Lumbar mechanics of floor to knuckle height lifting on sloped surfaces

Abstract

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). Relevance to industry Lifting from the floor places a person at risk for low back pain and injury. These risks appear to be increased when facing up or down an inclined surface. Therefore, additional care should be taken when working in this awkward environment.