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Biomedical subjects

W S Marras

Publications and source records attributed to W S Marras.

At least 19 recordsLinked to original sources
PubMed1992

A comprehensive evaluation of trunk response to asymmetric trunk motion.

An experiment was performed to determine the reaction of the trunk muscles, using electromyography, and intra-abdominal pressure to components of trunk loading commonly seen in the workplace during manual materials handling. These components included angular trunk velocity, trunk position in three-dimensional space and trunk torque exertion level. The experiment was performed using 44 subjects. Subjects produced constant trunk extension torque about the lumbosacral junction while moving the trunk under constant angular velocity (isokinetic) conditions. Significant reactions to trunk angular velocity, trunk torque level, and unique combinations of trunk position and velocity were seen in all muscles of the trunk. The other components affected the muscles selectively according to function. Intra-abdominal pressure only reacted significantly to trunk angle and some unique trunk angle-asymmetry positions. The biomechanical implications of these findings are discussed. The reactions of the muscles to the various workplace components also were described quantitatively through equations that predict muscle activity levels.

Abdomen↗
PubMed1992

Temporal patterns of trunk muscle activity throughout a dynamic, asymmetric lifting motion.

This study examined the effects of trunk speed and exertion level on temporal aspects of trunk muscle activity patterns during dynamic, asymmetric lifting. Electromyographic (EMG) data from eight trunk muscles were collected along with trunk torque output, position, and velocity data during several repetitions of four speed/loading combination conditions. During analysis, each muscle's EMG record was reduced to three key events: a start, a peak, and an end point. For each subject, temporally ordered event lists were constructed for each test condition. Networks of events that consistently occurred regardless of loading or speed levels were constructed for each subject. Two event pairs occurred consistently for all subjects under all conditions, whereas some pairs occurred in association with specific speed or resistance levels. Temporal information related to muscle activity could be used in biomechanical models in order to predict changes in spinal loading during the course of workplace tasks.

Adult↗
PubMed1991

The effects of method of use, tool design, and roof height on trunk muscle activities during underground scaling bar use.

Epidemiologic studies have shown that the scaling bar, a hand tool used in underground mining, is frequently associated with the risk of back injury. An experiment was performed to investigate the effects of method of tool use, mine roof height, and tool design upon the activity of six trunk muscles and the ability to exert force with the bar. Roof height and scaling bar design had the largest effects on levels of muscle activation. Striking force did not differ significantly between tool designs. A biomechanical model was used to evaluate the collective effects of the trunk musculature activities upon spine loading. It was found that a significant reduction in predicted spine compression and shear forces can be achieved through the use of a counterbalanced scaling bar. The implications of these results are discussed.

Back Pain↗
PubMed1991

A three-dimensional motion model of loads on the lumbar spine: I. Model structure.

Traditionally most biomechanical models that are used to estimate the loading experienced by the spine during work focus on static, two-dimensional representations of the work. However, most work tasks impose loads on the lumbar spine under dynamic, three-dimensional conditions. The objective of this study was to describe the structure and logic of a model that is capable of producing estimates of spine loading under three-dimensional motion conditions. This model is intended for use primarily under laboratory conditions. The model was designed initially for workplace simulation in which the trunk is moving under symmetric and asymmetric constant velocity lifting conditions. Future embellishments may enable the model to be used under free dynamic conditions. The model predicts lumbar spine compression, shear, and torsional forces as well as trunk torque production continuously throughout the exertion. This information may be compared with spine tolerance limits so that the risk of causing a vertebral end-plate microfracture by workplace requirements could be determined.

Biomechanical Phenomena↗
PubMed1991

A three-dimensional motion model of loads on the lumbar spine: II. Model validation.

A three-dimensional motion model has been developed that estimates loads on the lumbar spine under laboratory conditions that simulate manual materials handling conditions. Eleven subjects experienced spinal loading during an experiment in which conditions of trunk velocity, trunk torque output, and trunk asymmetric posture were varied in a series of isokinetic velocity trunk extensions. The electromyographic activity of 10 trunk muscles, subject anthropometry, and trunk kinetics were used as input to a biomechanical simulation model described in Part I of this study. The model calculated estimates of compression, shear, and torsion loading in the lumbar spine, as well as the torque production of the trunk, continuously throughout the exertion. Trunk torque estimates derived from this model were compared with measured trunk torque. The effects of trunk motion, posture, and torque level on spine loading as estimated by the model are discussed. It was concluded that this approach provides a straightforward means of assessing loading of the spine attributable to laboratory simulations of workplace conditions.

