It seems like every year, there’s a new health stat or category that our beloved fitness trackers and smartwatches keep tabs on for us. As wearable technology gets better and better, we get to take an even closer look at the data that makes us tick. One of the buzziest these days: heart rate variability, or HRV. Tracking devices like Oura Ring and WHOOP have brought this stat to the forefront of health-conscious people everywhere. So, if you’re wondering, “What is heart rate variability and why should I care about it?” you’re definitely not alone.

Below, Christina Kang, health coach and nutritionist at Parsley Health, shares what you need to know about HRV, if you should track it, and what you can do to improve it.

What is heart rate variability?

Simply put, heart rate variability refers to the variation in time between each heartbeat. So instead of there being the same amount of time between every single beat, the time from one to the next varies. Variation is a good thing. In short, it’s a sign that the nervous system is working optimally.

Here’s how it works: “The autonomic nervous system (ANS) acts unconsciously and is responsible for regulating the function of various organs, glands, and involuntary muscles throughout the body such as heart rate, digestion, blood pressure, and breathing,” Kang says. “It is divided into the two branches: sympathetic (‘fight-or-flight’) and parasympathetic (‘rest-and-digest’).” While the sympathetic nervous system is referred to as the “accelerator” and the parasympathetic nervous system is referred to as the “brakes,” it’s not really that one always decreases if the other increases, Kang explains. It’s not linear. Rather, a balance of both inputs is what dictates an increase or decrease in heart rate as needed. This balance naturally causes variation between beats, Kang says.

“For example, immediately following aerobic exercise, heart rate recovery involves PNS reactivation while SNS activity remains elevated,” Kang says. So it’s not that one powers down and the other powers up, but that they both keep working in tandem and in the right amounts to keep the body working as it should.

What is a normal HRV? (And why your number isn't the whole story)

One of the most common questions people have after getting their first HRV reading: Is this good?

The honest answer is: HRV varies significantly by age, sex, fitness level, and even time of day. A number that's excellent for a 52-year-old recovering from burnout looks different from the baseline of a 35-year-old endurance athlete. Comparing yourself to population averages is useful context, but your trend over time matters far more than any single reading.

That said, here's a general reference for where most healthy adults land by age range:

• 20-29: 55-105ms. Strong parasympathetic tone; high resilience
• 30–39: 45–90 ms. Healthy range; declines naturally with age
• 40–49: 35–75 ms. Midpoint; lifestyle factors become more influential
• 50–59: 25–60 ms. Wider variance; hormonal shifts play a role
• 60+: 20–50 ms. Lower baseline typical; trend matters most

Note that most consumer wearables measure RMSSD (root mean square of successive differences), the most common short-term HRV metric. Values shown are general population ranges. Your device's reference charts may differ.

A few important caveats:

• Athletes typically run higher. Endurance-trained individuals often show HRV 20–30% above their age-matched peers — a sign of robust vagal tone developed over years of aerobic training.
• Morning readings are most reliable. HRV fluctuates throughout the day based on meals, stress, posture, and activity. Most wearables recommend measuring immediately upon waking, before getting out of bed.
• High HRV isn't always ideal. Extremely elevated HRV can sometimes indicate atrial fibrillation or frequent irregular beats. Context and consistency matter.

The bottom line: don't fixate on hitting a number. Focus on what's moving your HRV in the right direction, and what might be silently dragging it down.

Why heart rate variability matters

“Increased variation between heartbeats means that the ANS is balanced and capable of responding to a wide variety of stimuli in a resilient manner,” Kang says. “We encounter a relentless onslaught of activating and deactivating signals every day (fighting a virus, sleep deprivation, pollution, a good belly laugh with a friend), so the stronger our ANS is, the easier we can adapt to these situations.”

Heart rate variability is often used to measure fitness levels. In general, high HRV is associated with general fitness and sufficient recovery, and low HRV is associated with too much stress or overtraining. Kang explains it like this: “If a person’s system is in more of a fight-or-flight mode, the variation between heartbeats is low. If one is in a more relaxed state, the variation between beats is high. In other words, the healthier the ANS, the faster you are able to switch gears, showing more resilience and flexibility.”

HRV is important beyond just the gym, and can actually help us measure how we handle stress. Being chronically stressed is associated with lower HRV. So is being a perfectionist. “The balance is tipped toward the SNS and this elevates heart rate, resulting in less room for variation in between heartbeats,” Kang says. So knowing you have a low HRV might be the reason you need to finally incorporate meditation into your routine, or prompt you to pick up some other stress management habits, like regular exercise.

Low HRV is also associated with other not-so-great health outcomes, like worsening depression or anxiety, increased risk of death from several causes including cancer, diabetes, and cardiovascular disease, Kang says.

What causes low HRV?

Low HRV is your nervous system telling you something is off. The harder question is: what, exactly?

The most common culprits:

Chronic stress. When your body stays locked in fight-or-flight — whether from work pressure, relationship strain, financial worry, or just an overscheduled life — your sympathetic nervous system stays elevated. That leaves less room for the variation that signals resilience. If stress is your baseline, low HRV often is too.

