading modes in the spine progressively changes from flexion, to compression, and extension from upper to mid‐ and lower level resulted in an “S” shaped deformation, indicating change of injury mechanisms along the spine. Localized spine deformation decoupled the torso‐borne mass from the high‐rate pelvis acceleration during the initial stage (20‐30ms). Under high pelvis acceleration, the spine may fail before the torso mass is engaged. Under low severity and lateral stage, motion of torso mass needs to be considered.