Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
7 Oct

Have You Checked Your Heart Rate Variability Lately?

Heart RatePeople 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.

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, an aspect of our physiology normally shrouded in mystery.

That’s why cardiac specialists have been using HRV for decades to track the health and recovery of their patients, and it’s why HRV is a predictive indicator of overall heart health, risk of heart attack, and other cardiac events. For instance, low HRV is associated with the development of coronary heart disease and multiple metabolic syndrome (diabetes, hypertension, high cholesterol). 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. Among the elderly, a high HRV is strongly associated with “healthy longevity,” or the kind of graceful aging relatively free of morbidity we all desire.

But the most enthusiastic proponents (and much of the research) are in the fitness world, where endurance athletes, pro footballers, Olympians, CrossFitters, and other high performance athletes use HRV monitoring to track their rest and recovery periods, pinpoint optimal training and competing times, and avoid overtraining. To understand why top athletes are finding HRV so valuable in their training and performance, read the following excerpt from Module 7 (“Exercise is Ineffective for Weight Management”) of the Primal Blueprint Expert Certification:

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 H7Zephyr 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 Journal about 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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  1. This is new to me so I’ve never tried it, but it’s definitely interesting. I’ve only tracked my heart rate while running to get into the training zone I want to be in and I really have no idea what my heart’s doing the rest of the day. Thanks for the info and additional resources.

    Michele wrote on October 7th, 2014
  2. I’m just glad the ticker’s beating!

    Groktimus Primal wrote on October 7th, 2014
    • +1

      Shary wrote on October 8th, 2014
  3. What? An hour and a half after the article’s been released and only one comment? Where’s the usual suspects? 😉

    On a different note, am doing PBE and this article’s a day late for the module, already did the test.

    Cody wrote on October 7th, 2014
  4. Thanks for this article! I’m really interested in using HRV to determine my monitor status.

    I’ve been using the “Stress Check” app on my Android phone for a while now. It’s easy to use and seems to give generally good information. It reports low percentages when I know I’m calm, and higher percentage readings after exercise. There are times though when I feel stressed but this app reads “low”, so perhaps it could be more sensitive? Also, the app only saves data to the author’s web page, so if you’re not into sharing you need to write down your readings to get any trends.

    Ralph wrote on October 7th, 2014
  5. I’ve been using HRV for almost a year at the suggestion of my trainer and have found it very beneficial for planning effective work outs and for recognizing when stress may be coming from something other than physical exertion. One thing I’ve learned (it was a little surprise) – even when I’m “green 10,” it doesn’t always mean that a hard work out, which I’m fit to do, feels easy.

    Susan wrote on October 7th, 2014
  6. Android users might want to search the Play Store for “Elite HRV” and “My HRV Beta”, both are free and work well with the Polar H7.

    Martin wrote on October 7th, 2014
  7. This is very interesting. My boyfriend worries so much about his heart. He also exercises somewhat chronically and inefficiently. He might be interested in this. Maybe I FINALLY found a good Christmas gift for him he won’t think to buy himself.

    Diane wrote on October 7th, 2014
  8. More attention needs to be drawn to this as the heart rate variability issue is so overlooked by people training.
    Sometimes a ‘balls to the wall’ approach is not ideal and this stresses the importance of recovery.
    The best thing you can do for the benefit of your fitness and health is to know where you’re at in regards to measurements like this
    -Jamie

    Jamie Logie wrote on October 7th, 2014
  9. Does this relate at all to premature ventricular contractions (PVCs)? They’re so common in a lot of people. If there are no known underlying causes, is this just an extreme version of high HRV… and therefore a good thing?

    Kate wrote on October 7th, 2014
    • I think this is something completely different.

      Harry Mossman wrote on October 7th, 2014
  10. I’ve never tried this, would love to give it a go. I can see how it would be good for stress reduction if you were aware of all the little things that sent you a bit erratic.

    Mark wrote on October 7th, 2014
  11. Glad there’s more attention being paid to HRV. When I was in Biology 2 in high school, a friend was checking my pulse and noticed that it would speed up and slow down quite a bit. She mentioned it to the teacher, whose response was that I probably had a heart problem and should have it checked by a doctor. What a relief to find out it was a *good* thing….

    KevvyB wrote on October 7th, 2014
    • HRV isn’t the same as your pulse rate…it’s the time between each beat. Say your pulse is 60 beats per minute. You might think ok…1 beat for second but that would actually give you a horrible HRV score. The beats would be at 0.83, 0.99, 1.02, 0.79 fluctuating like that. The more chaotic the better your HRV score.

