A dynamic analysis of spinal compression with different lifting techniques

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Abstract
Although it is commonly assumed that lifting with flexed knees and the trunk erect will lead to reduced compressive force on the lower back, the benefits are only realized when the load can be lifted between the knees, i.e., close to the body. The assumption has often been based solely on an analysis of the initial lifting posture, ignoring the inertial forces due to accelerations of the body and the load. A biomechanical sagittal plane model was developed to take full account of dynamic factors, based on direct recordings of body movements, accelerations of the load and forces at the feet. Subjects (20) lifted a 15 kg box from a 10 cm high shelf to knuckle height with 4 lifting techniques: leg lift, back lift, load kinetic lift and trunk kinetic lift. In the kinetic lifts the subjects tried to use the kinetic energy of the horizontally moving load or the vertically moving body, respectively, in order to reduce the spinal load. When the peak compressions were considered the leg lift produced least stress. The compression .times. time integral over the accelerative phase of the lift, relating the total stress of a lift, was smallest in the back lift. Results of the load kinetic lift did not differ markedly from the non-kinetic lifts, but the trunk kinetic lift was clearly the most stressful of the techniques studied.