The Characterization of Lumbar Acceleration in Rear-End Impacts Across Different Surrogate Occupant Types

Longitudinal lumbar acceleration is often overlooked as a key variable when biomechanically assessing lumbar response in rear-end collisions. Previous studies have assessed lumbar accelerations for occupant types individually, but comparative analyses between surrogate occupant types have been limited. Human volunteers best reflect kinematics in real crash scenarios but are limited to low-severity impacts due to ethical limitations. Post-mortem human subjects (PMHS) can be employed in higher speed impacts, however their lack of muscular input may not extensively capture occupant kinematics. Anthropomorphic test devices (ATDs) offer trial consistency and repeatability, however the widely used Hybrid III ATD's relatively simple lumbar spine may not fully emulate the human lumbar vertebrae. Based on these physiological differences between occupant types, there may be corresponding differences in lumbar spine acceleration that have not been objectively quantified. The aim of this study was twofold: (1) To conduct a comprehensive literature review of peak longitudinal lumbar acceleration data to statistically evaluate differences between surrogate occupant types and (2) To construct a mathematical model of occupant lumbar acceleration using vehicle change in velocity (delta-V) in rear-end impacts. Present literature identified that lumbar acceleration testing was conducted at higher delta-Vs with ATDs and PMHS and lower delta-Vs with volunteers. Accelerometer placement location was found to have a significant effect on lumbar acceleration with respect to both vehicle acceleration and delta-V. The predictive model (R2 = 0.93, p <0.01) obtained in this study enable forensic biomechanical experts to predict occupant lumbar acceleration from crash parameters in low-speed rear-end collisions.