The load on the lumbo-sacral joint and trunk muscle activity during lifting

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Abstract
Four modes of lifting 12-8 kg from floor to table were studied on healthy subjects. 1EMG was recorded from the lumbar erector spinae, the rectus and oblique abdominis muscles. The loading moment of force for the lumbo-sacral joint was calculated at regular intervals during the course of the lifts and the compressive loading force on the L5-S1 disc was estimated. Lifting with straight knees and lifting with bent knees and burden moved in front of the knees give about the same maximum loading moment of force at the beginning of the lifts, 217 and 200 Nm, respectively. The corresponding compressive forces on the L5-S1 disc were 4390 and 4425 N. Lifting with bent knees, straight back and burden moved between knees and close to the pelvis gave significantly lower values, 160 Nm and 3461 N. The proportion of the mentioned maximum loading moments of force for L5-S1 which is caused by the weights of the body-segments was found of be ∼ 70% for all lifts, and the loading moment of force caused by the burden was only 30%. In the final phase of the lifts there was a reduction of loading moment by at least 40% when the subjects advanced to the table before putting the box down, compared with keeping the feet in the initial position.