If you own a smartwatch, you may have encountered a metric called heart rate variability (HRV). On the Internet and social media, it certainly seems like HRV is a health stat many people are excited to self-monitor.
Vivian Mo, MD, clinical associate professor of medicine in the division of cardiovascular medicine at the University of Southern California, believes it's because technology is giving us the ability to track key health metrics easily in the way of wearable devices and apps (think: Whoop, Fitbit, and other smart health and fitness trackers). "When I typed 'heart rate variability' into Google, a definition of it came up, and right after the definition was just all the devices that measure HRV," she adds.
While Americans are more proactive about their own health these days and are self-tracking their health metrics, the interest in HRV may also be linked to the ever-increasing focus on wellness and lifestyle medicine. HRV may be a good metric to use to measure improvements in stress regulation and healthy lifestyle behaviors, says Tamara Horwich, MD, associate clinical professor of medicine and cardiology at the David Geffen School of Medicine at UCLA.
Maybe you're one of the many people who monitor their HRV or maybe you've noticed the HRV metric on your device or app but aren't sure what to make of it. Regardless, we asked the experts to explain everything you need to know about it.
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What is heart rate variability?
Heart rate variability is the variance in the timing between each heartbeat, says Dr. Mo. She explains it this way: When you are at rest, your heart rate sits at around 60 beats per minute. But if you were to examine the timing between each beat very closely, you'd discover that it's not exactly beating at one-second intervals all the time. Sometimes your heart will beat every second, and sometimes it'll beat after 1.1 seconds or 0.9 seconds. There's a difference, or variance, in the timing between each beat. This is your heart rate variability.
A normal HRV for people in their teens and 20s averages between 55 and 105 milliseconds, but most folks aged 60 years and up have lower heart rate variability, averaging between 25 to 45 milliseconds.
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What does heart rate variability tell you?
HRV is one way to measure what is happening with your autonomic nervous system, which is the part of the nervous system that regulates functions like blood pressure and breathing.
Per Dr. Horwich, the autonomic nervous system has two sides: the sympathetic nervous system (SNS), which is involved in the "fight or flight" response and raises your heart rate, and the parasympathetic nervous system (PNS), which helps you "rest and digest" and lowers your heart rate. These two sides are always opposing one another to create some form of balance in your body. HRV is one reflection of what is going on in the sympathetic versus parasympathetic "battle".
If you're tracking your HRV over 24 hours and notice it's lower than usual, this could mean that the sympathetic nervous system is dominating and being activated for longer than it needs to, while a higher HRV is a sign of more parasympathetic inputs to the heart, explains Dr. Horwich.
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How to compare HRV results
Dr. Horwich explains that having more parasympathetic inputs to the heart is healthy, so if you measured your HRV over a long period of time, for 24 hours for example, and it's higher than your usual HRV, this could be considered to be better for your health.
On the flipside, if you did the same monitoring over 24 hours and your HRV is lower than usual, "in general, that's a sign that something may be off in that person's lifestyle or their heart health," Dr. Horwich says.
While this seems straightforward enough, she adds that it may not always be the case, however, stating that HRV is also a reflection of many other things going on in the body. "There are complex mechanisms, different feedback loops and other things that feed into heart rate variability," she explains. This is a reason why doctors do not routinely use HRV as a measure of their patient's health, since there are more objective and definitive metrics they can use.
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Which lifestyle factors impact HRV?
Your HRV decreases, or "worsens," naturally as you age. Besides merely getting older, you may also notice a lowered HRV when you're under a lot of stress, dehydrated, drinking a lot of alcohol, eating unhealthily, less physically active, and having poor sleep, says Dr. Mo.
The opposite can happen, too: Your HRV may increase when you start managing stress and improving your food choices, getting regular exercise, staying hydrated, drinking less alcohol, and sleeping for a solid seven to nine hours each night. As Dr. Mo points out, it's possible for a 65-year-old who's physically fit and active to have a higher HRV.
"They've seen that if people engage in these [healthy lifestyle behaviors], they tend to trend toward having a better heart rate variability," she says. "But they currently don't really know the physiological basis for why that happens."
Dr. Mo says it may be tied to the effect of these behaviors on the autonomic nervous system. Dr. Horwich agrees. "If someone is not eating healthfully, for example, that is the time your sympathetic nervous system may kick in, and when this is activated all the time, it's not healthy for your body," Dr. Horwich says.
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How can you track your HRV?
According to Dr. Horwich, the most accurate way to track heart rate variability is by getting a continuous electrocardiogram, EKG, which records the electrical signal from your heartbeats. To record the heart rhythm over a period of time, the cardiologist will have the person wear something called a Holter monitor or patch, which captures an EKG even while the person is on the go.
What about smartwatches? Dr. Horwich says the HRV from smartwatches is based on the heartbeats it detects from your wrist pulse, so it may not be as accurate as the reading you get from an EKG that's reading the heartbeats from your chest.
This doesn't mean you need to discredit that number though, because your smart tracker's HRV can still be something you speak to your doctor about if you've noticed a stark change over time. But as you track it on your device, the main thing to remember is not to stress over it, because again, it may not be 100 percent accurate (or telling you the full story). So you can take note of it, acknowledge it, bring it up to your doctor—but don't panic over it.
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How much attention should you pay HRV as a health metric?
While you're encouraged to pursue healthy lifestyle behaviors, using HRV as your end goal (to see it trend up or down) may not be super helpful or motivating. In most cases, there's so much that contributes to the heart rate variability in any one person, and "it's hard to control so many variables in your life just to get your heart rate variability to improve," Dr. Mo says.
Pursuing these healthy behaviors and measuring their impact based on other metrics—like how far you can run without getting winded or what your anxiety or stress levels are—may be more rewarding.
As cardiologists, Dr. Mo and Dr. Horwich both say they do not use HRV very much to determine what treatment a patient needs, as it isn't recommended for use in clinical practice in cardiology at this present time.
"In my practice, I know that improving a patient's diabetes or cholesterol or blood pressure means their general health is going to get better, so it's not necessary to work towards improving HRV in addition to all of these," Dr. Mo says.
If you already own a smartwatch that tracks HRV, and you notice it rising or falling over a long period of time, don't hesitate to let your doctor know. If anything, discussing it with them will give you peace of mind.
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