WHOOP Podcast - Understanding Heart Rate Variability and Its Performance Potential with Kristen Holmes and Emily Capodilupo

Episode Date: October 19, 2022

This week we revisit an all-time classic episode all about Heart Rate Variability (HRV). VP of Performance Kristen Holmes  and SVP of Data Science and Research Emily Capodilupo dive deep into everything there is to know about HRV – and why it’s such a critical metric for evaluating your body’s readiness to perform. Learn what HRV is (3:00), why it’s so valuable to measure (6:35), and how it is a sign of fitness (9:40). Find out why WHOOP collects HRV data during sleep (17:05) and how it can impact your recovery score (22:27). Emily and Kristen explain how HRV can fluctuate on a daily basis (25:58) and how there is no true “normal” HRV (29:23). Hear some simple lifestyle choices that can improve your HRV (36:15) as well as how hydration (36:15), nutrition (38:43), and sleep (41:55) relate to HRV.Support the showFollow WHOOP: www.whoop.com Trial WHOOP for Free Instagram TikTok YouTube X Facebook LinkedIn Follow Will Ahmed: Instagram X LinkedIn Follow Kristen Holmes: Instagram LinkedIn Follow Emily Capodilupo: LinkedIn

Okay, folks, welcome back to the WOOP podcast, where we sit down with top athletes, researchers, scientists, and more to learn what the best in the world are doing to perform at their peak and what you can do to unlock your own best performance. I'm your host, Will Ahmed, founder and CEO of Woop. We're on a mission to unlock human performance. That's right. What a great mission that we get to attack every day. Well, this week we're bringing back one of our great.

hits and one of the most important whoop podcasts, which is, of course, about heart rate variability. Our own VP of performance, Kristen Holmes, and our SVP of data science and research, Emily Capitilupo, are here to help you understand the importance of

HRV heart rate variability. Kristen and Emily will discuss what HRV is and why it is so valuable to human performance, how it is a sign of fitness, what affects HRV on a day-to-day basis, why we measure HRV during sleep, how it impacts your recovery score, what a normal HRV can be and why it might fluctuate, and simple lifestyle choices around hydration, nutrition, and sleep that can impact your HRV.

A reminder, if you're new to Whoop, you can use the code Will when you're checking out to get a $60 credit on WOOP accessories. You can use that credit for new bands, battery packs, whoop body apparel, and more. That's at join.wop.com. Also, if you have a question, you want to see answered on the podcast,

email us, podcast at Woop.com. Call us 508-443-4952, and it might just be answered in a future episode. One last plug for heart rate variability. When I was doing research over 10 years ago

and thinking about starting this company, heart rate variability was the single thing that jumped off the page to me as being totally under-researched and an enormously important statistic if you could measure it continuously. So if you want to think about one of the main reasons that WOOP was founded, it was this question of can we measure heart rate variability continuously and accurately, effectively replacing an electrocardiogram. So that's why I love the statistic and it's been core to Woop ever since. But here are Kristen Holmes and Emily Capitouloupo to tell you everything you need to know about HRV.

Hey, everybody. I'm Kristen Holmes, VP of Performance here at WOOP. I am here once again with Emily Capital Lupo. Hey, Kristen. Today we're going to talk to you about heart rate variability, what it is, the factors that influence, how we use it at Woop, and just some of the behaviors that correlate with a good HRV relative to your baseline or a suppressed HRV relative to your baseline. and kind of what you can do behaviorally to kind of manipulate your heart rate variability. So just to start out, Emily, what is your kind of go-to definition for hearty variability?

