Polyphasic sleep or segmented sleep is the system of sleeping during multiple periods over the course of 24 hours, in contrast to monophasic sleep, a single period of sleep within 24 hours. Polyphasic usually means more than two periods of sleep, as distinct from biphasic (or diphasic, bifurcated, or bimodal) sleep, meaning two periods of sleep.

While today monophasic sleep is the norm, historical analysis suggests that polyphasic nighttime sleep was common practice across societies before industrialization. Scientific experiments and observational studies have supported a theory of biphasic sleep in humans. Polyphasic sleep is common in many animals, and is believed to be the ancestral sleep state for mammals, although simians are monophasic. There is no scientific evidence that this practice is effective or beneficial.

Historical examples

Biphasic sleep (also referred to as segmented sleep, or bimodal sleep) is a pattern of sleep which is divided into two segments, or phases, in a 24-hour period.

First sleep and second sleep

One biphasic sleep pattern is sometimes described as segmented sleep, involved sleeping in two phases, separated by about an hour of wakefulness. This pattern was common in preindustrial societies, and it was most common to sleep early ("first sleep"), wake around midnight, and return to bed later ("second sleep"). Along with a nap in the day, it has been argued that this is the natural pattern of human sleep in long winter nights. Ekirch draws evidence from more than 500 references to a segmented sleeping pattern in documents from the ancient, medieval, and modern world.

A 2015 study of three non-industrial equatorial societies showed that all three experienced monophasic nighttime sleep, but the authors' conclusions were questioned by Ekirch.

Single nap (siesta)

Another classic cultural example of a biphasic sleep pattern is the siesta, a nap taken in the early afternoon, often after eating lunch. Such a period of sleep is a common tradition in some countries, particularly those with a warm climate, where it allows people to avoid sunshine and heat during the hottest part of the day; many businesses in these countries open early in the morning (again to avoid the heat), close at 1 p.m. so employees can go home for a siesta, reopen at 3 p.m., and close at around 8 p.m. Historically common throughout the Mediterranean and Southern Europe, it is the traditional daytime sleep of China,

Modern proposals

The Everyman schedule involves sleeping 3 hours during the night ("core sleep"), and taking three 20-minute naps during the day. This totals 4 hours of sleep in a 24-hour period.

The Uberman sleep schedule consists of a 30-minute nap every four hours, totaling 3 hours of sleep in a 24-hour period.

In extreme situations

In crises and other extreme conditions, people may not be able to achieve the recommended seven to nine hours of sleep per day. Systematic napping may be considered necessary in such situations.

Claudio Stampi, as a result of his interest in long-distance solo boat racing, has studied the systematic timing of short naps as a means of ensuring optimal performance in situations where extreme sleep deprivation is inevitable, but he does not advocate ultrashort napping as a lifestyle.

</references>

Further reading

  • Polyphasic Sleep Wiki