The Split Nap Hack for All-Nighters

A new analysis of night shift nap studies points to the optimal snooze schedule for fending off exhaustion and drowsiness in early morning hours.

Asian Scientist Magazine (Nov. 27, 2023) —Irrespective of the work we do, many of us have used naps to pull all-nighters, whether to finish writing a grant proposal or to manage air traffic on airports. Healthcare professionals like on-call doctors and nurses are no stranger to non-traditional work hours. In Japan, nurses typically sleep up to 2 hours during their 16-hour night duties. A nap during prolonged workhours helps improve alertness, memory and cognitive performance, and reduce the risk for human errors.

In a study published in Scientific Reports, Sanae Oriyama, a nursing professor at Hiroshima University’s Graduate School of Biomedical and Health Sciences, reexamined her past pilot studies on night shift naps to identify the optimal snooze strategy for powering through the night.

Although nurses find a 2-hour shut-eye helpful, a single block of sleep is often insufficient to beat morning drowsiness and fatigue during the remaining wakeful portion of a night shift. Oriyama hypothesized that dividing this nap time into two separate breaks could prolong the restorative benefits.

To find out, Oriyama compared three pilot studies that she co-authored between 2012 and 2018, that assessed the effectiveness of ‘no-nap’, ‘one-nap’ and ‘two-nap’ within a 4 p.m. to 9 a.m. shift.

“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,” she said.

A total of 41 healthy female participants in their 20’s volunteered to sit at a desk in a windowless and sound-proofed laboratory as a night shift simulation. The participants either did not nap (no-nap), took a 120-minute snooze that ended at 12 a.m (one-nap), or a split nap of 90 minutes and 30 minutes (two-nap), ending at 12 a.m. and 3 a.m., respectively.

In addition to monitoring their heart rate and body temperature, the participants provided hourly self-assessment ratings of their fatigue and drowsiness levels. They also completed the Uchida-Kraepelin test (UKT), a timed basic math exam designed to evaluate task performance.

The results revealed that participants who had a single 120-minute nap concluding at midnight experienced heightened drowsiness, which began at 4 a.m. and lasted until the end of their shift. Conversely, those who underwent the split nap regimen were able to fend off sleepiness until 6 a.m. In terms of fatigue, while all three nap groups reported significantly increased levels of it between 4 a.m. and 9 a.m., the two-nap group experienced it with a relatively lower intensity than the other groups.

Nevertheless, neither the single nap nor the split naps resulted in a noteworthy improvement in cognitive task performance.

“A 90-minute nap to maintain long-term performance and a 30-minute nap to maintain lower fatigue levels and fast reactions, as a strategic combination of naps, can be valuable for early morning work efficiency and safety,” said Oriyama, sole author of the study.

Different nap start times explored in the previous studies also indicated that timing the nap later during the shift was more effective in staving off sleepiness and exhaustion. However, delaying it for too long could compromise focus and increase drowsiness before the nap.

These findings offer valuable recommendations for managing sleepiness and fatigue during restricted rest intervals and actual 16-hour overnight shifts. Oriyama highlights that this approach could also prove beneficial in combatting sleep deprivation for mothers caring for infants.

Source: Hiroshima University ; Images: Shutterstock

The article can be found at Effects of 90‑ and 30‑min naps or a 120‑min nap on alertness and performance: reanalysis of an existing pilot study.

Disclaimer: This article does not necessarily reflect the views of Asian Scientist or its staff.


Nishat is a science journalist. She graduated with an MSc in Biomedical Science from Monash University where she worked with a cellular model of Parkinson’s Disease. Nishat loves lending her voice to bring science closer to society.

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