So if I'm being a math nerd, it's literally the variability in the timing between beats of your heart. So a lot of people, you know, you go to the doctor and they tell you, you know, oh, your heart rate's 60 beats per minute. And that actually doesn't mean that it's beating like once a second on the second, you know, like a metronome. What actually is happening is that sometimes it's beating, you know, after 1.2 seconds, sometimes after 1.8, 1.9. And it averages out over the minute to be 60 times in a minute. You know, that's why at the doctor, they measure it for, you know, 30 seconds or something. And that variability comes from competing inputs from your nervous system. And so our bodies have sort of two opposing branches of your autonomic nervous system. You have the sympathetic that says sort of do stuff, activating part, and the parat sympathetic, which is that's, that's, that's, the rest, digest, the slow down, the recover. And so when both of these are sort of giving instructions to the heart, you get this kind of spastic increase, decrease, increase, which causes your heart rate to go up and down, up and down, and causes variability.

And that variability is actually a good thing, because over the course of time, we need to respond to both activating and deactivating signal. So, you know, we need to respond to threats and we need to dilate our pupils when there's too much light and all these little things that require action, but we also need to digest food and sleep and do all these things that require inaction. And so we're constantly trading all of that off. And when those systems are well balanced, you see a lot of variability because they're both sort of getting their way. And your heart's responsive to both signals and as equally as well. Right. So your heart is going to do whatever sort of it's being told to do. And if it's going up

and down a lot. It means it's hearing, for lack of a better word, the instructions from both sides. Now, what starts to happen when your heart rate variability goes down is that one of those inputs is sort of screaming more loudly than the other. And so your heart rate's getting, or your heart is getting one set of inputs, almost always the sympathetic is dominating. And so it's sort of getting its way, which is activate and do stuff, you know, produce cortisol and kind of have all these activating responses. and the parasympathetic isn't getting heard, which means a whole bunch of stimuli

that our bodies receiving are not getting actioned. And so heart rate variability is actually, it's a signal of your nervous system being balanced. And I think that that's really important and a source of confusion for a lot of our athletes. It's not so much it's good for your heart to go up and down, although it's certainly not bad. It's that it's good that your nervous system

is being responsive to a wide variety of stimuli because all of these stimuli are present. And so being able to action them in a balanced way is healthy. And it just happens to show up in your heart. So we could also measure this by sticking an electrode in your vagus nerve, but that would be very unpleasant. Heart rate variability is a very easy, cheap, non-invasive way of getting the same information. But we're actually seeing how, like, that balance is manifesting somewhere else.

It's an indirect measurement of what we actually care about, which is autonomic nervous system balance. Right. When I started using heart rate variability in my environment over a decade ago, what was striking to me is that it tells us different information than what just heart rate alone can tell us. So do you just want to expand a little bit on that? Because I think that's really critical for folks who are like, why do I need HRV? You know, why is this an important metric? I'm measuring my heart rate.

Like, I think that's really important to distinguish. Right. That's really important for folks to understand, you know, the difference. That's like such a good point because, you know, athletes have been measuring their heart rate for so long, you know, the two fingers on your neck. kind of method that's been around forever and it's been widely adopted. And, you know, when I started working at Whoop six years ago, like nobody had heard of heart rate variability. I mean, it was, you know, you had a couple, you know, in Australia where they're just like way ahead of us with all this stuff. They were just starting to. And you had a couple of just like really forward-thinking coaches who were starting to play with it. Princeton Field Hockey, for example.

Shout out. But really for the most part, you know, we were, nobody knew what it was. And they didn't really appreciate why it was important. And, you know, I think that it's precisely because heart variability is just your nervous system manifesting in your heart that makes it important and not redundant to the information that you're getting from heart rate. Now, for the most part, they will trend opposite to each other. So when your heart rate goes up, your heart rate variability goes down and vice versa. And that relationship can be a little bit predictable. And so, you know, maybe like nine days out of 10, you don't need both measurements. But you get a ton of really valuable information when all of a sudden they start to move together. And it's precisely

