||It has been suggested that this article be merged into Nap. (Discuss) Proposed since November 2010.|
A power nap is a short sleep which terminates before the occurrence of deep sleep or slow-wave sleep (SWS), intended to quickly revitalize the subject. The expression was coined by Cornell University social psychologist James Maas.
The idea of "power nap" has been around for centuries in Spain and Latin America. In Spain the "power nap" is known as "Siesta del Hidalgo" ("The Gentleman's nap"). Salvador Dali, the Spanish surrealist artist was fond of such kind of nap. He would slide off to sleep in a chair with his arm over the side, holding a spoon over a plate on the floor. The instant he fell asleep, his hand would loosen up and the spoon would fall out and hit the plate with a clatter that woke him up again. He claimed that the brief rest worked wonders.
The power nap is thought to maximize the benefits of sleep versus time. It is used to supplement normal sleep, especially when a sleeper has accumulated a sleep deficit.
Various durations are recommended for power naps, which are very short compared to regular sleep. The short duration of a power nap is designed to prevent nappers from sleeping so long that they enter a normal sleep cycle without being able to complete it. Going beyond sleep stages I and II but failing to complete a full sleep cycle, can result in a phenomenon known as sleep inertia, where one feels groggy, disoriented, and even more sleepy than before beginning the nap. Brief naps (10–15 minutes) can improve alertness directly after awakening without the detrimental effects of sleep inertia associated with longer naps.
Scientific experiments (see Benefits section below) and anecdotal evidence suggest that an average power nap duration of around 30 minutes is most effective. Any more time, and the body enters into its usual sleep cycle. People who regularly take power naps may develop a good idea of what duration works best for them, as well as what tools, environment, position, and associated factors help induce the best results. Others may prefer to take power naps regularly even if their schedules allow a full night's sleep. Mitsuo Hayashi, PhD and Tadao Hori, PhD have demonstrated that a nap improves mental performance even after a full night's sleep. New sleep sensors and sleep timers available on several mobile devices allow advocates of power naps to sleep for exactly as long as they would like to.
Power naps of less than 30 minutes—even those as brief as 6 and 10 minutes—restore wakefulness and promote performance and learning. A University of Düsseldorf study found superior memory recall once a person had reached 6 minutes of sleep, suggesting that the onset of sleep may initiate active memory processes of consolidation which—once triggered—remains effective even if sleep is terminated.
A Flinders University study of individuals restricted to only five hours of sleep per night found a 10-minute nap was overall the most recuperative nap duration of various nap lengths they examined (lengths of 0 min, 5 min, 10 min, 20 min, and 30 minutes): the 5-minute nap produced few benefits in comparison with the no-nap control; the 10-minute nap produced immediate 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; and 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.
Naps lasting more than 30 minutes appear to be associated with a period of impaired alertness (sleep inertia) immediately after awakening that takes some time to dissipate before wakefulness and performance improve.
For several years, scientists have been investigating the benefits of napping, both the power nap and much longer sleep durations as long as 1–2 hours. Performance across a wide range of cognitive processes has been tested. Studies demonstrate that naps are as good as a night of sleep for some types of memory tasks.
A NASA study led by David F. Dinges, professor at the University of Pennsylvania School of Medicine, found that naps can improve certain memory functions. In that NASA study, volunteers spent several days living on one of 18 different sleep schedules, all in a laboratory setting. To measure the effectiveness of the naps, tests probing memory, alertness, response time, and other cognitive skills were used.
The National Institute of Mental Health funded a team of doctors, led by Alan Hobson, MD, Robert Stickgold, PhD, and colleagues at Harvard University for a study which showed that a midday snooze reverses information overload. Reporting in Nature Neuroscience, Sara Mednick, PhD, Stickgold and colleagues also demonstrated that "burnout" irritation, frustration and poorer performance on a mental task can set in as a day of training wears on. This study also proved that, in some cases, napping could even boost performance to an individual's top levels. The NIMH team wrote "The bottom line is: we should stop feeling guilty about taking that 'power nap' at work."
Sara Mednick conducted a study experimenting on the effects of napping, caffeine, and a placebo. Her results showed that a 60-90 minute nap is more effective than caffeine in memory and cognition. 
The caffeine nap 
A caffeine nap is a short nap that is preceded by the intake of caffeine. In a driving simulator and a series of studies, Horne and Reyner investigated the effects of cold air, radio, a break with no nap, a nap, caffeine pill vs. placebo and a short nap preceded by caffeine on mildly sleep-deprived subjects. The last mentioned was by far the most effective in reducing driving "incidents" and subjective sleepiness. Caffeine in coffee takes up to half an hour to have an alerting effect, hence "a short (<15min) nap will not be compromised if it is taken immediately after the coffee."
See also 
- Maas, James B.; Wherry, Megan L. (1998). Miracle Sleep Cure: The Key to a Long Life of Peak Performance. London: Thorsons. ISBN 978-0-7225-3644-5.[page needed][non-primary source needed]
- McEvoy, RD; Lack, LL (2006). "Medical staff working the night shift: Can naps help?". The Medical journal of Australia 185 (7): 349–50. PMID 17014398.
- Dhand, Rajiv; Sohal, Harjyot (2007). "Good sleep, bad sleep! The role of daytime naps in healthy adults". Current Opinion in Internal Medicine 6: 91. doi:10.1097/01.mcp.0000245703.92311.d0.
- Lahl, Olaf; Wispel, Christiane; Willigens, Bernadette; Pietrowsky, Reinhard (2008). "An ultra short episode of sleep is sufficient to promote declarative memory performance". Journal of Sleep Research 17 (1): 3–10. doi:10.1111/j.1365-2869.2008.00622.x. PMID 18275549.
- Brooks, A; Lack, L (2006). "A brief afternoon nap following nocturnal sleep restriction: Which nap duration is most recuperative?". Sleep 29 (6): 831–40. PMID 16796222.
- "NASA: Alertness Management: Strategic Naps in Operational Settings". 1995. Retrieved 2012-04-16.
- Mollicone, Daniel J.; Van Dongen, Hans P.A.; Dinges, David F. (2007). "Optimizing sleep/wake schedules in space: Sleep during chronic nocturnal sleep restriction with and without diurnal naps". Acta Astronautica 60 (4–7): 354. doi:10.1016/j.actaastro.2006.09.022.
- "The National Institute of Mental Health Power Nap Study". 2002-07-01. Retrieved 2002-07-01.
- Mednick, S. C. et al. (2008). Comparing the benefits of caffeine, naps, and placebo on verb al, motor and perceptual memory. Behavioral Brain Research. 193: 79-86.
- Reyner, LA; Horne, JA (1998). "Evaluation 'in-car' countermeasures to sleepiness: Cold air and radio". Sleep 21 (1): 46–50. PMID 9485532.
- Horne, J. A.; Reyner, L. A. (1995). "Driver sleepiness". Journal of Sleep Research 4 (S2): 23–29. doi:10.1111/j.1365-2869.1995.tb00222.x. PMID 10607207.
- "Loughborough University researchers issue new warning to tired drivers". Retrieved 2007-09-23.
- Lifehacker article[full citation needed]
- Maas 1999 – Power Sleep : The Revolutionary Program That Prepares Your Mind for Peak Performance
- Fox News article: "Researchers: Power Nap Better than Caffeine to Fight Afternoon Fatigue"
- Boston Globe article on power-naps
- University of Miami : "Sleep, Napping and the Brain -The Power of Napping", YouTube