The experiment
In Brooks and Lack’s study, 24 healthy young adults limited their night’s sleep to about five hours. At 3 pm the next day, they took a 5-, 10-, 20- or 30-minute nap, or no nap at all. Their sleepiness, fatigue, vigour and cognitive performance were then measured for three hours.[1]
Results
| Nap | What happened |
|---|---|
| 5 min | Few benefits compared with no nap |
| 10 min | Immediate improvement on every measure, some benefits lasting up to 155 minutes |
| 20 min | Improvements started 35 minutes after the nap and lasted up to 125 minutes |
| 30 min | Grogginess right after waking (sleep inertia), then improvements lasting up to 155 minutes |
The authors concluded that, of the lengths tested, the 10-minute nap was the most effective.[1] In an earlier experiment, 30- and 90-second “micro-naps” brought no measurable benefit, while a 10-minute nap improved alertness and performance.[2]
Night shifts have different rules
In a simulated night shift at the University of South Australia, a 30-minute nap contained considerably more deep sleep than a 10-minute nap. The 10-minute nap was followed by minimal sleep inertia and helped maintain short-term performance. The 30-minute nap was not.[3]
Rule of thumb
During the day, 10–20 minutes works well. If you have time to wake up properly before getting back to work, a nap can be longer. On a night shift, a short nap at the start of the break is the safer choice, so the grogginess wears off before you return. Always set an alarm.
Sources
- Brooks A, Lack L. A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? Sleep. 2006;29(6):831–840. doi.org/10.1093/sleep/29.6.831 (opens in a new window)
- Tietzel AJ, Lack LC. The recuperative value of brief and ultra-brief naps on alertness and cognitive performance. Journal of Sleep Research. 2002;11(3):213–218. doi.org/10.1046/j.1365-2869.2002.00299.x (opens in a new window)
- Hilditch CJ, Centofanti SA, Dorrian J, Banks S. A 30-minute, but not a 10-minute nighttime nap is associated with sleep inertia. Sleep. 2016;39(3):675–685. doi.org/10.5665/sleep.5550 (opens in a new window)
