Effects of lumbar curvature on low back pain risk factors during repetitive postural loading

Abstract

Effects of lumbar spine curvature on reducing risk factors for reporting low back pain (LBP) at work were assessed for a "light" but repetitive simulated workplace assembly job. Nine women stood at a target trunk angle of 30° and assembled plastic toys on a table for 25 minutes in one minute work cycles, at a work/recovery ratio of 55/5 seconds. Flexed (rounded back) postures, often observed in industry, and lordotic (hollow back) postures maintained by back extensor muscles and proposed to reduce risk by reducing shear forces, were studied. Spinal loading was imposed by torso weight only. Twenty-five minutes of this simulated job produced discomfort scaled as "strong" to "very strong" regardless of spinal posture. Lordosis required median EMGs of 15% MVC. Flexed postures lowered back extensor EMG to as little as 5% MVC but not to zero. This apparently "light" job seems to expose people to quite high risk of reporting LBP (estimated at about 80%), mainly because of high cumulative spine loads, regardless of the spinal posture adopted.