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Biomedical subjects

D B Chaffin

Publications and source records attributed to D B Chaffin.

At least 55 records · Page 3Linked to original sources
PubMed1991

Validation of a biodynamic model of pushing and pulling.

Pushing and pulling during manual material handling can increase the compressive forces on the lumbar disc region while creating high shear forces at the shoe-floor interface. A sagittal plane dynamic model derived from previous biomechanical models was developed to predict L5/S1 compressive force and required coefficients of friction during dynamic cart pushing and pulling. Before these predictions could be interpreted, however, it was necessary to validate model predictions against independently measured values of comparable quantities. This experiment used subjects of disparate stature and body mass, while task factors such as cart resistance and walking speed were varied. Predicted ground reaction forces were compared with those measured by a force platform, with correlations up to 0.67. Predicted erector spinae and rectus abdominus muscle forces were compared with muscle forces derived from RMS-EMGs of the respective muscle groups, using a static force build-up regression relationship to transform the dynamic RMS-EMGs to trunk muscle forces. Although correlations were low, this was attributed in part to the use of surface EMG on subjects of widely varied body mass. The biodynamic model holds promise as a tool for analysis of actual industrial pushing and pulling tasks, when carefully applied.

Abdominal Muscles↗
PubMed1991

Biomechanical aspects of low-back pain in the older worker.

This paper reviews 92 papers related to the biomechanics of low-back pain and potential risk factors associated with age and heavy manual work. The functional anatomy of the lumbar region is reviewed with special emphasis on tissue changes caused by normal aging. A brief explanation of the biomechanics associated with load lifting, twisting, and bending tasks common to manual work in industry is given. It is argued that certain work conditions may present a special risk to an older individual's low back. The need for further research to test hypothesized risk factors believed to be associated with the older worker is indicated.

Aging↗
PubMed1991

Back disorders and nonneutral trunk postures of automobile assembly workers.

A case-referent study was conducted in an automobile assembly plant to evaluate the health effect of trunk postures, such as bending and twisting, that deviate from anatomically neutral. Cases of back disorders were all those of workers who reported back pain to the medical department in a ten-month period and met the severity criteria of an interview. The referents were randomly selected workers free of back pain according to medical department records, an interview, and an examination. For each of the final 95 cases and 124 referents, the job was analyzed for postural and lifting requirements with a video recording and software analysis system by analysts blinded to the case/referent status. Back disorders were associated with mild trunk flexion [odds ratio (OR) 4.9, 95% confidence interval (95% CI) 1.4-17.4], severe trunk flexion (OR 5.7, 95% CI 1.6-20.4), and trunk twist or lateral bend (OR 5.9, 95% CI 1.6-21.4). The risk increased with exposure to multiple postures and increasing duration of exposure.

Adult↗
PubMed1989

A technique for assessment of torso kinesiology.

A technique is described for monitoring and analysis of the angular displacement of the human torso. The technique is based on the use of miniature electromechanical inclinometers and video recording. The system was developed for continuous measurement of the angular displacement of spinal segments in the sagittal plane during all stages of lifting. Angular displacements of the cervical, thoracic and lumbar regions were obtained from a dynamic lifting case study using a digital processing system. The geometrical changes of the torso during five prescribed stages were measured. The system revealed good accuracy with high correlation coefficient scores for a wide range of lifting tasks in a comparative laboratory study. This paper describes the monitoring technique; the system's advantages, disadvantages and measuring accuracy are discussed.

Journal Article↗
PubMed1989

Shoulder posture and localized muscle fatigue and discomfort.

In many industries workers perform manual assembly tasks with hands postured above the shoulders. Awkward shoulder and arm postures are often viewed as acceptable given costs of workplace modification, postural exertions which are in compliance with current design recommendations, ready availability of strong workers, and numbers of electromyographic studies which fail to detect significant signs of localized muscle fatigue (LMF). An experiment was conducted to: (a) study the onset and severity of (LMF) in the shoulder when performing a stylus-to-hole Fitts reciprocal movement task under a range of postures, hand loads, ratios of work-to-rest, and task durations, and (b) to evaluate the efficacy of three techniques (i.e., changes in EMG behaviour, postural tremor, and cross-modal matching estimates) in detecting and monitoring posturally-based LMF and discomfort in the shoulder complex. Experimental findings showed that posturing hands above shoulder level significantly increased the risk of LMF and postural discomfort even in light-weight manual assembly environs where postural exertions are small, and that cross-modal matching estimates and postural tremor were more sensitive metrics of LMF in the shoulder complex than EMG RMS voltage and mean spectral power frequency metrics. The basis for experimental findings, as well as potential application of LMF metrics in future postural stress investigations, are discussed. Recommendations for workplace posture are provided for job designers facing work height decisions in manual assembly environs.

