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Oxygen Saturation (SpO2) and how to use it to your advantage

Only recently, have these readings been available from the comfort of our homes with the advent of small and precise sensors. Anybody can benefit from a preventive tracking of respiratory problems thanks to Circular and checking your blood oxygenation might just help you with that. 

Blood Oxygen Circular

How does it work?

When oxygen is inhaled into the lungs it attaches to a protein in red blood cells called hemoglobin. The red blood cells transport the oxygen into the bloodstream and flow through pulmonary veins, then into the left atrium and left ventricle, and finally circulates throughout the body’s organs and their cells. 

To know how much oxygen is in your blood, the sensor at the bottom of your ring emits red and infrared light. While passing through your finger, the light hits your blood cells, and is absorbed differently by the hemoglobin without oxygen (deoxyhemoglobin) than by the hemoglobin with oxygen (oxyhemoglobin) because of their concentration and resistance to light. The calculated rate is expressed as a percentage and a normal reading ranges from 94 percent to 100 percent.

Circular’s readings are accurate and provide results within a 2-percent difference either way of what it truly is. If your reading was 90 percent, your true oxygen saturation level may be anywhere between 88 and 92 percent. You should also keep in mind that external factors such as movement and temperature can impact the accuracy and that you should always consider your baseline and personal feeling as a primary assessment. Use your blood saturation as a tool.

We will first discuss how to interpret your readings for your wellness, and then discuss how it might help you.

Spo2 for health and prevention

Pulse oximetry is a method doctors use for rapid assessment and monitoring of a patient’s respiratory function. It may be used to monitor the health of individuals with any type of condition that can affect blood oxygen levels, especially while they’re in the hospital. But let’s leave this work to the doctors.

SpO2 for Sleep Apnea Evaluation 

You might correlate blood oxygenation to sleep apnea events (sleep disorder in which breathing repeatedly stops and starts). The good news is that it can be a great indicator and reflects these events well. 

There is around a twenty-second delay after the onset of the cessation of nasal airflow. The measurement of SpO2 level is useful for screening suspected sleep apnea events, but it might not be able to provide live and precise occurrences. It is a way to better understand sleep, not to necessarily diagnose sleep conditions. Best practice would be to check your readings in the mornings by keeping in mind these simple facts: Less than 5 sleep apnea events an hour is considered normal. You might want to check with your doctor if that exceeds 15. Look for sudden drops in the graph. 

Associated symptoms may be: frequent morning headaches, swelling in ankles and feet (edema), tiredness, shortness of breath, irregular heartbeats rhythms, high blood pressure,

lightheadedness, dizziness, skin and nail beds may turn bluish in color (cyanosis), confusion, memory loss, higher red blood cell count in blood (polycythemia).

SpO2 for Recovery

Oxygen saturation is a key factor in performance if you live or train at altitude, or tend to overtrain. Using SpO2 readings with your usual training metrics can, first and foremost, help you gauge whether you’re recovering properly.

An athlete that wakes up feeling “not right” after a hard training block and a poor night of sleep will tend to see his SpO2 reading lower than is baseline SpO2. This is a great case of an athlete who may feel well enough to go train, but his low sleep hours and low SpO2 corroborate his sense of “not feeling right.” Instead of continuing his training as planned, this athlete should focus on recovery and sleep more for the next days. Subsequently his SpO2 will normalize and the following training days should go very well.

Correlate your RHR, HRV and SpO2 after training days to see where your recovery is. Paying attention to the right numbers can result in a good training block and even help avoid an over-training.

SpO2 for Altitude Acclimatization

At altitude, where the air is thinner, it is more difficult for your body to get adequate oxygen to your muscles and tissues. For example, if you’re racing or training at 10,000 feet (3000 m), the amount of effective oxygen in the air is about 15 percent (compared to 21 percent at sea level). If you’re used to living at sea level, this change in oxygen availability will kick off a cascade of physiological adaptations, some of which are advantageous no matter where you’re racing.

To start, there will be an increase in your respiratory and heart rates; and the volume of blood ejected from the heart (stroke volume) will be reduced. Over your first 24-48 hours at altitude, blood plasma volume will also be reduced to improve the oxygen-carrying capacity of your blood by volume. These adaptations won’t necessarily feel good, in fact you’ll probably feel like you’re doing more work for less reward.

In the first couple of days at altitude you want to see a lower SpO2 and an elevated heart rate (HR) and respiratory rate (RR). This is your body attempting to balance out the lack of oxygen in the air by moving it faster through your body.

With prolonged stays at altitude, most people’s SpO2 will stay about the same or increase slightly; but your heart and respiratory rates should normalize, as well as your ability to perform an exercise at altitude. A SpO2 of 88 to 92 percent will give you the most beneficial training adaptations without causing undue fatigue.