for that moment when they sort of decouple in like their typical relationship that if you only had heart rate, you would completely miss a very valuable signal. And so what I'm talking about is it's called parasympathetic saturation. And so a couple minutes ago, I explained that like most of the time when your heart rate variability is low, it's because your sympathetic nervous system is dominating. And so what we tend to see there is that heart rate goes up and HRV goes down. now in the case of parasympathetic saturation you're parasympathetic that's the resting part of the autonomic nervous system it dominates and causes HRV to go down but when you see that happen you also see resting heart rate go down and that's actually a sign of being like hyper recovered yeah so you see taper Olympians Olympic swimmers we saw that actually in the data leading up to Rio is we saw this parasympathetic saturation effect happening and we thought it we were like, oh my gosh, what's happening? And then you started digging into it. And we're like, wow, this is this is actually the taper has been super, super effective. Yeah. So it's a pretty like rare state. You see it for the most part in highly trained endurance athletes. You know, this isn't like a sort of everyday occurrence. But when it happens, you definitely, if you were just looking at HRV, you would interpret it incorrectly as being run down when it's actually a sign of being like very primed to perform. And if you're just looking at heart rate, you wouldn't see that, you know, anything special happened. You would just feel a low heart rate, which they've probably had for a while. And so you wouldn't also, in that case, you wouldn't know that they were in this, like,

kind of really special, like, prime to perform state. Right. So if you see resting heart rate and heart rate variability trending downward at the same time, that's an indication that you could potentially be experiencing this parasympathetic saturation. Cool. So how just, like, generally, you kind of described, you know, this, you know, heart rate going up, resting heart rate going down, you know, just explain, like, how that's kind of a sign of fitness. Sure. So basically, like, with every heartbeat, our bodies need, like, they use that oxygenated blood to do stuff. And so when your heart rate goes down, your resting heart rate goes down, you can roughly assume that the amount of stuff you have to do stay the same. And so what that means that, like, if you're able to sort of do that same amount of stuff with fewer heartbeats, it means that each heartbeat is more effective. You know, so either your body got more efficient. And so, you know, it can kind of like, do more with less or your heart is actually beating like more sort of higher what they call stroke volume so more blood pumping per heartbeat and so given that our maximum heart rates are more or less

fixed they decline as we age but you don't really train that if you can sort of do more per heartbeat then that means that at your maximum heartbeat which is your absolute maximum capacity you can do more than somebody who's sort of doing less per heartbeat and so what we start to see is that, like, as somebody becomes more and more trained, and so their cardiovascular system is more efficiently pumping blood, they're able to do more at lower and lower heart rates, which means that they're sort of taking on less strain, they're able to do more before they hit their anaerobic threshold and start to go into oxygen debt. And so that's when you start to see people that they're, like, running faster and further.

So with HRV, when your HRV is going up, it just means that your system is more balanced. And so the more sort of you're not sympathetically dominating, the more room they're is for sympathetic activities to come in and dominate. So what we actually see is that like when you're exercising at a really high capacity, you are in sympathetic domination. And so your HRV gets really, really low when you're, you know, exercising close to your or above your anaerobic threshold. And that's normal and that's totally healthy as long as when you stop exercising, you know, balance gets restored. Right. And so when your HIV is sort of higher, there's sort of more capacity to like disrupt that and to allocate those resources towards exercise. If your sympathetic

nervous system is already kind of working hard just to sort of maintain your life because it is hard for you to do baseline or relatively harder for you to do baseline, then that means that there's less resources to like reallocate towards exercise. You want to think about like if I'm running, I want all of those resources going towards my cardiovascular system and the muscles in my legs, Right. I don't really want resources going towards growing my hair and like all these other things. And so that ability to like reallocate things away from nail growth and towards, you know, feet turning over, you know, is going to make me run better for like the same amount of, you know, muscle or whatever, you know, while else being equal. Right. Great. So there's a lot of things that affect HRV. Let's just kind of dig into, you know, the things that promote kind of a parasympathetic. kind of activity and the things that actually promote sympathetic activity and kind of how to think about balancing the two. Sure. So, you know, the major big things are obviously activity level, stress, fatigue, you know, illness is going to make your HRV, you know, plummet. But then there's

