As someone who has long suffered from sleep problems, I've always been curious about whether there's an efficient method to improve my sleep quality. It wasn't until I learned about the 90-minute sleep cycle method that my doubts were cleared—I'd found a scientific approach to sleeping.
What Are the Sleep Stages in a Normal 90-minute Sleep Cycle?
With a deeper understanding of sleep, it's been recognized that human night sleep is composed of several sleep cycles. Generally each sleep cycle include three non-rapid eye movement (NREM) stages (N1, N2, and N3) and a rapid eye movement (REM) stage.
NREM Stage 1 (N1): You're just dozing off
Transitioning from being awake, we enter this stage where we're half-asleep and half-awake. Both our brain activity and muscle power start to drop off. It's pretty easy to wake us up at this point.
NREM Stage 2 (N2): Light sleep
If we make it past N1, we move on to stage N2. Here, our heart rate and body temperature begins to decrease. But if someone calls our name or a mom hears her baby crying, we can still snap back awake pretty quickly. We spend the highest proportion of our sleep time in this stage.
NREM Stage 3 (N3): Deep sleep
After getting through the light sleep, we land in deep sleep, also known as slow-wave sleep. This is because our brains are generating the slowest type of brainwaves – Delta waves (as opposed to the high-speed Beta waves when we're awake).
It's tough to wake someone up from this stage. And if you do get woken up, you'll find yourself all groggy and confused.
We really hope to spend a good chunk of our night – around 20% – in this stage，as most of the body’s restorative functions occur in this stage
REM Stage: Dreaming stage
Our sleep is like a slide, after deep sleep, we ascend the stairs again to light sleep briefly before entering the REM phase. In REM stage, our muscle tension is almost zero, and we dream. Most of our dreaming happens here.
This stage is thought to be good for reorganizing and linking information, and unleashing creativity. Again, we expect this stage to account for about 20% of sleep time.
At the end of the REM stage, we wake up. But we usually don’t remember these awakenings and move on to the next sleep cycle. This oscillation between sleep-wake-sleep-wake transitions from one sleep cycle to the next.
Our brains complete a sleep cycle approximately every 90 minutes. That is where “90-minute Sleep Cycle” comes from.
Over the night, the amount of deep sleep decreases while REM sleep increases until we wake up in the morning.
How Many 90 Minutes Sleep Cycles Should You Get?
Generally, adults need about 4 to 6 complete sleep cycles per night, which equates to 6 to 9 hours of sleep. Ideally, most people feel energized with around 5 cycles per night.
However, individual needs may vary with age, lifestyle, and health status. Therefore, it’s essential to observe your own bodily reactions and find the number of sleep cycles that suits you best. Avoid blindly pursuing the "8-hour sleep" goal.
How to Do The 90 Minute Sleep Cycle
To reduce our anxiety about how long we sleep each night, we can measure our sleep in "90-minute sleep cycles" instead of "8-hour sleep".
(1) Set a Goal
Calculate the sleep cycles you have in a week and measure your sleep on a weekly basis rather than nightly. Even if you have an off night during the week, you won’t have as much mental burden.
If you need 5 sleep cycles per night, that totals 35 cycles a week, which can be your target.
You might start by aiming for 5 cycles each night and see how you feel after a week. If 5 cycles is too much to you, reduce to 4; if it is insufficient, increase to 6. Adjust your goals based on your own condition, to find what’s best for you.
(2) Fix Your Wake-Up Time
Having a fixed wake-up time helps establish a routine. Even if you go to bed late occasionally, you'll confidently know how many sleep cycles you’ve managed.
(3) Use Your Sleep Cycle Calculator
In order to wake up at the end of a sleep cycle, your sleep cycle calculator can be like this:
What Time Should I Go to Bed
Your Target: | 5 sleep cycles per night |
Time to fall asleep: | 30 minutes |
Wake up time: | 7:30 AM |
Time to go to sleep: | 11:30 PM |
Consider the time it takes you to fall asleep when estimating your bedtime. Otherwise, being woken up by an alarm in the middle of a sleep cycle can make you feel awful.
If one evening you’re home late and can’t make it to bed by midnight, you could aim for a bedtime of 1:00 AM, at least achieving 4 90-minute sleep cycles (6 hours). Just assure you can sleep the complete sleep cycles.
(4) Naps Count Towards Sleep Hours
If you miss a sleep cycle at night, you can slot one in during the afternoon. You could also consider a controlled 30-minute recovery sleep period, which perfectly aligns with our bodily needs.When calculating weekly sleep cycles, include nap times, whether they're 30 or 90 minutes.
However, try to avoid having less than the ideal number of sleep cycles for three consecutive nights and strive for at least 4 nights of optimal sleep cycles each week.
Factors Affecting “90-minute Sleep Cycle”
The number of sleep cycle doesn’t stay the same through our lives. Numerous factors can disrupt our sleep cycles, leading to excessive light sleep. These factors include noise, age, stress, worries, caffeine, snoring, sleep apnea or uncomfortable temperature.
If you’re stuck in light sleep, how long you sleep will become meaningless，as deep sleep is necessary for a complete 90-minute sleep cycle.
Summary
Sleep is not merely about quantity or quality. Try to understand how much sleep you really need. For most adults, achieving 35 90-minute sleep cycle per week is ideal. Of course, this number varies from person to person; find what works for you. Minimize factors that disrupt sleep cycle balance and become an efficient sleeper.
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