Biomedical subjects
Publications and source records attributed to E Grandjean.
An apparatus for measuring the sharpness, the oscillation degree and the stability of characters of 8 different VDTs were developed. Furthermore the contrast of luminances between the essential surfaces was measured. The following results were observed: 2 VDTs had good ergonomic qualities, one was only sufficient and 5 VDTs had insufficient ergonomic light conditions.
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In order to evaluate the extent of annoyance caused by air pollution and noise immissions, we measured the values in the small town of Uznach, which is crossed by a narrow and sloped street with a heavy traffic. The results revealed that noise immissions exceed the "alarm-value" of 70 dB(A) and that pollution of the air is situated in the range of limit values.
Four groups of office tasks were studied: Data entry terminals, conversational terminals, traditional office work and typing. Eye impairments are observed in every group of office employees, but the impairments are more frequent in VDU operators. The impairments persist during leisure time. High luminance contrasts between screen and source document are associated with an increase of eye troubles. Increased oscillating luminance of characters is associated with lower visual acuity, with a higher incidence of subjective and objective symptoms of eye irritation including more frequent use of eye drops.
In our laboratory study 19 students effected 4 repetitive tasks of 70 min each. All four conditions had a motor task at the base and in addition two had to deal with discrimination. In the 2 tasks with discrimination, the electromyography of the neck muscles was distinctly higher than in the 2 other conditions. The tasks with discrimination were accompanied by a higher subjective tension, a lower heart rate variability and a slightly increased urinary excretion. The main cause for an augmentation in the muscle tonus might be the immobilisation of the neck.
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A survey on localized fatigue was carried out in 119 accounting machine operators. In 51 cases the dimensions of the working places and different characteristics of the body postures were measured. The incidence of localized fatigue symptoms was found to be related to the degree of ulnar deviation of the hand, to the angle of the elbow as well as to the angle of the head inclination.
Two hundred workers of the Swiss watch industry were examined in a study of repetitive work effects on the well-being of workers. Repetitive work has shown to have two main influences on well-being: Relationships were found between subjective assessment of variety and autonomy, job satisfaction, psychosomatic complaints and headache. Repetitive work was always done under some positional constraint. This was shown to result in an increased rate of "arm, neck, shoulder syndrome" and visual problems.
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Physical fatigue is a painful phenomenon which is localised in overstressed muscles. Mental fatigue is a diffuse sensation of weariness; it is a functional state, one of several intermediate conditions between the two extremes of alarm and sleep. A neurophysiological model of fatigue, involving an activating and inhibitory system has been developed. Fatigue in industrial practice has clinical symptoms: psychic instability, fits of depression and increased liability to illness. Indicators of fatigue are work of performance, subjective feelings of fatigue, electroencephalography, flicker-fusion frequency and various psychomotor and mental tests. Several field studies do, to some extent, confirm the above-mentioned concept of fatigue.