Low back load in airport baggage handlers.

Low back pain (LBP) constitutes a major economic problem in many countries. The causes of LBP are still largely unknown and several risk factors have been suggested including heavy lifting, which causes high compression forces of the tissues in the low back. Micro-fractures in the endplates of the vertebrae caused by compression forces have been suggested as a source of unspecific pain. Although airport baggage handlers exhibit a high prevalence of musculoskeletal complaints the amount of biomechanical research within this and similar areas is limited. The aims of this thesis were to perform a general description of the lumbar loading in baggage handlers (Paper I), to develop a generically useful tool to examine specific lumbar compression in a valid manner (Paper II & III), and to investigate the spinal loading in common work tasks for baggage handlers. (Paper III). We recorded electromyography during baggage handling in the baggage hall, by a conveyor, and inside the aircraft baggage compartment. Electromyography was analyzed using amplitude probability distribution functions (APDF) on both tasks and full day recordings and root mean square (RMS) values on tasks. Furthermore, we estimated L4/L5 compression and moment along with shoulder flexor moment with a Watbak model based on more specific subtasks. In addition, we built an inverse dynamics-based musculoskeletal computer model using the AnyBody Modeling System (AMS). Motion capture recorded the movements in 3D during a stooped and a kneeling lifting task simulating airport baggage handler work. Marker trajectories were used to drive the model. The AMS-models computed estimated compression forces, shear forces and the moments around the L4/L5 joint. The compression forces were used for comparison with the vertebral compression tolerances reported in the literature. The RMS muscle activity was high in all tasks. The average peak RMS muscle activity was up to 120% EMGmax in the erector spinae during the baggage hall task. There were no significant differences between the tasks in the APDF analyses. The L4/L5 compression and extensor moment from Watbak were significantly higher in the baggage compartment task than in both the conveyor and baggage hall tasks. The stooped lifting task produced 5,541 N compression in the L4/L5 joint and a kneeling task produced 4,197 N in the AMS models. These compression forces were close to the average compression tolerance and exceed the recommended limits for compression during lifting.