Biomechanical Demands Attributed to Motion Platform Induced Interruptions of Manual Materials Handling Tasks

摘要

Growing demands for natural, non-renewable resources have forced exploration in challenging environments such as the polar ice-fields or ocean locations far from shore. These harsh environments impose added demands upon operators by virtue of the motion-rich conditions under which manual materials handling (MMH) have to be performed. MMH tasks become more difficult to perform in moving environments as stability under foot and load accelerations are affected by the unpredictable, multi-directional forces acting on an operator. While much is known about the risks of manual materials handling in stable conditions, little has been documented about the potential negative effects of working in motion-rich environments. The purpose of this study was to examine the biomechanical characteristics associated with MMH tasks successfully executed and those in which a platform-induced MII occurred during the MMH attempt. Twelve healthy male subjects performed four different lifts while exposed to a simulated ship's motion. A stable floor condition, collected in a laboratory, was used as a baseline for comparison. Deck motions were simulated using a 6 degree of freedom motion bed which incorporated mathematical models of deck motions typically observed on an offshore supply vessel. The primary platform motion was a pitch motion, which acts to rotate the body forward and backward in a sagittal plane. All lifts were done bimanually and the four lifting tasks were varied by mass, load stability and horizontal and vertical distances the load travelled during the lift. Dependent measures included electromyography (EMG) signals from several trunk muscles and thoracolumbar motions collected via a Lumbar Motion Monitor (LMM). A repeated measures analysis of variance was employed to examine the differences between thoracolumbar velocities and trunk EMG activities during successful lifts and lifts during which a motion induced interruption (MII) was identified. In general, the maximum EMG magnitudes of the erector spinae and external oblique musculature increased as MII events occurred. There were increases in the maximum thoracolumbar velocities in the lateral bending and twisting planes for lifts incurring a MII across all lifting conditions when compared to successful lifts in the pitch motion. These data suggest that performing tasks in moving environments will place an operator at an increased risk for musculoskeletal fatigue and injuries, particularly when the rate of MII is high. The work effort for performing MMH tasks in moving environments is considerably greater than those performed in stable underfoot situations. Existing guidelines recommended for such MMH activities should be considered with caution if employed as administrative controls to mitigate the ergonomic risks of working in a moving environment.