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Your own sleep cycle. Basics n°2 about sleep

Simply put, when we sleep we go through several stages of sleep. These stages together constitute a sleep cycle and these sleep cycles will repeat several times during our sleep until we wake up definitely (yes definitely, because we wake up many times without knowing it during our nights).

You will read everywhere that a sleep cycle lasts around 90 minutes. But this remains an approximation as a common average. In reality, sleep cycles duration is not the same for everybody, it’s completely personal. The duration of sleep cycles varies between 70- and 110+ minutes. Moreover, the length of your cycles varies throughout your nights, and will not be the same from one night to another. Several factors will also influence the structure of your cycle, such as your age, activity, your fatigue, and your stress.

Sleep cycle example

But why does it matter to know the duration of your own sleep cycles?

Knowing the duration of your sleep cycles helps you understand the structure of your sleep. And it will help you deduce how much sleep you need when you are physically active or not, when you are tired or not.

Knowing the duration of your sleep cycles can also be useful as long as you want to benefit from a smart waking up. Basically, not cutting off your recovery cycles by waking up in the middle of it and enjoying the full cycle by waking up at the right time. Indeed, waking up in the light sleep stage will make you feel more refreshed and will put you in a good mood to tackle your day. So if you want to be able to calibrate yourself to enjoy whole cycles and to wake up naturally in your light sleep stage, you will have to know the duration of your own sleep cycle to calculate your bedtime. That’s why this 90-minutes duration is used wrongly.

It is therefore complicated to know the duration of your sleep cycles on your own and without a tracking device.

The Circular ring detects at a clinical level, thanks to your heart rate & your movements, the duration of your sleep cycles and analyzes in real-time in which stage of sleep you are to wake you up silently during light sleep.

How to use Heart Rate Variability (HRV) with Circular?

Understand your HRV baseline 

Your HRV baseline is your typical HRV as you feel ordinarily. Your baseline is the starting point for your HRV explorations since it will help you compare your daily HRV value with a personal more long-term HRV. Circular automatically detects your baseline. 

During the first weeks, the app is establishing your baseline. It is looking to see what your average HRV values are as well as how much they fluctuate (standard deviation and coefficient of variation). 

Ideally, you’ll form your baseline during a “normal stress” week. Exercise, work, etc is fine during this first week. If you establish it during an abnormally stressful or high volume training week then it’s not a big deal because the baseline constantly adjusts and updates itself over time, so as your health or fitness levels change, it will learn what your new baseline patterns are. This happens on a rolling 14-day basis.

This value is tailor-made as Kira gets to know how your body works overtime! It is important to understand that HRV is an interesting metric to compare to your own trends and baseline because it is unique to you.

So what’s the big deal with HRV baseline? 

Well, it is used as a comparison to your HRV trends over time. Sometimes your HRV might lower after a workout and then spike up again after a couple of hours. It lowers and spikes up compared to your baseline HRV. These trends can unveil interesting messages your body is sending, that is why in the app’s graph, you will always find your baseline HRV as a comparison to your daily/monthly/lifetime HRV graphs. 

The goal is not to compare yourself with others but to get to know yourself.

Circular also calculates a “Lifetime Baseline”. It might get tricky to understand, but in practice, it is made easy to comprehend. This measure is the average of all the baselines calculated each week, your average baseline since you started using the ring. It is an important measure because it enables you to get the bigger picture. We compare it to your weekly calculated baseline in order to see if you’ve lowered your HRV or not over time.

When does Circular calculate my HRV?

Your HRV is tracked only during your sleep. It makes more sense as nocturnal tracking provides an excellent HRV measurement window where many of the environmental stressors aren’t present.

The time when you sleep is also the period when your body is at rest. Is also makes sense because HRV is the indicator for rest-related parasympathetic autonomic nervous system. That is why you will find the details in the sleep analysis section of the app.

Circular Heart Rate variability at Night

How does Circular calculate my HRV?

We apply the RMSSD calculation. RMSSD is strongly backed by research and is considered the most relevant and accurate measure of Autonomic Nervous System activity over the short-term (5 minutes or less). Root Mean Square of Successive Differences (RMSSD) is the industry standard for calculating HRV.

Where can I view my HRV data and baseline?

As mentioned above we take the values of your HRV during your night. You can, therefore, see the details of your nights data inside the “Sleep analysis” circle. Then we calculate the average of these values to give you one unique value per day. This will be the value that you can compare to your baseline. You can find it in the “Activity analysis” circle as well as in the “Sleep analysis” circle.

The interesting parts are when you switch to the -weekly- or -monthly- view. It might look more like the graph below where you can see clear variations and patterns over several days. That’s where we can interpret the ups and downs and recommend you at best.

Circular Heart Rate Variability

Comparing my HRV with my baseline

Circular makes it easy to understand what are your HRV trends. Every morning you can check your daily HRV value and compare it with your 14-days baseline to see where you are at. You can compare your values by visualizing the whole week, to know its evolution and compare each day between them. And you can also compare your data in a wider view; by month and by lifetime, where your monthly average can be compared to your lifetime baseline. This can allow you to see if you have succeeded in increasing your baseline over time.

