What Is Heart Rate Variability (HRV)?

Heart Rate

People are always looking for that one biomarker to rule them all, the number on a paper that absolutely determines your health, longevity, fitness level, sex appeal, happiness, and productivity. Throughout the years, it’s bounced around as researchers think they’ve found “IT”— from LDL to BMI to ApoB to CRP to blood pressure to A1c and back again. But we always come up wanting. The “one biomarker” never pans out because biology is complex and irreducible to a single number.

However, there is one biomarker that shows promise as a broad indicator of overall health and fitness: heart rate variability (HRV). In today’s post, I’m going to provide an overview of HRV—what it is, what makes HRV “good” or “bad,” why you should seriously consider tracking it, and how to get started. 

What is Heart Rate Variability?

HRV measures the variation in the intervals between heartbeats. If your heart beats like a metronome, with intervals of identical length between each pulse, you have low heart rate variability; this is “bad.” If your heartbeats follow a more irregular pattern, with beat intervals of varying length, you have high heart rate variability; this is “good.”

This probably sounds counterintuitive. Most people assume that a steady, consistent pattern of heartbeats is the healthiest. I mean, doesn’t the human body need a steady, consistent flow of blood and nutrients to its cells and tissues? But recall the musician’s lament about the drum machine: that it “has no soul.” The perfect metronomic unfoldment of the drum machine is too perfect. It’s robotic. It’s unnatural. Same with our hearts. A healthy heart (with soul) pumps as needed. It responds to the demands of the organism. It doesn’t follow preordained intervals.

In general, a high HRV indicates dominance of the parasympathetic response. Recall that the parasympathetic response side of the autonomic nervous system promotes relaxation, digestion, sleep, and recovery. The parasympathetic nervous system is also known as the “feed-and-breed” or “rest-and-digest” system.

A low HRV indicates dominance of the sympathetic response, the fight-or-flight side of the nervous system associated with stress, overtraining, and inflammation.

Therein lies the beauty of HRV: it offers a glimpse into the activity of our autonomic nervous system, the gatekeeper of so much of our endocrine function and, hence, the immune system, digestive system, reproductive system, and more. 

Why Track HRV?

I never really hopped on the self-quantification train, but I can see the value in measuring daily HRV. HRV essentially reflects how your nervous system is doing: how much stress you’re under from all possible sources and how your body is coping. To put it in the simplest possible terms, when HRV is high (more on what that means shortly), your body is rested, recovered, and not overstressed. When it’s low, it means you’re not doing so hot. You might be fooling yourself into thinking you’ve got things under control—the new project at work, the broken washing machine at home, the dog that needs to be taken to the vet, the 10k you’re training for—but your HRV tells the real story.  

Cardiac specialists have been using HRV for decades to track the health and recovery of their patients. The data consistently show that low HRV is a risk factor for disease and mortality.

  • Low HRV is associated with the development of coronary heart disease and multiple metabolic syndrome (diabetes, hypertension, high cholesterol).1  2
  • Low HRV is prevalent in people who’ve had heart attacks, and among patients who’ve had a heart attack, those with low HRV are at a higher risk of dying in the subsequent three years.3 4
  • Among the elderly, a high HRV is strongly associated with “healthy longevity,” or the kind of graceful aging relatively free of morbidity that we all desire.5

The most enthusiastic proponents are in the fitness world. This is where much of the research takes place, and it’s where endurance athletes, pro footballers, Olympians, CrossFitters, and other high-performing athletes use HRV monitoring to track their rest and recovery periods,6 pinpoint optimal training and competing times,7 and avoid overtraining.8 

But HRV isn’t just for elite athletes or cardiac patients. For the average person, HRV offers a metric to track your total stress load. Anything that stresses you, whether that’s physical (a hard workout, coming down with a cold, having a couple drinks after dinner) or mental (an argument with a friend, a sick parent) will be reflected in a lower HRV. 

How to Measure HRV

If this information has piqued your interest in tracking HRV, it’s easy to get started. There a few ways to measure your HRV:

  1. Sensor + app: Use a heart rate monitor chest strap (Polar and Wahoo are two popular and reliable brands) or finger sensor like the one made by iThlete to connect to an app (of which there are many options). In terms of pros and cons, chest straps have long been considered the most accurate way to measure HRV, although wearables (see below) are constantly improving their hardware and algorithms. With straps, you have to attach the device each morning and follow a protocol to get reliable readouts. You’ll also have to buy the sensor, which you might only use for this purpose, although you could also use a heart rate strap to ensure your aerobic training is really aerobic.
  2. Wearable health and fitness devices like the Oura ring, Whoop band, or Fitbit provide HRV along with tracking sleep, activity levels, and other health indices. So do most smartwatches (Apple, Samsung, Google) now. Since you probably have at least one of these devices already, you might as well start using it to track HRV.
  3. Some apps measure HRV using your smartphone camera via a process called photoplethysmography (PPG). This can be accurate if you follow the correct protocol as outlined by whatever app you are using (similar to using a heart rate strap), and it doesn’t require you to purchase any additional technology except perhaps the cost of the app.