Adult↗
PubMed1989

Lower back muscle forces in pushing and pulling.

In the investigation of lower back stress, the muscle forces of the erector spinae and the rectus abdominis are often calculated using the two-dimensional biomechanical model. These muscle forces are used to estimate the compressive forces at L5/S1 disc. This paper presents a study of the muscle forces predicted by a two-dimensional biomechanical model during pushing and pulling and myoelectric activity from the corresponding muscles. The goal was to investigate whether a simple two muscle torso model would reasonably estimate the muscle actions in pushing and pulling tasks. Six subjects participated in the experiment. EMG (rms) value was used as an indicator of muscle forces. The results show high correlation between the predicted muscle forces and the measured root-mean-square EMG values in trunk pushing and pulling (r2 = 0.93) and hand pushing and pulling (r2 = 0.96) in an erect posture with hips braced but low in hand pushing and pulling using a free posture (r2 = 0.37).

Abdominal Muscles↗
PubMed1989

Arm posture and human movement capability.

Many workers perform manual assembly tasks or use hand tools while the hands are postured above the shoulders or to the side of the body. Experiments were conducted to study the sensitivity of speed-accuracy movement performance to a wide range of hand locations around the shoulder under various levels of hand loads, ratios of work to rest, and task durations. Subjects performed a spatially constrained stylus-to-hole Fitts reciprocal movement task designed to simulate high-incentive manual assembly operations while providing basic information regarding changes in human move and positioning capabilities. Significant decrements in movement performance occurred when hands were postured above shoulder level. Move and positioning times increased 15.3% and 26.5%, respectively, with elevation of the hand from -15 to 60 deg respective to shoulder level. Posturally based decrements in movement capability were unrelated to differences in subject strength capability found among test postures. The consequences of elevated arm postures on human move and positioning capability are presented along with workplace design and methods recommendations for job designers facing work-height decisions in manual assembly environments.

Arm↗
PubMed1988

Isometric and isokinetic back and arm lifting strengths: device and measurement.

This study was conducted to measure isometric (static) and isokinetic (dynamic) back and arm lifting strengths at 20, 60 and 100 cm s-1 of young adults. Ten male and ten female volunteers without a history of back pain participated. The isokinetic lifting task was achieved by controlled motorized dynamic strength tester (DST). A regression analysis and analysis of variance was carried out on the strength data. The peak static strength values were significantly greater from the peak dynamic strength values. The peak dynamic strength was inversely related to the speed of motion. There were significant differences between the dynamic strengths at different stages of lift.

Adult↗
PubMed1988

Biomechanical model calculation of muscle contraction forces: a double linear programming method.

This paper presents a novel scheme for the use of linear programming to calculate muscle contraction forces in models describing musculoskeletal system biomechanics. Models of this kind are frequently found in the biomechanics literature. In most cases they involve muscle contraction force calculations that are statically indeterminate, and hence use optimization techniques to make those calculations. We present a linear programming optimization technique that solves a two-objective problem with two sequential linear programs. We use the technique here to minimize muscle intensity and joint compression force, since those are commonly used objectives. The two linear program model has the advantages of low computation cost, ready implementation on a micro-computer, and stable solutions. We show how to solve the model analytically in simple cases. We also discuss the use of the dual problem of linear programming to gain understanding of the solution it provides.

Biomechanical Phenomena↗
PubMed1987

Analysis of cumulative strain in tendons and tendon sheaths.

Twenty-five fresh frozen flexor digitorum profundus tendons stratified by sex were subjected to uniaxial step stress and cyclic loads in twelve intact human cadaver hands. By attaching specially designed clip strain gage transducers on tendons just proximal and distal to an undisrupted carpal tunnel, the interactions of the tendons, tendon sheath and retinacula were measured. The elastic and viscous response of the tendon composites to step stresses were found to fit fractional power functions of stress and time respectively. A significant and quantifiable decrease in strain from the proximal to the distal tendon segment was found to be a function of wrist deviation. The results indicate that an accumulation of strain does occur in tendinous tissues during physiologic loading.

Aged↗
PubMed1987

Manual materials handling and the biomechanical basis for prevention of low-back pain in industry--an overview.

