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A Biomechanical Basis for Low Back Injury Risk in High Exertion Tasks

Manual work is still very prevalent in many jobs today. This paper will explore the historic role that biomechanics has played in understanding these outcomes, as well as reviewing various prevention strategies used today. The focus of the presentation will be on occupational low back pain. The discussion begins with the fundamental biomechanical reality; that the lumbar spine is often subjected to extremely large compression forces when one stoops to pick up an object, even if the object is of moderate weight. The paper will discuss this outcome, as well as biomechanics research in the late 80s that lead to inclusion in 1994 of a torso twisting risk factor in the “NIOSH Lifting Guideline.” The growing use of mechanical aids (hoists, articulated arms and conveyors) has done a great deal to alleviate high levels of low back stress while lifting, but too often these same devices require people to twist and push and pull objects. High torso muscle antagonistic actions and vertebral shear forces were being predicted in such activities, especially when fast motions were involved. Concern also over shoulder injuries was growing related to the use of these devices, leading to the need to develop and use models of whole body exertions in industry to understand the full complexity of the problems for various groups of people. Recently some biomechanics research began to focus on another aspect of vertebral column function that makes it vulnerable to injury, particularly during fast motions with light loads. This vulnerability is due to the column's reliance on well coordinated torso muscle contractions to control its inherent dynamic instability.