At this point, any of these options will probably suffice for the average person wanting to track their recovery or general fitness. The important thing to remember about measuring HRV is that you want to test daily at the same time under the same conditions. Checking HRV first thing in the morning upon waking, before coffee, breakfast, or the day’s stresses commence, is the most effective time to test. If using a sensor plus app setup, the test will take just a couple minutes max. If using a fitness tracker, it will sample your HRV automatically throughout the day and as you sleep and record it in the app. 

In a short time, you will have established a baseline value/normal range for HRV, and the app will have plotted a graph of your HRV history that you can refer back to against your workout/health history. Remember that really awful week of 12-hour work days as the quarter ended? It’ll probably show up on your chart as a week of low HRV. Or how about that deload week you finally managed to take last month? That’s why your HRV was remarkably high. 

What Constitutes a Good (High) or Bad (Low) HRV?

I’d love to provide you with a simple HRV chart that could tell you if your HRV is “good” or bad,” but HRV doesn’t work like that. There isn’t a single benchmark against which you can compare yourself for a couple of reasons. First, there are multiple methods of measuring HRV, each calculated differently: rMSSD, the log of rMSSD, SDNN, LF/HF ratio, and others. Different apps use different methods, and many also have their own way of converting raw scores into something more intuitive. 

For example, a lot of fitness trackers use ln(rMSSD), which provides raw values typically in the range of about 2.9 to 3.8. Then they multiply by some value to create a score on an approximately 100-point scale… but they don’t all use the same formulas. So if you were to ask me, “Hey Mark, my average HRV for the past week has been 58. Is that good or bad?” I couldn’t say exactly. That 58 isn’t inherently meaningful, not without knowing exactly how it was calculated.

Moreover, average HRV varies by sex and age, with older folks typically being lower than younguns. Athletes, or people who train a lot, usually have higher HRVs than their less active peers. Thus, if you want to know if your HRV is “normal” or “above average,” you’ll have to compare yourself to a group of the same sex and age, similar activity/fitness level, and using the same HRV measurement. (The app or tracker you’re using might publish user data, although it’s often not broken out by activity level.) 

Rather than worrying about what’s normal for everyone, though, it’s more valuable to compare yourself against yourself. Sometimes extremely healthy folks have chronically “low” HRVs, and vice versa; that’s just their individual baseline. 

Track your HRV for a month or two. Get to know your average and what types of things move your HRV up or down on a daily or weekly basis. Then, when you see your HRV slipping below your own personal normal, you can take steps to increase it.

Using HRV to Tap into Intuitive Health and Training Decisions

What excites me most about HRV is its potential to encapsulate the Primal Blueprint spirit of using both modern technology and ancient primal intuition to attain optimal health and performance. Some people have that intuition dialed in; they may not need a chest strap monitor to tell them they’re overtrained or stressed out. But not everyone can do that, and by getting objective biofeedback, they can learn more about how their body works.

Anyone looking to self-experiment with HRV should spend a month or two recording daily HRV as well as subjective ratings of daily energy levels, motivation levels, health/immune function, stress levels, and sleep quality. See how your subjective ratings align with your objective HRV. (Side note: If your app allows you to journal or add tags, this feature can be invaluable in discovering the factors that drive your HRV up or down.) Ideally, you’ll start to draw connections between your behaviors, your environment, how you’re feeling subjectively, and what your HRV is telling you about your stress load. 

One interesting benefit I’ve personally noticed from measuring HRV: if I get a low (for me) HRV rating in the morning, I find myself actively and subconsciously calming myself and relaxing during the day. Dr. Ron Sinha, who uses HRV monitoring in his patients with metabolic syndrome, told me this might happen on a podcast once.  I’ll start breathing more deeply, get a lid on the racing thoughts, maybe go a little easier in my workout that day, and just generally slow down. 

And it works! (A study in musicians suffering from performance anxiety also confirms it.9) You know how when you’re driving and come across a speedometer on the side of the road flashing your speed, you automatically slow down and moderate your driving for a while after? The HRV monitoring had a similar effect for me. I found I was more tuned in to my stress levels and more prone to take steps to mitigate potential issues when I had tomorrow’s HRV readings to hold me accountable in a way.

Here’s an example: Shortly after a lively Sunday Ultimate Frisbee match, I tested it. As any regular Ultimate player knows, these are high-intensity and long-duration games; they’re pretty darn demanding. Predictably, my HRV was on the lower end after the game, indicating a need for rest and recovery.

The following morning, as I nursed the usual soreness, my HRV had improved from my immediate post-match score but was still low enough to indicate that I should be in rest and rebuild mode.

Tuesday, things were almost back to baseline, so I kept things light and went for a couple walks. Nothing strenuous.

By Wednesday—which is usually when I hit it hard with a high-intensity gym circuit—my HRV scores had recovered, giving me the green light to go for it. And sure enough, I had a productive session. I shudder to think how incredibly beneficial it would have been to have this technology by my bedside when I was cranking out 100-mile marathon training weeks come hell or high water back in the 70s and 80s. Maybe I’d still be running marathons today… or not!

Bottom line: I see HRV as a valuable tool for monitoring and managing not only athletic performance and recovery, but for general health, stress resilience and reduction, and productivity. It shouldn’t replace your intuition when it comes to these things, but it can complement your subjective self-awareness so you can make better-informed decisions. 

Have you tried monitoring HRV? Did you find it useful? Or are you of the mind that HRV monitoring is useless? Let us hear about your thoughts and experiences in the comment section!

TAGS:  hrv

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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