You can also receive recommendations on your feed. It will tell you if you are ready for the upcoming day if your HRV is largely higher than you baseline HRV and will tell you if you are not ready if it is largely lower than you baseline HRV. If it is lower and you receive such a recommendation in your feed we will recommend you to rest or at least take it easy for few days as you either need recovery from intense exercises or you are stressed or about to get sick.

If you clearly identify the source of an HRV drop yourself, there are no mysteries and taking a look at this list of things to do might get you on the right path to a higher HRV:

  • Reducing carbs and processed foods/ better diet
  •  Reducing alcohol quantity
  • Sleep  more or follow Circular’s recommendations about your sleep
  • Acupuncture/meditation/breathing exercises/listen to music  (HRV increase for a day or two afterward)
  • Exercise  more (aerobics is preferred)
  • Managed stressors  with acting & improv classes
  • Cold therapy with cold showers & sea swims
  • Avoid pollutants and toxins: Avoid canned foods (the linings contain BPA) and drink your water out of glass bottles or containers. Stay away from plastic containers as much as possible.

Noticeable trends might be:

  • It is interesting to note that your HRV can fall down if you are about to become ill before you even develop symptoms. If this is the case, and you can take it easy for a day or two, your body will fight the illness. Your HRV can stay very low even after the symptoms disappear. This indicates that your body is still recovering and is not ready for maximum performance.
  • You may notice that a very intensive exercise can significantly reduce your HRV, but if you recover well, it will come back to your baseline and above. This is usually a sign that your body is coping well with the training load. If your HRV does not rise back, you may have trained too hard or too often. However regular endurance exercises tend to increase your baseline HRV over the long term.
  • If you do not sleep well or become stressed, you may see your baseline HRV decreases, indicating that your energy may not be at its best and that you need to take some time to recover.
  • Smoking and alcohol consumption can reduce your baseline HRV.
  • You will most likely notice that your HRV drops down temporarily after a night out.
  • Overall, HRV decreases with dehydration and returns to baseline with good hydration. As mentioned, both exercise and alcohol can cause dehydration.

After changing your lifestyle to get a lower HRV, don’t expect it to get back to its baseline instantly. It usually takes a couple of days, so continue with the good habits a little longer, and see the difference in the graphs for yourself.

That’s it! You are only two steps away from improving your lifestyle with CIrcular, in ways you never could of before with such precision and ease.

Indeed, you shouldn’t compare your heart rate variability with other people, because HRV is affected by a number of internal and external factors, such as age, hormones and the overall body functions, as well as lifestyle.

You can still compare (for information purposes) to this table which depicts a picture of average HRV’s depending on your age and condition if you really want to. But it makes more sense to react accordingly to what your body needs, and not go for under or over realistic goals stated in this table.

HRV Norms Circular


HRV analysis is important for your wellbeing. The whole point is for you to understand what is causing a drop in HRV and if you are recovering or not. If you make changes to improve your HRV and act accordingly you will get rid of stress inducers and any negative action your body does not need. As weird as it seems, this simple metric is a very powerful tool and can get you very precise insights about your wellbeing. Adjusting your HRV is a scientifically proven method and is being more and more used by professionals. Being able to track it from your home at all times might just get you a head start over those who don’t. 

We remind you that the Circular™ ring is not a medical device and should not be used to diagnose or monitor a pathology.

Get rid of sleep inertia forever

Logically, if you have slept badly (not enough time or of poor quality), your inertia will be stronger. But sleep inertia happens even to the best sleepers since it does not solely depend on those factors. Here are the main causes of sleep inertia:

  • Inertia partly comes from the dehydration of our body during sleep since we are unable to drink enough water for long periods of time.
  • Sleep inertia is also due to the adaptation time that our body needs to restart some of its mechanisms after a period of partial inactivity. And a large part of the mechanisms that need a restart is triggered by biological events governed by the circadian rhythm (natural light/darkness cycle of the planet).
  • One of the reasons is also that we usually do not wake up in the right sleep stage due to our alarm clocks. Sleep is composed of different stages that can be summarized by light, deep and REM stages. Waking up during deep and REM will increase our inertia. The human being is programmed to wake up naturally at the end of its sleep stage, but our alarm clocks prevent just that from happening. 

The solutions to reducing inertia upon waking-up therefore naturally result from the origins of our problem.

  • First and foremost, we obviously need a good night’s sleep and I invite you to read the Circular blog at where many articles will help you better understand and improve your sleep.
  • We should drink plenty of water as soon as we wake up to rehydrate and maintain the level of water our body needs to function properly. Water is essential for all vital processes. Eating as soon as we wake up is also very important to restart our internal system and provide the necessary energy to our body.
  • Although it seems contradictory to our problems, getting quickly into action after waking up is very useful to restart the mechanisms of our body as quickly as possible.
  • To restart our cognitive mechanisms, we also need to expose ourselves to natural sunlight (or an artificial lamp if there is not much sun where you live).
  • And finally, it is preferable to wake up in a light sleep stage where you will feel like waking up naturally rested and alert. Waking up in deep sleep will be the main cause of our inertia even if we have slept well.

