Comparing the biomechanical and psychophysical demands imposed on paramedics when using manual and powered stretchers.

The aim of this investigation was to compare the effect of three different stretchers (two powered and one manual) on the biomechanical and psychophysical demands experienced by paramedics when performing routine stretcher handling activities. Eight experienced paramedics performed stretcher raising, lowering, unloading and loading tasks. Video data of task performance and static force requirements were recorded and input into a posture matching program with a quasi-static linked segment model (3DMatch) to compute peak and cumulative L4/L5 compression and shear forces and shoulder moments during each activity. Ratings of perceived exertion (RPE) were recorded from paramedics upon the completion of each task. Use of powered stretchers with load assist functionality reduced the demands on paramedics. Peak L4/L5 forces were reduced by 13-62% and 58-93% for compression and shear respectively when using powered stretchers to perform routine stretcher handling activities. Shoulder flexor moments and RPE scores were reduced by 16-95% and 29-60% respectively when using the powered stretchers compared to the manual stretcher. However, cumulative forces showed mixed results. Although powered stretcher use decreased peak forces, loading and unloading a powered stretcher took 1.5 to 3.4 times longer then when using the manual stretcher, which may explain the mixed results regarding cumulative forces. Based on the RPE scores, paramedics preferred power stretchers relative to the manual stretcher. This study demonstrates that powered stretchers can reduce peak biomechanical and psychophysical exposures associated with the development of musculoskeletal disorder (MSD) during routine stretcher handling activities with minimal increases in cumulative exposures.