also like so many little things. It's like one of the most sensitive metrics that there are. So like which makes it so powerful, right? Right. You know, it's just there's so much information. that's synthesized, which makes it very powerful, but also, like, a little bit tricky because it's not a very specific metric, right? So, like, my HRV could be low because I'm dehydrated. And so it could be as simple as, like, you know, I drink this glass of water and then it's going to shoot right up. And that's, like, a really easy fix. Whereas, like, if it's low because I'm tired and I actually need to, like, go to bed early tonight, that's like, that doesn't give me as much, like, room to affect it, you know, say, I have a game tonight or anything

like that. So obviously, like, alcohol is going to make it shot because you sort of divert all these resources towards your liver to sort of clear this poison out. And so that's like a very high, like our body's prioritized getting that out. And so then those resources get tied up. So you can basically think about like HRV as like we have this like finite number of resources. And our whole body is competing to use these resources for different things. And if my HRV is like very, very high relative to my baseline, it means all of my resources are available to be reallocated. Right. If my HRV is really, really low, it means that, like, most of those resources are spoken for. So there's very little to kind of move around. And so if I'm sick, right, my immune system is going to take just take a whole bunch of those. It's going to hold on tight and they're not going to be available. I can't stop fighting an infection in order to run a race. If my HRV is sort of low because I'm hot, right, I can change or I can turn on the AC and all of a sudden that's going to, like, bounce back really quickly. And so then I can take those resources that are working on. thermoregulating, right, you know, get into a thermo-neutral zone and then all of a sudden

those can be reallocated. If I just like ate a sandwich, a whole bunch are going to go to digesting that sandwich, but as soon as that's done, they get freed up again. And so HRV changes like a whole bunch, you know, day to day, but also like within the day. If I'm walking, for example, there's a lot of resources that are going to like keeping my balance and, you know, like watching all, you know, the space around me and just being like focused. And so all of those get tied up and then I sit down and they free up. So, you know, it's not just like, oh, a low HRV reading is bad. It's just a sign that, like, those resources are being allocated.

So anything that just requires attention, whether that's like mental attention, physical attention, things we're aware of or not, is just going to start to like pull those off of the ready-to-go pile. Right. And when you're exercising and you're trying to compete and do something impressive, you want to be able to say, like, I want to take all of these resources and, like, put them to the muscles and the cardiovascular system that's going to make. me win this game or this race or whatever it is. And I don't want to waste a whole bunch of them because like I had, you know, all this cheese at lunch that's like sitting in my stomach. And so like 10% are going to cheese processing. Right. And what you end up doing is

you end up sending just mixed signals to your body. Right. Like you want to send the right signal to your body at the right time based on what it is that you need to do. Right. So it's like why people would not recommend like having a big meal immediately before a game. But immediately after a game, it's a totally great time to eat because like, yeah, you know, like you need to recover. to get in the parasympathetic dominance and digest the food. Whereas you don't want your body to be focused on digestion right before you go out and run a race. Like that, you know, again, you're sending mixed signals to your body at that point. Right. So, like, I would definitely say, like, your goal is not to have, like, maximum HRV at, like, every second of every day because, like, you need to kind of. Toggle back and forth. Yeah, like, these resources need to go to stuff. Like, you have to do things that's part of being alive. But if you start to understand, like, how different things affect your HRV, you can start to. manipulate the timing of these things relative to moments where you need to peak, right?

Like, you don't want to be super stressing about, like, your exam tomorrow in the middle of a game day or a game. Right. But, you know, you should think about your schoolwork. Right, right. So day-to-day flexions are completely normal, right? I think we're remiss not to just mention why we've kind of chosen not to display HRB throughout the day because there are other wearables that kind of do.

