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PubMed1985

Anisotropic yield behavior of bone under combined axial force and torque.

In this study the yield behavior of cortical bone was determined under combined loading conditions involving tension, compression and torsion. The axis of each test sample coincided with the long bone axis. To minimize viscoelastic behavior, tests were conducted using an effective strain rate in the range of 0.01-0.06 s-1. Experimental yield loci for bovine and human cortical bone were determined using a strain offset technique to determine the 'common yield point' for combined loading. Several failure criteria which have been used for composite materials were examined for applicability to the experimental results. Data were obtained for bovine and human tibial and femoral bone. The Tsai-Wu criterion was in best agreement to the test data, although Hill's criterion could describe the individual compression-torsion or tension-torsion regimes with good accuracy.

Animals↗
PubMed1987

Recording electrophysiological signals from small moving animals: electrode fixation and low torque swivel for recording a weakly electric fish in a group.

A silicone rubber ring maintains an electrode on the electric organ of a mormyrid fish. The electrode is connected with a novel swivel, which allows free motion of the wire around its axis. The principle of the rotating contact is based on magnetic contact between a steel pin (moving) and a steel ball (fixed). Using this apparatus, a single fish within a group is recorded. The general electric activity of the group is recorded by means of two sets of fixed differential electrodes. These devices may be adapted for neuroethological studies of other small animals.

Animals↗
PubMed1995

Dynamic muscle strength training in stroke patients: effects on knee extension torque, electromyographic activity, and motor function.

The effects of training with isokinetic maximal voluntary knee extensions were studied in stroke patients. Two groups of 10 patients each trained twice a week for 6 weeks. One group trained exclusively eccentric movements and the other exclusively concentric movements. The effects were evaluated from the following tests before and after the training period. The maximal voluntary strength in concentric and eccentric actions of the knee extensor and flexor muscles was recorded together with surface electromyography at constant velocities of 60, 120, and 180 deg.s-1 on three different days. The body weight distribution on the legs while rising and sitting down was measured with two force plates. The self-selected and maximal walking speeds and the swing to stride ratio of the paretic leg were measured. After the training period, the knee extensor strength had increased in eccentric and concentric actions in both groups (p < .05). The eccentric and the concentric strength in the paretic leg relative to that of the nonparetic leg increased in the eccentrically trained group (p < .05) but not in the concentrically trained group. The restraint of the antagonistic muscles in concentric movements increased after concentric (p < .05) but not eccentric training. A nearly symmetrical body weight distribution on the legs in rising from a sitting position was noted after eccentric (p < .05) but not concentric training. Changes in walking variables were not significantly different between the groups. Eccentric knee extensor training was thus found to have some advantages as compared to concentric training in stroke patients.

Aged↗
PubMed1997

Selective activation of the external oblique musculature during axial torque production.

OBJECTIVE: To investigate whether different geographical regions of the external oblique musculature can activate at different levels and, if they do, to quantify the magnitude of these differences as a function of postural parameters during twisting exertions. DESIGN: Repeated measures design using electromyography on healthy subjects. BACKGROUND: The majority of the models currently used to assess spinal loading have represented the trunk musculature using single force vectors connecting a muscle's point of origin to its point of insertion. However, for muscles with large areas of origin and/or insertion (such as the external obliques), this single vector modelling approach misrepresents the multiple vector reality which, in turn, underestimates the complex loads these muscles can develop. METHODS: Nine subjects performed sub-maximal isometric axial twisting exertions (20, 40 and 60% of maximum voluntary contraction) while assuming six different postures defined by three levels of axial rotation (-20 degrees, 0 degrees and 20 degrees ) and two levels of sagittal flexion (0 degrees and 20 degrees ). As the subjects performed these isometric exertions, the integrated electromyographic activity was sampled using surface electrodes at five different locations over the right and the left external oblique muscles. RESULTS: The results showed significant (p<0.05) regional differences in the activation profiles and these activation profiles changed as a function of trunk posture. CONCLUSIONS: The external oblique musculature is capable of differential activation and the activation profiles of the different regions are affected by the posture of the torso. RELEVANCE: These findings suggest that the external oblique muscle is capable of selective activation of different regions along its cross-section and should, therefore, be modelled using multiple vectors. The result can have a direct bearing on the calculated spine loading, especially lateral and anterior/posterior shear forces.

Journal Article↗