One of my specific area of interest is about circadian cycles and sleep, for about two main reasons: better understanding of my mind and body and better efficiency. Both of them will translate directly in a better quality of life.

The afternoon nap is something that hasn’t a really good reputation: it’s seen as something that you do when you’re old, it’s perceived as a symptom of weakness, maybe even related to something you eat at lunch, and on the work place it’s associated with slacking. But is it really bad?

Let’s see a few studies about this topic.

“A study of planned rest periods in long-haul flight operations demonstrated the effectiveness of in-flight naps to promote performance and alertness during subsequent critical phases of flight (descent and landing).”

— Rosekind, Smith, Miller, Co, Gregory, Webbon, Gander, Lebacqz (1995) Alertness management: strategic naps in operation

This is a study from the NASA Ames Research Center, 1995. They add some criterion to define when it’s good to plan a mid-flight nap (an identifiable benefit, opportunity, corporate culture, operational demands, safety) but they are all external consideration to the suggestion of having a nap.

We now report that sleep-dependent learning of a texture discrimination task can be accomplished in humans by brief (60− 90 min) naps containing both slow-wave sleep (SWS) and rapid eye movement (REM) sleep. This nap-dependent learning closely resembled that previously reported for an 8-h night of sleep […] and it was additive to subsequent sleep-dependent improvement, such that performance over 24 h showed as much learning as is normally seen after twice that length of time.
Thus, from the perspective of behavioral improvement, a nap is as good as a night of sleep for learning on this perceptual task.

— Mednick S., Nakayama K., Stickgold R. (2003) Sleep-dependent learning: a nap is as good as a night

Yes, it requires to have a deep sleep, with both slow-wave sleep and rapid eye movements, two phases that seems related to memories, but nonetheless with 60-90 minutes you get the equivalent learning sedimentation of an entire night of sleep. It’s interesting also that there’s almost no difference between 60 or 90 minutes.

Another study — Nishida M., Walker M. (2007) Daytime Naps, Motor Memory Consolidation and Regionally Specific Sleep Spindles — shows that a 60-90 nap is able to increase the consolidation of a morning motor-skill training, raising the speed of the learnt task by as much as 15% with no loss in accuracy.

Ok, but so how much sleep is required? Well, for some kind of improvement such as the learning task above you need SWS and REM, so it needs some time, but for other tasks?

A nap during the afternoon restores wakefulness and promotes performance and learning. Several investigators have shown that napping for as short as 10 min improves performance. Naps of less than 30 min duration confer several benefits, whereas longer naps are associated with a loss of productivity and sleep inertia. Recent epidemiological studies indicate that frequent and longer naps may lead to adverse long-term health effects.

— Rajiv, Harjyot (2006) Good sleep, bad sleep! The role of daytime naps in healthy adults

In this research a flag is raised: there could be adverse health effects from longer naps. However, reading the paper, it doesn’t seem evident a causation, but just a correlation: the facts are related, but we still don’t know in which order.

The sleep inertia issue is addressed by another research:

The 5-minute nap produced few benefits in comparison with the no-nap control. The 10-minute nap produced im- mediate improvements in all outcome measures (including sleep latency, subjective sleepiness, fatigue, vigor, and cognitive performance), with some of these benefits maintained for as long as 155 minutes. The 20-minute nap was associated with improvements emerging 35 minutes after napping and lasting up to 125 minutes after napping. The 30-minute nap produced a period of impaired alertness and performance immediately after napping, indicative of sleep inertia, followed by improvements lasting up to 155 minutes after the nap.

— Brooks A., Lack L. (2006) A Brief Afternoon Nap Following Nocturnal Sleep Restriction: Which Nap Duration is Most Recuperative?

So the sleep inertia appears with 30-minutes naps (or longer), but it’s a temporary period after which you gain the same improvements of the 10-minutes nap.

And how should we nap?

The post-lunch sleepiness is considered to be part of biological rhythm. […] Measures of subjective sleepiness, mood, fatigue, and P300 component were taken before and after a 20 min nap. Results showed that sleepiness, fatigue, and mood for both nap-in-a-seat and nap-in-a-bed were improved after napping. Moreover, objective alertness was enhanced in nap-in-a-bed relative to nap-in-a-seat and no-nap, which showed the larger P300 amplitude after nap.

— Zhao D., Zhang Q., Fu M., Tang Y., Zhao Y. (2009) Effects of physical positions on sleep architectures and post-nap functions among habitual nappers

This research added to their tests also the analysis of the P300 brainwave, and discovered that the best position to nap is lying in a bed, while you can still get some improvements sleeping on your desk.

Some evidence in businesses

1. Google in Mountain View installed some special beds to allow power-napping, by Metronap. It’s interesting to see a solution like this one, that partially solve the silence requirement to make a healthy nap during work time (2010, via PSFK).
2. Le Gourmet’s CEO, Cynthia McKay, designed specific rooms to allow his chefs to nap. Many other companies are offering the “nap rooms” as a perk (2006, via Time).
3. The National Transportation Safety Board (NTSB) in the USA is promoting naps of ~26 minutes, because there’s evidence they improve performance by ~34% and alertness by ~54% (2011, via BBC).

Conclusions

So, all those researches are telling us that:

1. A 60 minutes nap with SWS and REM is equivalent for learning as a night of sleep.
2. A 60 minutes nap can increase your speed in a motor-skill task to up to 15%.
3. If you sleep more than 30 minutes give you some time to recover from sleep inertia.
4. A 10 minutes nap improves you performance for 2.5 hours.
5. It doesn’t matter how you sleep, but try to sleep laying in a bed or on a couch if possible.

All those suggestions will allow you to plan better study days and work days, however don’t take them as strict rules: even if we have a lot of confirmations that an afternoon nap works well, every person is different so you have to try it for yourself and check the effectiveness before using it.

How to nap with maximum efficiency

Before napping we should ask ourselves a simple and obvious question: is it possible for me to have a nap? If you’re in an office, the answer is probably no, but you still can find a way to have a small rest or suggesting your boss how much a nap would be valuable to improve the efficiency of the work.

Analysing those researches we could safely say that the best way to nap is:

1. Lay: lay in a bed or on a comfortable surface.
2. 10+2 minutes: set a timer to 12 minutes, in order to give you a few minutes to get asleep.
3. Up: get up right when the timer rings, don’t lay more than the required time.

I suggest also to avoid harsh timers to wake up, use gentle ones. I might suggest Pzizz because it’s designed to help also to getting asleep, but in the end just use what works for you, even a soundtrack can get the job done.