But you wonder how we can do this. Since we set our alarm clock to a certain fixed time, the alarm clock will wake us whether we are in deep sleep or light sleep.

For this, we need to use a smart alarm clock. You can read about the solution offered by the Circular ring against sleep inertia “Circular® smart alarm clock: Wake up with motivation and energy and get rid of sleep inertia”

Recover when you don’t get enough sleep

The only cure for sleep deprivation is sleep. And the good news is that the human body is well thought out and built against lack of sleep. We’re programmed to recover.

It’s nice to know that the body is incredibly adept at making up for a short-term lack of sleep. Allocate more sleep to your body the night after and it will take care of getting you in shape. Even if you got a brutal 2 or 4 hours of sleep last night, your body can usually recover fully if you get a solid 9 or 10 hours of sleep on the next night. Your body will simply spend more time in REM and in Deep sleep stages to catch up for the lack of sleep of last night. 

Of course, you can not abuse this system, if you have several nights with very little sleep straight, your body will simply not be able to catch up in one single night.

Having said that, some tips can help your day go better after a bad night: 

Eat healthily and stay hydrated 

The key is to drink a lot of cold water. It will “wake up” your organs. Avoid heavy meals. You want to avoid your body to spend more energy than necessary on digestion.

Enjoy sunshine

No need for caffeine. Light of the sun will restart your body clock and will give you a natural boost. However, be careful not to stay too long under a hot sun, it may make you more tired afterward.

Try to look and feel better than you really feel 

This is kind of a brain hack that works in many situations. Take care of your look and convince yourself that you are in shape. You will trick your brain. If you neglect your hygiene, you may start to look and feel worse than if you did the opposite.


Try to stretch in the morning. Even if it’s not very motivating and it’s probably the last thing you want to do when you’re tired, stretching is one of the best things you can do to wake up your brain and body. It will allow your whole cardiovascular system to work more efficiently, which essentially, boost your energy. But don’t do moderate-intensity or high-intensity activities, you will feel even more tired.

Of course, take a power nap

Collapsing on the couch for a nap seems like the most obvious thing to catch up on lost sleep. But do not let this nap last longer than 25 minutes. This duration will help ensure that you stay in Light sleep when you wake up to be alert and ready. When having a power nap, the goal is to avoid falling into deep sleep otherwise you will feel bad when you will wake up. The power nap is the best way to allows a quick recovery to regain your energy.

What most people find difficult with napping is not being able to wake up at the right time and fall asleep while encroaching on your day and also on your real sleep since you will not be tired anymore at night. And for that, you need an alarm clock. But the problem is that it is very hard to time effectively your alarm clock according to the real moment you fall asleep. Let’s say you want your sleep to be about 25 minutes, if you take 10 minutes to fall asleep, you will not get up to delay this alarm. What if you could now predefine the length of your sleep and not be woken up at a fixed time.

The circular ring can help you with that. Try the smart napping circle of the app, click here to know more about Circular ® smart nap. It allows you to create a nap alarm, you give it a name, for example, “power nap”, you set manually its duration or chose the predefined power nap duration detection. Let’s say you have chosen the automatic power nap settings. Then when you want to take your nap, you activate your created alarm. The ring will automatically detect your nap and wake you up with vibration at the end of your light sleep phase for maximum efficiency. You will not have to worry anymore about timing your alarm according to your falling asleep time.

Photo credits to Pexels from Pixabay

Better sleep, the key to your problems. Basics n°1 about sleep

Sleeping is such a daily and frequent moment that the majority of us forget its importance. When your schedule gets busy, sleep is often the first thing to get neglected. “Oh I slept only 5h last night, it’s okay, the day is going to be harsh but I’ll survive”. You probably once said that to yourself because you already managed to resist days where you slept badly.

However, it has been proven that losing even one hour of sleep during a night can affect your mood, your energy, your mental sharpness, your cognitive ability and ability to handle stress. 

Sleep researchers discovered that 3% of the population has a rare gene that enables them to do well on less than six hours of sleep a night. For the other 97% of us, six hours is not enough at all.

Average sleep duration and percent of the population

Many people may not even remember what it feels like to be truly wide-awake and fully alert. But how do we know if we are sleep deprived?

You lack sleep if you recognize yourself in one of these situations:

  • Feeling sluggish in the afternoon
  • Getting sleepy in meetings, lectures, or warm rooms
  • Getting drowsy after heavy meals or when driving
  • Falling asleep while watching TV or relaxing in the evening
  • Feeling the need to sleep in on weekends
  • Falling asleep within five minutes of going to bed

The problem is that we often do not manage to catch up on the lack of sleep. And over the long-term, sleep loss can weaken your mental and physical health. After several years, this is where your body suddenly drops out without warning you and makes you fall into a burnout. And that’s what the Circular team wants you to avoid. 

Your sleep is a reflection of your stamina during the day. No other activity delivers so many benefits with so little effort! 

At Circular we believe that the day starts with the night before. That’s why we give a lot of importance to understanding your nightly sleep and how to bounce back from sleep loss. By getting on a healthy sleep journey, you will find your vitality back and your best stamina for you to perform to your true potential.