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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Eight highly-skilled hammer throwers were studied using film analysis procedures. The location and velocity of the center of mass (c.m.) of each thrower, hammer and thrower-hammer system were calculated. The vertical component of motion of all three c.m.s followed cyclic patterns with one fluctuation per turn. ⋯ In the horizontal direction, the c.m.s of the thrower and of the hammer followed roughly trochoid patterns as a result of the combination of rotation with forward displacement across the throwing circle. Their rotations were out of synchrony by approximate synchrony with the hammer, or an essentially straight trajectory. The results of this study suggest that the investigation of the hammer throw might be facilitated by the use of a quasi-inertial non-rotating reference frame that follows the general motion of the system c.m. while ignoring its fluctuations within each turn.
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A mathematical model of the patellofemoral joint taking into account movements and forces in the sagittal plane is described. The system parameters of the model are the locations of the attachments of the quadriceps muscle and the patellar ligament, the length of the patellar ligament, the dimensions of the patella and the geometry of the articulating surfaces. ⋯ The model enables calculation of the relative position of the patella, patellar ligament and quadriceps tendon, the location of the patellofemoral contact point and the magnitude of the patellofemoral compression force and the force in the patellar ligament as a function of the location of the tibial tuberosity at different flexion-extension angles of the knee. The model is validated by comparing model data with experimentally determined data.
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Journal of biomechanics · Jan 1984
The pattern of hammer speed during a hammer throw and influence of gravity on its fluctuations.
Hammer speed at release is one of the most important factors contributing to the distance of a hammer throw. Hammer speed follows a generally increasing trend during the throw, with one fluctuation per turn. The purpose of the present paper was to quantify the influence of gravity on the speed fluctuations. ⋯ These values were subtracted from the corresponding values of hammer speed. The amplitude of the fluctuations was reduced in the corrected speed functions, indicating a contribution of gravity to the original fluctuations. However, the fluctuations were still clearly present in the corrected speed functions, indicating the existence of other causal factors.
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Journal of biomechanics · Jan 1982
Mechanical properties of traumatized rat tendo-achilles and the effect of an anti-inflammatory drug on the repair properties.
This paper reports on the effect of orally administered flurbiprofen, a potent inhibitor of prostaglandin synthesis (cyclo oxygenase inhibitor), on the mechanical properties of traumatized rat tendo-achilles to see if the F2 alpha prostaglandin was affected and hence the repair process. The drug (1 mg) was administered daily for 7 days to 18 rats whose tendo-achilles were traumatized by crimping using a predetermined force (50 N) applied for 10s. ⋯ Forty non-traumatized, untreated rats were examined as controls. In vitro studies showed that there was no significant difference in the stress--strain and relaxation characteristics between the three groups and no histological differences were observed.