That means you’ll be able to race and train as normal at altitude, and will likely enjoy some extra endurance at sea level.

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

Scientific sources:

How does Circular track my Resting Heart Rate (RHR) and how to use it?

Resting Heart Rate can help you get an idea of your overall wellness and fitness, and can help you set fitness goals.

The fitter you are, generally the lower the Resting Heart Rate. This is due to the heart getting bigger and stronger with exercise, and getting more efficient at pumping blood around the body, so at rest, more blood can be pumped around with each beat, therefore fewer beats per minute are required. 

Usually, the best moment to measure RHR is just after waking up but we can’t force you not to be active after waking up. So we find that the best measure is taken when getting in your bed before going asleep. We give one average reading per day inside the “Activity analysis” circle.

Circular takes a measure of your Resting Heart Rate when resting, although not sleeping (as your heartbeat significantly drops then).

Your own baseline RHR

A RHR between 60 and 100 beats per minute (BPM) is considered normal, but 60 to 80 is optimal. Generally, a lower resting heart rate indicates more efficient heart function and greater cardiovascular health. Research has connected a higher Resting HR with a higher risk of cardiac events like stroke and heart attack.

Many factors influence what’s normal for any one person. Genetics, age, and gender all have an impact on your baseline HR and play a part in determining your normal range. Those aren’t really things that you can change, but there’s one factor you can: your fitness level.

Circular automatically determines your baseline RHR for you. You are able to find it in the “Activity analysis” circle, by swiping to the RHR graphs. It is represented as a blue line for comparison. As your fitness levels are what can impact the most efficiently your RHR for the better, Kira is made to recommend certain activity programs or lifestyle changes for you.

Average Resting Heart Rate Circular

What can be deduced from RHR:

You’re not active enough

If you’re sedentary most of the day, your RHR likely approaches or exceeds the top end of the range above. This may be because your heart is less efficient. The good news? By regularly engaging in moderate to vigorous aerobic activities (brisk walking, biking, swimming), you will help your heart become more efficient at pumping blood which will lower your Resting Heart Rate over time. Even modest reductions in RHR can dramatically reduce your risk of cardiovascular disease and add years to your life!

You’re overtraining

While pushing your body can lead to great gains, it can also be detrimental. If you notice an increase in your Resting Heart Rate when you’re going heavy on the training and light on the rest, your body may be telling you that you need to scale back. By giving it the proper rest it needs, your body can repair and adapt and you may bounce back stronger than ever.

You’re too stressed

Prolonged mental and emotional stress can also cause your RHR to creep up over time. Try adding relaxation into your day: read, meditate, go for a walk with friends. Regular relaxation activities may help you combat your stress and which could lead to a lower RHR.

You’re sleep-deprived

Always exhausted? Chronic sleep deprivation which can lead to fatigue, a slower metabolism, and extra snacking can also raise your RHR. Aim for at least 7-9 hours of sleep each night.

You’re dehydrated

During a hot summer day, if you notice a temporary increase in your RHR, your body might simply be trying to cool down. However, it could also mean you’re dehydrated especially if you’re thirstier than usual, your mouth is dry, and your pee is more yellow than normal. To help lower your RHR, drink more water.

You’re developing a medical condition

If you experience shortness of breath, unusual fatigue, dizziness, and your RHR has increased, you might be at risk for a medical condition. High RHR can be a sign that something is abnormal. However, even if you have a low RHR combined with symptoms (like those above), it could indicate an issue.

Don’t just look at the RHR, combines it with all the metrics especially HRV. If your RHR looks unusual but you don’t feel lightheaded, weak, short of breath, dizzy, then there is nothing to worry.

Resting Heart Rate increases with age
Most of the time your RHR can be modified. Unfortunately, as you get older, your RHR tends to increase. To reduce the impact that aging can have on your cardiovascular system, you can help maximize your results by exercising within your target HR zone to help lower your RHR. You can compare to other people your sex and age to get a good idea if you’re in the averages. But keep in mind an average isn’t personal (genetics too are involved!) and doesn’t necessarily reflect the best practices and target RHR. We recommend you to stick with Circular’s recommendations.

Medication affects Resting Heart Rate
Changes in your RHR can also result from over-the-counter or prescription medications. Medications to treat asthma, depression, obesity, and attention deficit disorder tend to increase your RHR. However, medications prescribed for hypertension and heart conditions (beta blockers, calcium channel blockers) typically decrease your resting heart rate.


Circular will send you recommendations concerning your wellness if it detects something abnormal. Never forget to never just look at the numbers, but also evaluate how you feel for yourself.

The RHR is a very good tool to correlate with your HRV, your sleep and, your activity. If the HRV and RHR indicators are relevant together then you can consider analyzing your vital signs over the next few days.

