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Sleep cycles and states: Fact file

yawning baby sleep clocks change bedtime
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Sleep cycles and states: Fact file

yawning baby sleep clocks change bedtime
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What are sleep cycles

In a single night of undisturbed sleep your body will complete several sleep cycles. One sleep cycle is completed when you have passed through all four sleep states. After a sleep cycle is completed you will either start the cycle again, or wake up. If you wake naturally in the night it is often between sleep cycles. You are most easily roused at that point in your sleep cycle. This is true for babies and toddlers too. 

The sleep states

Stage 1: 

A drowsy state or very light sleep; your eyes are usually closed but it’s easy to wake you up.

Stage 2: 

Early sleep; muscles relax and you are in a light sleep. Your heart rate slows and your body temperature drops. Your body is getting ready for deep sleep.

Stage 3:

Deep sleep; your heart rate and body temperature continue to decrease.

It’s harder to rouse you during this stage, and if someone woke you up, you would feel disoriented for a few minutes.

During this stages of deep non-REM sleep, the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system.

Stage 4: R.E.M sleep (Rapid eye movement) 

Your body is immobile but your brain is highly active. Your heart rate and breathing quicken. This is the stage of sleep in which you may experience intense dreams.  You are more rousable in this state.

Sleep cycle length

Adult sleep cycles

An average adult sleep cycle lasts around 90-120 minutes.

Adults spend around 20% of their sleep cycle in REM sleep.

Baby sleep cycles

Babies’ sleep cycles tend to last between 45-60 minutes. This is half the length of adult sleep cycles.

Newborn babies spend around 50% of their sleep cycle in active sleep, which is similar to REM sleep.

By 6 months old babies spend 35% of their sleep in REM sleep.

Toddler sleep cycles

An average adult sleep cycle lasts around 90-120 minutes.

Adults spend around 20% of their sleep cycle in REM sleep.

Child sleep cycles

Between the ages of 4-5 most children’s sleep cycles become a similar length to that of an adult: around 90-120 minutes. At this point they spend about 25% of their sleep in REM sleep. Between the age of 5 and teenage the REM percentage of their sleep cycle is around 20%, like adults’ sleep.

Teen sleep cycles

in the teenage years REM sleep increases to around 25% of the  sleep cycle.

REM sleep

REM sleep is thought to be the period of sleep that is associated with the brain doing lots of processing and consolidation of memory and learning. During periods of intense development, such as the first 5 years of life, and the teenage years, we have more REM sleep than during adulthood. This may be linked to the increased learning and brain development occurring in those periods. 

During REM sleep we are most rousable, and noises or disturbances can cause us to wake. For parents this can be very significant. Look at a baby’s sleep. They spend around 50% of their time in an active or REM like sleep from which they are easily roused. Sleeping like a baby actually means being easy to wake a lot of the time! 

It isn’t until 4-5 years old that the percentage of the time in REM sleep becomes similar to an adult’s 20% of their total sleep cycle.  Around this age parents often notice that their child is waking less and disturbing them less during their sleep. This is when parents often start reporting that their child starts sleeping through the night more reliably, and  needing less frequent parental input to resettle. Research suggests that around 50% of preschool children still wake at night and need assistance to resettle, although this may not be every night. 

 

At the end of a sleep cycle

At the end of all 4 stages of sleep in a sleep cycle we either wake, or drop back into stage 1 of sleep. During REM sleep, and stage one sleep we are very rousable, and we will often wake in the transition period between sleep cycles. As adults we often simply adjust our sleeping position and fall back to sleep without rousing fully. For babies and toddlers this is a key waking point, and often when they may signal for parents, either for hunger, or because they have realised they are alone and feel scared. 

When we talk to parents about using sensory sleep cues to help their baby, toddler or child feel sleepy, we often mention that, where possible, maintaining these throughout the sleep can help. This is because if a baby begins to rouse having the smells and noises that help them feel sleepy gives the greatest chance of them falling back into another sleep cycle without waking and becoming distressed. Thinking about what might help them resettle between sleep cycles can be helpful if you’re trying to reduce your sleep disturbance as a parent.

Recommend0 recommendationsPublished in Baby sleep, Child sleep, Science, Sleep science, Toddler sleep
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