[Transcript] – Everything You Need To Know About Heart Rate Variability Testing

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Transcripts

Podcast from:  https://bengreenfieldfitness.com/podcast/self-quantification-podcasts/heart-rate-variability-testing/

[00:00]  About Ronda Collier

[02:12]  What Is Heart Rate Variability?

[06:31]  Algorithms of the SweetBeat

[15:10]  Ben’s Heart Rate Variability Results

[19:44]  Regarding Food Sensitivities

[25:18]  Tracking & Verifying Heart Rate Variability

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[30:27]  End of the Podcast

Ben:  Hey folks, it’s Ben Greenfield here, and if you’ve listened to the podcast for any period of time, you know that we’ve talked about a bit about something called Heart Rate Variability, or HRV.  And this is something that I’ve talked about before as a method that I use to track my own training status and my own risk of, for example, being overtrained or over-working my body, but today, I wanted to really focus on all the aspects of measuring heart rate variability and focus a little bit more on the science of it and really geek out on this whole HRV concept.  Now one of the tools that I’ve been using each day to measure my heart rate variability is basically a chest strap that sends information to an app on my phone, and this particular measuring system is made  by a company called SweetWater Health, and it’s called the SweetBeat, and I simply put that on and can monitor my HRV stress levels as I’m walking around the house or lying in bed in the morning or exercising, etcetera.  Now one of the people who is very, very well-versed in heart rate variability and who was behind the development of this particular measuring tool that I use, her name is Ronda Collier, and Ronda has more than 25 years of experience in high-technology product development ,and she’s spent the past several years studying and developing health monitoring techniques, non-invasive health monitoring techniques such as this heart rate variability system that I’ve been using.  So, I figured she would be a perfect person to get on to the call today and talk about heart rate variability with.  So, Ronda, thank you for coming on the call.

Ronda:  Thank you for having me, Ben.

Ben:  Well we’ve talked about heart rate variability on the show before, like I mentioned.  So, don’t be afraid to geek out on us.  Since our audience is…

Ronda:  Oh, I can geek.

Ben:  Kind of familiar with the basic concept, so we can put our propeller hats on.  Can you explain heart rate variability?  And we can lay down a basis and maybe delve into the nitty gritty details a little bit more after you explain the basics but go ahead and just launch into heart rate variability and set a foundation here for us.

Ronda:  Okay, great.  Well heart rate variability is the pattern of the heartbeat, and that is mutually exclusive from your heart rate.  So, let’s say you have a nice resting pulse of 50, you could have a low heart rate variability.  Similarly, you could have a high resting pulse of 85 and have a high heart rate variability.  So once again, it’s really mutually exclusive from heart rate.  So, the best way to describe heart rate variability is say you have a resting pulse of 60 beats per minute.  Intuitively, you would think that your heart rate would beat once every second.  Well that’s actually not true, and that’s actually not healthy.  A healthy heart rate variability would beat something like one second, 1.02 seconds. 1.04, 0.98, 0.92, back to 1, 1.02, and so it would average out to one second which would mean 60 beats per minute.  But each heartbeat interval varies, and so the reason that it varies is that if your heart rate is controlled by your autonomic nervous system.  The autonomic nervous system consists of the sympathetic branch, which is commonly known as fight or flight, and also the parasympathetic branch, which is also known as rest and repair.  The fight or flight branch speeds the heart up, and the rest are repaired branch slows it down, and so it’s the interplay of these two branches of the nervous system that causes the heart rate variability.  And so, a high heart rate variability is an indication of a robust nervous system.

Ben:  Gotcha, so when you’re looking at the heart in this manner and your testing heart rate variability, what exactly is going on in terms of the way that the nervous system is actually communicating with the heart?

Ronda:  Well, I think a physical is the easiest to describe.  So, when you’re lying down and standing up, your nervous system responds.  Your heart rate increases to now keep your blood pressure steady because, as you know, your blood pressure will change from when you lie down and stand up or sit down and stand up and so on, and so the nervous system is really all about keeping your body in balance and equilibrium, keeping a stable blood pressure, keeping a stable heart rate, and so that’s why a flexible nervous system and high heart rate variability is an indication of health, and that’s why your body does.  It’s really to manage and keep your temperature the same, your blood pressure steady and so on.

