What is heart rate variability?


Heart Rate Variability (often referred to as HRV) is the measurement of the variation in time between each heartbeat. These variations are so small that unless you’re hooked up to a specialized device, you won’t be able to detect them on your own, but they are nonetheless extremely important to your overall health and well-being.

HRV is a metric recorded by many of the best fitness trackers (opens in a new tab)including Apple Watch, Garmin Fenix ​​7 Sapphire Solar (opens in a new tab) and several Fitbit bands. It shows you how well your body is able to respond to signals from the parasympathetic and sympathetic nervous systems (the latter controlling the body’s fight-flight response and the former acting as a brake) and adapting to environmental change.

The results give you a good indicator of fitness, fatigue and stress, with a higher HRV generally considered positive, but making sense of heart rate variability readings from a wearable device requires a bit more. of context as your resting heart rate or – athlete’s favorite – VO2 Max.

Read on to learn more about what HRV actually is and what it can suggest about your health and fitness.

What is heart rate variability?

HRV is a measure of the difference in the intervals between your heartbeats over time. If your heart beat, like a robot, at 60 bpm, there would be an interval of 1000 ms between your heartbeats. But that’s not how our hearts work. If one beat lands 1024ms after the other, then the next one is 1080ms later, that’s a variability of 56ms.

Young woman looking at fitness tracker data on smartphone and wrist

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While there are several mathematical ways to calculate HRV, they all deal with the gravity of a metronome that our hearts would make – it’s an average of these temporal disparities in a time window. Heart rate variability is also a more accurate measurement than your heart rate due to the tolerances involved.

For example, a fitness tracker might give you an HRV reading of, say, 68ms. This equates to an average variability equivalent to just over 4 bpm during the test period. But if your heart rate reader is only accurate to within a handful of bpm of the actual reading anyway, the data becomes largely meaningless.

What does HRV mean for your health?

Why should we care about HRV in the first place? A stack of studies have been undertaken over the years that link it to several different aspects of health. A meta-analysis published in Psychiatry Investigation (opens in a new tab) concluded that “HRV is affected by stress” and that it can be used in the “objective assessment of psychological health and stress”. A low HRV score is therefore an indicator of stress.

A large dataset study by the Fitbit research team that was published in The Lancet (opens in a new tab) found HRV is impacted by exercise, making it a potential metric to judge how well you manage your workout routine. HRV decreases directly after exercise, but after recovering from a diet that advances your fitness, you should see a general upward trend in HRV results.

Senior man exercising in rural area wearing fitness tracker

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A 2018 study published in Aging (opens in a new tab) also proposed the use of HRV as a means of predicting heart attacks, although he concluded that further research was needed.

Ways to interpret HRV may seem amorphous, but that’s because it relates to one of the essential functions of the human body. It is an indication of the interaction between the sympathetic and parasympathetic nervous systems. One of them, the sympathetic, releases hormones to raise your heart rate, while the parasympathetic releases the hormone acetylcholine to lower it.

Exercise or think about your bills, and your heart rate goes up – which you think might not be a big deal since your heart rate changes all the time, right? However, HRV can provide insight into how this interaction between the sympathetic and parasympathetic nervous systems is taking place.

A higher HRV suggests your cardiovascular system is more easily adaptable, and that’s a good thing.

How HRV is recorded

However, using heart rate variability in your daily life is not straightforward. Your HRV readings will change throughout the day, even if there is no obvious stimulus to cause such changes. And it will naturally be affected by stress and exercise, where your sympathetic nervous system grabs the steering wheel and causes your heart rate to increase.

Results also vary from person to person, and are not just related to obvious factors such as physical condition. So you really only have to compare your own results over time. Don’t fall into the trap of being jealous of your friend’s video game-style “high scores”.

Woman looking at fitness tracker data on phone

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Garmin uses it to power training recommendations, for example. “It gives you insight to make a clearer decision on your training intensity. HRV status feeds into the other metrics such as training status, suggested workouts for even better feedback and advice Garmin told us.

However, when we measure HRV, we are also not interested in the rate of change of your heart rate during exercise – look at a measurement like VO2 Max (opens in a new tab) for that. Instead, HRV is usually recorded when there is no obvious stimulus that could skew the results, such as when you are sleeping.

