And found that a single 120-minute nap ending at midnight experienced worse drowsiness.
However, two naps — the 90-minute one lasting until midnight and the 30-minute one ending at 3 a.m. — staved off drowsiness.
Winning Formula for Overnight Alertness
“I want to be able to combine multiple naps, depending on the type of work and time of day, and choose naps that are effective at reducing drowsiness, fatigue, and maintaining performance,” Oriyama said.
“During a night shift that, for example, lasts from 4 p.m. to 9 a.m. the next morning, a split nap of 90 minutes and 30 minutes, ending at 12 a.m. and 3 a.m., respectively, is thought to be more effective than a 120-minute monophasic nap ending at midnight,” she explained.
Interestingly, people who took longer to fall asleep during the 90-minute nap session showed poorer scores in the Uchida-Kraepelin test (UKT), a timed basic maths exam meant to measure speed and accuracy in performing a task.
Oriyama said the findings could also be helpful to new parents. “The results of this study can be applied not only to night shift workers but also to minimize sleep deprivation fatigue in mothers raising infants,” Oriyama added.