      Linda wrote on October 21st, 2014
    • A pulse which speeds up and slows down erratically for no reason (eg, if you’re just sitting still) is indeed a medical issue. It’s called atrial fibrillation (AF). Not to freak you out, but it is a leading cause for strokes. Instead of NSR (Normal Sinus Rhythm), when someone is in AF the atria (top part of heart) is quivering instead of beating rhythmically. This causes blood flow to be somewhat erratic, which can cause blood clots (particularly in the LAA – Left Atrial Appendage).

      But don’t freak out. You’re not going to drop dead in a matter of minutes (as with VF, Ventricular Fibrillation). But you should definitely see a MD.

      With some people, AF is very infrequent (it goes away on its own and rarely happens). In that scenario, no medical intervention is needed. But if one is in AF a lot (or constantly), then medical intervention (Rx, or catheter ablation) is recommended.

      Ted wrote on July 16th, 2015
  12. I have downloaded the android app – I am investing in grass fed, no budget for new gadgets – but, wanted to try.
    I have been thinking for a while that my work environment is kinda too stressful…but I did not expect to measure 84%.
    So I went outside, to sit in the green, kick off the heels, put my bare feet in the grass, breathe some air – down to 40% in minutes. Come back in the building – 56%. 10 minutes in front of my computer – back to 80%.
    Thank you! I know I need to do something to relax and get rid of this stress. Yoga class, here I come!

    Monika wrote on October 7th, 2014
  13. With the ‘hustle & bustle’ of today’s ‘modern’ world I believe most of us are not quite ‘connected’ to our bodies. Using HRV could be a great way to learn to ‘reconnect’ and live the way we are meant to, intuitively. Will definitely investigate this further!

    Brynn wrote on October 7th, 2014
    • Go low-tech! Several hundred years ago one of my ancestors was reported to have monitored his “heart rate” by grinding green tea!

      SumoFit wrote on October 7th, 2014
  14. No mention of the emWave??? Mark, do you have an issue with this product?

    Lee wrote on October 7th, 2014
  15. This is very intriguing to me; thanks so much for posting this! Back in the 90’s I did a couple of workshops at the Institute of HeartMath, in Boulder Creek, CA, where I was introduced to the science of measuring HRV as an indicator of emotional health. I learned a simple exercise that brings your focus to that of appreciation and gratitude, which can then be measured via HRV. This way you can train yourself to reduce emotional stress as soon as you become aware of it. However, I was not at all familiar with using this to monitor the effects of training and avoid over-training. As I get older (I am 54) this feels more important.

    Lisa Wolfe wrote on October 7th, 2014
  16. This is a really awesome article. I’ve been told by doctors that I have a “good heartbeat”, but recently as I worked out more and checked my heartbeat more I’d been noticing that my heartbeat doesn’t seem regular like I expected. I was a bit worried about it(but didn’t go to a doctor since I’m 25 and have never had trouble), but this article makes me feel great!

    M wrote on October 7th, 2014
  17. w00t, my HRV has long been high! I’m going to have a pint of B&J tonight!

    Rick wrote on October 7th, 2014
  18. I have been using it for awhile and feel like it guides me as well. Can’t wait until it gets baked into Apple’s HealthKit or Android Wear and their smart watches!

    Dr. Anthony Gustin wrote on October 7th, 2014
    • Can’t wait til there’s an app for windows phone. 😛

      Darcie wrote on October 8th, 2014
      • We’ll be releasing on Windows phone and Windows 8 likely be year end.
        Cheers! :)

        Jason wrote on October 9th, 2014
        • great, looking forwards to it 😊

          chris wrote on February 21st, 2015
        • Is there a windows phone app for this yet? looking to track my HRV with a bluetooth heart monitor.

          ronan wrote on May 28th, 2015
    • Mmmmm, baked apples.

      Joshua Crosby wrote on August 12th, 2015
  19. Mark, Dr. Sinatra suggests that grounding (earthing) has a beneficial effect on HRV. I know you like to sink your feet in the sand on a regular basis, but you could get your hands on a grounding sheet and use it during sleep. Looks like you are tracking your baseline already, but it would be interesting to see if grounding affects your baseline even further. I use a grounding sheet every night, and my HRV is fantastic – suggesting that constant low dose voltage might be a source of stress on our bodies.

    t-bone wrote on October 7th, 2014
  20. HRV has been used and deeply studied in connection with managing stress and even in mapping possible coherency of heart rates across the planet when major global events happen. The place to learn about it and get lots of useful free stuff related to stress management is the Heart Math Institute. Holistic meet Science!

