Circadian rhythms and behavior of permanent nightworkers

Summary This paper describes rest/activity rhythms of permanent shift workers: rotary printers. They reported during one week the hours of their sleep onset and of their meals, and their subjective appreciation of tiredness and mood. The average sleep duration (7.84 h) can be compared with that of day workers and is fairly longer than the duration of day sleep of shift workers when they are on nightshift. This long sleep can be accounted for by: (1) the early bedtime (around 05.00 h), (2) an adjustment of biological rhythms to the schedule inversion.Other evidence (naps, meal time) supports the hypothesis of a physiological adjustment. It is pointed out that this adjustment is fragile: the printers must have very rigid life habits and schedules (sleep, meals). Each time they change this strategy (especially during week-end) it is subjectively felt as detrimental.