Effects of rapidly rotating shifts on sleep patterns and sleep structure

Six young adult males were assigned to a rapidly rotating shift work schedule (2 d 6 am-4 pm, 2 d 4 pm-10 pm, and 2 d 10 pm-6 am). They lived in the laboratory and completed two rotations. Their nonshift activities were ad libitum including sleep times. The patterns and structure of sleep were analyzed. Shift times systematically affected sleep patterns. Within shifts, Ss slept as late as possible prior to the morning shift, went to bed shortly after the night shift, and slept approximately midway between shifts on the afternoon shift. In transitioning to a new shift, the new shift time tended to determine sleep time. Sleep was significantly longer in transitions between shifts. Sleep structure was not markedly changed.