By Hannah Singleton

Heart rate variability has become the wellness scene’s favorite recovery score, but experts say most people misunderstand the actual meaning of the number.

In August 2025, Mick Rouse, woke up one morning to an alert from his Eight Sleep mattress cover. As Rouse recalls, the app on his phone said something like: Are you feeling sick? We’ve noticed your data is out of the normal range. Rouse felt totally fine, but his biometrics—specifically his heart rate variability, or HRV—had dipped overnight, from his usual 40 milliseconds down to 21. Sure enough, “three days later, I was legitimately on-my-ass sick,” he says.

While Rouse uses his Eight Sleep more for cooling features than granular sleep analysis, this kind of algorithmic prophecy has become routine for tens of millions of people. According to the American Academy of Sleep Medicine, nearly 50 percent of American adults have tracked their sleep. Before coffee or emails or deciding whether to work out, people are opening their apps and checking readiness scores, including overnight HRV data from devices like WHOOP, Oura, Garmin, and Eight Sleep.

HRV, which measures the subtle variation in time between heartbeats, was once a niche metric reserved for elite athletes and sports scientists, but has now gone mainstream as the wellness world’s favorite score for stress, recovery, and overall health. Thanks, in part, to more people wearing health trackers that put this data front and center for users. In late 2025, Oura reported that its fastest-growing demographic wasn’t typical gym rats, it was young women. Their rings have been spotted on the fingers of Gwyneth Paltrow, Jennifer Anniston, Kim Kardashian, and Prince Harry, while athletes like Cristiano Ronaldo, Lebron James, and Rory McIlroy wear (and have invested in) the Whoop.

The HRV metric’s clinical importance has a long history. It was first recognized in the 60s as an indicator of fetal distress. But it wasn’t until the 80s when physicians discovered that HRV was a predictor of mortality after a heart attack, according to an article in Circulation. In more recent years, as wearables have turned HRV into a consumer-facing metric, it has also become a point of obsession for biohackers and longevity bros alike. Influencers post videos wondering why their number is so low: “My friend just told me that her HRV levels, on average from her Oura Ring, are between 100 and 150,” says wellness creator Alessia Scauzillo in an IG Reel. “I’m so shocked, I don’t understand. Am I not okay with my 30 HRV?” One new app even takes that fear and promises to raise your HRV if you follow its training program (although the experts I spoke to say this is unnecessary.)

What started as a useful physiological signal has increasingly become another number to scrutinize, and sometimes spiral over. And as everyone from endurance athletes to stressed-out office workers become fixated on improving it, experts say your ability to improve your HRV—and whether it should be a goal in the first place—is far more nuanced than most automated recovery dashboards would have you believe.

What can HRV tell you?

HRV measures the subtle variation in time between heartbeats, offering insight into how your autonomic nervous system is responding to everything from hard training and poor sleep to alcohol, illness, and everyday stress. In general, higher and more stable HRV tends to signal stronger recovery capacity and adaptability, while significant dips can suggest your body is under strain, says Andrew Flatt, HRV researcher and sports medicine graduate program director at Georgia Southern University. The number ranges from around 20 to nearly 200. A 2025 Oura report showed that, among its user base, the average user score hovers around 40. (Last year the company said it had sold 5.5. million rings but has not offered public data about how many people who purchased those rings are active users.)

For athletes, “it's an indicator of gas and brakes,” says Cody Stephenson, endurance coach and training expert at TrainingPeaks, who uses HRV with some of his athletes. Some studies have examined what happens when athletes train based on their HRV scores—determining when to go hard, train moderately, or recover based on whether the number is high or low. A 2020 meta-analysis found small yet significant improvements to VO2max in already well-trained endurance athletes.

Another 2025 study in Nature also found HRV-based training was effective, especially when paired with resting heart rate and subjective well-being measurements. The problem, though, when you try to translate these findings to everyday exercisers is that this data came from pro cyclists with super high volumes of exercise—around 30 hours a week. “For people like that, the majority of stress in their life is their training. And so HRV is a good indication of training inching up like pass what they can tolerate,” says Stephenson. “It’s almost a direct indicator of training stress.”

