Journal of biomechanics
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Journal of biomechanics · Jan 1989
Influence of the direction of the cable force and of the radius of the hammer path on speed fluctuations during hammer throwing.
Hammer speed increases gradually during a throw, but this general increasing trend has one fluctuation superimposed in each turn. In some throwers, gravity and the forward translation of the system produce most of the fluctuation; in others, a marked fluctuation remains after the effects of gravity and of the forward translation of the system have been subtracted out. The remaining fluctuation could be produced through two mechanisms: (a) pulling on the hammer cable in a direction alternately ahead and behind the position of the centroid of the hammer path and (b) alternately shortening and lengthening the distance between the hammer head and the centroid of its path. Three-dimensional film analysis of eight highly-skilled throwers showed that the portion of the hammer speed fluctuation not due to gravity nor to the forward motion is produced mainly by pulling alternately ahead and behind the position of the centroid of the hammer path.
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Journal of biomechanics · Jan 1988
Moment-rotation relationships of the ligamentous occipito-atlanto-axial complex.
The relationships between applied pure moments at the occiput (C0) and the resulting rotations at the atlanto-occipital (C0-C1) and atlanto-axial (C1-C2) joints are quantified. In axial twist, with a moment of 0.3 Nm, a mean rotation of about 2.5 degrees and 23.3 degrees was observed at C0-C1 and C1-C2 units respectively. Both the atlas and axis contributed to produce lateral bending motion. ⋯ Lateral bending and axial rotations were strongly coupled to each other. The occipito-atlanto-axial complex exhibited a large 'neutral zone' compared to lower cervical spine segments. The likely clinical significance of these findings are discussed.
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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.