Adult↗
PubMed1990

Muscle activities during asymmetric trunk angular accelerations.

The objective of this study was to characterize trunk muscle and intra-abdominal pressure behavior during extensions of the trunk when angular trunk acceleration levels and trunk twist were varied during lifting exertions. Since force is related to acceleration, it was believed that changes in trunk acceleration would cause activity changes in the muscles and abdominal cavity pressurization mechanics that load the spine during manual materials handling tasks. The electromyographic activity of 10 trunk muscles and intra-abdominal pressure were studied in 39 subjects as they moved their trunks under high, medium, and low constant angular acceleration conditions. The results indicated that almost all the muscles were affected by acceleration and asymmetry. Muscle activities of up to 50% of maximum were observed even though a minimal amount of torque was being produced by the back. Coactivation of muscles was also apparent. Muscles located at the greatest distances from the spine, such as the latissimus dorsi and oblique groups, increased their activities the most as trunk acceleration increased. Muscles located farthest from the spine also played an important role as the trunk became more asymmetric. Intra-abdominal pressure changed minimally over the test conditions. The nature of these responses and their impact on spine loading are discussed.

Acceleration↗
PubMed1990

Lumbar motion response to a constant load velocity lift.

An experiment was performed to evaluate the motions of the lumbar spine during a constant load velocity lift. For the purposes of this study, a constant load velocity refers to the linear vertical velocity of the load. This vertical load velocity was controlled using a modified angular isokinetic dynamometer, which produced linear isokinetic motion during a lift. A lumbar monitor was used to observe the position, velocity, and acceleration changes that occurred in the lumbar spine during the lifting task. The results indicate that under constant load velocity conditions, significant angular accelerations occur at the lumbar level. The nature of these accelerations was found to depend on several variables associated with a lifting task, such as the load velocity and the asymmetry of the lift. The physical significance of these results would be increased spinal loading above that which would be predicted using a static model.

Biomechanical Phenomena↗
PubMed1989

Simulift: a simulation model of human trunk motion.

In this paper, the authors present a deterministic simulation model, which they call Simulift, of trunk-muscle activity and intra-abdominal pressure during a sagittally symmetric trunk exertion. Simulift is a descriptive model that quantifies the time-varying loading of the spine based on observed internal forces. Recent findings about the time sequence of events during trunk motion and established equilibrium formulas provide the theoretical bases for the simulation. A profile of electromyographic activity in ten trunk muscles and intra-abdominal pressure is updated as simulated time passes, or as the trunk motion is simulated. Input to the model includes a list of motion-event times and a set of profile-component-behavior data. Simulift is an "impulse" model that computes instantaneous and time-integrated statistics on individual muscle activity, intra-abdominal pressure, compression, lateral shear, and anterior shear as the profile components of the simulated subject change. Computer results for the simulation model are presented.

Biomechanical Phenomena↗
PubMed1989

The effects of preview and task symmetry on trunk muscle response to sudden loading.

The effect of warning time (preview) and task symmetry on the trunk muscular response to sudden loading conditions was investigated. Eleven subjects were asked to catch falling weights with four levels of preview (0, 100, 200, and 400 ms) in saggitally symmetric posture and asymmetric posture. For each of the eight muscles sampled with surface electrodes, the integrated electromyographic (EMG) signal was interpreted in terms of its peak value, mean value, onset rate, and lead/lag time with reference to the weight drop. Results show linear relationships between preview times and peak EMG, preview times and mean EMG, and preview times and lead times. The results show significant change when going from symmetric to asymmetric conditions across most dependent measures. Analysis of peak changes in compression were performed across all conditions but yielded unexpected results.

Adult↗
PubMed1989

Effects of handle angle and work orientation on hammering: I. Wrist motion and hammering performance.

