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How sleep tracking can help you optimise your sleep?

You probably heard the common recommendation for sleeping for 7-9 hours each night, and whilst most of us follow this advice regularly, have you ever wondered why?

Let me explain.

Sleep is a complex process. Every night, as you drift away your body and mind transition through four different stages, which complete a full cycle of sleep. On average, one sleep cycle lasts about 90 minutes. Your body usually completes 4 to 6 of them over the night, which makes about 7-9 hours of sleep, hence the guidelines.
It is important that, aside from sleeping long enough, you get a good quality of sleep as well and that means spending a sufficient amount of time in each of the four stages, as they all play particular roles in helping you to wake up refreshed the following day. Every stage of sleep is characterised by specific shifts in the activity of the brain waves occurring during every phase. That is why cycling through all of them is critical to your health and wellbeing.

Three of the four stages are considered non-rapid eye movement (NREM) sleep ( also described as quiet sleep), whilst stage 4 is known as rapid eye movement (REM/ or active) sleep.

Let us take a closer look at each of the sleep phases:

1. Stage 1.

It is the lightest of all stages, transitioning between wakefulness and sleep. During stage1 sleep, breathing occurs at a regular rate and muscles begin to relax but may occasionally twitch. Brain activity slows down as your mind begins to drift. The body prepares itself for a deeper sleep.

“This stage tends to last 1 to 5 minutes, consisting of around 5% of the total cycle.”^[1]

2. Stage 2.

During stage 2, the body temperature starts to drop, breathing and heart rate slows down, muscles relax and the eye movement stops.^[2] Due to brain waves slowing down, deeper sleep is facilitated, therefore it is more difficult to wake someone from this stage than the previous one.

“Stage 2 sleep lasts around 25 minutes in the initial cycle and lengthens with each successive cycle, eventually consisting of about 50% of total sleep.”^[3]

3. Stage 3.

This stage is recognised as the deepest sleep and it is very difficult to awaken from this phase. Research^[4] indicated that even noises reaching over 100 decibels (for instance a leaf blower, a motorcycle or a jet take-off) might not awaken some people from this stage of sleep.

Those that do awake from deep sleep often experience sleep inertia.^[5]
Commonly referred to as brain fog, sleep inertia is a transitional state between wakefulness and sleep. It may last from a few minutes to a few hours and causes slow functioning and reduced cognitive performance.

Most of the restorative processes occur during this stage of sleep. The body regenerates its cells, replenishes the energy and strengthens the immune system. Owing to the increased production of the human growth hormone( HGH), it also regrows the tissues, builds muscles and bones and retains memory. Stage 3 sleep is also known as delta sleep due to slow brain waves (or delta waves) beginning to appear at this point.

4. REM sleep.

REM (Rapid Eye Movement also known as active) sleep usually begins about 90 minutes after falling asleep. The first REM stage lasts about 10 minutes and it progressively gets longer with each following cycle. The last REM sleep could last up to an hour. This stage constitutes about 20-25% of the whole night. This phase of sleep is where dreaming takes place. Breathing becomes irregular, eyes move quickly and brain activity resembles this of an awake person^[6]

Although neural activity is high, skeletal muscles remain atonic (paralysed, exhibiting no muscle tone). At this stage the body is not able to regulate its temperature, so you might begin to feel hot or cold during the night. REM sleep, or active sleep, is considered to help regulate mood and enhance memory. That is why it is important to get enough sleep after learning something new or preparing for the exam. If you consistently deprive your body of a sufficient amount of sleep, you most likely prevent it from reaching the REM stage. Thus, you may have difficulty concentrating or memorising.

How can sleep tracking help you optimise your sleep?

Nowadays, in the era of digital wearables, tracking sleep has become very common and easily accessible. Increasingly popular smartwatches measure your daily activities by tracking the number of steps you take each day, the number of calories you burn and your sleep patterns.

Most of the companies that offer smartwatches utilise technology based on motion detectors and heart rate sensors that may help recognise the phases of sleep and analyse its quality. Thanks to this, you may be able to analyse how much time you spend during each stage of sleep. Moreover, sleep trackers often measure the continuity of sleep, detect any interruptions in the sleep pattern and, based on that, calculate the actual time spent sleeping.

However, besides monitoring heart rate and movement, more data is needed to accurately measure sleep quality and detect potential sleep problems. The most accurate sleep tracking devices focus on monitoring respiration and brain wave activity as well. For this reason, even though the technology is evolving rapidly, it is safe to assume that currently, when it comes to tracking sleep, digital watches present estimates rather than accuracy.

To spot potential sleep disorders and receive the most accurate readings, most researchers and sleep doctors recommend a polysomnogram (a sleep study) that measures brain waves and eye movement during sleep. The tests are usually performed overnight in hospitals or at sleep centres. Nonetheless, there are more convenient alternatives available on the market these days that were closely studied and are believed to be just as accurate as polysomnograms, according to the researchers.^[7]
We are talking about the at-home EEG (electroencephalogram) wearables, usually in the form of a headband that connects to your phone. The headband is equipped with sensors that recognize sleep patterns, including changes in the brain waves throughout the night.

Whichever method of sleep tracking you choose, if you consistently keep an eye on your sleep patterns, you might be able to detect any behavioural or/and environmental factors that impact the quality of your sleep and thus, make necessary adjustments. By regularly analysing your sleep, identifying the areas for improvement and methodically applying changes in your routine and sleep environment, you may be able to bring your sleep game to a whole new level.

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Research references

1. https://www.ncbi.nlm.nih.gov/books/NBK526132/
2. https://www.sleepfoundation.org/how-sleep-works/stages-of-sleep
3. https://www.ncbi.nlm.nih.gov/books/NBK526132/
4. https://www.ncbi.nlm.nih.gov/books/NBK526132/
5. https://www.sleepfoundation.org/how-sleep-works/sleep-inertia
6. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep
7. https://sleepreviewmag.com/sleep-diagnostics/consumer-sleep-tracking/wearable-sleep-trackers/at-home-eeg-wearable-accurate-as-sleep-center-experts/