Influence of the time to start napping during night shift on fatigue and work efficiency among nurses working the 16-hour night shift

In this study, we analyzed the differences in fatigue and work efficiency among taking a nap at different time to start during the 16-hour night shift, in order to determine the most effective time to start napping for recovery from fatigue. We conducted an experiment with 11 adult female students as subjects. The 16-hour night shift hours were scheduled for 16:00 to 9:00, with a 120-minute nap (22:00-0:00; "22:00 nap", 0:00-2:00; "0:00 nap", and 2:00-4:00; "2:00 nap"). We measured their fatigue using the Visual analog scale (VAS) and the fatigue check list. With regard to the work efficiency, they perform single-digit calculation for ten minutes every hour. As a result, according to the VAS, the fatigue in the case of the "22:00 nap" had increased at 6:00 more significantly than in the other groups. According to the fatigue check list, the fatigue had increased at 5:00 and 9:00 in the groups of the "22:00 nap" and "0:00 nap", but a sign of recovery from fatigue was observed at 9:00 in the "2:00 nap". A significant decline of the work efficiency at 16:00 was observed after 6:00 in the groups of the "22:00 nap" and the"0:00 nap". In the group of the "2:00 nap", significant decline of the work efficiency was not observed between 16:00 to 9:00. Thus, these results suggest that, starting nap at 2:00 during the 16-hour night shift is more effective than 22:00 and 0:00 for minimizing the fatigue and maintaining work efficiency.