The study concerned the long-term effects of a weekly rotating day-night shift schedule on circadian functions. It was performed 1 h after the introduction of an increase in nighttime work and was a follow-up of a study performed one month after the change of workhours. Fourteen male typesetters were observed in connection with the first, fourth and seventh nightshifts of the "night week" and the two dayshifts of the "day week." Measurements were taken of body temperature and self-rated activation during awake periods, of adrenaline excretion during work and sleep, and of choice-reaction time during work. The results showed that a different pattern of variation in circadian functions was present 1 h after the increase in nighttime work when compared to the pattern one month after the increase. The change in pattern consisted mainly of a general flattening of the curves during both day and night work, although some changes from the beginning to the end of the nightshift week could still be noticed.

Key terms adrenaline excretion; body temperature; circadian rhythm; follow-up field study; follow-up study; long-term adjustment; nighttime work; psychophysiological activation; reaction time; rotating shift work; rotating shift worker; self-rated activation; shift work; shift worker; short-term adjustment; temporal pattern