Biomedical subjects

J Trafimow

Publications and source records attributed to J Trafimow.

6 recordsLinked to original sources

PubMed1995

The effects of lateral trunk bending on muscle recruitments when resisting nonsagittally symmetric bending moments.

STUDY DESIGN: Surface electromyographic activities were measured in 15 subjects as they maintained a static laterally bent trunk posture and resisted sagittally symmetric and asymmetric moments applied to their torsos. The moment magnitudes were 20 and 40 Nm and had transverse plane directional components in 30 degrees increments surrounding the subjects' torsos. OBJECTIVES: To quantify the myoelectric responses from eight trunk muscles as asymmetric loads were applied to the laterally bent torso. SUMMARY OF BACKGROUND DATA: Asymmetric material handling frequently results in lateral bending of the torso. Each of these factors have been linked via epidemiologic investigations to the incidence of low back disorders. Little information is available that describes the response of the trunk muscles when the trunk is bent to the side. METHODS: Subjects stood in a reference frame and adjusted their trunk posture to marks on a video display that indicated when a 20 degrees lateral bend to the right had been achieved. Moments were applied to the torso by connecting weights via cables and pulleys to a chest harness. Electromyographic activities were recorded bilaterally from the erector spinae, latissimus dorsi rectus abdominis, and external oblique muscles. RESULTS: The electromyographic data indicated that the muscles showed the greatest activity when they were in opposition to the applied sagittal and frontal plane moments. The left external oblique showed the greatest response and was sensitive to the widest range of moment direction conditions. All of the muscles, except for the left latissimus dorsi, at times contributed antagonistic moments in the sagittal plane or the frontal plane, or in both planes. These data were compared with previously obtained data from an upright neutral posture. CONCLUSIONS: Statistical analyses indicated that the responses of both external obliques and the left erector spinae to the moment direction conditions were significantly different between the laterally bent and neutral postures.

Abdominal Muscles↗

PubMed1994

Trunk muscle activation. The effects of torso flexion, moment direction, and moment magnitude.

OBJECTIVES: This study was performed to quantify the electromyographic trunk muscle activities in response to variations in moment magnitude and direction while in forward-flexed postures. METHODS: Recordings were made over eight trunk muscles in 19 subjects who maintained forward-flexed postures of 30 degrees and 60 degrees. In each of the two flexed postures, external moments of 20 Nm and 40 Nm were applied via a chest harness. The moment directions were varied in seven 30 degrees increments to a subject's right side, such that the direction of the applied load ranged from the upper body's anterior midsagittal plane (0 degree) to the posterior midsagittal plane (180 degrees). RESULTS: Statistical analyses yielded significant moment magnitude by moment-direction interaction effects for the EMG output from six of the eight muscles. Trunk flexion by moment-direction interactions were observed in the responses from three muscles. CONCLUSIONS: In general, the primary muscle supporting the torso and the applied load was the contralateral (left) erector spinae. The level of electromyographic activity in the anterior muscles was quite low, even with the posterior moment directions.

Adult↗

PubMed1993

The influence of load knowledge on lifting technique.

The purpose of this study was to analyse the influence of load knowledge on lifting technique. Ten men lifted a box containing either no weight or weights of 150, 250 or 300 N with and without knowledge of what was inside the box. The kinetics and kinematics of the lift were analysed using a force plate, an optoelectronic motion analysis system, and a rigid body link model. At 0 N lifting, the unknown load resulted in a jerk-like motion and a significantly increased peak L5-S1 flexion-extension moment. At 150 N there was also a significant increase in the speed of trunk extension with unknown weights, but the L5-S1 moment remained unchanged. At higher load levels there were only minor differences between lifting techniques when knowing and not knowing the load. We conclude that lifts are approached assuming a certain weight, and that when the assumption is wrong and the load lighter than anticipated lifting is performed with a 'jerking' motion, creating unnecessary loads on the lower back.

Adult↗

PubMed1991

Motion of the lumbar spine. Reliability of two measurement techniques.

A computer-assisted instrument, the isotechnologies B-200, was compared with double goniometer technique for measuring flexion-extension and lateral bending and a compass technique for measuring axial rotation. Test-retest measurements were performed, and the reliability of each method was determined. Generally, low correlations were obtained between two tests performed 1 week apart. The B-200 had poor reproducibility in flexion-extension, particularly when measured separately. Somewhat better results were obtained in lateral bending and rotation. With the goniometers r values close to 0.8 were obtained in flexion, and statistically significantly repeatable data were also obtained in combined flexion-extension and right rotation. Because of the poor repeatability statistical analysis comparing the two instruments was not meaningful. The authors conclude that an instrument such as the B-200 should not be used to measure range of motion. Inexpensive tools allow accurate measurements of, at least, flexion and extension. Small changes should not be taken to indicate true improvement or deterioration. Measurements to a single degree are not meaningful.

Adult↗

PubMed1991

The role of facet joint tropism and facet angle in disc degeneration.

In this study, the relationship between facet geometry (joint angle and tropism) and disc degeneration was analyzed. Magnetic resonance imaging and computed tomographic scans of 46 subjects less than 50 years of age were evaluated. Magnetic resonance imaging was used to determine disc degeneration, and computed tomography was used to measure facet joint angles and determine tropism. Subjects with tropism had a significantly higher prevalence of disc degeneration at all three lumbar levels examined (L3-4, L4-5, L5-S1). The average facet angles increased from L3-4 to L4-5 and further to the L5-S1 level. There was no statistically significant relationship between the magnitude of the angle and the presence of disc degeneration at any of the three levels. It was concluded that the risk of disc degeneration is increased in the presence of facet joint tropism.

Adult↗

PubMed1987

Simple constitutive model for a cortical bone.

This short study presents a simple, one-dimensional constitutive model for the cortical bone with haversian structure. The model is developed within the general framework of the continuum damage theory. The kinetic equation is derived (rather than assumed a priori) through consideration of the irreversible changes of the mesostructure. As a consequence the analytical results closely approximate experimental measurements even though the theory does not introduce a single experimentally unidentifiable material parameter.

Biomechanical Phenomena↗