But I think, listen to almost explanation on all the things. that go into it, it is a complicated and kind of noisy metric during the day, which is why we kind of don't display it. To really untangle it is a bit of a challenge. And that's why, you know, we've chosen as a company to kind of measure HRV while we do constantly taking HIV throughout the day, 24-7, we choose to measure during sleep. And that's when, you know, the moment where we can really essentially kind of mitigate the noise that's associated with all these inputs that go into HRV. Yeah, that's such a good point because our users ask about that all the time. Because we do record our intervals which give us HRV throughout the day. And what we've kind of found is that

like, you know, if I'm working on a new algorithm, my HRV is going to be lower than if I'm sort of responding to a social email. Looking at like average HRV over the day becomes like not that meaningful. And every time we've like tried to go look at it, what you see is that it's just like, it's very noisy and without a lot of understanding about like what was going on at every moment, it's really hard to interpret. So unless we wanted our users like every 10 minutes to be like, hey, like, how are you feeling right now? What are you doing? Like, you know, are you happy, sad, focused? Yeah, you go to the bathroom. Do you just drink water? Like, literally if I drink water right now, my HRV is going to go up. Um, because I've been bad and haven't had that much today. And like, that's not going to be a sign of like fitness, right? Like, it could be, or preparedness or readiness or anything. Like, yeah, I should probably have a glass of water before I work out. But like, if I do that now versus in 20 minutes, like, I'll have 20 more minutes of, you know, high HRV. But like, that doesn't actually really mean anything if I'm not going to work out till after work anyway. Right.

So what we wanted to avoid was like just creating more data for our users that like doesn't, is not actionable. Right. It doesn't add anything. We try to be very intentional with everything that we do. And so that every piece of information on our system, there's like a very obvious, you know, if you see this, do this. If you see that, do that.

And not just like to try and be the wearable that gives you the most numbers, but then you have to have a PhD to understand what to ignore and what's meaningful. Data for the sake of data is just not useful. Yeah. But one of the other things you mentioned that I think is also worth diving into is sort of our specific decision to take it during sleep. When we first started doing that, we actually have a patent for doing that. The sort of dominant protocol among people who were using HRV was to take it first thing in the morning. And if you actually read the papers about doing this by people like Daniel Ploos and Martin Bouchet out of New Zealand,

they all admit that they sort of do that for convenience, not actually. actually because it's a good time to do it. Because as soon as you wake up in the morning, you start thinking about what you have to do for the day, and it was very, very noisy metric. Yeah, you have to do a lot of modeling. Yeah. Like, HRV is responsive.

Five years. It's not. A lot of people, when they know they're being measured, they start to, like, breathe at, like, a very even, like, low rate. And respiratory rate affects heart rate variability a ton. Like, I can make my HRV do all kinds of funny things by, like, changing the way that I'm breathing. It doesn't mean.

anything about fitness. It's just a reflection of your respiratory rate. And so what we actually did was, we actually, this is so backwards in retrospect, but it had made a lot of sense at the time. Our whole sleep platform came out of, we're like, if we want our HRV measure to be meaningful, we have to take it during sleep. And we have to specifically take it during slow wave sleep. And I'll get into that in a second. So our whole sleep staging and sleep auto detection and all of that came out of, like, was inspired by this need to get the most perfect. HRV reading for the day that we possibly could. And, you know, now all the sleep stuff is like our user's favorite feature, but like if

we're being totally honest, that was like in order to enable HRV, like, that's how important it is. And the reason why slow-wave sleep is that actually your HRV changes a ton during sleep. It's really high in REM sleep. It's obviously high like during disturbances and stuff when you're awake, but that's because of changing activity levels, not because of anything meaningful. And then it's sort of in the middle and light sleep. And it's actually the lowest in slow-wave sleep.

But what's really important with HRV is not, like, what the measurement is. It's how it compares to previous measurements. And so we wanted to make sure that, like, night after night, it was comparable metric and that, you know, it really meant something that today's measure is higher than yesterday's measure or lower than the day before or whatever it is. And during slow-wave sleep, you're actually, like, the most kind of, I like to say, dead to the world. Like, you don't respond to environmental stimuli.