Ben:  Got it.  How does the nervous system actually speak to the heart?  Is there a specific nerve that information travels from the nervous system to the heart via?  How exactly does the communication occur?

Ronda:  Yeah, so heart rate variability is specifically concerned with what’s called the vagal nerve.  The vagal nerve is the tenth of twelve cranial nerves and is an important factor in mediating heart rate, and so heart rate variability once again is very much concerned with the vagal nerve.  It goes from the top of the spine, all the way down into the lower organ function, so it not only controls heart rhythm.  It also controls liver function, kidney function and so on, so it’s very important.

Ben:  Okay, gotcha.  Now when I am using this app to measure my heart rate variability, and I’m wearing this chest strap which is sending information to my phone wirelessly, and I have the app open, on one side, it’s telling me heart rate variability, and it gives me basically this score.  I think it’s 0 to 100, right?

Ronda:  Right.

Ben:  Now if I push a little button on the app for more details, it shows me a bunch of other numbers like RR, LF, HF, RMSSD.   What are all these other numbers that you see correlated with heart rate variability?

Ronda:  Okay, so RR is the interval of your heartbeat.  If you think of an EKG, I don’t know if you’re familiar with an EKG, but EKG has several components to it.  The QRS and T points in the EKG.  That’s when different valves of the heart open and close and pump blood.  The R interval, which is what you see is that the spike on the EKG, the RR interval is the difference between spikes, so it’s your beat to beat interval, and then the 60 beat per second example, it would be one second, 1.02 seconds, 1.05 seconds, 0.98, and so on, okay?  The RR intervals are extracted from your heart rate, and what you end up with is a time series really, which is why we electrical engineers are fascinated by this.  Because now, we can do lots of processing with it, okay?  So, once you understand the RR interval, we can move next into what HRV is.  HRV is a general term that really just means heart rate variability.  Now there are different ways to analyze this time series.  We have the time domain, which is really statistics, it’s standard deviation, it’s root, mean, square and so on.  We also have frequency domain, and this gets more into electrical engineering and signal processing, but that’s where the frequency, the low frequency and high frequency comes in.  Also, the really interesting aspect of heart rate variability is the nonlinear complex analysis of it.  It turns out that a healthy heart rhythm is fractal and chaotic in nature, which really isn’t surprising because we see fractals and chaos throughout nature.  In terms of a broccoli, if you tip off a piece off the broccoli, it looks like the whole all the way down, and so actually, a healthy heart rate variability has that fractal characteristic as well.

Ben:  And I’m sure that probably surprises a lot of folks to hear about the chaotic nature of that, and that’s simply a matter of your nervous system being well tuned, so to speak, right?

Ronda:  Right, that’s right.  So back to the numbers on the screen, so we have the RR intervals, which I just explained, then we have RMSSD, which is a time domain measure of the RR interval time series, and it stands for Root Mean Square of Successive Differences, and it’s similar to a standard deviation.  It’s a root, mean, square, and it turns out that RMSSD is an indication of your vagal tone, which is the vagus nerve that I just spoke of.  And also, a high RMSSD is an indication of a strong vagal tone.

Ben:  Okay, that makes sense.

Ronda:  And then the LF.  Then you have LF and HF.  These are the frequency components, so LF is the low frequency, and that actually correlates with your sympathetic or fight or flight branch of the nervous system, and the HF, which is high frequency, correlates to your parasympathetic rest to repair a branch of the nervous system.  So, you can actually look at your nervous system and vagal tone in real time using SweetBeat.

Ben:  That’s very cool, so low frequency, the LF on this is sympathetic nervous system.  HF, high frequency, that’s parasympathetic.  So, if I’m seeing, for example, that the LF, the low frequency, the feedback from the sympathetic nervous system is say, consistently low, would that be something that could indicate to me, for example, that I’ve been overworking my sympathetic nervous system, my fight or flight nervous system?

Ronda:  Actually, it probably shows that you’ve got some deep relaxation or you’re in a depressed state or fatigued.

Ben:  Okay, and when you say in a depressed state or fatigued, would that be the kind of fatigue that would be a result of over-exercising or pushing my body too hard?

Ronda:  It could.  Now once again, the important point for heart rate variability is it varies person to person, so some people may turn out to have a chronic stress from over-exercising, so we’ve seen that.  I tend to have a depressed sympathetic for over exercising, so it does vary.  That’s why really for athletic training, we use the vagal tone or the RMSSD, and we use the LF and HF for stress levels, so that will show your fight or flight versus your rest and repair.

