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The primary goal of the ergonomist is to develop systems and products that increase productivity, function intuitively, and minimize the user’s risk of injury and illness. Injuries occur when a system or product does not fit or was not designed for the capabilities of the user. The physical ergonomist plays an important role in litigation in reducing the risk of large damages or settlements through improved design. This article outlines three cases that demonstrate how a physical ergonomist uses established methods and techniques to analyze litigation cases.

A laboratory experiment using 15 male subjects was conducted to document lifting physical work capacity over the frequency range of 2 to 12 lifts per minute and to compare these values to bicycling physical work capacity. Results indicate that bicycling PWC is significantly higher than lifting PWC at the 0.05 level. A variation in lifting PWC as a function of frequency was observed. This could be attributed to lifting technique. Task design should, therefore, not only consider lifting PWC but also the frequency of lift.

An experiment documented the choices of verbal anchors or word triggers by subjects observing five different videotaped work operations. Their surveyed numeric scalings and word selections were compiled to form a list of ten words which are recommended to describe amount or degree of work being performed. This study acknowledges that there is inherent risk in applying words to work measurement scales, but the list may be helpful as a guide to choosing appropriate words to indicate work content or for job descriptions.

An experiment was conducted to assess the differences between various equations and devices for estimating body fat percentage. Valid estimation of body fat is an important variable in determining the individual differences in energy expenditure or physical work capacities of workers performing various tasks. Twenty male volunteers participated in this study. Results indicate that no significant differences exist between device type. However, there were significant differences between derived estimations of body fat content with several widely used equations. These results were also related to estimation of body fat content derived from the bioelectrical impedance procedure. Results from this study indicate the need for comparison between subject population and population of prediction models before determining body fat and possible use of an average of several equations.

An investigation was performed to assess the effect of forearm rotation (pronation and supination) and elbow orientation upon maximum grip strength of 10 male and 10 female subjects. Seven positions of forearm rotation which ranged from 90 degrees pronation to 90 degrees supination in both the 90 degree elbow flexion (arm adducted, forearm horizontal) and 0 degree flexion (shoulder flexed, whole-arm extended forward and horizontal) postures were examined. Thus a total combination of 14 postures were documented. Results indicate that maximum grip strength decreased significantly with forearm pronation, relative to the “neutral” forearm posture (p= 0.086). Other rotation postures did not yield significantly different grip strength from the neutral, but there was a clear decreasing trend in grip strength with forearm rotation away from neutral, particularly in pronation. The 0 degree elbow flexion showed the highest average grip strength values compared to 90 degree elbow flexion postures. Also, in the 90 degree elbow flexion posture, grip strength tended to increase with some supination from neutral rotation. It is recommended that for repetitive grasping activities, the arm and forearm postures should be considered in evaluating maximum grip strength. A regression model is presented to estimate maximum grip strength as a function of forearm rotation and elbow posture.

Objective measures of anthropometry, strength, range-of-motion, muscle activity, and task performance, and subjective ratings of pain were observed in a group of individuals diagnosed with carpal tunnel syndrome (CTS). These measures were compared to a control population showing no symptoms of CTS. Results indicate that individuals with CTS had significantly lower values on some strength tests, less range of motion on several measures, and reduced performance on a simulated task than did the control group. Ratings of pain and distress for the CTS group were also significantly higher than the control group. Occupational and personality factors associated with the CTS group were also identified and discussed.

An experiment was conducted to determine isokinetic wrist flexion and extension strengths of females diagnosed with carpal tunnel syndrome (CTS). Static strength measures were also documented. These values were compared to values from a matched control group. Results show a significant reduction in isokinetic wrist flexion force, grip and tip pinch strengths within the CTS group compared to the controls. Range of motion in wrist flexion also showed a significant decrement for the CTS group. Finally, regression models were developed to predict isokinetic strength based upon static measures.

Two laboratory experiments were conducted; first, to utilize the psychophysical approach (method of adjustment) to establish maximum acceptable frequency (MAF) for a sheet metal drilling task and, second, to examine the effect of sustained, static exertion upon objective and subjective measures under similar task conditions. In both experiments, the wrist posture (flexation, ulnar deviation) required by the task was varied. Twelve healthy females served as subjects. Results show that the psychophysical adjusted task frequency was significantly lower when wrist deviation was required, particularly flexion. MAF for one-third (25°) and two-thirds (50°) flexion were 88% and 73%, respectively, of those selected in the neutral posture. Furthermore, these results were supported by trends in grip strength, heart rate, blood pressure, EMG and perceived exertion. Results from the sustained exertion trials revealed that significant increases in physiological parameters occurred during 3-minute sessions and that this trend was exasperated with deviated wrist posture, particularly flexion. Considering results of both experiments, it was concluded that while the neutral wrist posture may be preferred for a drilling operation, task frequency should be reduced for deviated postures when redesign is not feasible and it is further recommended that deviation be limited to one-third maximum flexion (25°) and two-thirds maximum ulnar deviation (30°). It is also suggested that the psychophysical approach may be utilized to establish 'acceptable' parameters for other industrial tasks involving upper extremity stress, particularly in the current absence of more objective biomechanical and/or physiological criteria for reducing the risk of exposure to cumulative trauma disorders.

A self-report musculoskeletal assessment tool was adapted following field use by ergonomic analysis teams and was administered to 797 employees of a public utility company. Results were analyzed to determine if the self-reports could adequately predict whether or not an employee reportedly sought medical or therapeutic treatment for a work-related discomfort. A discriminant analysis was used to show that the ratings could identify those who had sought treatment. Tabulation of a joint frequency distribution of the ratings (Discomfort Level × Frequency of Discomfort) and discriminant function probabilities resulted in a convenient separation of the population into three “zones”. These zones were labeled: (1) “very likely”, (2) “somewhat likely”, and (3) “not likely” to seek treatment. This tool is not intended to be a diagnostic instrument since the criterion was not a specific cumulative trauma diagnosis. Rather, it can be utilized as an easily administered, proactive surveillance instrument to assist in early identification of ergonomic concerns and to help prioritize jobs for intervention.Relevance to industry