W. Monroe Keyserling

Postural analysis of the trunk and shoulders in simulated real time

A new method for analysing and describing the posture of the trunk and shoulders was developed and used to describe the posture of workers performing automobile assembly operations. The system used a videotape to create a permanent record of the jobs and a personal computer to perform the clerical and time-keeping tasks associated with posture analysis. In experiments using an experienced analyst to evaluate a videotape, highly reproducible results were obtained. Furthermore, the new system required substantially less time than existing posture analysis methods to analyse and reduce postural data.

Isometric strength testing as a means of controlling medical incidents on strenuous jobs

This investigation was performed to determine if isometric strength tests can be used to select workers for strenuous jobs and to reduce occupational injuries which are caused by a mismatch between worker strength and job strength requirements. Twenty jobs in a tire and rubber plant were studied biomechanically to identify critical strength-demanding tasks. Four strength tests were designed to simulate these tasks, and performance criteria were established for passing the tests. New applicants were administered the tests during their preplacement examinations to determine if they possessed sufficient strength to qualify for the jobs. The medical incidence rate of employees who were selected using the strength tests was approximately one-third that of employees selected using traditional medical criteria. It was concluded that isometric strength tests can be used to reduce occupational injuries and should be considered for implementation in industries with strenuous jobs.

Workplace Risk Factors and Occupational Musculoskeletal Disorders, Part 1: A Review of Biomechanical and Psychophysical Research on Risk Factors Associated with Low-Back Pain

Injuries and disorders caused by overexertion and repetitive motion are the leading causes of compensable lost-time cases in the United States. Epidemiological and laboratory-based research methods have been used to evaluate the significance of various risk factors associated with overuse injuries and disorders. The National Institute for Occupational Safety and Health performed a comprehensive review of over 600 epidemiological studies in 1997 and concluded that there was evidence of a causal relationship between low-back injuries and disorders and workplace exposures to forceful exertions, awkward posture, and vibration. Although epidemiological studies provide important insights to understanding the causes of work-related overuse disorders, they are sometimes criticized for their inability to measure precisely how people respond to specific risk factors found in the workplace. This article presents a review of recent laboratory studies and biomechanical models of work factors believed to be associated with increased risk of low-back injuries and disorders. Biomechanical models and laboratory studies do not replace epidemiological studies. However, these approaches provide important complementary information that is needed to understand the complex process of how exposures to physical risk factors result in strain that may ultimately lead to injury or disease. These studies also provide important insights as to how people react and respond to specific physical risk factors found in the workplace. Combined with epidemiological research, laboratory studies are an essential element in understanding the causes and prevention of work-related overexertion injuries.

A method for evaluating the biomechanical stresses resulting from manual materials handling jobs

Manual materials handling tasks are inherent to many different jobs in industry today. The performance of such tasks exposes the worker to a variety of biomechanical hazards. This paper proposes a formalized algorithm for evaluating such hazards, and demonstrates the use of the algorithm in four different jobs. Medical data from these jobs are presented which serve to confirm the types of biomechanical stresses quantified by the biomechanical evaluations.

Workplace Risk Factors and Occupational Musculoskeletal Disorders, Part 2: A Review of Biomechanical and Psychophysical Research on Risk Factors Associated with Upper Extremity Disorders

Injuries and disorders caused by overexertion and repetitive motion are the leading causes of compensable lost-time cases in the United States. Epidemiological and laboratory-based research methods have been used to evaluate the significance of various risk factors associated with overuse injuries and disorders. The National Institute for Occupational Safety and Health performed a comprehensive review of over 600 epidemiological studies in 1997 and concluded that there was evidence of a causal relationship between workplace exposures to forceful exertions, repetition, awkward posture, and vibration and disorders of the neck, shoulder, and upper extremities. Although epidemiological studies provide important insights to understanding the causes of work-related overuse disorders, they are sometimes criticized for their inability to measure precisely how people respond to specific risk factors found in the workplace. This article presents a review of recent laboratory studies and biomechanical models of work factors believed to be associated with increased risk of upper extremity injuries and disorders. Biomechanical models and laboratory studies do not replace epidemiological studies. However, these approaches provide important complementary information that is needed to understand the complex process of how exposures to physical risk factors result in strain that may ultimately lead to injury or disease. These studies also provide important insights as to how people react and respond to specific physical risk factors found in the workplace. Combined with epidemiological research, laboratory studies are an essential element in understanding the causes and prevention of work-related overexertion injuries.