Ben:  And all of these variables, the high frequency and low frequency, the SSD, these are being used in basically an algorithm to spit out this value of 0 to 100 for heart rate variability?

Ronda:  That’s right.  There are some standards that we follow, the European Society of Cardiology and the North American Society of Pacing Electrophysiology have some standards for computing these really standard heart rate variability measurements, and so it really is standardized.

Ben:  Got it, interesting.  So, when I’m getting my heart variability score, we can take our propeller hats off here for a second, and I’m getting this number from 0 to 100 and I’m watching this on a day to day basis and let’s say that it starts to drop low.  For me, can that actually predict that I am going to get sick or that I’m inadequately recovered or that I’m overtrained, and if so, I mean is it that accurate?  Have you guys been able to do studies or look at what kind of things this can actually predict as HRV drops?

Ronda:  Yes, this is been pretty well studied.  There’s hundreds of papers on this, and as you know, elite athletes are starting to really use heart rate variability as a measure for overtraining.  It turns out that when you have not done enough repair and recovery after training, that your vagal tone is what’s affected, and so your RMSSD will drop.  Now the algorithm we used to compute the number from 0 to 100 is really we take the log of RMSSD, and then we scale it from 0 to 100 for consumers because a real RMSSD varies from some strange numbers like 15, which is kind of low, up to 75 or 80 for a healthy person, and from moment to moment, they vary.  That’s why we took the log and scaled it, so that a consumer can really get a more meaningful value from the RMSSD.

Ben:  Okay, interesting, so in terms of the HRV system, the SweetBeat system that I’ve been using, do different systems use different algorithms ’cause there’s seems like there’s more and more devices popping up that are going to tell you your heart rate variability?  If someone’s using one device versus another device, are they going to see a lot of variation, or are all these devices using the same algorithm that you just explained, the LF and the HF and the RR and the RMSSD and all this stuff?

Ronda:  Right, if they’re following the European Society of Cardiology guidelines, then you would have the same results.  SweetBeat has been compared to an EKG, and we matched.  So, it really is a standard algorithm to compute RMSSD.  That being said, the scaling from0 to 100 could vary a little bit, depending on what exactly the producer of the app is doing.  Generally, it’s pretty much the same, and RMSSD should absolutely match the standards.

Ben:  Got it.  Now I’ve been tracking my data over the past month, tracking my HRV data, waking up in the morning, anywhere from five to ten minutes, putting on this heart rate strap and letting it feed data into the SweetBeat app, and I can upload all this to a website where I can actually see what’s happening with my HRV scores.  When you’re doing something like that, I don’t know if you’ve had a chance to look over my data or seen any of it come through, have you?

Ronda:  Yes, we have.

Ben:  Oh, you have.  Okay, cool ’cause I figured we could use mine as an example if you’re able to look at it, but when you’re looking at that data, what kind of information can you glean from it?  When someone is tracking this stuff on a day to day basis, doing the whole self-qualification thing, besides just seeing heart rate variability maybe go up or down or something like that, what are you looking, what kind of information can people glean from something like this?

Ronda:  Okay, well I’ll comment on yours since you asked.  We see that your LF and HF power levels are quite high, meaning that you have a really strong nervous system and a lot of what’s called power in the frequency domain of your nervous system.  So, what it really shows is that you have the ability to respond and recover from physical, emotional and mental stressors.  Also, what we noticed about your readings are that you have a really balanced nervous system, meaning that your sympathetic or fight or flight branch is really balanced with your parasympathetic rest and repair branch.  People with chronic stress show up as an over-active fight or flight, and people with a depressed nervous system would show up with a low power in the LF and HF measurement.  So, you’re looking extremely healthy in a trophy example of good HRV.

Ben:  Can I ask you to repeat that part one more time that you just ended with, the two different types of people?

Ronda:  Okay, someone with chronic stress, which actually a lot of athletes are.  We’ve learned in our case studies that drives them to work out.  They show up as an over-active fight or flight, meaning that the sympathetic nervous system is way out of balance compared to the parasympathetic.

Ben:  Okay, gotcha.  Which value did you say that you can see something like that from?

Ronda:  That is an LF and HF.

Ben:  Okay, and you’re going to see low LF and high HF in a situation like that.