Although, when thinking solely about your wellness, RHR is a great tool and the programs designed in the programs circle might help you out. Don’t forget to also follow Kira’s recommendations about your sleep schedule. You will always have a great companion by your side in your Circular app (Kira), that’ll try to do its best at helping you higher you RHR in good proportions. And remember that her recommendations are measured and have a good chance of reflecting situations you’ll be better off changing.

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

In practice 

In your Circular app, dive into the activity analysis circle. On the first page is displayed, along with other metrics, your daily RHR measure. As stated previously, there is one measurement a day.

Resting Heart Rate Circular

The sleep stages that compose your sleep cycle. Basics n°3 about sleep

Let’s break down sleep together.

The royal way to study sleep is through an impressive device called Electroencephalogram (EEG). It tracks and records brain wave patterns thanks to electrodes that are attached to your head. The electrodes analyze the electrical impulses in the brain and send signals to a computer that records the results.

Thanks to this system, we can analyze the brain’s activity of someone that sleeps and draw some conclusions about it. The first thing that you will see is that there are two major phases of sleep that are very clearly distinguished by their waveforms; the REM stage (Rapid Eye Movement) where the brain is very active (low-amplitude, high-frequency waves, and alpha rhythm, as well as the eye movements for which it is named) and the non-REM stages where the brain is less active. 

By analyzing brain waves more deeply we might realize thatsleep stages are even more complex than that. The NREM phase is divided into 4 stages (N1, N2, N3, N4) while the REM phase represents another stage (N5), for a total of 5 stages.

Circular Sleep Stages

NREM Light sleep is composed of N1 and N2

NREM Deep sleep is composed of N3 and N4

REM sleep is composed of N5

Light sleep: 

Light sleep is the phase in which sleep begins. It is also an intermediate phase between Deep sleep and REM sleep. It is precisely during this phase that the moment is most optimal to wake up and feel rested and alert. It is also during this phase that an individual is most sensitive to external factors, sensory stimulation such as noise, light or vibration.

The Circular ring knows precisely when its user is in a Light sleep stage since it corresponds to the stage with the most movements of the body and a heart rate close to normal, even if decreased.

Deep Sleep

Deep sleep is one of the most essential sleep stages because it holds the secret of our performance and recovery. Deep sleep is responsible for energy restoration, growth, immunity and muscle repair. It is very difficult to be woken up at this time (and you really don’t want to) since the brain is much less sensitive to external stimuli. Indeed, waking up during this phase is at the origin of this feeling of fatigue in the morning (called sleep inertia).

The Circular ring knows precisely when its user is in Deep sleep since the body moves only very little and the heartbeats are at their lowest and become regular.

REM sleep 

REM sleep is the most famous sleep phase since it refers to dreams. It usually occurs at the end of the sleep cycle. It is considered very important because it is responsible for repairing the mind and consolidating the information you have learned during the day so that it can be stored in your long-term memory. It is also responsible for consolidating the memory of motor skills, daily gestures and stimulating your creativity. 

Circular Sleep Stages

The Circular ring knows precisely when its user is in REM sleep since there are fewer physical movements. This is thought to be a neurological barrier that prevents us from “acting out” our dreams) and the heart rate is very unstable, it often accelerates. 


We understood that our sleep is comprised of cycles that are personal to us, that these cycles are comprised of several stages whose main categories are Light sleep, Deep sleep, and REM sleep and we understood their importance for our body restoration. 

That’s great! But what is the order of these different sleep stages, the patterns of our sleep cycle, how do we go from one cycle to another and in what proportions? Let’s discuss this in the next article of the series:The architecture of your sleep. Basics n°4 about sleep

How to lower your time to fall asleep?

First of all, you have to know that sleep experts assess that a healthy adult should fall asleep between 5 to 30 minutes once the person climbs into bed and closes his eyes in a dark place. Falling asleep below 5 min or above 30 minutes is not considered as normal. 

Time to Fall Asleep Circular

But for most people, falling asleep outside of this slot does not mean that you are suffering from sleep disorders. The causes can be multiple and it takes just a little bit of willpower to fix that.

Experience both daylight and darkness

Light influences your body’s internal clock, which regulates sleep and wakefulness. Irregular light exposure can lead to disruption of circadian rhythms, making it harder to fall asleep. That’s why if you live in a country where there is not a lot of sun or winters without sun, it is normal for you to have episodes where you sleep badly. It is important to expose your body to bright light or artificial bright light during the day and sleep in a dark room at night. (Click here to know more about Circadian Rhythm)

Respect a regular schedule

The second most important tip is to follow a regular schedule. This means going to bed at the same time each night to regulate your inner clock and to wake up at the end of your sleep need. 

