Estimating 3D L5/S1 Forces for Heavy Lifting Work Performed by Emergency Medical Technician

Emergency medical technicians (EMTs) routinely perform heavy lifting tasks that impose substantial biomechanical demands on the lower back and may increase the risk of low-back injury and disorders. This study estimated the loading of the L5/S1 joint during three EMT relevant lifting tasks using an inertial motion capture (IMC) based top-down inverse dynamics framework. Fifteen certified EMTs performed simulated equipment and patient lifting tasks while wearing IMCs to estimate their body segment kinematics. Their L5/S1 compression and shear reaction forces were estimated from segment kinematics, anthropometric parameters, and hand-derived external loads. Across all lifting tasks, 53–80% of participants exceeded the compression action limit, and 13–87% exceeded the 1000 N shear reference limit. Equipment lifting produced the highest estimated compression force, likely due to an asymmetric one-handed lifting strategy. These findings suggest that equipment and patient lifting tasks can impose a significant risk of low back injury for EMTs.