You don't see, like, HRV getting affected by things like temperature. The way it would be when you're awake, you don't see, like, sort of the stress. of the day and all those things kind of coupling in quite in the same way because they can affect like how much REM sleep you get. And if you just take the average over the whole night, you're almost going to be looking at, well, how much time do I spend in these different sleep stages gets like coupled into what your average HRV was. So, and then the other huge advantage of slow wave sleep is that for any kind of like sleep disorder breathing, like sleep apnea or, you know, it's precursors. You tend to have the most like disturbances and stuff during REM sleep. And you actually don't tend to have these apnea.

events during slow wave sleep. And those sudden changes in respiratory rate can really affect HRV in a way that's not physiologically meaningful to readiness. Right. And so we wanted to sort of minimize the likelihood that like our HRV was reflecting that. And so by taking it during slow wave sleep, we sort of maximize the likelihood of just a really clean signal that like night to night is like meaningfully comparable. Yep. I love it. So Emily, maybe just explain a little bit about HRV's role in WOOP recovery? Sure. So the recovery score is primarily based on HRV.

And then earlier we talked about how sort of resting heart rate in HRV when obviously normally will sort of trend opposite to each other. And when that relationship sort of decouples and breaks down, that can be really interesting. And so we also use heart rate in the recovery score, although it gets like much less consideration. Yeah. And then we put just a little bit of information from sleep. So the bulk of the recovery score, you're going to see it's very highly correlated with your HIV and sort of with this sort of interpreted in the lens of what's going on with your resting heart rate and what's going on with sleep. And then we just explain briefly why these three inputs together are more powerful than any single kind of metric alone. So sleep has been sort of used as a proxy for recovery for like a really long time, right?

Like coaches, I know a whole bunch of different universities would, like, ask their athletes, oh, how much sleep did you get last night? And it's actually a great metric a lot of the time. But think about what happens as soon as you get sick, right? You sleep 16 hours and feel horrible. So sleep is sort of one of those things that, like, it's mostly going to be a good sign of recovery, right? And, like, be highly correlated with being more recovered. But sort of when, sometimes when you get the most sleep, that's a sign that, like, something's really wrong. And the reason why we don't give sleep a lot of weight in our algorithm is because when it's misleading, it's so misleading, right?

Like you get the most sleep when you're the least recovered or like, you know, people, we see this a lot with like athletes go out and celebrate. They get hammered, right? And then they go and sleep a whole bunch. But it's like they're just nursing a hangover, right? So again, they're not recovered. And so sleep can be really misleading like that. We do know that like if you got two hours of sleep, there's pretty much no world in which you're going to be recovered. So that is very meaningful.

But the reason why even in that case, we don't give it a ton of weight in the recovery score is that we sort of let HRV and resting heart rate sort of tell that story. So, like, if I get two hours of sleep, like, yeah, I'm not going to be recovered, but HRV is going to be low. Resting heart rate is going to be high. Like, I'm going to show all these other signs. And so it's sort of in that case where it's a really good indicator, it's a redundant indicator. And trying to say, like, oh, you can only be 20% recovered if you got two hours of sleep is sort of, it's not mathematically. valuable, it's not sort of useful, and it doesn't really end up adding anything. And then on the flip side, like when you get a lot of sleep, either that's because you're behaving well and going

to be well recovered, in which case, again, we'll see that in the resting heart rate or HRV, or in the case where you're hungover or sick, it's going to be massively misleading. And then it's also true that, like, there's good quality sleep and bad quality sleep. So if I'm on a red eye, I might get six hours of sleep, but it's going to be really crappy. So like to put into the algorithm, like, you know, oh, six hours equals something nice. Right. When my resting heart in HRV are sort of saying, like, yeah, she got six hours, but not good. Yeah, she didn't spend much of it asleep. Right. Like, we wouldn't want, like, that high sleep score to, like, prevent the algorithm from giving you a red recovery. That's clearly what your body's

