The Science Behind Sleep Cycles

The key to feeling refreshed in the morning is understanding, and optimising, the different stages your body cycles through during sleep. 

A sleep cycle is one journey through the sleep stages you’re probably familiar with: light sleep, deep sleep, and REM sleep. Every night we go through a number of these sleep cycles.

The arrangement of sleep cycles and stages that make up your sleep is known as your Sleep Architecture. While everyone’s – and every night’s – exact architecture will differ, sleep stages are standard across all sleepers.

The typical sleep cycle duration is between 90-110 minutes, and most sleepers will experience 4-6 cycles a night. Non-REM (NREM) sleep represents 75-80% of total sleep time, and REM makes up the remainder of the sleep cycle. The rough breakdown of sleep stages looks something like this (yours may differ!)

Sleep StageCategoryOther namesDuration per cycleDuration per night
Stage 1NREMN1, Light sleep, Drowsiness, Presleep1-5 Minutes30 mins – 1 hour
Stage 2NREMN2, Light sleep10-60 minutes3.5 – 4.5 hours
Stage 3NREMN3, Deep sleep, Slow Wave Sleep (SWS), Delta sleep20-40 minutes1.5 – 2 hours
Stage 4REMREM sleep10-60 minutes1.5 – 2 hours

Sleep cycles won’t necessarily progress in order from Stage 1 to 4 and back again. It’s more common to move from light to deep sleep, back to light sleep, and then to REM in one cycle: the pattern N1-N2-N3-N2-REM is typical. You’re also likely to experience more deep sleep earlier in the night and longer REM stages later, so stage durations also differ as you sleep.

While the importance of a good night’s sleep is well understood, people are generally less familiar with the importance of maintaining healthy sleep cycles. Each sleep stage has a critical role to play in ensuring cognitive function, emotional regulation, and physical well-being, so getting your sleep cycle sorted is well worthwhile.

Understanding Light Sleep

We spend most of our nights in light sleep: sleep stages 1 and 2. This is where we transition between wakefulness and the deep and REM sleep stages. Without light sleep providing this buffer, our brains and bodies wouldn’t be sufficiently relaxed to take advantage of the later stages of sleep

Stage 1 is relatively brief – only minutes long. It’s very light sleep where heartbeat, eye movement breathing slow, and muscles relax. If you’ve ever felt yourself twitch or jerk as you’re falling asleep, you’ll be familiar with the feeling of Stage 1! This stage is purely transitory, and we can easily be roused from it.

Stage 2 is longer, and it’s usually the majority of a night’s sleep. In this stage, heartbeat and breathing slow even more, temperature drops and eye movement ceases. Brain activity slows except for occasional electrical bursts that help our brains filter out sensory information, so we’re less likely to be woken by external stimuli.

While there’s generally less recovery and restoration taking place during light sleep compared to the rest of the sleep cycle, the presence of sleep spindles and K-complexes suggests that there may be some memory consolidation happening at Stage 2. 

The Benefits of Deep Sleep

Deep Sleep, or Slow Wave Sleep (SWS), is the third and most restorative stage of the sleep cycle. This is the sleep we need to wake up feeling refreshed in the morning. Generally, the longer we’ve gone without sleep or the more intense our awake time, the more deep sleep we need.

During this stage, brain waves, heartbeat, temperature, and respiration are at their lowest, and muscles are the most relaxed. Because our brains are even less receptive to external stimuli at this stage, It’s difficult to wake someone out of deep sleep. Someone roused at this stage will usually experience a period of grogginess known as sleep inertia – where they’re not quite properly awake.

The majority of deep sleep happens during the first part of the night, gradually giving way to increased REM sleep later on.

The benefits of deep sleep are largely physiological, and include:

– Growth and repair of tissues, including muscle and bone

– Strengthening of the immune system

– Metabolic regulation and hormone release

Because brain and muscle activity are at their lowest at this stage, the body is deeply relaxed and can prioritise internal processes for repair and growth.

REM Sleep Explained

This is where dreams happen! REM stands for Rapid Eye Movement, and as you’d expect, this stage is characterised by rapidly moving eyes under closed eyelids. Additionally, brain activity increases to near-wakefulness, while skeletal muscles are temporarily paralysed to prevent us from inadvertently harming ourselves by flailing around in our dreams.

