On our journey to better sleep, we have discovered that knowledge really is power. One of the first things we delved into in order to understand how to improve our sleep was sleep cycles. Once you understand how they work, you can tweak your habits to ensure you are maximizing sleep effectiveness. Along with “How long should I sleep?” and “Should I nap?”, one of the questions many people ask is “How Long is a Sleep Cycle?”
Sleep cycles average 90 minutes but can be anywhere from 70-120 minutes. This changes throughout life—and even throughout a full night of sleep—but the average adult has 90-minute sleep cycles, consisting of four phases, and ideally sleeps between 7-8 hours per night.
Every 90 minutes we cycle through the four sleep phases. The first three are non-REM (Rapid Eye Movement), and the final one is REM. Let’s break those phases down.
Phase One: Wakefulness to Sleep
This phase of the sleep cycle is a very light sleep phase. In all likelihood, it won’t take much to wake a person from Phase One sleep. During this sleep phase, your muscles begin to relax, your heart rate begins to slow, and your breathing slows.
Often this is when something known as “hypnogogic hallucinations” will happen. These are visual or aural sensations that can recur from any repetitive activity throughout your day. For example, if you have been on a boat, you may feel as though waves are still rocking you. If you’ve played a game, visuals or actions reminiscent of that game may occur. Something most people have experienced is a feeling of falling. This experience is what causes hypnic jerks—when you jerk or kick yourself awake.
Phase Two: Intermediate Sleep
The second sleep phase usually lasts around 25 mins. This is the phase of the sleep cycle in which the heart rate and breathing continue to slow, eye movement slows, brain activity lowers, and body temperature lowers.
It starts to become a little more difficult to wake someone from this sleep phase, but this is actually the sleep phase that it’s best to wake from. When taking a nap, waking from the second stage of sleep will allow you to wake gently from light sleep, having had some rest.
During this phase your brain also starts to suppress external stimuli like noise and light, so that you can stay asleep and prepare memory centers, moving into Phase 3.
Phase Three: Slow Wave Sleep
The third sleep stage is named such because this is when your brainwaves slow. This is the phase primarily responsible for healing and recuperation.
When you reach this stage your muscles are at their most relaxed throughout the sleep cycle. This is the key stage of the cycle for athletes and fitness fans, as muscles are recovering, bones are healing and growing, and immunity is strengthened.
Also in this sleep stage, your heart rate is at its lowest and it’s difficult to wake someone up. Because your body is still active during this phase, this is where sleep talking or walking occurs.
Final Phase: REM Sleep
Phase four is when you will enter REM sleep, which stands for Rapid Eye Movement. If phase three is the phase important to your body, phase four is for your mind. As your heart rate and blood pressure increase, your brain is busy committing learning and memories to long-term storage.
This is the phase in which you are most likely to have vivid dreams, but your limbs are paralyzed so that you don’t physically act them out. It’s sometimes called paradoxical sleep because your brain is most awake, but your body is paralyzed.
Making the Most of Your 90 Minute Sleep Cycle
Contrary to popular belief, throughout a full night of sleep, we don’t cycle through the above phases in consecutive order repeatedly. A full night of sleep usually looks more like the diagram below, which contributes to the slightly varied duration of a sleep cycle.
To understand or optimize your own sleep cycle, we always recommend using a sleep tracker. You can also find out more about when you should go to bed or wake up, or read more about alternative sleep schedules.
