Scheduling overview

Scheduling sleep is a complex topic that involves many aspects and must be done in accordance to one's individual needs. With a poorly designed polyphasic schedule, you will experience crippling sleep deprivation and most likely never adapt, wasting weeks or months of your life. This page details the current consensus on scheduling.

Sleep stages

Sleep is a complex phenomenon that causes physiological changes all over the body. However, it mainly affects the brain. According to the electrical activities in the brain, sleep is divided into rapid-eye movement (REM) and non-REM (NREM) stages. NREM sleep is further divided into three stages according to the frequency and amplitude of brainwaves.

NREM Stage 1, accounting for 5-10% of total sleep in monophasic adults, is the lightest of all NREM Stages. During this stage, awareness to the external environment and consciousness is diminished. Some people experience hypnic jerks or hypnagogic hallucinations during this stage. A mix of alpha waves and theta waves are present in this stage.

NREM Stage 2, accounting for 45-55% of total sleep, is deeper than the first one. It is more difficult to be awaken from than from the NREM 1. This stage is characterized by K-complexes and sleep spindles, which are abrupt interruptions in alpha waves activity. This stage of sleep also plays a role in maintaining wakefulness over long periods.

NREM Stage 3, accounting for 15-25% of total sleep, is the deepest of all sleep stages. This stage contains primarily delta waves, which are high-amplitude and low-frequency. Hence, this stage is also known as slow-wave sleep (SWS). It is very difficult to wake up from this stage; attempts at doing so tend to result in sleep inertia -- a period intense grogginess and impaired cognitive function. This stage of sleep plays a critical role in the maintenance of the brain through the glymphatic system. This process takes about 30 to 60 minutes of continuous NREM3 to complete, and could be hindered by schedules containing only short naps.

REM, accounting for 20-25% of total sleep, is characterized by high frequency, low amplitude activity that resembles that during wakefulness and rapid eye movements. In this stage, muscles are also paralyzed and body temperature becomes unregulated. Vivid dreams are also often experienced during this stage, and the muscle atonia (paralysis) prevents the sleeper from acting them out.

Sleep reduction through polyphasic sleep

SWS and REM (collectively termed vital sleep stages) are the most necessary for the body, and in general cannot be cut. When a sleeper does not get a sufficient amount of SWS or REM, the respective pressure starts to build up. As the pressure builds, the body starts to favour that kind of sleep over others. At some point, this can lead to sleep-onset REM (SOREM) and sleep-onset SWS (SOSWS), which enables a sleeper to gain the required amount of SWS and REM in a shorter amount of time. Moreover, when sleep is restricted, vital sleep stages displaces light sleep (NREM 1 and 2), which further reduces the amount of total sleep needed to sustain the body.

However, as NREM 2 gets reduced, the ability to stay awake for long periods diminishes. This is why schedules with less total sleep time (TST) need more sleeps spread throughout the day to be sustainable. Taking a ~20-minute nap or a ~90-minute single-cycle core helps a polyphasic sleeper sustain wakefulness. Maximum wake gaps are dependent on the schedule, time of day, as well as the sleeper's individual needs. With gaps too large, one will always experiences bouts of tiredness during it and be unable to fully adapt to the schedule.

Circadian rhythm

The circadian rhythm is the body clock aligned to local solar time by light exposure, among other factors. It produces hormonal effects that changes throughout the day consistently to produce effects on the body. One of the main effects is the secretion of melatonin, the presence of which is essential for entering SWS, and also affects the timing of REM sleep.

After sunset when light levels reduce, the body starts to secrete melatonin to promote sleep. The rising levels of melatonin early in the night allows the body to gain SWS in the first few sleep cycles. In contrast, as melatonin levels drops in the morning, REM becomes the preferred sleep phase to be gained.

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Melanopic sensitivity function

In modern times with the advent of artificial light, many people's circadian rhythms have been pushed forward (i.e. later). However, this exposure to artificial light sources also compromises people's ability to gain SWS efficiently. The extent to which light influences the circadian rhythm is given by the melanopic sensitivity function, which peaks at ~480nm (blue) and drops off on both sides. To reduce this effect, a dark period must be employed, during which blue and green lights must not enter the eye. This can be done in many ways, such as with red goggles or screen filters.

To maintain the stability of the circadian rhythm, all polyphasic sleep schedules must stay relatively consistent day-to-day, without large changes in core or dark-period timings. As such, schedules that are not aligned with the 24-hour day are unsustainable and unhealthy.

Minimum sleep threshold

Since vital sleep stages are generally not possible to reduce, the amount of compression required to sustain a schedule increases dramatically as total sleep time reduces. Compressing sleep, however, requires adaptation, and greater levels of compression necessitates harsher and/or longer adaptations. As such, schedules can be classified by their difficulty level, which is mostly a function of the amount of sleep cut.

The necessity of vital sleep stages also implies that certain schedules, such as Uberman or Dymaxion, will be unachieveable for most people as its total sleep is below the total vital sleep required for most people.

Here is a basic classifcation of schedules by their difficulty level, assuming a typical sleeper with 8h monophasic sleep and normal levels of SWS and REM:

Difficulty	Example schedules	TST range	Sleep time cut	Note
Easy	BiphasicX, E1-ext, Siesta-ext, Segmented-ext	7-8	<1 hour
Moderate	E1, E2, E3-ext, Siesta, DC1, Triphasic-ext, Segmented, DC1-ext	5-6	1-2 hours
Hard	E3, DC2, Triphasic	4-5	2-3 hours
Very hard	DC3, Bimaxion	4	3-4 hours
Extremely hard	E4, E3-shortened, Uberman, Dymaxion	<4	>4 hours

Sleep block lengths

Sleeps on polyphasic schedules are broadly characterized as cores and naps.

Cores are long blocks of sleep that contain at least one full sleep cycle. They are typically scheduled to be a multiple of a 90 minutes, which is a common sleep cycle length. However, alternative core lengths can be done to either to plan for alternative cycle lengths or in an effort to gain extra time in SWS or REM. Cores are generally considered to be essential, because they provide the necessary amount of SWS to sustain life. As such, schedules without cores (i.e. nap only schedules) have extremely low success rates.

Naps are short blocks of sleep, typically about 20 minutes on default schedules. Naps allow for a small amount of REM to be gained. Moreover, naps help sleepers sustain wakefulness through gaps. Longer up to (~45 minute) naps can be used in during the REM peak around dawn to gain even more time in REM. Longer naps in other times of the day can lead to SWS wakes, which can be exceptionally difficult to wake from for some people, especially during periods of high SWS deficit.

Core sleeps are favoured during night time, as they allow sufficient time to complete SWS-filled sleep cycles. They are also easier to schedule at night for most people due to social obligations. Naps are favoured in the day, since deeper sleep stages are less likely to appear then. After adaptation, naps can be relatively flexible, whereas cores are much harder to move.