Bridging the gap: examining circadian biology and fatigue alongside work schedules

We compared three different work schedules in a large oil company: 1) two days of 12 h of daytime shifts followed by two consecutive 12 h night shifts, followed by four work-free days ("2 x 2 x 4"), 2) four consecutive 12 h daytime shifts and four consecutive 12 h night shifts, flanked by four work-free days ("4 x 4 x 4"), 3) a non-rotating schedule involving continuous 12 h daytime shifts during 40 days ("fixed 12 h"). We measured wrist-actigraphy, peripheral temperature rhythms, and subjective self-reports regarding fatigue, somnolence, and psycho-affective features. Sleep duration on the resting period was significantly less than the recommended 7 h. The "2 x 2 x 4" schedule resulted in decreased sleep regularity and increased circadian disruption, higher levels of insomnia, increased fatigue impact, lower alertness levels, and heightened symptoms of depression associated with more nocturnal sleep time after diurnal work. Our findings indicate that health and safety vary depending on the type of schedule employed.