showing. So it gets us, like, kind of very little, like, hey, let's, like, look at what's going on with sleep. But it's almost no weight. Because we have these wonderful HRV readings that we put all this care into making sure are reliable. And then, you know, obviously, resting heart rate for the cases of like parasympathetic saturation to sort of just give a little bit of color to that. Right, right. So just explain, you know, I think a lot of us are trying to kind of hyperoptimized the week, right? We're looking like day to day. Just kind of explain, you know, how to use HRV from day to day versus kind of trends over time and what that difference means and how to think about it. Yeah. So like if my HRV is like high every single day, it means that I'm probably not

doing too much, right? Right. Like there's this great paper. that came out in 2014 by this guy Daniel Ploos down in New Zealand, and he basically showed that like variability in heart rate variability is a really good thing. And so actually like the athletes whose day-to-day HRV was sort of all over the place ended up, I think he was looking at Olympic rowers. So they ended up like improving their time and sort of doing better, I guess in the 2012 Olympics it must have been. Yes. Then those athletes that had sort of maybe on average, higher HRV, but like with sort of less variability. And what's so interesting about this is that it's sort of permission to get run down, right? Like we all kind of know that in order to get more fit,

like you have to go hard. Right. Or functionally overreach. Yeah, functionally overreach, right? And so you have to kind of go hard and you have to have these more challenging days. And it's normal if your body responds by like the next day being run down. Right. But then you have to take that information and sort of apply to your training. Right. Like actively recover and do things. And so you get it back up. And so what you start to see with people who are functionally overreaching followed by constructively resting, you know, followed by sort of like periodized training models is that like they're going to get more fit than people who just sort of like exercise at maintenance every day. And so they might like have a lot more yellow and green days,

but they're not going to make the same amount of progress. So, you know, we definitely don't want people to like feel bad about themselves or think they're doing anything wrong if they ever end up red. That's like a normal part of the training cycle. It's just that the information that you need to then action. You don't want to be read, you know, all week long. Right, right. And I think that's where, you know, I've seen, I think, our elite teams and athletes on the platform benefit from this data is that, you know, we've been able to kind of, to degree, move away from some of these more kind of broad brush stroke kind of periodization models and really think more day to day. With this, you know, broader periodization concept in kind of the back of the mind, but then be able to,

okay, what does this week actually look like? What does today actually look like? And be able to kind of hyper-optimized across the week, weeks, months, I think has been enabling, I think, fitness gains in a really powerful way. Yeah, because it helps you, like, stay on the right side of, like, functional overreaching and not non-functional overreaching. So, like, if I have this really tough workout and I'm read the next day, like, that's totally fine, that's normal, healthy. But if I then, like, engage in, you know, some recovery modalities and I'm read again the next day, like, now that's a good sign that, like, you're not really functional. Like, you're not in this adaptive state. You're run down.

And so that's a good sign that's sort of like you didn't quite get that cycle, right? And you can immediately kind of recalibrate and kind of move forward from there. Whereas, like, if you're green, do a tough workout, you're red the next day. You do recovery things. You're green the next day. That's totally functional. That's healthy. You know, go hard again.

Like, you're on the right side of that one. And we'll talk a little bit in a second about just behaviors, you know, because it's not just training alone that's going to influence your hearty variability. But obviously, there's lots of behaviors that can help contribute to a next day kind of higher HRV. So we'll get to that in one second. I think the final question is just around gender. You know, people ask all the time, you know, what's a good HRV? What's a bad HRV? And there are some kind of global kind of metrics, I guess, that we can kind of point to. But what's your viewpoint on just how do you answer? or kind of what's good and what's bad relative to HRV. Yeah, I hate that question because it's so much variability, right? Heart size, like genetics, yeah. Yeah, so, and again, like we talked about at the beginning of this recording that heart rate variability is just how this autonomic nervous system, like, happens to be manifesting in your heart rate, but it's not actually, like, perfectly one-to-one with, like, what

your vagus nerve, which is where, like, ideally we'd be measuring this, it would just hurt. So what we see is that, like, as people get older that that pathway between the vagus nerve and like how this just manifest in the heart seems to get dampened, even if fitness and sort of athletic ability doesn't seem to fall as much. And so we do see HRV like declines dramatically with age much faster than say like resting heart rate increases with age and much, much faster than we see, you know, like athletic ability declining with age. That's not something to like get upset about.