Generally, night people tend to have difficulty in falling asleep quickly. And people tend to comfort themselves with the fact that they are not morning people so they can’t do anything about it. Even if it is genetic, I personally am a night person and I succeeded in decreasing my time to fall asleep. To make the changes, you have to be patient. Do it slowly, over days or weeks, and then stick with them for maximum effect. It takes discipline, but it can be done.

If you are a night person, I’ll give you a tip to adapt very quickly. Force yourself to wake up earlier than expected by an hour or two. Tired in the following days, you will be able to easily fall asleep sooner and faster. Once you see the change, stick to this bedtime and you will see that you will adapt easily.

The Circular app can help you with that because it will analyze for you, your sleep needs and tell you at what time you should go to bed depending on your time to fall asleep and your waking up time.

No nap for you

If you are having naps, get rid of them.

Be active

If you are not already doing physical activity, be active during your day. But be careful, do not do sports too close to the time you go to bed or your system will still be stimulated and you won’t be able to fall asleep correctly. Give your system at least 3 hours before sleeping.

Avoid digital screens

The following factor is the number one cause for extremely high falling asleep time. SCREENS. Digital screens are a plague for sleep and this for two main reasons. Firstly because watching something on a screen requires a lot of effort for your eyes and is very stimulating for your brain. This will make your brain think unnecessarily (even unconsciously) before and during your sleep. And secondly, because the blue light of these screens will disrupt your circadian rhythm. Blue light is harmful to your internal clock since it delays the release of melatonin, the hormone responsible for making you sleep. It will make think your inner clock that it is not time to sleep, and therefore delay your sleep even if you put yourself in the dark. 

So don’t watch digital screens before sleeping. And if you want to watch your screen, install an app/software to make rid of blue light, lower the brightness to the minimum and do not look at your screen in the dark but rather in a lit room. Finally, do not look at your screens in your bed while lying down. Because lying in bed for a long time without sleeping will also disrupt your inner system. The gesture of lying indicates to your system that you want to sleep, so don’t miss your opportunity to sleep.

Be smart about what you eat and drink

Minimizing caffeine, alcohol, and nicotine before sleeping seems logical. But less known, avoid having heavy and late dinner. A light dinner, without quick sugars and red meat but with a portion of slow sugars.

Do not eat within 4 to 6 hours of the time you want to sleep. 

Create a comfortable environment for sleep. 

Don’t work too late to free your mind (within 2 hours of the time you want to sleep).

Sleeping in a quiet, dark room and at a cool and comfortable temperature will help you sleep faster. The ideal room temperature for sleep is between 18 – 22 Celsius degrees (64.4 – 71.6 Fahrenheit degrees).

Practice meditation

Meditation and relaxation training will help you improve fall asleep faster and sleep better. There is a simple but powerful breathing method called 4-7-8 method that is used by the military and ancient yogi that will lower your heartbeat, calm yourself and make you fall asleep faster, sleep better and increase your natural defense. 

Here are the steps. Exhale completely through your nose until you empty your air. Close your mouth and inhale through your nose until you are filled with air (belly and lung) while mentally counting to four. Hold your breath and mentally count to seven. Close your mouth and exhale completely through your nose, and mentally counting to eight. If 4-7-8 is easy for you to double the ratio to 8-14-16 and so on. The higher the ratio the better it is. Repeat this cycle 7 times. Do it at least three times a day, the more you do it the better it will be. 

Do not pay attention to time

People who can’t fall asleep often tend to watch the clock and are obsessed with the fact that they cannot fall asleep. But this behavior causes anxiety and that’s what you want to avoid. So get rid of any clock in your bedroom that shines in the night or forces yourself not to watch it. Even if it is tempting, watching the time is useless. Anyway, you will have to wake up at the time you have to and it is not by looking at it that you will fall asleep faster.

Fight anxiety and stress

One of the major cause of falling asleep issues is anxiety and stress. I am anxious myself and I hate it when my brain starts working hard just before sleeping when I have my eyes closed. It causes me trouble relaxing and turning off my thoughts. 

There are techniques that I tested and that I can confirm are helping. Try to visualize something that makes you happy and smile while you have your eyes closed. This technique will help you occupy your mind with good thoughts instead of engaging with worries and concerns during the pre-sleep time. But if you think of something important and you feel that it develops in your mind. Stand up and write it down on a piece of paper. At first glance, one may think that getting up will make you start over from the beginning but on the contrary, it will allow you to move on and fall asleep more quickly.

But the best techniques to clear your brain before sleeping are still meditation and breathing exercises.


Yes, there are a lot of parameters to take into consideration to find a good sleep. But you are certainly doing great on some of these factors. And if you are not, it is okay, try to apply these changes step by step. This may take several weeks of adaptation, but anyway you are used to taking a long time to fall asleep or sleep badly for a while now. 

Photo credits to Shingo_No from Pixabay