The relation between trunk strength measures and lumbar disc deformation during stoop type lifting

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DeBeliso, M, O'Shea, P, Harris, C, Adams, K & Climstein, M 2004, 'The relation between trunk strength measures and lumbar disc deformation during stoop type lifting', Journal of Exercise Physiology, vol. 7, no. 6, pp. 16-26.

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Low-back pain and injury are responsible for a major portion of lost workdays and injury compensation claims. Strong well-conditioned trunk musculature has been forwarded as a counter measure towards reducing low-back injuries. The purpose of this study was to determine if strong well-conditioned trunk muscles relieve stresses encountered by the lumbar spine during stoop type lifting. Twelve male subjects (49.7±3.7 yr) performed a session of stoop type lifting with a loaded milk crate (11.5 kg), at 4 reps/min, for 15 min in accordance with the NIOSH lifting equation. Lateral fluoroscopic images were collected prior to and following the lifting session with the subjects positioned at the initiation (flexed trunk), mid-range, and completion of the lift (erect standing). The initial series of images were collected under a no-load condition, while the second series were collected with the subjects lifting the 11.5 kg milk crate. Images were imported into AutoCAD where lumbar disc deformation and joint angles were measured by calculating changes in position of adjacent vertebra (L3-4 and L4-5). A reduction of deformation was deemed indicative of reduced stress. Trunk extension and flexion strength were measured with a Kin Com isokinetic dynamometer. Trunk flexion endurance was measured via a 60 s curl-up test. Trunk strength and endurance were compared to disc deformation and joint angles to determine if any meaningful relationships existed. Significant inverse relationships were detected (p<0.05) between: abdominal strength and shear deformation (flexed trunk: positions: r=-0.63 thru -0.96), abdominal endurance and shear deformation (erect trunk: r=-0.74 thru -0.75), and spinal erector strength and L3-L4 joint angle (erect trunk: r=-0.60). Strong, well-conditioned trunk musculature is associated with reduced lumbar disc deformation and presumably, less stress on the lumbar spine.

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