The influence of fatigue and rest period on the circadian variation of error frequency in shift workers (engine drivers)

TL;DRAbstract

It has been well-known for a long time that "vigilance" functions undergo a circadian variation. Fig. 1 shows as an example (top curve) the daily course of auditory reaction time in healthy subjects. There is a predominant 24-hour-period with optima of performance in the forenoon and in the early evening, with a slight indication of a "post-lunch dip" in between. The second curve shows the daily course of error frequency obtained by Bjerner and Swensson (1953) in industrial shift workers. Besides the usual nightly maximum there is also a quite distinct secondary maximum in the early afternoon, indicating the additional presence of a 12-hour-period. When the potential extent of performance deficit is so marked that you may even fall asleep when driving a car, the amplitude of this secondary maximum in the early afternoon can be as great as the night one (Prokop and Prokop, 1955); this is shown in the third curve.

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