Three dimensional moments in the lumbar spine during asymmetric lifting

Objective. To better understand the loads placed on the spine during asymmetric lifting. Design. Analysis of variance was used to test the effects of asymmetry (0, 45, 90 °), event (up, down, min and max), and trial (first and second) on applied spine moments and resulting EMG signals in the lumbar spine. Background. Loading conditions resulting from symmetric lifting are well documented in the literature, yet free-style asymmetric tasks have not been intensively studied. Methods. Infrared markers and EMG electrodes were fixed to ten subjects. Subjects were asked to lift a 45 N weight from three different positions in relation to the sagittal plane. External loads on the L3-L4 and L4-L5 disc planes were calculated. Maximum moments and EMG were compared with those at lift off and set down of the burden. All lifts were repeated twice. Results. Introducing asymmetry to the lift increased lateral bending and twisting moments. Flexion moments increased by approximately 5% after lift off of the load. During the second repetition of the lift, flexion and twisting moments decreased and increased, respectively. EMG signals were greater on the contralateral side during asymmetric lifts. Conclusions. Asymmetric lifting places complex loads across the trunk, which may become increasingly asymmetric with repeated trials.