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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

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.

What increases and decreases Heart Rate Variability (HRV)?

But your HRV is not to be compared to the others. Everyone has their own baseline and you have to compare your daily HRV with your own baseline to find out if it is higher or lower than your baseline. Knowing that your baseline reflects a neutral state where you normally feel.

Besides physiological factors, in general terms, HRV should increase during relaxing activities, for example, sleep or meditation and on the other hand, HRV naturally decreases during an effort or stress. 

So what are the physiological factors, lifestyle habits and external factors that influence your HRV?

Circular Factors Influencing HRV

Physiological factors

Non-influenceable physiological factors include age and gender. After reaching the age of 15, HRV decreases as we grow older. It also seems clear that there is a difference between men and women in the way the autonomous nervous system is regulated and thus in the sympathetic-parasympathetic balance, and this manifests itself in differing HRVs. This difference between genders seems to become less prominent when people reach the age of 50, a fact that is attributed to the postmenopausal hormonal changes that take place with women.

Pain and Sickness

The effects of pain and sickness on HRV have been examined in many studies. HRV is lower among people with sickness or pain than among healthy persons.

Physical exercises

While your short term HRV will lower during physical activities, people who have an active lifestyle and maintain a good or high level of physical fitness or above average sporting activity can achieve an increase of their HRV baseline.

However a cumulative or too intensive sporting activity (e.g. long competition series, overtraining) will lower your long term HRV.

The best way to increase your HRV gradually is to introduce regular aerobic exercises into your routine. Even if you only exercise a little, it counts. However, the American Heart and Stroke Association recommends moderate to intense exercise for at least 2.5 hours a week, provided you are in good health. Fast walking is a good example of this type of exercise.

  • Try to do 40 minutes of moderate to intense exercise three to four times a week.
  • Also, do stretching and flexibility exercises such as yoga.
  • Try to combine these exercises with two strength-training sessions per week.

Studies show adaptation after several months of training. When starting an endurance sport, it is essential to start slowly and increase the duration, frequency and, intensity of exercise as you go along.

Improved sleep

Sleep is the foundation of good wellness, the more rested you are and the more in shape you will be. Give your body time to regenerate. Try to get as much Deep sleep as you can. It is the one that will regenerate you the most and increase your HRV further. Without rest, your HRV can only be low.

You can read the article about Tips to increase your Deep sleep.

Healthy Diet

Elevated body weight or elevated free-fat correlates with a decrease in HRV.

In addition to good sleep, practice a healthy diet. When you are overweight, your heart works harder to pump your blood through your whole body, thus increasing your baseline HRV.

Avoid smoking

Both active and passive smoking leads to an increase in HRV.


Several medications have a direct or indirect influence on HRV.

Avoid alcohol

Alcohol consumption has been shown to be associated with a decrease in HRV.

Reduce your stress level

It is not easy to reduce your stress level, but it will increase for sure your HRV. Try to take some time every day to relax and take a deep breath.


Exposure to noise leads to a decrease in HRV because it increases sympathetic nervous system activity.

Practice meditation and breathing exercises

Meditation and relaxation training will help you increase your HRV and improve your overall wellness. One of the most important sets of breathing exercises is ancient Pranayama breathing exercises. These exercises have been utilized for centuries by Yogi’s to greatly improve overall health while at the same time increasing your natural defense. This is the 4-7-8 method.

You can read the article on How to lower your time to fall asleep to know more about the 4-7-8 method.