Effects of lift conditions on three-dimensional trunk kinematics
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The objectives of this study were to determine how box size, box weight and task duration affect three-dimensional lumbar kinematics and moment placed on the low back during manual materials handling. A simulation of a lifting task was carried out in which 16 participants repetitively lifted 1 of 4 different box sizes containing 5 kg and 10 kg for 30 minutes. Low back kinematic data were collected with a Lumbar Motion Monitor (LMM) at three times for five minutes during the task. The resulting external peak moment and estimated risk of low back disorder (LBD) were also evaluated. Results indicated that weight condition influenced all the sagittal kinematic parameters, with the more extreme bending and low back flexion velocities associated with the 5kg load condition. Participants also exhibited greater velocities when reaching for the box with the lowest height. The data collection recording period influenced most of the sagittal motion parameters and lateral bending parameters, with the largest range of motion and highest velocities associated with the last run. The lifting component of the task introduced significantly higher sagittal peak acceleration than the lowering component. Increases in box size and box weight increased the moment arm but only the increase in box weight increased the estimated LBD risk. These results demonstrate that light manual material handling may be associated with faster body motion that can influence the loading placed on the low back, and that biomechanical differences exist between lifting and lowering tasks. Additionally, it is recommended that researchers consider the changes in kinematics that occur over time when evaluating repetitive lifting tasks such as those in this study.