Finding Your 90 Minute CycleAlthough we live in a 24 hour society and there is plenty to do at night, most of us choose this time to sleep. It is natural to sleep during the hours of darkness, working with the Circadian Rhythm and fitting in with work and social demands.

In some situations sleep cannot be confined to the night. Challenges where the human body needs to be on call and alert for long periods means that sleep must be put ‘on hold’, and other ways found to allow the body and mind to rest. Solo flights, around the world, yacht races and diplomatic negotiations all rely on individuals staying awake for long periods of time.

Ninety Minutes Sleep Cycle

Studies are now looking into the value of napping, and whether large blocks of sleep are really necessary to keep the body functioning and the mind alert. It is suggested that it is not the overall length of sleep time that matters, but the number of complete Sleep Cycles that influence the quality of sleep.

A Sleep Cycle consists of:

Stage 1. Electrical activity in the brain slows down and muscles start to relax. Lasts a few minutes.

Stage 2. Rapid bursts of activity in the brain.

Stage 3. Deep Sleep showing slow wave activity in the brain.

Stage 4. Deep Sleep showing a further slowing down of brain activity.

REM Sleep. Rapid Eye Movement Sleep. Movement of the eyes under the closed eyelids, increased brain activity and deep muscle relaxation during the ‘dreaming’ stage.

Separate Sleep Cycles

Those who practise the ninety minute sleep system aim to complete blocks of ninety minutes sleep before waking. They believe that even one complete cycle is more refreshing than waking in the middle of a cycle during a longer sleep. This would mean sleeping for 6 or 9 hours but not 7 or 8 hours. Each cycle is separate and there is a sort of twilight zone between finishing one cycle and starting the next. It is important that a cycle should be completed before waking. This is the ‘natural’ time to wake and the mind is alert and the body rested as long as the cycle has been completed.

The ability to limit sleep and remain alert is of interest to the military and other employers. Sailors, astronauts, travellers and others, who need to go for long periods without sleep, need to adapt their sleep patterns in preparation for their challenge.

It is claimed that cognition and analytical ability are retained and that the body and brain adapts to any loss of sleep. Supporters believe that REM sleep is the most important sleep stage and that multiple ‘naps’ provide them with the right type of sleep and adequate rest.

Criticisms of Ninety Minute Sleep

Critics believe that it is more natural to sleep at night and have one solid block of sleep. By limiting the amount of sleep, some sleep stages are reduced and there is a risk of Sleep Deprivation. This may result in fatigue and a drop in alertness which can be dangerous to the individual and others.


There is increasing evidence that napping helps cope with lack of sleep and fatigue. Elderly people often benefit from an afternoon nap and experience a reduction in night time sleep. Infants often find it difficult to give up their afternoon sleep. The siesta is still kept in many countries and many people will be familiar with a dip in concentration and a feeling drowsiness in the afternoon. Winston Churchill and Napoleon Bonaparte are both reputed to have relied on napping and limited sleep.

Length of Naps

Research shows that 10 minute naps improve productivity better than longer naps. Lord Byron and Ellen McArthur are both believed to have relied on short naps to keep them alert.

Polyphasic Sleep

Supporters of Polyphasic Sleep claim that afternoon napping is evolutionary and is more refreshing than restricting sleep to one main block at (Monophasic Sleep).

The length and amount of naps needed to ward off fatigue depends on the individual and the circumstances.

Uberman’s or Da Vinci Sleep is a well known type of Polyphasic Sleep practice. Six naps of between 20-25 minutes are taken every 4 hours.

Core sleep suggests napping with an additional block of several hours sleep replacing one or two of the naps.

Dymaxion sleep consists of 30 minute naps every six hours.

As our knowledge of sleep develops, it seems that the amount and type of sleep needed varies between individuals and their circumstances. There is convincing evidence that napping is beneficial for a number of people. Shift workers, travellers, long distance drivers, pilots and individuals suffering from sleep debt or other sleep disorders may all need to take regular naps to maintain alertness.

Adapting to a 90 Minute Sleep Cycle may not be suitable for some individuals. Sleep cycles vary between individuals and most people will benefit from a good night’s sleep. A 90 minute nap during the afternoon may show increased alertness during the evening, but is likely interfere with the night’s sleep.