A Computer-Aided System to Evaluate Postural Stress in the Workplace

Stress caused by awkward working posture of the trunk and shoulders can result in fatigue, musculoskeletal disorders and nerve entrapment syndromes. To aid in evaluating the relationship between work activities and postural stress, a computer-aided system was developed. This system produces a detailed description of work tasks and a continuous record of trunk and shoulder activity on the same time scale. The system was used to evaluate postural stresses on a case study job in an automobile assembly plant. The results of the postural analysis were used to identify specific causes of postural stress and to develop recommendations for changes in work station equipment and methods to reduce stress.

Establishing an industrial strength testing program

This study was performed to develop and evaluate a scheme for matching the strength of workers to the strength demands of their jobs. Biomechanical analyses were performed on production jobs in an aluminum reduction plant to identify and quantify strength demands. These data were used to design a set of nine strength tests which simulated job activities with the greatest strength requirements. A cross section of plant employees assigned to these jobs was strength tested and monitored for medical incidents for a period of over two years. Significant relationships were found among job strength requirements, worker strengths, and medical incidents. Workers with strength abilities (as determined by the tests) less than job strength requirements suffered a higher rate of medical incidents than workers whose strength abilities matched or exceeded job demands. It was concluded that strength testing can be used to identify workers who would be at increased risk of suffering medical incidents if placed on jobs which exceeded their strength abilities.

A Model for Protective Clothing Effects on Performance

Personal protective clothing (PPC) enables people to work in hazardous environments, but PPC can have a detrimental effect on worker performance. Predicting garment effects on worker performance is difficult because quantitative relationships among garment properties and human responses are not known. Presents a systematic structure for studying the relationships among garment properties and their immediate effects on the worker. Using a survey of 118 studies, previous work was categorized according to garment parameters and dependent measures. Except for studies of heat stress, most of these studies compared competing garments or simply measured physiological response, rather than relating these effects to garment attributes. Such results are seldom transferable to other clothing systems or tasks. Proposes a conceptual model based on this systematic structure. Introduces garment impediment indices (GIIs) as response functions of garment attributes, and offers an approach for developing quantitative models of PPC effects on worker performance.

Evaluating posture behavior during seated tasks

A method was developed to evaluate posture behavior of the trunk, neck, eye, and upper extremity in three-dimensional during the performance of static, seated tasks. Body postures were measured using an ultrasonic measurement system to determine the Cartesian coordinates of joints and the angles between adjacent limbs. Posture preferences for a variety of visual and manual tasks were then determined. Pilot studies using three subjects performing visual and right-handed tasks showed that the postures were affected by target location, body size, and target size. These experiments suggest that the preferred horizontal location of visual targets is within 10 o of the saglttal plane of the head. The preferred vertical location of visual targets is 10 o to 35 o below the seated eye height. For manual reaches, the target-to-shoulder distance should be at least one-third the length of the upper extremity to avoid extreme elbow flexion. In addition, the seat pan should swivel and should allow a person to move fore and aft in order to adjust to a comfortable work posture. Relevance to industry

Three methods for measuring range of motion while wearing protective clothing: A comparative study

This paper evaluates three methods for objectively measuring ROM while workers are wearing protective clothing: a universal goniometer, a Leighton Flexometer, and an electrogoniometer. Ten male subjects performed a set of nine gross body movements while semi-nude and while wearing each of nine configurations of coveralls. Coveralls varied in relative size and fabric weight, Changes in joint angles were measured simultaneously with the goniometer and the electrogoniometer, and then simultaneously with the Flexometer and the electrogoniometer. The goniometer and Flexometer data were positively correlated across garment treatments, but the electrogoniometer data were not highly correlated with either the goniometer or Flexometer data. Precision was similar between the goniometer and Flexometer, but the goniometer was found to be much less invasive than the Flexometer.