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Understanding Heart Rate Variability (HRV)

Heart rate variability (HRV) gets a lot of attention nowadays. It has uses for athletes to optimize their training, for people wanting to reduce their stress and check on their overall wellness and is studied globally for its correlation to our autonomic nervous system. The HRV analysis is a powerful and reliable metric that is made easy to track with Circular.

The basics: what is HRV?

HRV measures the specific changes in time (or variability) between successive heartbeats. The time between beats is measured in milliseconds (ms) and is called an “R-R interval”.

R-R interval Circular

A healthy heartbeat contains healthy irregularities. If your beats per minute is 60 for example, your heart will most likely not beat once every second for a whole minute. It will rather have different interval lengths between each heartbeat. One interval could be 0.75 seconds for example and the next one could very well be 1.25 seconds.

The healthiest you are, the more your heart must be able to adapt to any situation, to accelerate as well as to slow down, that’s why your R-R interval will be irregular. If it is more regular it means that you are out of shape and that your heart will not be able to easily adapt.

RMSSD calculation method which is the root mean square of successive RR interval differences is often used and will give you an easier score number to study. The higher the score the better you are, the lower the score the less healthy you are.

HRV is measured within a specific time frame. For Circular, the measurement time frame is 5 minutes. Generally speaking, if the intervals between your heartbeats are rather constant, your HRV is low. And if their length variates, your HRV is high.

How is HRV measured?

Each contraction of the heart results in a blood volume pulse which propagates through the bigger arteries towards the small capillaries. We can all feel this by placing a finger on top of our arteries on our neck or the palmar side of our wrist. This blood volume pulse signal can be tracked optically. Optical measurement is based on the absorption of certain wavelengths of light when reflected towards blood veins. In this case, we talk about (PPG) measurement.

PPG Circular Ring

This method allows for non-invasive HRV tracking methods such as… a ring! 

A great benefit of having a device like the Circular ring on your finger is that it is most likely one of the most optimal places for PPG-based HRV tracking. The reason being that it has the suitable arteries and capillaries for clear blood volume pulse signals, making the optical measurement more reliable and accurate. In addition, there are no moving parts between the joints in fingers, meaning that the ring sits firmly and doesn’t move. 

So how can HRV help me?

Circular automatically detects your baseline HRV which is your long term average HRV as you feel ordinarily. Then Circular makes the average of all your HRV readings to give one average of your daily HRV. When your daily HRV is greater than or equal to your baseline HRV then you are good to push yourself. When your daily HRV is lower than your baseline then you need to keep it cool.

Heart Rate Variability Circular

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. There are a couple of main applications for its use that can help you out:


In recent literature, a group of runners performed better when starting intense training blocks only under good physiological conditions, despite having actually trained less than the control group. Good physiological conditions meant simply having their baseline HRV within their normal values or trending positively. A negative trend was a no go.

We aim at using HRV to quantify recovery. There is quite a strong relationship between intense aerobic workouts and reductions in HRV the following day. This is a typical acute stressor, and the reduction in HRV (and a smaller increase in HR) can be used to quantify recovery and understand if we need an extra day off. 

High HRV, which shows larger gaps between heartbeats shows positive adaptation and fitness while lower HRV with smaller gaps indicates fatigue and overtraining. 

Knowing your heart rate variability means understanding your body and its response to physical overload so you can tailor your training regime for optimal results.

Wellness Analysis 

It has been proved that the healthier you are, the higher the variation between heartbeats, in other words, the higher your HRV is. 

People who have high HRV may have greater cardiovascular fitness and be more resilient to stress. 

Over the past few decades, research has shown a relationship between low HRV and worsening depression or anxiety. A low HRV is even associated with an increased risk of death and cardiovascular disease.

HRV may also provide personal feedback about your lifestyle and help motivate those who are considering taking steps toward a healthier life.

It is fascinating to see how HRV evolves as you do your activities (especially physical), as you meditate and as you sleep. For those who love data, this can be a nice way to track how your nervous system is reacting not only to the environment, but also to your emotions, thoughts, and feelings.

If you are sick, you have trained physically, or if you have slept badly you will definitely see the impact on your HRV.

Stress Analysis

Heart rate variability is an excellent, non-invasive way to measure stress. Stress is an important metric to track as many people don’t recognize the signs and symptoms, which often leads to deeper health issues if left unmanaged. Studies have shown that changes in heart rate variability are tied to a variety of health problems, from heart diseases, diabetes to post-traumatic stress disorder (PTSD).

Improving Meditation

Higher Heart Rate Variability is a strong biomarker for general health and resilience as high HRV indicates a relaxed, low-stress mind, while lower HRV suggests the need for sleep and rest. As meditation requires a calm, relaxed mind, measuring heart rate variability and training for a higher HRV is an effective way to improve your meditation state.

Anxiety Treatment

It has been shown that anxiety disorders are associated with low heart rate variability values. Anxiety disorders are the most common psychiatric disorders today and have been shown to increase the risk of heart disease. So monitoring heart rate variability of anxiety patients is important as changes in HRV reflect the effectiveness of a treatment.


On the whole, high Heart Rate Variability is an indication of overall health as well as general fitness. Generally speaking, it tells us how recovered and ready we are for the day. Also, HRV can react to changes in our body even earlier than heart rate. This makes it a particularly sensitive tool that gives us insights into our wellbeing. This can help you detect if you are getting weak before you get sick. 

Remember that Circular and Kira do the work for you and will alert you based on your unique profile for HRV changes. But it is also nice to sometimes manually check HRV readings and understand how your body reacts to it yourself.

You can now learn about how to use Heart Rate Variability (HRV) with Circular 


Aside from that, there are multiple studies indicating that HRV is quite useful as a way to quantitatively measure physiological changes caused by various interventions both pharmacological and non-pharmacological during treatment of many pathological conditions having a significant manifestation of lowered HRV.

However, it is important to realize that clinical implication of HRV analysis has been clearly recognized in only two medical conditions:

1. Predictor of a risk of arrhythmic events or sudden cardiac death after acute heart attack

2. Clinical marker of diabetic neuropathy evolution

Nevertheless, as the number of clinical studies involving HRV in various clinical aspects and conditions grows, HRV remains one of the most promising methods of investigating general health in the future. 

Scientific sources:

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