Sleep cycles – how do they affect our rest?

You sleep 8 hours a day, but wake up tired? Or maybe 5 hours of sleep sometimes guarantees much higher quality rest than 9 hours of nightly sleep? This feeling is familiar to more than just you! The quality of our sleep is influenced not only by the number of hours we sleep but also by our sleep cycles – the individual fluctuations of sleep stages in our bodies.

Sleep Cycles

During sleep, various physiological processes occur cyclically in our body. For example, eye movements and muscle tension levels change. Scientists, after long observations of these bodily changes during sleep, identified four main sleep stages – three stages of non-rapid eye movement, abbreviated as NREM (Non-Rapid Eye Movements), and one rapid eye movement phase, known as REM (Rapid Eye Movements). Together, these stages form a sleep cycle lasting between 90 and 120 minutes, repeating 3-5 times during the night.

The ideal night’s sleep for a young person – 5 sleep cycles. Photo from ouraring.com

Sleep Stages

NREM 1 – this is the first and shortest sleep stage, taking up only 5 percent of the total sleep time. During this stage, a person’s muscles relax, breathing slows down, body temperature drops, and the person begins to doze off. In the first stage, one may experience limb jerks, startles, or a feeling of falling. During this stage, the person remains sensitive to external stimuli and may wake up from the slightest noise, thinking they never actually fell asleep.

NREM 2 – this is the second sleep stage, where we spend the most time, up to 45-55%! During this stage, the body relaxes even more, sleep becomes deeper, and the person loses consciousness. However, it is relatively easy to wake up from this stage. Therefore, if you want to nap during the day and wake up feeling energized, try to sleep for 20 to 30 minutes. As sleep progresses to the third stage, waking up becomes more difficult, and if woken up in the middle of this stage, you’ll feel tired and unproductive.

NREM 3 (until a few years ago, it was split into NREM 3 and NREM 4, but over time, scientists merged them into one – NREM 3) – during this stage, the person enters the deepest sleep. The body’s muscles completely relax, breathing rate, blood pressure, and body temperature drop to their lowest point. During the third stage, growth hormones are produced, immune system activity is regulated, and muscle tissues are restored. If a person is awakened from this stage, they will not be oriented to their surroundings for a while.

REM – after the NREM phases, the person enters the rapid eye movement phase. During REM sleep, brain activity increases, heart rate accelerates, body temperature rises, and breathing becomes irregular. This sleep phase is of particular interest to neuroscientists because it is during this phase that a person experiences dreams. Additionally, during the final sleep stage, the brain processes and stores information in long-term memory.

The Relationship Between Sleep Stages and Age

Our sleep cycle model changes as we grow. In the first year of life, infants spend the majority of their sleep in REM – the dream phase. Later, around the fourth year of life, the duration of REM decreases by about 20%. As we age, the time spent in this phase decreases further – people over 60 years old spend only about 15% of their total sleep time in the REM phase.

Source: academic.pgcc.edu

Factors That Damage the Sleep Cycle

However, our sleep cycle is not just a biologically programmed process. It is important to remember that certain substances we consume or even an improper lifestyle can negatively affect our sleep stages. For example, if we drink coffee in the evening, it will not only make it harder to fall asleep, but caffeine will also negatively affect the quality of our sleep during the first half of the night. Another enemy of sleep is alcohol. While there are still myths circulating that alcohol helps people fall asleep, halfway through the night, the body starts processing it, disrupting the normal sleep rhythm.

Quality Rest – Waking Up in REM Stage

Although it is usually stated that adults need 7-8 hours of sleep, sleep specialists advise taking not only the number of hours into account but also the sleep stages. If the alarm rings during deep sleep, even after 8 hours of rest, we will feel sleepy and tired. For this reason, we should always aim to wake up at the end of the fourth – REM – sleep stage.

You can calculate this by adding the average length of a sleep cycle. However, a much simpler and more accurate way, allowing you to consider factors such as your age, weight, and sleep depth, is to use automatic sleep cycle calculators online, specialized watches, and smartphone apps. When using these, make sure to enable flight mode before sleeping – mobile network signals can negatively affect your sleep quality and rhythm.

Read more in the Facebook group: GOOD SLEEP CLUB