    Kay wrote on October 7th, 2014
  21. This is a bit reassuring. Sometimes I feel my pulse with my fingers or watch my veins twitch and I seem to have high HRV and it used to somewhat worry me. I guess I’m better off than I thought. I also guess I should still be worried when it’s brought on forcefully or artificially like by a lot of caffiene, which has given me minor palpitations plenty of times. Generally that would happen from caffeine when I gulp or chug back excessive strong coffee without pacing myself so I can stop drinking it at a smart time.
    As long as I don’t go past my comfort threshold by pushing myself too hard or ignoring my signals to take it easy I enjoy the feeling of my heart going all out during / after something strenuous like carrying stuff up a hill.
    I think all the (usually a bit more than) moderate drinking I’ve done and cacao I’ve eaten have helped my circulatory system a bit.
    I got bloodwork done fairly recently and once again, this from another hospital, exactly what I was told was, “Everything is great.” The doctor looked a bit puzzled when he said so since apparently I was possibly on the verge of death the night before when I was passed out and had stopped breathing due to a pyschoactive and alcohol overload and was hooked up to a respirator. Well surprise surprise, if the most notable difference in my lifestyle in the last few years is eating better and not much else has changed, it makes sense I’d get a bit more indomitable and apparently have a decent buffering and cleansing/purifying ability.

    Animanarchy wrote on October 7th, 2014
  22. I have been using this product for a few months now. It is the future in human performance monitoring. Medical grade ECG at a consumer price. It tracks HR, respiratory, temp and movement. Wear it when you sleep and it illustrates exactly how your sleep patterns are going through the night. Wear it when you train and you can see if you are breathing correctly. So many uses.

    Dave wrote on October 7th, 2014
  23. As someone who is currently a Ph.D. candidate in physiology, and is studying HRV, I’d like to point out that low HRV is not necessarily only due to an increase in sympathetic tone. It could also be due to a decrease in parasympathetic tone as well. In addition, I found your description of high HRV rather interesting as humans are predominantly parasympathetic in nature, so perhaps normal instead of HRV would be a better term. Nonetheless, it seemed like you most of the bases and it’s good to see the individuals other than doctors and scientists begin informed on the topic, as it is a valuable indicator of ones well being.

    Isabel wrote on October 7th, 2014
    • Well put. I was waiting for this response. I’d like to add that heart rate variability is really a nonspecific “broad-band” measurement of a lot of good things. HRV has been linked to cognitive ability, executive function, social skills, and anxiety.

      Cara wrote on October 8th, 2014
  24. I did have an unexplainable heart arrhythmia a few years back, when I was following a standard diet high in all the crap the “experts” recommend, and I was doing daily chronic cardio running – I was doing all “the right things”, yet all health indicators were showing the reverse !. The long distance running for me definitely set of, and probably created, my heart arrhythmia.

    Four years later on the primal blueprint plan, my arrhythmia has actually disappeared. I have a varying heart rate, but not arrhythmia’s any more – I knew about the fractal thing with the heartbeat because I plotted my own one, and strangely found a correlation with fractal patterns in nature, and the share market – an unnaturally regular pattern in natural systems almost always precedes a “chaotic” change. I also gear all my training and eating to a “fractal” approach, with no set times or amounts – I even run/lift in a fractal pattern of fast and slow / heavy vs plyo’s – I like the PB as it basically follows the whole idea of the “fractal” approach, a seemingly random order, but with an overall governing pattern.

    This proved to myself that the primal blueprint methodology really works. My blood pressure has consistently dropped each year I have been on the PB, despite my doctor being “perplexed” that my BP should be rising year to year because I’m hitting my mid-40’s, and the “unexplainable” arrhythmia has gone.

    Yes, I’m “switching off my targeting computer” – but I’m ok

    Storm wrote on October 7th, 2014
  25. This is FASCINATING! Now I want to know how my heart is doing. :)

    Wildrose wrote on October 7th, 2014
  26. I don’t believe the StressCheck app…I measured 4 times in a row 85%-11%-100%-8% .Hahaha…

    Sam wrote on October 8th, 2014
  27. A few years ago, I was connected to a machine at work by a consultant teaching stress management. From memory, it was connected to my ear lobe! It was strangely accurate at recording stress, which was quite fascinating and eerie. A friend of mine said he wouldn’t connect as it was some form of mind control. I like the idea and have thought of it ever since, but not on my current budget. I don’t even have a smart phone. I have to be the smart one in my phone relationship.

