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.
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.
“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.
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.”
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.”
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.
“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.
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 .
“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.
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.
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.)
“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.
If you still have suboptimal HRV despite adopting healthy habits and trying to boost HRV, it’s a good idea to dig into the root cause(s). “Our practitioners may order additional tests (e.g., stool test, cortisol testing) to help uncover and guide treatment to optimize the member’s health which correlates with higher HRV,” Kang adds.
Amy is a freelance journalist and certified personal trainer. She covers a wide range of health topics, including fitness, health conditions, mental health, sexual and reproductive health, nutrition, and more. Her work has appeared on SELF, Bicycling, Health, and other publications. When she's not busy writing or editing, you can find her hiking, cooking, running, or lounging on the couch watching the latest true crime show on Netflix.