An increasing number of wearable health and fitness trackers now provide heart rate variability (HRV) data, including the popular Apple Watch.
But, is the Apple Watch HRV accurate? How does Apple Watch HRV work? What does HRV on Apple Watch mean?
In this Apple Watch heart rate variability guide, we will explain what HRV on Apple Watch means and the Apple Watch HRV accuracy so you can track your fitness level.
We will cover:
- How to Use Apple Watch HRV
- Is Apple Watch HRV Accurate?
- How Accurate Is the Apple Watch HRV?
Let’s get started!
How to Use Apple Watch HRV
Before we look at Apple Watch HRV accuracy, let’s discuss what HRV is and how to use Apple Watch HRV data.
Heart rate variability, more commonly referred to as HRV, is a measure of the fluctuations in the length of time between each beat of your heart.
A low heart rate variability number means that your heart is beating at a very steady and consistent rhythm whereas a high HRV means that there is more variability or greater fluctuations in the timing or interval length between each heartbeat.
The higher your heart rate variability, the more variety there is in the spacing between each heartbeat, or said another way, the less consistently steady your heart rate is.
Unlike many cardiovascular-related metrics, such as resting heart rate and blood pressure, wherein a lower number is ideal, with heart rate variability, you actually want to have a higher number.
It certainly sounds counterintuitive that this would be optimal because most people would assume that having a very steady consistent heart rate would indicate a healthy heart that is not prone to experiencing some sort of arrhythmia.
However, research demonstrates that a high heart rate variability indicates that your heart is “ready” to handle stressors, such as vigorous exercise or just everyday stress.
Your heart rate variability is ultimately a result of the instantaneous differences in the autonomic control of your heart rate.
Apple Watch HRV can provide insight into which branch of the autonomic nervous system is primarily controlling your body, which, in turn, can inform you as to the degree of stress that you are under.
When your body is being predominantly controlled by the sympathetic nervous system (“fight or flight”), your heart rate variability is low.
Thus, when your HRV is low, your body and brain are operating in a stressed state.
On the other hand, if your HRV on Apple Watch is high, your physical and mental stress levels are low and your body is therefore able to handle a higher amount of stress.
This is because the parasympathetic nervous system (“rest and digest”) is associated with a higher heart rate variability.
So, how do you find HRV on Apple Watch?
As long as you are at least 18 years old, Apple Watch HRV data is automatically recorded when you wear a watch.
However, in order to see your Apple Watch HRV metrics, you have to use the iPhone health app.
Here are the steps for how to find HRV numbers on Apple Watch:
- Open the Health app on your iPhone.
- Tap Browse in the bottom right corner.
- Select Heart and then Heart Rate Variability.
- Your Apple Watch HRV data will be displayed. You can change how you view this data by day, week, month, sixth-month, or year intervals by tapping the D, W, M, 6M, or Y letters at the top of the screen.
Is Apple Watch HRV Accurate?
So, how accurate is the Apple Watch HRV?
Of course, using Apple Watch HRV data to provide insight into your body’s state of readiness, recovery, and nervous system balance is only useful if the HRV Apple Watch analysis is accurate.
While the Apple Watch shines in many areas, including some of the high-tech metrics and health analytics, most people who have looked specifically at Apple Watch HRV accuracy have found that it is an area where this wearable health and fitness tracker falls short.
Consequently, because HRV on Apple Watch may be fairly inaccurate, it is generally recommended that you don’t put too much stock in your Apple Watch heart rate variability analysis—at least not without considering numerous other tangentially related biomarkers to have a broader context of your fitness and health.
There are several criticisms of how Apple Watch measures heart rate variability, and these potential pitfalls are likely to contribute to the low accuracy of Apple Watch HRV analysis.
Let’s examine how Apple Watch HRV data is obtained:
One of the biggest problems with Apple Watch HRV accuracy and analysis is the fact that the protocol or how Apple Watch measures HRV doesn’t make sense when you think about heart rate variability as a metric.
The entire purpose of heart rate variability is to look at the variability in the beat-by-beat rate of your heart.
Heart rate variability is most notable and most meaningful as a biometric when the parasympathetic nervous system is predominating.
Therefore, most cardiologists and health experts agree that the best time to assess HRV is first thing in the morning as well as throughout the night while you are sleeping to get a sense of the balance between your sympathetic nervous system and parasympathetic nervous system and the body’s recovery.
The autonomic nervous system, which is the branch of the nervous system that controls heart rate is affected by many things, so we want to be consistent when assessing the health or state of the autonomic nervous system.
Otherwise, you are taking and comparing random snapshots at all different points in the day under different contexts wherein the autonomic nervous system might be responding appropriately but to very different types of stressors.
As with any sort of scientific study or investigation, you want to minimize the number of variables as much as possible so that you can only isolate the one you are interested in.
Apple Watch HRV data is taken randomly throughout the day, so we are introducing too much influence from all of the many environmental and physical stresses that can change the autonomic nervous system regulation and that your instantaneous HRV from minute to minute across points in the day.
Apple Watch HRV analysis takes sporadic HRV measurements throughout the night while you sleep but also uses other random, sporadic HRV captures throughout the 24-hour period.
There are some potential workarounds to improve Apple Watch HRV accuracy by using the Apple Watch Breathe app to control when or how Apple Watch HRV recordings take place, but the default settings lead to fairly inaccurate—and frankly not useful—heart rate variability information.
How Accurate Is the Apple Watch HRV?
The good news is that while Apple Watch HRV accuracy can be poor if you use the Apple Watch Breathe app for HRV, the heart rate variability metrics have been shown to be quite accurate.
In fact, some studies have found that Apple Watch HRV accuracy is on par with heart rate metrics from Polar heart rate monitors.
As a company, Polar has earned a reputation for manufacturing some of the best heart rate monitors and wearable fitness trackers, not just in terms of being at the forefront of wearable HR tracking and technological features in heart rate monitors, but also in the accuracy of heart rate metrics.
Polar chest strap heart rate monitors are essentially considered to be the “gold standard“ of heart rate monitor technology for everyday consumers.
The accuracy of fitness watches that use wrist-based heart rate monitoring or optical heart rate monitoring is generally evaluated or measured relative to Polar chest strap HR monitors.
In fact, while Apple Watch HRV was initially poor, some recent studies have found that the R-R intervals from Apple Watch heart rate data are strongly correlated or in alignment with R-R intervals from Polar HR monitors.
Note that R-R intervals refer to looking at ECG signals, and the R-R interval represents the timer for one heartbeat.
Therefore, for Apple Watch HRV analysis, looking at the changes in R-R interval durations provides heart rate variability.
All of this is to say that the recent studies looking at HRV accuracy with the Apple Watch have confirmed that the Apple Watch HRV accuracy is quite good and significantly better than it once was.
But, the important caveat here is that the accuracy of HRV on Apple Watch is excellent with the Breath app, and not necessarily just with the default settings on the watch.
This is because the Apple Breathe app takes HRV measurements at specific and logical times. Plus, you can control when HRV is measured or self-select to measure it on the spot, so you can be in charge of being consistent with these measurements yourself.
Curious to learn more about Apple Watch metrics? Check out our guide to: “How accurate is the Apple Watch VO2 Max” here.
