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 performance, subjective feelings of fatigue, electroencephalography, flickerfusion frequency and various psychomotor and mental tests. Several field studies do, to some extent, confirm the above-mentioned concept of fatigue.

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A field study was conducted to assess the preferences of VDT operators with regard to their body posture and the settings of an adjustable VDT workstation. Subjects came from four different companies, and the study took place during subjects' customary working activities. Means and ranges of the preferred settings are given. The operators preferred body postures that are distinctly different from those recommended in textbooks and other publications. Some of the workstation settings they preferred also strongly deviate from such recommendations.