Ronda:  High LF and low HF.

Ben:  Okay, got it.  The reason I’m asking you this is also for safest for selfish reasons, too.  Because I want to be able to look at my athletes HRV values and make sure I really interpret them correctly.

Ronda:  Yeah, and I think it’s important to distinguish between the balance of LF and HF and then the power levels of LF and HF, okay?  So, you have the balance which is, let’s say LF is five and HF is five.  That’s balanced, okay?  But that’s a low power level.  Someone like you would have an LF for 50 and an HF of 50.  So, it’s power levels and balance, and you show both high power levels and excellent balance.

Ben:  So, we’ve got that one person that might have high LF and low HF and be potentially overworking their sympathetic nervous system, and then what was the type of person that you mentioned?

Ronda:  Then you have someone with low power, say an LF of ten and an HF of two.  That would be chronic stress with not a lot of power in the nervous system, and so not a lot of overall resilience and ability to respond and recover from daily stressors.

Ben:  Okay, interesting.  This stuff is fascinating how much you can tell just from what the vagus nerve is telling the heart.  That’s very cool.  Okay, so when data is getting uploaded via something like your app, you can literally just go in.  I could go into one of my clients’ HRV data and look at something like this and not just look at HRV, but also potentially look at LF and HF and some of these other variables.

Ronda:  Absolutely, I think that’s an important addition to just looking at the HRV score.

Ben:  Now you have a food sensitivities, part of this app, where you can put your food in and it can detect food sensitivities.  Is it HRV that you’re using for something like that or how are you detecting food sensitivities?

Ronda:  So actually, we’re currently not using HRV for food sensitivities, and we’re excited to see what’s going to happen to HRV with food sensitivities because it really has not been researched.  What we use is what’s called the Coca Pulse test, and it was created by Dr. Arthur Coca who was a renowned immunologist in the 50s.

Ben:  The Coca Pulse test, is that what you said?

Ronda:  It’s called the Pulse test, yeah, and what he discovered was that when we eat food that we have sensitivities to, that our pulse will increase up to an hour and a half after eating that food.  So, for the pulse test, we just use your heart rate.  Now what you do is you take a baseline in the morning to figure out your baseline, and then you take your pulse before you eat to make sure you’re still within the baseline range, and you want to make sure that you’ve recovered if you worked out in the morning, and then you tell the app that you’ve finished eating, and it takes your pulse three times at 30 minutes intervals after you’ve eaten.  And if your pulse goes up more than 16 beats per minute, after you’ve eaten, it’s an indication that you have eaten something you’re sensitive to.

Ben:  More than 16?

Ronda:  Yeah, and that’s per Dr. Coca’s test.

Ben:  And that’s a lot more than what you’d see if you had, for example, maybe had a cup of coffee with a meal or included some type of metabolism boosting compound like cayenne pepper or something like that.  I mean we’re talking about something pretty significant in terms of heart rate increase?

Ronda:  Yeah, and caffeine and peppers and things like that tend to be a short-term increase as well.  Not only is it usually not 16 beats per minute.  If it is, you’re allergic, but it also tends to be short term.  So, the Coca Pulse test takes it at 30, 60 and 90 minutes after you’ve eaten.

Ben:  Gotcha, okay.  Interesting.

Ronda:  We’ve seen heart rates increase 20 beats, an hour and a half after the food was eaten while the person was sitting quietly at their desk.  Another person laying on the couch, watching TV, and an hour later, the pulse went up about 20 beats as well.

Ben:  Now when it comes to exercise, and let’s say we’re going to have the SweetBeat app open while I’m out, say on a bike ride, and whatever, say have the phone in my jersey pocket and the heart rate strap on and be sending heart rate variability data during the actual exercise session rather than when I’m lying in bed the next day recovering.  Can you glean any data from what’s going on with heart rate variability during the actual exercise session itself?  Is there any value to be gained from something like that?

Ronda:  Well, there is.  With the current SweetBeat product, what you should see if you’re healthy is that your HRV will go way down, and your sympathetic or LF will go way up, relative to your HF.  So, if you’re healthy, that’s what will happen.  If you’re not healthy, which happens to people who are developing heart disease, your heart rate won’t go up and your nervous system won’t respond to the exercise, which often leads to heart attacks because your nervous system and heart are not responding to the exertion you’re putting on it.

