In less than ten years, the Apple Watch became the prototype of what a smartwatch could be and of the many benefits it could bring for measuring health vitals and other psychological and physiological indicators.
Despite not being a new concept, Heart Rate Variability (HRV) has been gaining dramatic interest in recent years as an easy to collect and process physiological indicator of mental and physical health.
It only makes sense to use a top-of-the-line smartwatch such as the Apple Watch for heart rate variability measurement.
In this article, we will analyze what are the benefits of measuring the HRV? Is the Apple Watch reliable and accurate enough to allow a peek at the autonomic nervous system?
At first, let’s define what heart rate variability is and why it matters.
What is heart rate variability?
The Heart Rate Variability is different from the Heart Rate. However, the two metrics should not be confused. While most smartwatches or even fitness bands will all offer the possibility to check on your Heart Rate, the HRV measurement is more complex to measure and interpret in a meaningful way.
In a nutshell, the heart variability relates to the time in msec between two consecutive heartbeats. The heart is not ticking like a clock, and even if your heartbeat averages 60 beats per minute, it does not mean that each beat will be spaced by exactly one second. Differences exist, and these differences will correspond to the heart variability.
What can you learn from the HRV?
The HRV is widely used to assess the autonomic nervous system state. Heart Rate Variability is very sensitive to psychological and physiological changes.
Moreover, HRV modifications have been associated with various diseases, including heart attacks, mental disorders, stress, and workout efficiency.
The overall status of the autonomic nervous system can be measured using various physiological indicators such as temperature, breathing pattern, Galvanic skin response, and heart rate from which the HRV is derived.
A high HRV is an indicator that the body has the ability to cope with stress or is recovering from prior psychological or physiological accumulated stress. A low HRV is indicative of stress which could potentially lead to various diseases. But do not worry too much, when low HRV can be improved.
How can you measure your heart rate variability with an Apple Watch?
Taking an HRV reading with the Apple Watch is as easy as finding a quiet place, sitting or lying down, and breathing. It could not be simpler.
Some devices will favor a controlled environment, such as during sleep, to collect reliable data. The YHE BP Doctor smartwatch is doing just that and relies on its sleep cycles analysis algorithm to define the optimal time for collecting RR intervals and calculating what the HRV is. Heart Rate Variability is very dependent on your physical and mental state. So checking it just after climbing a flight of stairs will be useless.
The HRV during sleep carries numerous predictive values even though the Apple Watch may not be the ideal device for continuous recording.
The sensitivity of your Heart rhythms to external stimuli explains why the Apple Watch records it when using the Breathe app. This way, the settings are more controlled, reliable and the data more comparable. While breathing, the heart rate data is collected and processed by the Smartwatch or the iPhone depending on the app. used to check the HRV results.
The Apple Health app is an easy way to look at the data while other apps may provide more comprehensive analyses and even advice on how to improve your stress levels and overall autonomic nervous system, which will, in turn, increase the HRV.
Several apps are purely devoted to analyzing your HRV and can be paired with the Apple Watch for data collection. Among the most famous, we can cite Heart Analyzer or HRV4Training.
The Heart Analyzer app. is available for both iPhones and Apple Watches. At the time of this writing, this app. has been rated 4.6 stars by more than 8,400 users.
Offering numerous data analyses and making the most of the Apple Watch sensors, the dashboard and functionalities include Vo2max, HR, Blood O2 saturation, resting heart rate, and, of course, Heart Rate Variability.
The App. acts as a complete dashboard to analyze your heart health and is optimized to work smoothly with the data collected from the Apple Watch sensors.
Heart Analyzer is free to use in the standard version. Thus, contrary to becoming an expensive norm for users, there is no need to pay for a monthly subscription.
For 4.49 GBP, it is possible to store up to four years of data, customize the app to your liking and benefit from what the company refers to as deep analytics algorithms for additional insights.
HRV4Training is one of our favorites. True, the app. is not for everyone as the amount of data and information provided can become quite overwhelming. However, the interface was revamped a couple of months ago and is now much easier to use.
The previous one was utterly complex and reminding me of my years spent processing motoneurons electrophysiological signals. Not the best way to get a clear indication about your HRV data, especially when a magnifying glass was needed to read the value.
Apart from the numerous variables, HRV4Training will consider while assessing your HRV (did you drink the day before the measure, had to sport, slept well,…), one of the points that definitely differentiate HRV4Training from the other apps is that an Apple Watch or other sensors are not needed to get an HRV score.
The App offers the possibility to use the camera of the phone as a heart rate monitor. When compared to other wearable devices, the results are surprisingly accurate.
HRV4Training also collects the data from the Apple Watch, Polar chest strap, or Scosche Rhythm24.
As with the HRV4Training app., a single payment of $9.99 is enough to unlock the functionalities fully.
What is a good heart rate variability level?
In a nutshell, there is no real good or wrong HRV even though, at rest, a high HRV is considered a positive factor. When active, this is just the opposite.
Measuring the HRV is basically getting insight into how your Autonomic Nervous System regulates the autonomic process of the body.
The Whoop wearable and the Oura Ring have collected a huge dataset of HRV data. According to them, a normal HRV can fall anywhere between 20 and 200 msec in adults.
More than a specific value cast in stone, what matters is to check the evolution of the HRV over time. A decreasing HRV trend can mean that your body has difficulty coping with the daily stress and thus could become more prone to diseases.
When analyzing your HRV, always think longitudinally over the course of several days or weeks, and do not worry too much about a low HRV day. Especially if you had a party the previous night, studies showed that alcohol could impact Heart Rate variability for up to one week.
How accurate is the apple watch in measuring HRV?
In an article published in 2018 in the journal Sensor by the team of Pr. Hernando and Bailon from the University of Zaragoza in Spain, twenty healthy volunteers, were submitted to mild levels of cognitive stress and relaxation exercises. The Heart Rate Variability derived from the RR interval analysis obtained from the Polar H7 chest strap and the Apple Watch was compared. The Polar H7 is recognized as one of the most accurate consumer devices for measuring heart rhythm. Hence it was used as the reference device. The study showed that the Apple Watch HRV data were very reliable and agreed with those obtained with the Polar H7.
As we saw, the calculation of the HRV is directly linked to the accuracy of a device or smartwatch to detect heart rate. In 2017, Shcherbina and colleagues checked just that in a study analyzing the accuracy of various wrist-worn sensors and other wearable devices. Again, the Apple Watch was the best and most accurate device in detecting heart rhythm variations.
Based on these scientific studies and many others, the Apple Watch can accurately detect RR intervals and ultimately compute a reliable HRV reading.
To wrap up
The Apple Watch series include some of the best smartwatches available for a reason. Its sensors allow to accurately detect numerous vital signs and the heart rate is just one of them.
By extracting the RR intervals between two heart beats and relying on internal or external applications, it is now possible to get a precise outlook of your stress level. Thanks to the HRV metric.