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The Heart Rate Variability or HRV for short represents the time in ms between two heartbeats. A heart rhythm of 60 beats per minute (bpm) does not mean that your heart is precisely ticking one time per second. There will be a slight variation measured in ms between each beat.
These differences will represent the strength of the parasympathetic branch of the autonomous nervous system. The Heart Rate Variability will focus on the constant fight in our autonomous nervous system. The parasympathetic branch is responsible for decreasing our heart rhythm and bringing us in a “rest and digest” mode. Conversely, the sympathetic branch will put us in a “fight or flight” mode and increase our heart rhythm and stress levels.
In numerous scientific studies, a high HRV has been correlated with good health. The higher the HRV, the more adaptable to change and resilient you will be. On the opposite, a low HRV may be the sign that your health is not optimal, and that action should be considered, such as exercising more, losing weight, sleeping better, meditating,…etc.
In a nutshell, Heart Rate Variability is a simple biomarker to assess our physiological and psychological states. But, how can we measure it? To do so, we will need three components: Mathematical equations to extract meaningful information, a device to precisely record the heartbeats, and finally, an app or built-in software to process the raw data collected by the recording device.
What is the RMSSD?
The Root Mean Square of the Successive Differences or RMSSD, in short, is the most commonly used method to measure the HRV. Without entering into the mathematics behind, the RMSSD is the square root of the mean squared differences of successive intervals between heartbeats.
Most of the algorithms and devices will use this formula to measure the Heart Rate Variability. The RMSSD is considered reliable, reproducible, and comparable between studies. Other methods such as the HF/LF ratio or the Poincaré plots can also be used, but the RMSSD is certainly the one favored by most.
How to precisely record heartbeats?
Several wearables or even a simple iPhone can collect heartbeats precisely enough to extract a reliable Heart Rate Variability Trend. Important to remember that the HRV is a biomarker that should not be analyzed in complete isolation. A night of partying with a few too many drinks will affect your Heart Rate Variability for up to five days. HRV trends are critical to understanding sympathetic activation.
Measuring the resting heartbeat can be done using several devices. We will present the ones that are considered suitable to measure the HRV. Our selection is far from exhaustive but offers enough choice to find the wearable that will fit your lifestyle. Recently Nelson et al. (2020) from the University of Oregon published guidelines for wrist-worn heart rate monitors.
The Polar H10 is already three years old but is still considered the gold standard heart rate monitor. When properly strapped around your chest, the H10 is comfortable to wear, so much that you will even forget you are wearing it. The battery life extends up to 400 hours, which gives plenty of time for training.
With built-in memory, there is no need to carry your phone with you at all times. The data will be synchronized once the H10 is connected with an app. Not only is the Polar H10 very precise, but it also opens the doors to numerous fitness and health apps. To get accurate heart rhythms data, the waterproof H10 is undoubtedly the number one sensor on our list. Check it on Amazon for more information.
While the Polar H10 is more intended for serious sports enthusiasts, the Oura ring combines design and reliability. The Oura ring is discreet and continuously records a huge amount of data to provide a more holistic healthcare view.
With its minimalist design, the Oura ring will look like just a fashion accessory. The perk being that Heart Rate, breathing pattern, body movements while sleeping, and even the temperature will be analyzed in real-time. The raw data will synchronize with the Oura App to calculate the HRV and much more. Like the Polar H10, the Oura ring is compatible with numerous health apps, including the excellent HRV4Training.
The Scosche Rhythm 24 is an evolution of the chest strap. It is an arm strap! While the H10 relies on electrodes, Rhythm 24 relies on optical sensors. With a 24 hours battery life, built-in memory, and using two different color optical sensors for improved accuracy, the Scosche Rhythm 24 is accurate and comfortable to wear while training.
The raw data synchronize with more than 200 compatible apps, and the HRV can also be extracted using the HRV4Training app. If you do not like wearing a chest strap but want reliable data, the water and sweatproof Rhythm 24 is undoubtedly a choice to consider. Check on Amazon for more information.
Apps to measure Heart Rate Variability
Once the data are collected, it is now time to analyze them to know more about our parasympathetic nervous system state. More than just a measure of a healthy heart, the Heart Rate Variability will offer numerous information on our training load, stress and recovery mechanisms, and the evolution of our day to day health.
One of the benefits of the HRV4 Training app is that there is no need to use an external device to record the resting heart rate. The camera of your iOS or Android device will be used to collect the data. This app is certainly the most accurate and extensive when dealing with HRV. It offers multiple information and parameters to fine-tune. Designed by a data scientist, HRV4Training is not really in the design or UX but mainly in analyzing the HRV and insights provided. I use it daily and certainly plan to continue doing so.
Elite HRV is a different animal. The app is beautifully designed and will also offer numerous insights to understand and improve our HRV. HRV Elite recommends their own sensors, the Corsense, even though we consider that a chest strap may offer more versatile uses.
Like HRV4Training, Welltory takes advantage of the smartphone camera to measure the HRV. The app is easy to use but requires a monthly subscription to take advantage of all of the functionalities available. We only used the free version of the app and can say that it looked really well done and complete. The only issue we have is that there seemed to be a difference in the HRV reading compared to HRV4Training.