Ben:  So, if LF and HF are low, would that also be something?  During exercise, would that also indicate potentially that you just were too stressed to be exercising at that point?

Ronda:  Well, if LF and HF are low during exercise, that would not be good because your LF should go way up because you’re stressing your body, and that’s what your fight or flight branch is for.  So that would be the indication of some systemic health problem.

Ben:  Right, like adrenal fatigue or something like that?

Ronda:  Yes.

Ben:  Interesting.

Ronda:  An interesting point, while we don’t have a SweetBeat at this point is that using HRV, you’re able to detect VT1 and VT2 or aerobic to anaerobic transition using HRV.

Ben:  Can you explain that?

Ronda:  You probably know more about the details of the physiology than me, but if when you go from aerobic to anaerobic, you’re able to detect that, and what happens is that all of a sudden, your HF, which has been depressed during exercise will increase a little bit, and I don’t understand the deep physiology behind it, but there are algorithms that allow you to detect your lactate threshold using HRV.  That’s just to get another interesting aspect and possibility of HRV for fitness training versus having to wear, go into a lab and measure these sorts of things.

Ben:  Right, exactly, or carry around some blood measurement like a lens with you.

Ronda:  That’s right, and it’s been tested against the blood measurements.

Ben:  Wow, I hadn’t seen any of those studies before, that’s cool.  I’m going to dig into that now and check it out.

Ronda:  I can send you a paper.

Ben:  That would be fantastic.  Now if you could track other elements related to overtraining or too much stress, if we were going to say look at a few things aside from HRV, are there other things that you think are pretty good to be able to combine with HRV and say okay, well my HRV is low, so I might be overtrained or over-stressed but I’m going to check out these few other things to see, to verify.  Are there other markers you’d like to see, quantitative or qualitative markers?

Ronda:  The ones that we really have noticed are the qualitative markers.  Now that’s mood.  Many of the folks who we’ve done case studies with have noticed that their mood is grouchy and grumpy on the day that their HRV drops from overtraining.  Also, their clarity of thinking and they’re a little fatigued.  We had one athlete that did a case study with us, that had measured as HRV.  It was low, he went out anyway and then drove into the garage with his bike on top and crushed his bike.  It’s not funny, but these are the things that we’ve discovered that correlate with low HRV.  And while they are subjective, they’re really important to pay attention to.

Ben:  Yeah, I’ve been there.  Funny story, I have gotten myself to the point where my thinking was so fuzzy from training too much, and this was way back in the day before understood how to recover properly.  I even had one day where I went swimming and went into the men’s locker room, and my thinking was so fuzzy, and I was just overworked that I didn’t even put my swimsuit on, and I walked out and was standing there, swinging my arms, getting ready to jump into the pool, and I had literally nothing on the except for my goggles and my swim cap.  So certainly, been there in an embarrassing way.

Ronda:  Yeah, and these.  They’re subjective and very real results of overtraining and shows what happens when your nervous system is fatigued.

Ben:  Yeah, so the SweetBeat.  For people who want to use this measurement for HRV testing, it is an app that you download to your phone.  Is it just the iPhone right now, Ronda?

Ronda:  Yes, just the iPhone or iPad or iPod Touch.

Ben:  Gotcha, and then you need a wireless heart rate monitor, and then basically an Ant Plus adapter, a Wahoo Ant Plus adapter?

Ronda:  Right, we support the Wahoo Plus adapter, and now we support the Polar H7 Bluetooth low energy, as well as the Blue HR Bluetooth, low energy as well.

Ben:  Okay, so a lot of this stuff that you could also use when you’re on a bike ride or whatever, send data in real time to your phone.  From a power meter or from a heart rate monitoring device, and same type of deal.  You’re setting it from your heart rate variability, data from your heart rate strap.  Cool, well that was that was a true propeller hat episode.

Ronda:  I wanted to point out one thing you said that I think is important for your listeners.  One thing about heart rate variability is that it does have a circadian rhythm, and so when you’re doing heart rate measurements for training, you want to do it at the same time a day and you want to do it for the same length of time, usually a minimum of five minutes.  So, you need to pick ’cause you’d mentioned five or ten minutes.  You really want to pick a standard amount of time and standard time of day.

