BenGreenfield-HeartRateVariability.mp3

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 a bit about something called heart rate variability or hrv. And this is something 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 over trained or overworking 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 measurement system is made by a company called Sweetwater Health, it's called the Sweet Beat. 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, etc. Now, one of the people who is very, very well versed in heart rate variability and who was behind the development of this particular method measuring tool that I use, her name is Rhonda Collier. And Rhonda 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 onto the call today and talk about heart rate variability with. So, Rhonda, thank you for coming on the call.

Hey, thank you for having me, 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, oh, I can geek. Kind of familiar with the basic concept. We can put our propeller hats on. Can you kind of explain heart rate variability? And you know, we can kind of 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.

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 1 second, 1.02 seconds, 1.04, 0.98, 0.92, back to 1:1.02. And so it would average out to 1 second, which would mean 60 beats per minute. But each heartbeat interval varies. And so the reason that it varies is that 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. The rest and repair 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.

Gotcha. So when you're looking at the heart in this manner and you're testing heart rate variability, what exactly is going on in terms of the way that the nervous system is actually communicating with the heart?

Well, I think a physical is the easiest to describe. So when you're lying down and stand 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, is really to manage and keep your temperature the same, your blood pressure steady, and so on.

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 or. Or how exactly does the communication occur?

Yeah, so heart rate variability is specifically concerned with what's called the vagal nerve. The vagal nerve is the 10th of 12 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.

Okay, gotcha. Now, when I am using this app to measure my heart rate variability, and, you know, I'm wearing this chest strap, which is sending information to my phone wirelessly, and I have the app open there on one side, it's telling me heart rate variability. And it gives me basically this score of I think it's 0 to 100. Right.

Right.

Now, if I flip the. 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?

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 an EKG has several components to it. The Q, R, S, and T points in the ekg, that's when different valves of the heart open and close and pump blood. Okay, The R interval, which is what you see as the spike on the ekg, the RR intervals is the difference between spikes. So it's your beat to beat interval. And in the 60 beat per second example, it would be 1 second, 1.02 second, 1.05 seconds, 0.98, and so on. Okay, so 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. 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. Its standard deviation, its 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 or 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 heart rate. Like a broccoli. If you pull a piece off the broccoli, it looks like the hole all the way down. And so actually, a healthy heart rate variability has that fractal characteristic as well.

And I'm sure that probably kind of 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, right. That's 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 really just a. 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 so a high RMSSD is an indication of a strong vagal tone.

Okay, okay, that makes sense. All right.

Yeah.

So when.

And then the lf, then you have LF and hf. LF is. 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 or rest and repair, a branch of the nervous system. So you can actually look at your nervous system and vagal tone in real time using sleep aid.

That's very cool. So low frequency, the LF on this is sympathetic nervous system, HS or 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, like 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?

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

Okay. 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?

It could. Now, once again, an 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 because that will show your fight or flight versus your rest and repair.

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

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

Okay, got it. Interesting. So when I'm getting my heart rate 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 I see 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 over trained? And if so, I mean, is it that accurate? I mean, have you guys been able to do studies or look at what kind of things this can actually predict as HRV drops?

Yes, this has 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 use 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, you know, 75 or 80 for healthy persons. And they vary from moment to moment. They vary. And so that's why we took the log and scaled it so that a consumer can really get a more meaningful value from the rmssd.

Okay, interesting. So in terms of the HRV testing system, the sweet beat system that I've been using, do different systems use different algorithms? I mean, because it seems like there's, 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, I mean, are they going to see a lot of variation? Or all these devices using this same kind of algorithm that you just explained, the LF and the HF and the RR and the, and the RMSSD and all this stuff.

Right. If they're following the European Society of Cardiology guidelines, then you would have the same results. Suite beat has been compared to an EKG and we matched. So it really is a standard algorithm to compute RMSSD. That being said, the scaling from 0 to 100 could vary a little bit depending on what exactly the producer of the app is doing, but generally it's pretty much the same and the RMSSD's should absolutely match the standards.

Got it. Now, I've been tracking my data over the past month, tracking my HRV data, waking up in the morning and for anywhere from five to 10 minutes, putting on this heart rate strap and letting it feed data into the Sweet Beat app. And I can upload all this to a website where I can actually see what's happening with my HRV scores. Or, you know, when you're doing something like that, you know, I don't know if you've had a chance to look over my data or seen any of it come through. Have you?

Yes, we have.

Oh, you have? Okay, cool. Because I figured we could use mine as an example if you were able to look at it. But when you're looking at that data, what kind of information can you glean from it? Or you know, when someone is tracking this stuff on a day to day basis, doing the whole self quantification thing, besides just seeing, you know, heart rate variability maybe go up or down or something like that, I mean, what, what are you looking for? What kind of information can people glean from something like this?

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 state 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 overactive 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 and a sort of a trophy example of good hrv.

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

Okay. Someone with chronic stress, which actually a lot of athletes are, we've learned in our case studies that drives them to workout. They show up as an overactive fight or flight, meaning that the sympathetic nervous system is way out of balance compared to the parasympathetic.