This research investigated the range of wrist motion characteristics associated with the ergonomic principle of "bending the tool and not the wrist" as applied to the hammer. It is thought that bending the tool reduces angular wrist motion, which has been shown in the literature to be a risk factor in hand/wrist disorders such as carpal tunnel syndrome and tenosynovitis. Hammer handles angled at 0 (straight), 20, and 40 deg were investigated in this study. For novices, hammer handles bent at 20 and 40 deg resulted in less total ulnar deviation than straight hammers. However, there was a trade-off in beginning and ending positions of the wrist in that the angled hammers reduced ulnar deviation at the impact position but increased radial deviation at the starting position of a hammer stroke. Handle angle did not significantly affect hammering performance. Wrist motion was affected minimally by hammering orientation, but hammering performance was significantly worse in the wall orientation compared with the bench orientation. This research suggests that for novice users, hammers with handles bent in the range of 20 to 40 deg could possibly decrease the incidence of hand/wrist disorders caused by hammering.

Adult↗
PubMed1989

Effects of handle angle and work orientation on hammering: II. Muscle fatigue and subjective ratings of body discomfort.

This research investigated how changes in hammer handle angle and hammering orientation affected muscle fatigue in the forearm and subjective ratings of body discomfort. Forearm muscle fatigue and discomfort ratings were not significantly affected by handle angle, but they were significantly higher in the wall hammering orientation than in the bench orientation. The research in this article and in the companion article (Part I) reveal that for novices, hammers with handles angled in the range of 20-40 deg are advantageous because (1) they reduce ulnar deviation and may possibly decrease the incidence of hand/wrist disorders, and (2) they do not significantly affect hammering performance in the bench conditions, forearm muscle fatigue, or subjective ratings of body discomfort.

Environment↗
PubMed1989

Trunk strength during asymmetric trunk motion.

It is important to understand how trunk strength varies as a function of workplace factors so that the work environment can be designed to minimize the risk of low back injury. In this study maximal trunk torque production around the lumbosacral junction was measured in 44 subjects as trunk concentric and eccentric isokinetic velocity and trunk asymmetric line of action were varied. Trunk torque decreased by approximately 8.5% of maximum for every 15 deg of asymmetric trunk angle. Increases in concentric velocity decreased trunk strength, whereas increases in eccentric trunk velocity increased strength. Significant interactions were also found, and it was determined that the common finding that eccentric strength exceeds concentric strength is true only for forward trunk angles at all asymmetric angles. These results should have significant implications for the design of manual materials handling tasks.

Adolescent↗
PubMed1988

Networks of internal trunk-loading activities under controlled trunk-motion conditions.

Many attempts have been made to describe the activity of the internal trunk-loading components (muscles and intra-abdominal pressure) in response to external forces acting on the trunk, as is often the case in the workplace. Most models that describe the activity of these internal components are static and do not consider the time series of events that occurs during performance of a task under dynamic conditions. This research has investigated the time sequence activity of ten trunk muscles and intra-abdominal pressure in ten males as they produced sagittally symmetric maximum trunk extension motions (lifting motions) at different velocities. These exertions include an isometric exertion and isokinetic exertions equal to 25, 50, 75 and 100% of a subject's maximum extension velocity. Several event times were noted for each internal trunk-loading component, and hypothesis tests were performed to determine which of these event times were statistically different from each other under the various motion conditions. This information was used to construct networks of internal trunk-loading activities under the various motion conditions. Time-series events that occur under all conditions, as well as those that changed as a function of velocity, have been identified. This information will be useful for the construction of dynamic internal trunk models, and will facilitate the assessment of dynamic loading of the lumbar spine in the workplace.

Back↗
PubMed1986

Flexibility and velocity of the normal and impaired lumbar spine.

Trunk mobility, as defined by trunk angle, has long been considered an acceptable means to evaluate the degree of impairment in patients with low back pain (LBP). However, biomechanically, there is reason to believe that patients with LBP may exhibit significant sensitivity to trunk velocity of motion as well as angular mobility factors. An experiment was performed to study the trunk action of patients with LBP and of a normal control group. A lumbar monitor was used to monitor both trunk angle range and trunk velocity. The results indicate significant differences between the two groups for both angle and velocity measures. However, the velocity measure revealed more dramatic difference between groups and was the only parameter that was capable of distinguishing between the particular experimental tasks for both LBP and normal groups. Thus, it is suggested that trunk velocity be used as a quantitative measure of low back disorder and that it be used as a means to monitor the rehabilitative progress of patients with LBP.

Adult↗