REM sleep is considered essential for memory consolidation, learning, and creativity. 

In this stage, the hippocampus strengthens memories by replaying the day’s experiences, processing and categorising them before moving them into long-term memory. The amygdala processes emotional memories, tagging feelings and prioritising them for storage.

This emotional regulation is a key feature of REM sleep. Because the rational side of the brain is less active in this stage, emotions are more likely to be processed apart from factual content, and so less likely to be filtered. It’s also possible that by replaying emotional moments while dreaming, we’re able to experience them with less intensity, so we can deal with them in a more balanced way.

How Long Should Each Sleep Cycle Last?

The optimal sleep cycle duration for adults is 90-110 minutes. This is enough time to go through every sleep stage, and to experience 4-6 cycles per night. 

Uninterrupted sleep is the goal. This means you’ve been through the full sleep cycle: your brain has had time to process everything it needs to, and your body has had time to restore. If your sleep is interrupted mid-cycle, you’ll know it! You’ll feel tired and irritable, have trouble remembering or processing information, and might turn to caffeine to get through the day. 

Of course, different people have different sleep needs. Babies sleep the longest and have the shortest sleep cycle duration, which gets longer as they grow. Cycles settle at about 20 years old and shorten again as we get older. There are also differences between men and women. Men typically fall asleep faster, sleep lighter, and experience shorter cycles. Women have longer sleep cycles and spend longer in deep sleep, but their sleep is disturbed more often. As a result, they’re more likely to report feeling sleep-deprived than men.

Prolonged sleep loss is associated with a range of systemic effects and chronic conditions including obesity, diabetes, heart disease, anxiety, and depression. That’s why it’s important to enhance sleep cycles for a properly restorative sleep. 

How to Enhance Sleep Cycles

Our physical and mental health depends on getting enough restorative sleep. If you’re having trouble remembering things and can’t get through the day without coffee, there are some simple steps you can take to enhance your sleep cycle:

– Create a supportive sleep environment. Remove distractions including anything too bright or noisy (although consider white noise if you find it helps!) Make sure your room is relatively cool. 

– Limit stimulants during the day. It might be a struggle, but cut down on caffeine and try not to have any after midday. Try drinking herbal teas in the evening, or give this Golden Milk a try.

– Relax before bed. Take a bath, use lavender oil, and listen to relaxing music. Avoid watching exciting movies, exercising, or playing computer games. Anything that raises adrenaline will make getting to sleep that much more difficult.

Avoid screens! Trade your phone for a good book.

– Take care of your daily well-being. Make sure you get exercise and fresh air, eat well, drink enough water, and manage your stressors so they don’t follow you to bed.

And the number one thing you can do is establish a consistent sleep routine. Work out how many sleep cycles you need to feel refreshed in the morning. If you feel better after seven and a half hours of sleep, that’s five sleep cycles. If you need 9 hours of sleep, that’s 6 cycles. Work out when you need to wake up (probably the time your alarm is set). Then work backwards! If you need 5 cycles, then bedtime is 10:45. If you need 6, then you should try to be asleep by 9:15. Try to keep to these times, or at the very least, to the number of cycles – even on weekends.

It goes without saying that having the right bed is super important. If your bed is unsupportive, too hot, lumpy, or just generally uncomfortable, you’re more likely to have a disturbed night’s sleep. Sleepyhead has spent almost 90 years designing and manufacturing mattresses that solve these problems: providing the right support, temperature control, and stability to ensure you experience the best sleep cycle. We’ve got your back (literally)!

Embrace Better Sleep

We all know getting a good night’s sleep is important, and in this case, quality is definitely more important than quantity! For sleep to be truly effective, we need to go through complete sleep cycles and experience every stage of sleep. 

Without light sleep we won’t be relaxed enough to take advantage of the other sleep stages, without deep sleep our body doesn’t have the opportunity to repair itself, and without REM sleep our cognitive functions including memory, learning, and creativity will suffer. So optimising our sleep cycles is the key to waking up refreshed and restored!

At Sleepyhead, we have a variety of sleep solutions available so everyone can find that perfect sleep, no matter their lifestyle – or sleep architecture. Browse our collection of beds and bedding accessories online now or head into our store to try out the range of Sleepyhead beds and discover the difference a quality mattress can make to enhancing your sleep.

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