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A theory of fatigue.

Early research on fatigue in industry dealt almost exclusively with variation in productive output which resulted from prolonged work. Later research, typified by studios of pilot performance, developed methods of measurement which were more sensitive to time-correlated variations in performance and were applicable to tasks which involved little physical effort. Neither approach has been outstandingly successful in uncovering the nature of fatigue phenomena. Recent research has taken a broader view of fatigue as a generalised response to stress extending over a period of time, and has had some success in explaining the paradoxical results of earlier studies in terms of activation theory. This approach requires the time scale of fatigue studies to be extended greatly, to allow for cumulative effects over periods of days, weeks or months and for the effects of disturbed sleep habits, which appear to be very important. Fatigue effects are closely related to the effects of sleep deprivation. The importance of...