Journal of biomechanics
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Journal of biomechanics · Jan 1987
Effects of an anatomically detailed erector spinae model on L4/L5 disc compression and shear.
Biomechanical models utilized for analysis of tasks that load the lumbar spine often predict the resultant moment, disc compression and sometimes shear. Usually the extensor muscular and ligament forces of the lumbar spine are assumed to act 5 cm posterior to a disc centre of rotation. This study has re-examined the generation and pathways of muscular force transmission within the extensor musculature. ⋯ The shear force estimates could be altered from more than 500 N (L4 tending to shear anteriorly on L5) to less than 200 N with L4 tending to shear posteriorly on L5. Using the combination of input variables considered by the authors to be most feasible to estimate compression, a single 'equivalent' extensor soft tissue moment arm of 7.5 rather than 5 cm would be needed to equate the compression. This simplification of course, does not accommodate the shear force estimate problem.
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Journal of biomechanics · Jan 1987
Mechanical characterisation of human postburn hypertrophic skin during pressure therapy.
Postburn hypertrophic scar commonly occurs among the Chinese resulting from serious burn injuries. A non-invasive method of preventing and controlling such scars is using pressure therapy. Its mechanical properties are used as a quantitative indicator for scar assessment and maturation. ⋯ A correlation is obtained between the clinical scar grading and these mechanical properties. Altogether 300 individual measurements were made on fifteen Chinese patients of ages ranging from 18 to 44 with burn injuries of superficial to whole skin thickness burns which necessitated surgical graft procedures. This in vivo study of the mechanical properties of hypertrophic scar tissue lasted 2 yr.
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Journal of biomechanics · Jan 1987
The relationship between trunk muscle electromyography and lifting moments in the sagittal and frontal planes.
In this study, we explore the relationship between moments in the frontal and sagittal planes, generated by a lifting task, vs the electromyographic (EMG) activity of right and left trunk muscle groups. In particular, we postulate that the functional dependence between erector spinae muscle activity and the applied lifting moments about the spine is as follows: the sum of left and right erector spinae processed EMG depends on the sagittal plane moment, and the difference of left and right erector spinae processed EMG depends on the frontal plane moment. A simple out-of-sagittal plane physical model, treating the lumbar spine as a two degree-of-freedom pivot point is discussed to justify these hypotheses. ⋯ The processed EMG signals of the left and right erector spinae muscles are summed and differenced for comparison to the measured sagittal and frontal plane moments. A linear correlation (r2) of 0.96 was obtained for the sum of erector spinae EMG vs the sagittal plane moment; a corresponding value of r2 = 0.95 was obtained for the difference vs the frontal plane moment. No correlations (r2 less than 0.004) was found for the sagittal plane moment and the difference of the left and right erector spinae EMG, and the frontal plane moment and the sum of the left and right erector spinae EMG.