Sitting posture: analysis of lumbar stresses with upper limbs supported

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Abstract
The analysis of lumbar stresses in the sitting posture is performed for situations in which upper limbs are fully or partially supported by a worktable. A method is presented for biomechanical evaluation of moments and compressive forces acting on the lumbar intervertebral disk, based on the use of a force platform, a TV camera and a integrated system for the elaboration of signals. The on-line pictures given by this equipment show the ground reaction vector superimposed on the subject''s image and allows a detailed analysis of the intervertebral loads. The results obtained in the subjects under study (six males and five females) are analysed statistically and extrapolation on the basis of body weight is demonstrated to be possible in situations where the arm support forces are not known. The myoelectric activity of the erector spinae muscles was also assessed. The aim of the study was to furnish a tool that can be used in all occupational environments and that will allow evaluation of the lumbar stresses in the sitting posture to be made with a minimum use of complex equipment. An example of the practical application of this concept is presented.