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 cholesterol to LDL to BMI to small dense LDL to CRP to blood pressure to pulse rate 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 showing promise as a broad indicator of overall health and fitness: heart rate variability (HRV), or the variation in the intervals between heart beats. 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 heart beats follow a more fractal 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 heart beats 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, the side of the autonomic nervous system that promotes relaxation, digestion, sleep, and recovery. The parasympathetic system is also known as the “feed and breed” or “rest and digest” system.
Surprisingly, and perhaps counterintuitively, a high HRV score – greater variability in the time gap between heart beats – indicates a healthy, fit, well-rested heart. Elevating your average HRV values over time is indicative of improved cardiovascular fitness. A low HRV value (a heart beating closer to a fixed rhythm, such as one second apart in the example) is believed to be an indication of a poorly functioning heart–perhaps an overtrained athlete or a person who is unfit, overstressed, or has developed cardiac disease risk factors. By tracking HRV regularly, one can establish a baseline value and then be alerted to excessive stress or insufficient recovery when HRV readings are lower than normal.
If this information has piqued your interest in trying HRV, it’s easy to get started. You will need some equipment to get the best results. It’s difficult to track your heart rate variability without a sensitive instrument because the variations are relatively slight and to the naked eye (or ear, or finger) might look or sound perfectly linear. A finger on a pulse doesn’t quite do the trick.
Here’s what you’ll need to get started right away:
A heart rate monitor. Either get a chest strap (more accurate, more expensive) or a finger sensor (slightly less accurate, less expensive). Try to go for a Bluetooth-enabled model, like the Polar H7, Zephyr HxM, or Wahoo Chest Strap.
Heart rate variability smartphone app. Check to make sure your monitor is compatible with the app before you buy it. iThlete and Bioforce seem to be the most popular apps; both are available for Android and iOS. SweetBeat is another popular choice.
If your heart rate monitor isn’t Bluetooth enabled, you’ll also need an ECG receiver that connects to the monitor and plugs into your phone.
Begin your n=1 odyssey by monitoring HRV with a daily test at the same time under the same conditions. Traditionally, 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. The test will take just a couple minutes and the values will be recorded by the app. Do this every day. 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.
If you want to check this concept out without spending any money on fancy equipment, download the free “Stress Check” app for iOS or Android. This app seems to deliver some reasonable data with a simple percentage score equating with your supposed stress level. e.g., I tried it after an easy cardio workout and I was at 35% (labeled “moderate stress”). An hour later, working in the office, I was at 18% (“low stress”). After a short afternoon nap I was at 3%. Realize that app doesn’t give you a proper HRV value like the SweetBeat app (which requires a chest strap transmitter to process data). It’s likely they are creating a simple percentage score inverse to the HRV value that they are taking an educated guess at from your pulse rate.
As mentioned in detail in the Primal Blueprint 90-Day Journalabout general self-experimentation, anyone looking to self-experiment with HRV should track subjective 0-10 scores in daily energy levels, motivation levels, and state of health/immune function and try to calibrate these scores with the degree of difficulty of your workouts. I’d venture to guess that if you are well aligned with these subjective scores, you will see a pattern emerge with favorable corresponding HRV scores. Conversely, if you’re drifting toward or locked into a chronic exercise pattern or period of high stress, low HRV scores should follow.
I’ve been following the HRV fitness literature for years with great interest, but until recently had yet to really pursue it on a personal level because, well, I’m no longer a high-performance athlete. As I did more research in preparation for releasing the certification, however, I realized it had broader applications that applied to just about everyone.
So lately, I have been testing HRV and can attest to its value. 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 immediately 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 or interval cycling session – 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….NOT!
One interesting non-fitness benefit I’ve personally noticed from measuring HRV: if I get a “high-stress” reading on the monitor, I find myself actively and subconsciously calming myself and relaxing. Dr. Ron Sinha, who uses HRV monitoring in his patients with metabolic syndrome and covers the topic extensively in The South Asian Health Solution, told me this might happen on our podcast a while back. I’ll start breathing more deeply, get a lid on the racing thoughts, and just generally slow down. And it works! I know it works because the instant feedback allows me to see the effects of my response in real time (and a recent study in musicians suffering from performance anxiety also confirms it). You know how when you’re driving and come across a speedometer on the side of the road flashing your speed, you immediately slow down and moderate your driving for awhile after? The HRV monitoring had a similar effect for me.
Simon Wegerif, founder of iThlete and one of the driving forces in creating affordable HRV measuring technology, says HRV is so accurate that you can essentially override your intuitive signals and get your butt out there even if you don’t feel like it. I’ve heard exercise scientists offer similar nuggets for many decades, things like “prick your finger and get a blood lactate value that will dial in the proper workout that day.” That’s the “better living through chemistry” argument, and while I totally respect exercise science and am super enthusiastic about HRV being a huge breakthrough in tracking overtraining and burnout symptoms, I can’t downplay the value of intuition and subjective variables when making training decisions. Every single elite athlete I’ve coached or known, in any sport, has shared a similar point of view. So I caution you against getting overly obsessed with technology and being robotic in your approach, even if you are honoring HRV and going easy when mandated by low values. Use both your gut/intuition/subjective impression of how you feel and the objective measurements of the HRV monitor to make decisions and optimize your training and health. After all, the indomitable human spirit of Rocky Balboa and his raw training methods were still able to knock out the laboratory perfected robo-athlete Ivan Drago in the famous boxing documentary Rocky IV!
What excites me most about HRV is its potential to encapsulate the PB 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 that instant objective feedback, they can learn more about how their body works.
I’m interested to see where HRV monitoring can help, not just in athletic performance and recovery, but for general health, stress resilience and reduction, and productivity. I think I’ll be playing around with HRV more and more, and I hope to report back in the near future.
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!
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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.