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The influence of torso flexion on fatigue failure of lumbosacral motion segments.

Marras-WS; Gallagher-S; Litsky-AS; Burr-D
Transactions of the 50th Annual Meeting of the Orthopaedic Research Society, San Francisco, California, March 7-10, 2004, 2004 Mar 7; Vol. 29, poster No. 1119 :79
Recent reviews of the epidemiology literature have concluded that a number of work-related physical factors show consistent and positive association with the occurrence of low back disorders. Among the workplace factors showing positive associations are jobs involving manual materials handling, those involving frequent bending and twisting, and those where workers endure heavy loads. One common thread among the workplace factors linked to low back disorders is that they all involve situations where the tissues of the lumbar spine are repeatedly placed under high levels of compression and shear loading. An important determinant of the load experienced by the lumbar spine in manual load lifting is the degree to which the torso is flexed. Torso flexion is quite common in occupational lifting activities. Epidemiologic studies have shown that torso flexion is an important risk factor for low back disorders. Biomechanical analyses suggest that spinal loads can double or triple as a function of torso flexion angle when lifting a given weight. Not only is the load magnitude greater when the torso is flexed, the mixture of compression and shear forces acting on the spinal segments is also altered, with an increasing shear component in flexed postures. Moreover, the rate at which these loads is applied to the spine becomes greater when the torso is flexed. All of these factors may have a significant impact on the development of fatigue failure in tissues of the lumbosacral spine.
Biomechanics; Back-injuries; Manual-materials-handling; Manual-lifting; Materials-handling; Musculoskeletal-system; Musculoskeletal-system-disorders; Spinal-cord
NIOSH Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236
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Transactions of the 50th Annual Meeting of the Orthopaedic Research Society