    Kit wrote on October 8th, 2014
  28. I am a BioForce HRV Certified Pro Trainer and am currently working towards my Primal Blueprint Expert Certification. My plan and one of the many reasons I decided to take the PB certification was to incorporate HRV monitoring in to my and my clients training and overall lifestyle. I am very excited about using HRV monitoring to help people make better choices in regards to stress management, training, rest and recovery. I will be tracking and commenting on my own N=1 experiment with HRV & The Primal Blueprint first with a 21 day Transformation Challenge, then continuing through my 90 Day Journal and beyond. It will be very interesting to see how making Primal choices affect my HRV and overall health.
    One interesting thing I learned was that people with a high(good) HRV score make better choices when it comes to food and lifestyle.

    Tom Taylor wrote on October 8th, 2014
  29. check out hrvtraining.com and a few podcast of Ben Greenfield interviewing Ronda Collier. Although I can’t stand Dave Asprey he does have some good interviews and one of them is Ronda Collier. and these too http://hrvtraining.com/2014/08/19/hrv-monitoring-podcast-episode/

    Butch wrote on October 8th, 2014
  30. Hi Mark and all,

    You might want to check out the book:

    “The Pulse Test” by Arthur Coca, MD 020108.coca.pdf — On Web.

    He talks about using elevated heart rate to indicate food allergies. His procedure is well documented in this book.

    I have been most interested in testing myself, but have been too cheap to buy hardware and to lazy to build it.

    Maybe you can suggest some cheap hardware for us lazy New Englanders.

    warm regards,

    John

    John wrote on October 8th, 2014
  31. DHEAS is also one of the most popular aging and health biomarkers, though relying only on one parameter can be decieving.

    And about HR, I recently watched a talk by a prominent neuroscientist who said that reducing the whole spectrum of HR to an average of 70 bpm is like reducing a Mozart masterpeace to an average of the tone Do. Word.

    Sandy wrote on October 8th, 2014
  32. Mark, thanks for this fantastic post!

    As a PhD candidate who uses various fractal analysis methods on time series data, I’d like to offer one quick clarification. Biophysical systems with a fractal (often multifractal) pattern are more like the old Goldilochs and the Three Bears metaphor…there is a sweet spot where the pattern is not too simple and not too complex, but just right.

    A diseased heart may display both very low and very high fractal dimension as measured by interbeat HRV. A healthy heart beats with enough complexity it can adapt to stressors but not so much it moves from “order at the edge of chaos” into complete noisy disorder. Both too simple and too complex are maladaptive and suggestive of dynamical disease.

    I haven’t had time to review or test any of these smartphone apps as they integrate with the bluetooth heart rate monitors. But suffice it to say that if they are simply “creating a simple percentage score inverse to the HRV value that they are taking an educated guess at from your pulse rate,” then they are not giving an accurate and complete picture of the health of your heart as a dynamical system.

    Fractal Physiology and the Fractional Calculus: A Perspective
    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3059975/

    As excerpted from the above article, “excursions outside [i.e., too low and too high] the narrow interval of fractal dimension values for apparently healthy individuals may be indicative of hidden pathologies.” And this seems to apply to all sorts of biophysical systems as evidenced in time series for heart rate variability (HRV), stride rate variability (SRV), breathing rate variability (BRV), cerebral blood flow (CBF), neuronal activity, etc.

    “Classical control theory has been the backbone of homeostasis, but it is not sufficient to describe the full range of variability in HRV, SRV, and BRV time series, and the variability in other physiologic networks, since it cannot explain how the statistics of these time series become fractal, or how the fractal dimension changes over time…The well-being of the body’s network of networks is measured by the fractal scaling properties of the various dynamic networks and such scaling determines how well the overall harmony is maintained. Once the perspective that disease is the loss of variability (complexity) has been adopted the strategies presently used for combating disease must be critically examined.”

    “The biological advantage of multifractal processes is that they are highly adaptive, so that in this case the brain of a healthy individual adapts to the multifractality of the inter-beat interval time series. Here again we see that disease, in this case migraine, may be associated with the loss of complexity and consequently the loss of adaptability, thereby suppressing the normal multifractality of CBF time series.”

    So all this said, and as usual for Mark and his worker bees, the Primal lifestyle is leading the way into a healthier paradigm for humans and the Earth. Just as Mark (and Nassim Taleb) suggests, introduce a degree of randomness into your life. Don’t cycle the same path everyday in your daily bike commute. Don’t eat all of your meals at approximately the same time everyday. Don’t fast on a schedule…do it intermittently. Etc., etc.