For everyone else, though, HRV may still be useful, though not as straightforward. If you’re balancing work stress, poor sleep, travel, alcohol, parenting, or the general chaos of modern life, fluctuations in HRV may still reflect strain, but not necessarily because your workout programming needs adjusting, Stephenson adds. A sudden dip might signal that you’re fighting off illness (like Rouse), mentally taxed, ate a big meal the night before, or running on too little sleep.

When your stress metric starts stressing you out

The problem is that HRV has increasingly been marketed as a metric to improve—as if pushing ever higher and higher is inherently better—when, in reality, it’s not that simple.

Everyone has a wildly different HRV baseline influenced by age, genetics, fitness level, stress exposure, and even measurement conditions. A low score isn’t automatically bad. A high score isn’t automatically good. In some cases, unusually elevated readings can be just as alarming as low ones, as it can be a sign that the parasympathetic nervous system is kicking in to recover from illness, injury, or an especially strenuous activity, explains Marco Altini, HRV researcher and advisor at Oura, on his personal Substack.

“If you're under the misconception that only high is always good, and you don't get a high score, then you're stressed or upset about it,” says Flatt. “Which is not helping anything.” It then becomes paradoxical: when a metric meant to measure your body’s ability to regulate stress becomes a source of it. Stephenson points to a client who has a naturally low HRV, which no amount of training or good habits could improve. They stopped paying attention to the number, because it wasn’t helping. “Anytime a metric becomes the goal, it ceases to become a good metric,” he says.

And people who aren’t interpreting the data alongside a coach or physician may not know how to take it. “Once it does tell you you’re getting sick, it feels like, well, what am I supposed to do? Am I destined to be sick?” says Rouse. “It’s very dystopian, kind of like—well I guess I accept my fate and in three days I shall be sick because Eight Sleep told me.”

Then there’s the issue of accuracy. Flatt, who has tracked his own HRV daily since 2011, is skeptical of consumer wearables—to the point that he says he can’t recommend them. “There's an overhype right now in heart rate variability, because the way people are using it is largely through wearable devices,” he says. “And overall, these are not valid tools.” Many studies evaluating wearable accuracy can present data in ways that overstate precision. According to Flatt’s research, this becomes especially problematic at higher HRV levels, where many devices grow less reliable.

Most wearables measure your HRV overnight while you sleep, yet much of the foundational HRV research relies on more controlled testing conditions. Flatt, for example, uses a standardized one-minute standing test every morning wearing a chest strap—right after he uses the restroom because the sympathetic nervous system is active when holding the bladder—to get more consistent readings. (When you’re standing, you’re exposing your body to stress and seeing how it responds, unlike when you’re sleeping.)

How to use HRV without losing your mind

For all of HRV’s limitations, wrist and finger-based devices can still be valuable for identifying long-term patterns and significant deviations from your norm, even if day-to-day precision isn’t perfect. Flatt recommends that you take a casual approach to monitoring your HRV at first. Go in without expectations and just watch the numbers. If you get a low score, take note and reflect: Did you experience some type of stress that day? Poor sleep, two glasses of wine, an intense exercise class? Over time, you may start to see a pattern of behaviors that lead your score to dip.

Once you understand your normal range, Stephenson says that HRV can become one useful input among several other data points, like your sleep quality, your motivation, and how much energy you have. “Modern people in the Western world have just gotten bad at listening to their bodies,” he says. “Things like HRV or resting heart rate can almost help you recalibrate that sense.” If your HRV is unusually low, take a moment to assess how you feel. Perhaps you’re experiencing fatigue, and it would be wise to swap an intense pump for a yoga class. But if you’re excited and ready to train, don’t let a low number alone stop you.

And despite what the wellness optimization crowd may suggest, there’s rarely a magical shortcut to sustainably boosting HRV. The fundamentals remain relatively straightforward: better sleep, regular exercise, balanced nutrition, lower chronic stress, and less alcohol.

“What's nice is that once you see the lifestyle factors that reduce your values and the ones that improve it, it makes you realize—oh, that's why we should be doing those things that doctors have been recommending all this time,” Flatt says.

Of course, there’s also a limit to how strict most people actually want to be. HRV is highest and most consistent with “the most stable, boring, habitual routine that is completely absent of novelty and uncertainty,” says Flatt. And while understanding your body is useful, structuring your life entirely around maximizing a recovery metric raises an obvious question: At what point does optimizing your health start interfering with actually living it?