Abstract
An analysis was performed to estimate compression and shear loads on three motion segments of the lumbosacral spine in neutral and flexed torso postures. 87 lifting tasks were evaluated using a biodynamic lifting model for lifts starting at 0, 22.5 and 45 degrees torso flexion. Results indicated that the compressive loading on the L5-S1 disk in the 22.5 and 45 degree torso flexion conditions were approximately double and triple those observed in the 0 degree condition. Shear reaction forces acted anteriorly in neutral and moderate flexion, but acted posteriorly in full flexion. Load rates were also dramatically affected by posture, with the load rate in the fully flexed posture being seven times greater than in the neutral posture. Analysis of the upper lumbar levels (L1–L2 and L3–L4) suggested significant shear forces; however, shear forces at L5-S1 remained moderate in all conditions. Results of this analysis will be used in a study examining the fatigue failure of lumbar motion segments when subjected to loads experienced at different angles of torso flexion.
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