During slow, symmetrical lifts the anterior abdominal wall buckles at about the level of L3 vertebra, causing a local reduction in the cross-sectional area of the abdominal cavity. Calculations are made on the effect this buckling has on both lumbar vertebral compression and erector muscle tension. A simple exercise in statics shows that the size of the diaphragm is not relevant in determining the load relief due to intra-abdominal pressure, nor are the tensile loads in the abdominal muscles arising from this pressure.
Finally a description is given of a simple harness worn on the torso, which is predicted to reduce substantially the loads in both the erector muscles and the lumbar vertebrae.
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