Two different but dependent strategies must be developed to prevent low-back pain in industry. One is of an administrative nature and is concerned with whether the worker who performs activities that stress back tissues is appropriately evaluated and trained for such work. The second strategy is of an engineering type, dealing with methods to assure that the workplace and work tasks are specified in ways that minimize injurious stresses to the low back. Both of these strategies rely on knowledge of the biomechanical requirements of a job. These must be carefully evaluated by informed observers using prescribed measurement and analysis procedures. The fundamental biomechanics of heavy lifting and observational procedures developed by an expert panel for NIOSH are described. The procedure rates the difficulty of a lifting task and then recommends whether administrative or engineering controls are warranted to reduce low-back stresses. Some suggestions for preventing excessive low-back stress by redesigning the workplace are presented also.

Back Pain↗
PubMed1986

A biomechanical evaluation of five lifting techniques.

Five lifting methods which cover the range of techniques recommended by various back schools have been biomechanically analysed with a static sagittal-plane computer model. The analysis was performed with two load-types (compact and bulky) and three weights in the hands (44 N, 222 N and 400 N). The methods were compared in terms of predicted L5/S1 disc compression, low-back ligament strain and strength requirements at the shoulders, L5/S1, hip and knee joints. In general the method entailing a squat posture, straddle foot stance and flat back (oriented as when standing erect) yielded lower compressions, ligament strains and overall strength requirements than the other methods.

Journal Article↗
PubMed1986

A study of lumbosacral orientation under varied static loads.

This paper describes a study of lumbar and sacrum orientations in select standing postures with the patient holding different loads in the hands. Vertebral rotation data were gathered from two young, healthy men and two young, healthy women while they performed static lifts at two load levels and in postures ranging from erect standing to deep squatting. The results disclosed a predictable reorientation of the sacrum and lumbar spine for both men and women as a function of torso and knee angles. Nonlinear second-order regression models of torso angle and knee angle versus reorientation angle were fit to the data with resulting r2 values of about 0.89. Load was not found systematically to affect the sacrum/lumbar reorientation.

Adult↗
PubMed1986

Correlation of aerobic capacity of Brazilian workers and their physiologic work requirements.

Aerobic capacities of workers vary a great deal, as do the metabolic energy expenditure requirements of various manual jobs. This study was conducted to determine if the metabolic energy requirements on 11 jobs correlated with the aerobic capacities of 78 young male workers employed on the jobs. The results disclosed that the workers' mean aerobic capacities were correlated with the job energy requirements (r = .84), and that the average job metabolic rates were at approximately 35% of the estimated aerobic capacities of the workers. The jobs requiring a high energy expenditure rate (ie, those above 5.0 kcal/min-1) were associated with heart rates above 110 beats per minute averaged over eight hours. At this higher energy expenditure rate level, no age decrement in aerobic capacities was found, although a significant decrease was found with age in those employed in less demanding jobs.

Adult↗
PubMed1986

Occupational ergonomics--methods to evaluate physical stress on the job.

Ergonomics is the study of people at work to understand the complex relationships among people, machines, job demands, and work methods. All work, regardless of its nature, results in stress. As long as stress is kept within reasonable limits, work performance will be satisfactory and the worker's health and well-being will be maintained. However, if stress is excessive, undesirable outcomes may result in the form of accidents and injuries. A variety of musculoskeletal injuries and disorders can be caused by physical stress in the work environment. Because of the high medical and compensation costs associated with these problems, it becomes essential in many manufacturing situations to implement programs for controlling physical stress. An important part of any control program is job evaluation. We have presented several analytical methods for measuring and evaluating physical stress in the workplace. In almost all instances in which it is found to be excessive, stress can be reduced to acceptable levels by applying ergonomic principles to the design of facilities, processes, equipment, tools, and work methods. This design effort should be multidisciplinary, with inputs from medical personnel, engineers, ergonomists, and workers.

Accidents, Occupational↗
PubMed1985

A biomechanical model of the lumbosacral joint during lifting activities.

A biomechanical model of the lumbosacral region was constructed for the purpose of systematically studying the combined stresses and strains on the local ligaments, muscles and disc tissue during sagittal plane two-handed lifting. The model was validated in two ways. The first validation was a comparison of experimental study results with model predictions. In general predictions compared very reasonably with observed values of several authors with the exception of strain predictions on the articular ligaments. Second, a sensitivity analysis was performed over a wide range of lifting tasks. The predicted stress/strain values followed anticipated patterns and were of reasonable magnitudes. On the basis of the results of the sensitivity analysis it was concluded that typical lifting tasks can lead to excessive disc compressive forces, muscle moment generation requirements, and possibly lumbodorsal fascia strains. Conversely, annulus rupture of a healthy disc due to overstrain appears very unlikely.

Biomechanical Phenomena↗