Relative contributions of the lumbar spine and pelvis to trunk motion during sagittal plane manual materials handling

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McKean, Christopher R.
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University of Guelph

Eleven males and 11 females participated in a sagittal plane motion analysis study in which they lifted and lowered a symmetric load under two different conditions. Independent variables were sex (Male vs. Female), lifting condition (Freestyle vs. Constrained), and direction (Lift vs. Lower). The Constrained condition simulated handling loads in an industrial bin. The Freestyle condition had no obstruction. Dependant kinematic variables were mean peak trunk, pelvis, and knee flexion, and mean peak percent of maximum lumbar spine flexion (θ\sb%LUM). The sagittal plane pattern of movement between the lumbar spine and pelvis was studied by monitoring angular displacement time-histories, and via the calculation of phase angles between the two structures. Dependant kinetic variables were mean and peak thoracic and lumbar erector spinae EMG levels. Synchronous movement was illustrated between the lumbar spine and pelvis for all conditions but the constrained lift. Sagittal plane movement between these two structures was more sequential for the constrained lift. No sex effect existed for any variables. θ\sb%LUM was significantly greater during the lift than the lower, indicating slightly higher risk for low back injury during lifting. Mean peak trunk flexion was substantially greater for the Constrained condition versus the Freestyle condition. This was a result of an increase in mean peak pelvic fusion. θ\sb%LUM remained constant between these two conditions, and did not reach the level of flexion required to elicit the flexion-relaxation phenomenon.

Lumbar spine, Pelvis, Trunk motion, Sagittal plane, Materials handling