Changes in trunk and spine biomechanics during repetitive fatiguing exertions

The objective of this study was to document trunk motions, muscle activity and spinal load during repetitive fatigueing lifting tasks. Ten warehouse employees transferred twelve pallets of 23 kg. boxes at a rate of 125 lifts per hour. Prior to transferring the load on each pallet, controlled "test" exertions were performed. Results from test exertions indicated lifts performed under more fatigued conditions were accomplished with greater pelvic flexion and reduced trunk angle. Compressive load on the spine decreased but shear loads increased significantly with fatigue. These findings may help explain how fatigue increases the risk of LED during repetitive lifting.