    Hal Knowles wrote on October 8th, 2014
  33. I’m of the mindset that less is more. I don’t need another piece of technology to tell me how “good” or “bad” things are. I just listen to what my body tells me.

    James wrote on October 8th, 2014
    • In general I agree with you but sometimes body’s signalling could be off or misconstrued unless you have really honed this skill. I stay away from devices in generally but HRV is too important to be left to ‘I will just feel it’.

      Nitin wrote on October 8th, 2014
  34. I believe heart math device is one of the best out there and the one I intend to buy:

    http://store.heartmath.org/emWave2/emWave2-handheld

    Nitin wrote on October 8th, 2014
  35. Just thinking of getting an iPhone app (or an iPhone at all to track anything), makes my heart beat faster and I feel like I’ll get a heart attack. I’ll use my fingers.

    Nocona wrote on October 8th, 2014
  36. Thanks for a great article! As always, Mark does his homework :). Also, great discussion here in the comments already.

    (Full disclosure – I own Elite HRV (the free HRV app), and have been entrenched in the Primal/Paleo community for several years now)

    Just want to clarify for folks real quick:

    The article mentions finger sensors/cameras not being accurate enough and that is absolutely correct. There are also wrist bands and watches with optical sensors that claim to offer HRV which are also not accurate enough.

    These can pick up a general rise and fall of Heart Rate (which is a form of variability). This is neat to test out and can get you a ball park estimate as long as you are perfectly still and have healthy blood flow to the measurement site.

    But the calculations of daily readiness for exercise and making important stress decisions that are talked about in the article require a higher degree of accuracy. To actually pick up accurate inter-beat intervals you currently need a chest strap. Even the optical ear clips are not really accurate enough for that yet.

    There are a lot of great apps and hardware out there, including the ones Mark mentions. Just be aware of the varying degrees of accuracy if you are making real decisions off of them! Love to see this topic on MDA.

    Jason Moore wrote on October 8th, 2014
  37. I have tried the Stress Check app, I got reading between 0% and 2% of stress. Maybe I am not stressed at all, but I have a wife (!), three Kids (!!!), I train (run) 6 days a week and I am finalising my training for a Marathon at the end of the month.
    If nothing else I should be more stressed after an heavy workout, like the one of yesterday, and instead, I got a 0% reading this morning!
    So either it does not work, or my telephone’s camera (Google Nexus S, produced by Samsung) is not a good match for the Stress Check app.
    Did anyone experience similar issues? And which phone are you using?

    Nicola wrote on October 9th, 2014
    • Hi, Nicola. I was also getting between 0% and 2% with a Samsung Galaxy 3. I let my daughter try it and she got a 28% . Not sure how helpful that is. Maybe let your wife and kids try it and see how they score.

      April wrote on October 10th, 2014
  38. Strange, today it seems to work much better.
    Toward the end of a very tedious meeting, that I would have rather exited after the first 10 minutes, I run a check and got 11% “stress level”.
    And no after a 10K easy run I got 36%, which is still “green”, but somewhat higher than before the workout, as expected.
    Maybe some initial calibrations had to take place? I do not know.

    Nicola wrote on October 10th, 2014
  39. Check out this HRV app that uses the iPhone’s camera and flash to perform the readings. No expensive heart rate monitor required!!! I found this after searching the web. It looks to be complete enough to achieve what Mark is talking about in the article above. I have no affiliation or relationship with the creator of the app.

    https://itunes.apple.com/us/app/camera-heart-rate-variability/id788460316?ls=1&mt=8

    PBnewby wrote on October 10th, 2014
    • I use this app (Camera Heart Rate Variability). It seems to work great, as long as you are very still. It has no trouble picking up my pulse and measuring the interval between beats. Unfortunately, there is no guide for interpreting the results… what is a good score and what is a bad score. I’ve noticed my HRV goes down when I’m sick, after I eat, and on days after I work out.

      Matt wrote on October 15th, 2014
    • Apps using the flash can give you an accurate pulse rate, but not an accurate HRV score. A sensor that picks up electrical impulses (almost all chest strap based), is necessary to accurately measure the dwell time between beats, which determines variability.

      Lars wrote on January 21st, 2016
  40. I have a love/hate relationship with the Polar H7 heart monitor. Measuring HRV with it is tricky because you’re not sweating, so you might have to wet the sensors more than once. Also, sometimes you have to ‘discharge’ it by wearing it without the battery to get it working. (I know some computers with the same problem.)

    tam wrote on October 23rd, 2014

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