Poor or insufficient sleep. Sleep is when your parasympathetic nervous system does its repair work. Cut it short, fragment it, or compromise its quality (alcohol is a major offender here), and your HRV will reflect it the very next morning.

Overtraining. High-intensity exercise without adequate recovery stresses the nervous system the same way chronic psychological stress does. Many athletes are surprised to find their HRV dropping during heavy training blocks despite doing "everything right." Rest is part of the training.

Hormonal imbalance. This one is underappreciated. Cortisol dysregulation, whether it's chronically elevated or blunted from prolonged stress, directly affects HRV. Thyroid dysfunction can suppress it too. For women, HRV naturally fluctuates across the menstrual cycle and often shifts meaningfully during perimenopause and menopause (more on that below).

Underlying health conditions. Persistently low HRV, especially alongside other symptoms, can be associated with anxiety and depression, metabolic dysfunction, and cardiovascular risk. It's not a diagnosis, but it is a signal worth investigating.

If you've cleaned up sleep, dialed in stress management, and your HRV still isn't moving, that's a sign to look deeper. Root-cause testing, including cortisol, thyroid, and other key biomarkers, can reveal what lifestyle changes alone can't.

HRV and women's health: what most trackers don't tell you

If you track HRV and notice it doesn't behave the way the charts suggest it should — especially if you're a woman — there's a reason for that.

HRV isn't static. It fluctuates throughout the month in sync with your hormonal cycle. In the follicular phase (the first half of your cycle), estrogen tends to support higher parasympathetic activity — meaning HRV often runs higher. In the luteal phase (post-ovulation), progesterone rises and heart rate increases, which can suppress HRV. This is completely normal. It's also why comparing week-one readings to week-three readings, or benchmarking yourself against population averages that don't account for cycle phase, can feel confusing or discouraging.

During perimenopause and menopause, this picture gets more complex. As estrogen declines, so does its protective effect on vagal tone. Many women see their HRV trending lower during this transition, not because they've done anything wrong, but because the underlying hormonal environment has shifted. Understanding that context changes what "improving your HRV" actually means at this stage of life. It's less about adding more cold plunges and more about addressing the root hormonal picture.

Hormonal imbalances — including high or low cortisol, thyroid dysfunction, and sex hormone disruption — are also among the most commonly missed reasons women have persistently low HRV despite healthy habits. If that resonates, it may be worth looking at the full picture through a comprehensive lab panel before adding more interventions to your routine.

Should you monitor HRV?

Data-driven people may find that tracking HRV can motivate them to work on improving it. For example, athletes use it to monitor their recovery and adjust their upcoming workouts to ensure they’re not overtraining, Kang says. Anyone experiencing chronic stress, HPA dysfunction (adrenal fatigue), or simply looking to optimize their health can also benefit.

“Often, we adjust to a new ‘normal,’ in that ‘normal’ can actually be suboptimal, but we don’t recognize that since it is how we feel every day and may have forgotten what it feels like to be in an optimal state of health,” Kang says. “Tracking HRV can be a more objective measure.”

Many fitness wearables make it easy to track HRV. Kang recommends the Oura Ring and Whoop. The Apple Watch and some Fitbits also have features to track HRV. A note on accuracy: no consumer wearable measures HRV with the precision of a clinical ECG. They're best used for trend-tracking rather than treating any single reading as definitive.

While HRV isn’t a one-for-one measure—having high HRV doesn’t mean you’re the picture of perfect health, and low HRV doesn’t mean you’re ill—it can help you measure trends and suggest that it may be time to make a healthy change. “For example, we see a lot of high-functioning people with HPA dysfunction, which is correlated with lowered HRV. For those with a proclivity towards empirical data, tracking HRV trends can be very impactful and reassuring that adopting certain behaviors (e.g., meditation) are truly helping them.”

How to improve your heart rate variability

If your HRV is relatively low, or you’ve noticed it decrease, there are some things you can do to modify it. Even if you don’t track your HRV, these tactics below can help you make sure yours is in a good range.

Get quality sleep

“Sleep deprivation puts the body in the fight-or-flight mode, increasing the stress hormone cortisol and raising heart rate,” Kang says. “A shift to parasympathetic dominance occurs during deep sleep. Furthermore, quality sleep is also a period of restoration and repair for the body so skimping on sleep can reduce the much-needed recovery processes that occur during this time.” By getting at least 7 hours of sleep per night (more if you feel you need it!), you can help your body decrease stress and maintain balance.

Do breathing exercises regularly

Deep belly breathing through the nose, focusing on longer exhales, can help activate the PNS and send signals (via the vagus nerve) to slow the heart rate, Kang says. “Multiple studies have shown that a respiration rate of six to 10 breaths per minute exerts beneficial, calming effects, but interestingly, six breaths per minute seems to be the sweet spot in maximizing HRV.” Here are some great breathing exercises to try.

