Occupational Ergonomics

Maximum torque strength, muscle strain and subjective responses were evaluated in a series of screwdriver tests with 10 varied handles, performed under different working conditions. Screwing in and unscrewing tasks that affected inward and outward rotations of the upper extremity muscles were measured. Maximum torque strength for supination and pronation was determined under the conditions of dry hands, using industrial gloves, and with oily hands, consecutively. Physiological cost of performance was simultaneously determined by measuring electromyographic activities (EA) of 5 muscles of the hand-arm-shoulder system that were expected to be involved in screwing tasks. Subjective assessments were made through a questionnaire before and after each experiment. Significant differences were determined between maximum torque values produced during inward and outward rotations for the three operational cases. Maximum torque values exerted by the twelve subjects using industrial gloves were substantially higher than the values obtained by dry and oily hands during both supination and pronation. EA values of the 5 muscles investigated differed significantly. However the subjective assessments of the handles did not vary in the pre and post assessments.

The epidemiological literature is critically reviewed to evaluate the evidence supporting a causal relationship between computer work and musculoskeletal symptoms and disorders (MSDs) of the hand, wrist, forearm, and elbow. Since 1990, 33 publications were found that met the selection criteria –11 were prospective in design and 22 were cross-sectional. All prospective studies that measured extent of computer use found a positive association between computer work and upper extremity musculoskeletal symptoms. The two prospective studies to conduct physical examinations both found a relationship between hours of computer use and increased risk of upper extremity diagnoses. Of the 22 cross-sectional studies, 17 studies found positive associations. Two of the five studies reporting no association found increased risks of certain disorders under certain combinations of computer use and other factors. The remaining three studies were limited by either a small sample size or low variation of computer use hours within the study population. We conclude that there is consistent evidence of a positive relationship across numerous prospective and cross-sectional studies with increased risk most pronounced beyond 20 hours/week of computer use or with increasing years of computer work. The disorders confirmed with physical examinations are wrist tendonitis and tenosynovitis, medial and lateral epicondylitis, and DeQuervain's tenosynovitis. The risk of carpal tunnel syndrome is increased with use of a computer, especially with mouse use for more than 20 hours per week.

In this investigation posture restriction caused by back belt is studied. Two-dimensional kinematic data was collected from ten participants using nine marker positions. Angular displacement of nine body angles was compared. Effect of the back belt on the lifting posture was studied using postural index values and kinematic relationship hypothesis. Influence of back belt on the lifting technique throughout a lift was understood using the concept of interjoint coordination. Out of the nine body joint angles, five showed decreased flexion, three increased flexion and the remaining one showed no change in the flexion values. Kinematic relationship was found to exist between hip, knee, trunk and lumbar-thoracic joint. The behavior of postural index values supported the kinematic relationship hypothesis. The back belt affected the proximal to distal interjoint coordination between hip, knee, trunk and lumbar-thoracic joint, thus disturbing the natural style of lifting.

This paper discusses thermodynamic basis for quantifying human physiological stresses. The deterministic nature of the second law of thermodynamics (entropy approach) and classical Maxwell relations were used to develop formulas to quantify human stress due to the artifact-human interactions. The illustrative examples establishing the validity of the proposed stress indices were presented.

Expressing absolute workload as a percentage of maximum oxygen uptake (VO_2max), commonly known as relative workload, is recommended by many work physiologists because it provides a subject-specific workload and enables accurate assessment of physical fatigue. The specific aim of this research is to develop a direct method to predict relative workload from in-situ collected sub-maximal oxygen uptake data without the need to determine maximum oxygen uptake. The method is developed based on a hypothesis that oxygen uptake data are serially dependent, and that by using data dependent systems (DDS) modeling and time series analysis techniques a regression model between relative workload and a statistical characteristic of collected oxygen uptake data can be developed. The technique was developed using twenty subjects and validated on five. The estimated standard error of prediction using the developed technique for relative workload (%VO_2max) is ± 3.4% and maximum oxygen uptake (VO_2max) is ± 0.5 litre · min^-1. Validation subjects’ results indicated that the mean square error of the regression model is not seriously biased and gives an appropriate indication of the predictive capability of the selected regression model. With further development, the technique presented will be valuable in identifying excessively demanding tasks based on a more subject-specific workload.