Ben:  Okay, gotcha.  For me now, it’s pretty much ’cause I won’t do it otherwise.  For me, it’s just I keep it on my bed, by my bed, and when I wake up in the morning.  I mean I don’t sleep with my heart monitor on, I’m not that geeky, but I put it on when I wake up and then I take the measurement.  So, I think for a lot of people, that’s an easy way to do it, so cool.

Well folks, for those of you listening in, I will be sure that I link to some of the resources that Ronda and I talked about in the show notes.  I’ll try and find a link for people who want to learn more about the Dr. Coca’s Pulse Rate test for food sensitivity.  I’ll also put a link to the SweetBeat app and a compatible heart rate monitor and Wahoo Ant Plus adaptor and you can use or something like that, and then also, I’ll link over to their website if you guys wanted to explore some of the resources available over on the SweetWater HRV website, so anything else you wanted to mention, Ronda?

Ronda:  No, I think I geeked out enough this morning.

Ben:  Awesome, all right, well folks, if you have questions, which I would imagine some folks may have ’cause we went over some advanced stuff today, you can leave them in the comments underneath the show notes to this episode over at bengreenfieldfitness.com.  And thanks for coming on the call today, Ronda.

Ronda:  Okay, thank you so much, Ben.

 

When it comes to tracking the health of your nervous system, your ability to bounce back from a training session, and even your mental, spiritual and emotional stability, nothing is as effective as heart rate variability (HRV) tracking.

In the article “What To Do When You’re Overtrained“, I explain how I personally use heart rate variability testing to identify whether or not I’ve pushed myself too hard (and exactly how I dig myself out of the overtraining hole if my numbers are not ideal).

And recently, in the podcast episode “What Is The Best Way To Track Your Heart Rate Variability“, I explain that the system I currently use is the SweetBeat HRV App for real time monitoring of heart rate variability using a smartphone app and a compatible heart rate chest strap.

But to get the most out of this type of self-quantification, you really need to geek out on this and learn everything you need to know about heart rate variability testing and analysis.

So in today’s audio interview, I speak with Ronda Collier (pictured right), B.S.E.E., M.A. Psychology, who has more than 25 years of experience in high technology product development with a proven track record of delivering leading edge consumer electronic products.

Ronda has spent the last 3 years as an independent scholar researching non-invasive health monitoring techniques to improve overall personal well-being, and this research led to the founding of SweetWater Health.

Want to find out exactly what I ask Ronda, listen to the interview, get some screenshots of what heart rate variability analysis looks like, and learn exactly what you need to get started?

Then keep reading…

During the interview above, I ask Ronda:

-What is heart rate variability (and don’t spare the nitty-gritty details!)?

-When it comes to analyzing your numbers, what is the significance of RR, LF, HF and rMSSD?

-Can HRV be used to predict overtraining, inadequate recovery, “chances” of getting sick, etc.?

-Do different HRV testing systems use different algorithm to give you your HRV score?

-How can HRV be used to detect food sensitivities?

-And much more!

For SweetBeat HRV monitoring using the methods Ronda and I describe,  you need:

-The SweetBeat phone app:  + a wireless Polar H7 chest strap: http://goo.gl/L9asj

OR

–The SweetBeat phone app:  + a regular chest strap: http://goo.gl/L9asj + a “Wahoo” wireless adapter for your phone: http://goo.gl/ha5gV

Regarding my own personal HRV, which I sent to Ronda for 30 days to analyze, she said:

“I ran your SweetBeat sessions through some of our more advanced algorithms to get an even more precise view of your nervous system.  Your numbers were great.  You are truly a personal testament to your work!”

The following are the total averages of your sessions.  I frequently see you in the 8,000 – 12,000 range for low frequency (LF) and high frequency (HF). Your HRV is normally 100, the highest possible score.”

It’s good to know that I’m doing something right!

In a future episode, I’m going to share with you some of the personal meditation and recovery techniques I use to enhance my HRV score, but for now, this article would be a good place for you start.

Finally, the following charts (click to enlarge) are an additional analysis on my personal HRV and a photo of how the SweetBeat system works. Here is also a very helpful .pdf from Quantified Self if you want to dig into the nitty-gritty science a bit more.

 

 

 

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One thought on “[Transcript] – Everything You Need To Know About Heart Rate Variability Testing

  1. Chris Woolley says:

    Hi there,
    Where can we upload our data to express in more details our HRV Scores?
    Chris

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