There are reasons why your resting heart rate and estimated VO2 Max are generally more useful and easier to understand than metrics for the average person just looking to stay healthy. However, we are starting to see HRV scores being more important in fitness tracking apps.

What is a “good” HRV?

The first thing you’re going to ask yourself when you get your first HRV reading is “is it good?” Is it bad? Am I dying? It’s the wrong way to approach this stuff, but we reacted in exactly the same way.

Wearables maker Whoop has released an interesting graph that shows how HRV stats tend to grow with age (opens in a new tab). Much like VO2 Max, there is a steady downward trend between the ages of 20 and 30, seeming to bottom out when you hit your 60s.

This graph shows the middle 50% of the recorded results, eliminating outlying high and low readings. At the age of 20, therefore, you can consider a normal range to be between 55 ms and 105 ms. At age 40, this trend drops to 36-64 ms.

We must reiterate, however, that you can easily record HRV scores above these limits – as well as above and below – within hours.

Look for trends in readings, rather than focusing on a single result. However, many wearable device manufacturers make this easy to do in the way they present the data and manage when they take recordings to limit the wild deviations you can see in those variability scores.

HRV in Apple Watch

Apple Watch Series 7

(Image credit: Lloyd Coombes)

Apple introduced HRV readings on the Apple Watch in WatchOS 4 in 2018 and they remain available on their latest offering, the Apple Watch Series 7 (opens in a new tab). They are taken automatically, in the background, at convenient times. However, you can also manually collect HRV data by starting a Breathe session in the Mindfulness app.

However, you will not see the result when you complete the one-minute breathing exercise. The data is transferred to the Apple Health app. If you tap All Health Data from the app’s home screen, you should see an entry for Heart Rate Variability.

This takes you to a screen that displays your HRV over time, with optional timescales of 1 day, 1 week, 1 month, 6 months, or 1 year. It’s a sensible way to relay data, sitting outside the usual fitness zone and encouraging you to look at trends and averages, not single results.

HRV in Garmin watches

Garmin Venu 2 Plus wristwatch

(Image credit: Garmin)

Garmin initially required you to use a chest strap for HRV readings, but not anymore. With the release of 2021’s Garmin Venu 2 (one of Garmin’s best watches), we discovered Health Snapshot, a 2-minute relaxation mode that spits out a bunch of stats, including HRV.

You can find it in Garmin watches with Elevate v4 heart rate reader technology, like the Venu 2, Fenix ​​7, and Garmin Epix 2. Some older watches, like the Fenix ​​6, also measure heart rate. HRVs in their stress test modes.

Garmin dramatically opened up heart rate variability logging in 2022. The Forerunner 955 and Forerunner 255 introduced HRV status, which takes measurements overnight and shows you the results as part of a “Heart Rate Report.” morning”. It’s a much more user-friendly and passive way to try HRV monitoring. We hope to see these features coming to other Garmin watches, like the Fenix ​​7, in the future.

HRV in Fitbit watches

Fitbit Sense worn on the wrist with background fence

(Image credit: Lloyd Coombes)

HRV has been added to the best Fitbit (opens in a new tab) watches in 2021. It’s not too picky about which device you use, as Inspire, Fitbit Luxe, Fitbit Sense, Charge 4 and Versa 2/3 watches are compatible.

The readings are taken overnight, perhaps prompting Garmin to offer us its HRV Status mode a year later. We didn’t find Fitbit’s HR accuracy as good as Apple’s or the latest Garmin watches. But part of a good HRV algorithm deals with eliminating erroneous readings, so it may not impact Fitbit’s scores.

There is a problem, however. Fitbit maintains long-term stats monitoring behind a Fitbit Premium paywall. It’s a subscription service that also unlocks guided workouts and nutrition plans. HRV statistics aren’t particularly useful if your data is only a week old, so if you want to monitor variability effectively, you’ll need a Premium subscription.

HRV in Samsung Watches

Samsung uses HRV in its Galaxy Watches, but currently doesn’t let you see the data. It feeds stress readings, much like Garmin’s old approach.

Third-party apps that claim to measure HRV are available on Samsung’s Galaxy Store, but we can’t comment on their accuracy. Still, if you’re desperate to try HRV tracking, it’s at least somewhat possible with a watch like the Galaxy Watch 4.


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