Okay, gotcha. And which value did you say that you can see something like that from.

That is an LF and hf.

Okay. And you're going to see low LF and high HF in a situation like.

That or just you're gonna see high LF and low hf.

Okay, got it. The reason I'm asking you this, high fighter high is also for selfish. For selfish reasons too, because I want to be able to keep it. I want to be able to look at my athletes HRV values and make sure I really interpret them correctly. Okay. So that's, that's one thing.

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 of 50 and an HF of 50. Okay.

Okay.

So it's power levels and balance, and you show both high power levels and excellent balance.

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 other type of person that you mentioned?

Then you have someone with low power, say LF of 10 and an HF of 2. 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.

Okay, interesting. This stuff is fascinating how, how much you can tell just from what the vagus nerve is telling to the heart. That's very cool. Okay. All right. 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 variations.

Okay, absolutely. In fact, I think that's an important addition to just looking at the HRV score.

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?

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 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.

The Coca Pulse test. Is that what you said?

It's called the pulse test? The pulse test.

Okay.

And what he discovered was that when we eat foods 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 sort of 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 minute 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.

More than 16.

Yeah.

Okay.

And that's per Dr. Koca's test.

And that's a lot more than what you'd see if you had, for example, like 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, we're talking about something pretty significant in terms of heart rate increase.

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.

Gotcha. Okay. Interesting.

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 was laying on the couch watching TV and an hour later the Pulse went up about 20 beats as well.

Now, when it comes to exercise and, you know, let's say I were going to wear the Sweet Beat or have the Sweet Beat app open while I'm out, say, on a bike ride and, you know, whatever, say, have the phone in my jersey pocket and the heart rate strap on, I'd be sending heart rate variability data during the actual exercise session rather than say, 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?

Well, there is with the current Sweet Beat 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.

So if LF and HF were low, would that also be something during exercise? Would that also indicate potentially that you just were too. You're too stressed to be exercising at that point?

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 an indication of some systemic health problem.

Right, like adrenal fatigue or something like that.

Yes. Gotcha.

Interesting.

Yeah.

Okay.

Now an interesting point, while we don't have it in sleep beat at this point, is that using HRV, you're able to detect VT1 and VT2 or aerobic to anaerobic transition using HRV.

Can you explain that?

You probably know more about the details of the physiology than me, but it's 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 thresholds using hrv. So that's just yet another interesting aspect and possibility of HRV for fitness training versus having to wear, go into a lab and measure these sorts of things.

Right, right, exactly. Yeah. Or carry around some kind of a blood measurement, like a lancet.

And it's been tested against the blood measurement.

Wow. I hadn't seen any of those studies before. That's cool. I'm going to have to dig into that now and check it out. I can send you a paper that would be fantastic. Now, if you could track other elements related to overtraining or too much stress, like 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 low. So I might be overtrained or overstressed, but I'm going to check out these few other things to see if, you know, to kind of verify. Are there other markers you like to see or quantitative or qualitative markers?

The ones that we really have noticed are the qualitative markers. Now, that's mood. Many of the folks we've done case studies with have noticed that their mood is grouchy and grumpy on the day that their HRV drops from over training. 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 his hrv. It was low. He went out anyway and then drove into the garage with his bike on top and crushed his bike.

You know what I just thought?

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.

Yeah, yeah, I've been there. I actually, 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 I 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 so. So 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 except for my goggles and my swim cap. So I've certainly been there in an embarrassing way.

Yeah. And these are very. They're subjective and very real results of overtraining.

Yeah.

And shows what happens when your nervous system is fatigued.

Yeah. Yeah. So sweet beat 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, Rhonda?

Yes, just the iPhone or iPad or ipod touch.

Gotcha. And then you need a wireless heart rate monitor. And then basically like an Ant adapter. A Wahoo Ant adapter.

Right. We support the Wahoo ANT plus adapter, and now we support the Polar H7 Bluetooth Low Energy as well as the 60 beat Blue HR Bluetooth Low Energy as well.

Okay. So a lot of this stuff that you could also use to, you know, like when you're on a bike ride or whatever, send data in real time to your phone.

Right? That's right.

From a power Meter or from a heart rate monitoring, your device, same type of deal. You're just sending it from your heart rate variability data from your heart rate strap. Cool. Well, that was a true propeller hat episode. I know that freaks out.

I wanted to point out one thing you said that I think is important for your listeners.

Sure.

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 of day and you want to do it for the same length of time, usually a minimum of five minutes. So you need to pick, because you'd mentioned five or 10 minutes, you really want to pick a standard amount of time and standard time of day.

Okay, gotcha. Yeah, that's what I would like. For me now, it's pretty much because 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 rate 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 Rhonda 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. Koch'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 adapter you can use with 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, Rhonda?

No, I think I geeked out enough this morning.

Awesome. All right, well, folks, if you have questions, which I would imagine some folks may have because we went over some kind of advanced stuff today, you can leave them in the comments underneath the show notes to this episode over@BenGreenfieldFitness.com and thanks for coming on the call today, Rhonda.

Okay, thank you so much, Ben.