Biomechanical Trade-Offs in Manual Material Handling: Some Tasks Reduce Lumbar Loading But Increase Thoracic Loading

Abstract

Job design that is protective of the lumbar spine may inadvertently increase stresses on the thoracic spine, potentially leading to thoracic injury. In this study, we determined the ratio of thoracic to lumbar loading during various tasks, including stoop and squat lifts. Loading on the thoracic spine was calculated based on previously reported thoracic intradiscal pressures and cross-sectional areas, and compared to loading on the lumbar spine calculated using the same methodology. Results demonstrated that the ratio of thoracic and lumbar loading is not uniform and varies with the posture used during manual material handling tasks. Specifically, the loading of the thoracic spine increased during squat lifts, as compared to stoop lifts, whereas the loading on the lumbar spine decreased during squat lifts. This study adds to the body of knowledge that there are trade-offs between squat and stoops lifts and neither are without risks.