Understanding Sleep Cycles and Duration — 5 principles you need to know to improve your sleep

Science-based content to boost your performance

In this article, we will explain to you how and why you can significantly improve your sleep and performance by:

  1. Tracking your sleep to get up when you are in light sleep
  2. Sleeping as long as possible when you need to perform mentally
  3. Going to bed early when you want to recover physically
  4. Sleeping at least 6 hours (on average)
  5. Sleeping no longer (!) than 8 hours (on average)

How we sleep

Our previous articles (1, 2, 3) investigated our circadian rhythm and focused on improving sleep quality and ease of falling asleep. During this article, we will have a look at what actually happens when we are asleep — not only from a hormonal perspective as did the previous articles, but also from a neurological perspective. And as always, there will be a lot to infer to improve our sleep.

If we want to understand what our body does when asleep, we need to understand that our brain emits different frequencies of waves. While delta waves — the lowest frequency — indicate very deep sleep, beta waves — one of the highest frequencies — indicate alertness. When we are very alert and highly focused, for example when writing or memorizing something, our brain is emitting beta waves. During sleep, our brain oscillates between beta and delta waves. It goes almost through the entire spectrum. Gamma waves are a more cryptic phenomenon — one we might investigate later during our article series on flow.

Our brain waves

Figure 1: Brain waves; source: https://www.petegakos.com/single-post/2017/03/20/Beta-to-Theta-The-Science-Behind-Meditation

Most of us believe sleep is a process of our body calming down to a maximum level until we have achieved a delta-wave-like frequency, remain there for most of the time and finally become more alert and wake up.

The truth about sleep

The truth is quite the opposite: In fact, we go through all of the phases, from light to deep sleep — up to six times! Hence, we sleep in cycles, each lasting approximately 90 minutes. Understanding these sleep cycles and phases of deep sleep and light sleep is the key to managing your sleep better. To make this veiled phenomenon a bit clearer, let us visualize it. Researchers map sleeping behavior in so-called hypnograms:

Figure 2: Hypnogram; source: https://upload.wikimedia.org/wikipedia/commons/3/3e/Sleep_Hypnogram.svg

A cycle or phase means you going from REM sleep to stage 4 and all the way ‘up’ to REM again. While the different phases are often highly over-interpreted, there are two major things to take away from this graph and hypnograms in general:

1. The spectrum between two extremes: REM vs. (deep) Non-REM stage 3 and 4 sleep

All that matters is understanding the spectrum, i.e. the polarizing relationship, between REM and stage 3 / 4 sleep. The rest can be inferred logically.

REM Sleep: Is often regarded as the ‘deepest’ sleep, even though the truth could not be farer from that. Our brain is very active during REM-phases and emits a frequency which is usually between alpha and beta. We dream during REM-phases and the increased cognitive activity is indicated by our eyes moving very quickly — thus the name Rapid Eye Movement (REM). While REM sleep still remains an arcane phenomenon [1], it is said that mental recovery is highest during this stage [2][3].

Deep Sleep: During deep sleep, our brain goes down to a delta state brain wave frequency and our breathing as well as our heartbeat slow down to a minimum level. Muscle relaxation also peaks during deep sleep and important hormones, such as growth hormones, are released during that time [4]. Therefore, it is often stated that deep sleep is for physical recovery.

The key is to stand up during stage 1 or REM sleep, not when your body is in deep sleep. If your brain is on delta-waves, suddenly waking up and being able to think clearly and sharply is impossible. Stay with us, we will explain how you do that in the last section of the article.

2. Sleep Cycles

Sleep happens in cycles of approximately 90 minutes. Note that deep sleep typically happens only in the first two cycles as indicated in the hypnogram, while REM stages are often followed by periods of being wake — especially after the first two cycles. Waking up during the night is completely normal, and if it is below 2–3 minutes, we usually do not remember it [5]. The length of REM periods also seems to increase during later cycles.

Moreover, while those 90 minute cycles vary between people and tend to get shorter for each cycle, they usually stay the same for individual probands. Knowing how long your cycles are hence matters. This will help you to get up during stage 1 sleep or REM sleep.

adorable cat sleeping…

Action Steps

If you have a healthy circadian rhythm your sleep will be fairly regular. This allows you to make use of the following action steps.

