Trunk muscle control of human lumbar spine stability

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The spine is a very complex biological and mechanical structure. The lumbar spine, or low back, is particularly susceptible to injury and pain and has been the focus of a great deal of research attempting to understand how it operates and how work and everyday activities can lead to tissue damage. When loads are handled, the body must find a way to use the many muscles and ligaments of the spine to perform the task with a number of objectives that must be considered. First, we want to keep the metabolic cost low. Next, we need to select from a large number of combinations of muscle forces that will successfully complete the task. Finally, we must recruit muscles that will maintain some level of stability in the lumbar spine so that it does not buckle. Often, these three objects conflict with each other. The purpose of this research is to further our understanding of how the body resolves these three different objectives and, in particular, what role mechanical spine stability plays under a variety of loading conditions. In particular, sudden trunk loading and prolonged, fatiguing tasks have been found to be particularly good perturbations for studying spine stability. We plan to use a variety of these types of perturbations to challenge the spine and further our knowledge of how we maintain stability in an effort to avoid injury. First, we will have to further refine a complex computer model of the spine, including its muscles, vertebrae and ligaments. This model will allow for stability to be calculated about the lowest six joints of the spine and about each of the three anatomical axes (flexion/extension, lateral bend, axial twist). Next, we will use this model and muscle electromyography to predict individual muscle forces and stability contributions for a wide variety of trunk perturbations. Subjects will be exposed to sudden and prolonged loading through force rapidly applied to a chest harness, to hand held loads and through movement of a robotic platform on which they will sit. The long term objective of the proposed research is to reduce low back injuries through a further understanding of trunk muscle contributions to lumbar spine mechanics.