The Biomechanical Stresses on the Lumbar Spine during Lifting and Lowering

The biomechanical approach was explored to examine the risk difference between lifting and lowering tasks with several task parameters in this study. An experiment was conducted to collect the variables of kinematics in the laboratory where motion analysis system and force platforms were performed and a 3D biomechanical lower model was used to obtain the estimates of the biomechanical stresses of the L5/S1 spinal disc. Ten male subjects were recruited and performed twelve experimental tasks of lifting and lowering tasks with three asymmetry angles (0,45 and 90) and two handling speeds (1s/lift and 2s/lift) in the experiment. The load of lifting and lowering was 10kg (including box weight). The range of lifts and lowers was designed between floor level and waist height of subjects. Free style lifts and lowers were the posture that subjects performed in the experiment. The results showed that the mean peak values of L5/S1 biomechanical stresses on lifting tasks were larger than those of lowering tasks with various handling angles and speeds. The compressive forces for L5/S1 disc both on lifts and lowers ranged between 572 and 723 N and were larger than shear forces and torsional forces (60 to 466 N). The lumbosacral stresses on lifting tasks were larger than those of lowering tasks at different handling speeds. When the results for two handling speeds were considered, the mean peak value of lumbosacral stresses was mostly larger at 1s/lift. The experimental results showed that the risk of MMH-related low back injuries would increase on lifting tasks.