1. Get up when you are actually awake. Track your sleep cycles and experiment with different times. While there is a myriad of apps out there, we do not recommend a tracking app. Firstly, sleeping directly next to your phone is not a healthy thing to do. Secondly, those apps are not yet perfectly accurate. What you can do instead is very simple: Track when you

  • Go to bed
  • Get up in the morning
  • How long it takes you to fall asleep
  • How you feel during the day and how easy it was to get up

You might want to go to bed at 10.45pm and get up at 6.30am. If you need approximately 15 minutes to fall asleep, you will have slept 7 hours and 30 minutes. Divide this by 5 (as there are usually 5 sleep cycles for that length of time) and you get exactly 1 hour and 30 minutes. Bingo — that was it! And for most of you it will most likely be that easy. For those of you who do not feel fit after getting up exactly 7 hours and 30 minutes, try 7 hours and 40 minutes or 7 hours and 50 minutes. Continue adding 10 minutes to your sleep until you feel awake. If you finally do, repeat it to make sure that sleeping time works for you. Again, divide by 5 to find out how long your sleeping cycles are. If you need 8 hours, your sleeping cycle might be 96 minutes. Getting up during a phase of deep sleep can be really detrimental and might affect your hormone cycles throughout your entire morning, leading to less energy and alertness. Therefore, getting up earlier, if it prevents you from falling into another phase of deeper sleep, often results in you feeling more alert.

2. If you need to mentally perform during the next day, make sure to sleep as long as possible. Especially when there is an important presentation the next day, a difficult exam or anything that requires mental preparation, we tend to pull allnighters and not sleep at all. Yet, aiming for 8 hours — factoring in some time to fall asleep — usually allows for 5 cycles. As your mental recovery tends to be highest during the later stages of your sleep, sacrificing on those can come with a high price.

3. If physical recovery is important during the next day, because of a work out for example, make sure to wind down properly and go to bed early. If you go to bed later than you usually do, your melatonin secretion will kick-in too late and your growth hormone release might be deferred [6], which leads to even more disturbed sleep. You want to prevent that especially after heavy work-outs. Interestingly though, to recover physically you will not need to sleep that long. As we had observed in the hypnogram, our physical recovery seems to happen during the first two sleep cycles, which allows us to sleep less.

4. Sleep at least 6 hours. The amount of sleep you need is influenced by your genetics and is highly individual. Some of you might cope with 6 hours, but this is rather the exception than the rule. If you wake up naturally or feel alert and fit during the day, the amount of sleep you get is fine. Sleeping less can have severe effects on your overall health, such as higher risk of depression, cancer and Alzheimer’s [8][9][10].

5. Sleep no longer than 8 hours. There are a couple of superbly interesting papers suggesting that longer sleep rates are connected to higher mortality. The studies are valid and were conducted by analyzing up to a million probands for up to 50 years [10].

This was the last piece in our series of articles about sleep. You can find the other articles on our website. After you have read our four articles, not only will you have a thorough understanding of your body and your inner workings, but you will also be able to put that knowledge into use and apply it flexibly throughout your live to design your individual desired plan of winning life.

Sources

[1] Siegel, J. M. (2011). REM sleep: a biological and psychological paradox. Sleep Medicine Reviews, 15(3), 139–142. https://doi.org/10.1016/j.smrv.2011.01.001

[2] Hobson, J. A. (2009). REM sleep and dreaming: towards a theory of protoconsciousness. Nature Reviews Neuroscience, 10(11), 803–813. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/19794431

[3] Vyazovskiy, V. V., & Delogu, A. (2014). NREM and REM Sleep: Complementary Roles in Recovery after Wakefulness. The Neuroscientist, 20(3), 203–219. https://doi.org/10.1177/1073858413518152

[4] U.S. Department of Health and Human Services (2011). Your Guide to Healthy Sleep. Washington: NIH. Retrieved from https://www.nhlbi.nih.gov/files/docs/public/sleep/healthy_sleep.pdf

[5] Bonnet, M., & Arand D. (2007). EEG Arousal Norms by Age. Journal of Clinical Sleep Medicine, 3(3), 271–274. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2564772/

[6] Van Cauter, E., & Plat, L. (1996). Physiology of growth hormone secretion during sleep.The Journal of pediatrics, 128(5), 32–37.https://doi.org/10.1016/S0022-3476(96)70008-2

[7] Orzeł-Gryglewska, J. (2010). Consequences of sleep deprivation. International Journal of Occupational Medicine and Environmental Health, 23(1), 95–114. https://doi.org/10.2478/v10001-010-0004-9

[8] Van Dongen H.A., Maislin, G., Mullington, J., Dinges, D.F. (2003). The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. Sleep, 26(2), 117–26. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/12683469

[9] Durmer, J.S., Dinges, D.F. (2005). Neurocognitive consequences of sleep deprivation. Seminars in Neurology, 25(1), 117–29. https://doi.org/10.1055/s-2005-867080

[10] Youngstedt, S.D., Danie,l F., & Kripke, D.F. (2004). Long sleep and mortality: rationale for sleep restriction. Sleep Med Rev, 8(3), 159–74. https://doi.org/10.1016/j.smrv.2003.10.002