Drink more water

“Adequate hydration promotes optimal circulation and delivery of oxygen and nutrients to your body,” Kang says. “Dehydration is also linked to reduced sleep quality, which indirectly impacts HRV.” There isn’t a one-size-fits-all recommendation for exactly how much water to drink each day, and the exact amount you need will vary based on your age, size, activity level, and how much you sweat. You can get water from both foods (like watermelon, lettuce, berries, and cucumber) and drinks. The best way to make sure you’re hydrated is to listen to your body.

Exercise regularly (and make time for rest)

Research suggests that exercising is one of the best ways to improve HRV. Kang suggests Zone 2 training to improve HRV over time. “In zone training, a person exercises within specified heart rate zones. This is commonly measured by a percentage of max heart rate (MHR). Zone 2 falls somewhere in the ~60-75% of MHR range,” she explains. The only way to measure MHR precisely is in an exercise lab, but Kang recommends using this as a general, albeit crude calculator: 220 – your age. “You can also use a perceived level of exertion, where you should be able to hold a conversation, but just barely.” Exercising in Zone 2 can help stimulate mitochondrial growth and function, which is paramount to metabolic health and longevity, Kang says.

But it’s also important to scale back on exercising when needed to give your body adequate time to recover in between workouts and to avoid putting more stress on the nervous system.

Decrease alcohol consumption

Alcohol can impact HRV very differently from person to person, Kang says. “Where one may be able to consume two glasses of wine at dinner whereas another may experience a drop in HRV with just half a glass.” But why does alcohol matter, anyway? “The impact on HRV may be due to indirect effects in that alcohol consumption generally reduces sleep quality and dehydrates the body, both of which are known factors to reduce HRV,” Kang explains. (Here’s a primer on the healthiest alcohol to consume.)

Try cold water immersion

“Any activity that stimulates the vagus nerve will promote the SNS,” Kang says. Cold water can do just that, and has been shown to accelerate post-exercise parasympathetic reactivation, she adds. One 2018 study published in JMIR Formative Research found that cold stimulation via a thermode instrument applied to the neck resulted in higher HRV. If you’re trying cold immersion, start slow, Kang says. You can even start by putting cold water on just your face. Then, try a 30-second bout of cold water in the shower. “The initial ‘cold shock’ will activate the SNS, but adaptation to the cold decreases it and increases the PNS. Over time, you won’t experience the ‘shock’ and you may see your HRV trending upwards,” Kang explains.

Frequently ask questions about heart rate variability

What is a good heart rate variability score?

There's no single "good" number — HRV varies by age, sex, and fitness level. Most healthy adults fall between 20–60 ms (RMSSD), with younger and more aerobically fit people often running higher. What matters more than any absolute score is your personal baseline and whether it's trending up or down over time. A consistent downward trend is worth paying attention to.

Can you improve HRV quickly?

Some interventions — like slow, controlled breathing and adequate hydration — can nudge HRV upward in the short term. But meaningful, sustained improvement typically takes weeks to months of consistent changes: better sleep, regular Zone 2 exercise, stress management, and reduced alcohol. There's no shortcut that substitutes for the fundamentals.

Does HRV change with age?

Yes. HRV naturally declines with age as autonomic nervous system function changes. That said, the decline is far from inevitable — research consistently shows that lifelong aerobic exercisers maintain significantly higher HRV than sedentary peers of the same age. Staying active matters more here than almost anything else.

What does low HRV actually mean?

Low HRV means your nervous system has less flexibility to respond to demands — it's spending more time in a stressed, activated state than a recovered, regulated one. Common causes include chronic stress, poor sleep, overtraining, hormonal imbalance, and certain health conditions. It's not a diagnosis, but it is a signal that something in your system deserves attention.

Is high HRV always a good sign?

Generally, yes — but not always. In healthy people, high HRV reflects strong parasympathetic activity and good recovery. In some cases, an unusually high or erratic HRV can reflect an irregular heart rhythm like atrial fibrillation. If your HRV suddenly spikes and feels inconsistent with how you feel, it's worth checking with a clinician.

How does HRV relate to stress?

HRV is one of the most sensitive biological markers of stress. When you're under chronic stress — psychological or physical — your sympathetic nervous system stays elevated, which reduces variation between heartbeats. This is why HRV is increasingly used as an objective way to measure whether your stress management practices are actually working. If meditation or breathwork is genuinely helping, you'll often see it in your HRV trend before you feel it.

Improve your HRV with Parsley

If you've made real changes — sleep, exercise, stress, alcohol — and your HRV still isn't responding, that's information. It usually means something upstream needs attention: cortisol dysregulation, thyroid dysfunction, metabolic issues, or other biomarkers that lifestyle changes alone can't fix.

Parsley's Longevity Labs panel tests 80+ biomarkers, including cortisol, thyroid markers, and key metabolic indicators, with a live clinician review included. It's the clearest picture of what your body is actually doing underneath the data your wearable is tracking. Sign up for labs here.