Lumbar mechanics of floor to knuckle height lifting on sloped surfaces

摘要

Lifting a load from a sloped floor, where both the lifter and load are on the inclined surface, may be encountered in a variety of manual materials handling situations. The goal of this study was to determine the effects of lifting from a sloped floor surface (both facing up and down 10° and 20°) on the lumbar region and compare with the level surface. Twenty-one men and 22 women completed a single session of six freestyle lifts in each condition while sagittal plane kinematics and erector spinae (ES) muscle activities were measured. Secured in a milk crate, the men lifted 25 kg while the women lifted 15 kg. A top-down inverse-dynamics model calculated the net moment at L5/S1. Subject-selected foot placement relative to the crate was significantly affected by lifting condition (p< 0.001) with subjects tending to stand further from the load as slope changed from down hill to up hill. Maximum L5/S1 moments were not affected by lifting condition (p = 0.330). However, the static contribution from mass location significantly increased when facing up hill (p< 0.001). At the time of the maximum moment, forward torso lean was increased (p< 0.001) and the natural lordosis of the low back spinal curvature was reduced in the down hill lifting conditions (p<0.001). ES activity was not affected by slope (p = 0.932). No significant interactions were observed between the men and women (p> 0.007).