It just is something we see across the board. If you're older, your HRV is probably lower. We see slightly lower HRVs in females than in age-matched males. There's a bazillion exceptions there, but sort of globally that is a trend that's been observed. And we do see, you know, things like higher HRV endurance athletes than in, you know, kind of strength-based athletes. But really, like, we discourage as much as possible athletes from sort of, like, looking over at their neighbor's whoop and comparing HRVs to each other. And we also really discourage people from, like, measuring their HRV once and being like, oh, my HRV is, you know, 132, as if that means anything. You know, it's only meaningful when you're looking at your own data day after day after day and starting to understand, like, what's good for you, what's bad for you.

But there's very little, like, oh, if this is your baseline and my baseline higher or lower, like, I might be outrunning you and I might not be. Right. So, you know, how we apply this in elite environment is we're always looking at kind of the percent standard deviation. relative to your baseline. Like we, you know, that is the way to really think about it is. It's me versus me. And, and what is my HRV today relative to my baseline? Yeah. If there's a big standard of V8 percent inhibition, that means that, all right, I'm either positively or maybe, you know, negatively adapting to training or my lifestyle is, is such where it's, it's not contributing positively or my lifestyle is contributing positively to my HRV. Yeah, and that's like why

we gray out, you know, recovery for the first four days on WOOP, because it doesn't mean anything until you've established this trend. Right. And I bet like if you look at all of our elite teams on whoop, the person who's, you know, the big name athlete that everyone's excited about, like probably doesn't have the highest HRV on the team. Yeah, it definitely varies. And, you know, I think let's get into lifestyle because I think that's, that's really important, an important conversation I think our users will really benefit from. And I've definitely seen, you know, we talk about age and HRV. I've definitely seen some of our older, I say older, you know, athletes in their 30s, you know, early 30s, mid-30s, who have actually improved their HRV and resting heart rate

over time by just quitting tobacco and just being really discriminating around when they choose to drink alcohol and when they don't and obviously dialing it on sleep, you know, being more attentive to recovery modalities. They've really started to think more intentionally about their behaviors because they see this direct correlation between their behaviors and their next day recovery. So maybe we can kind of dig into just, you know, some of the lifestyle factors that really influence your autonomic nervous system. Yeah, so we did a study back in like 2014 and we saw that like after drinking alcohol, it took four days for this one like collegiate squash team to get their HRVs back to baseline. And I think it's totally crushing. What was

amazing was that like after we shared those results with them, they all went dry for the season and then went on to win the NC2A championship. So, you know, some of the stuff, like, yeah, it's, you know, it's crushing to realize that, like, you know, your cheese addiction is, like, causing problems. But, like, it's also wonderful to, you know, be told that. Right. I mean, if you look at, like, so many sports, right, the difference between, like, winning and losing, it's so small.

And if it's, like, the difference is, like, reducing cheese. I'm going to probably make the choice to reduce cheese. Yeah. I mean, I think, like, that's, like, the thing that's so wonderful about whoop, right? Like, we're not telling you to do anything. We're just giving you this information so that you can do what you want to do. Like, if it's not worth it to me to, like, shave a minute off of my 5K time because, like, I love cheese or whatever, then, like, go for it. But, like, you know, at least now you have that, like, information and, you know, something that can help you understand that, like, that is something that, like, if things change and that, like, sacrifice is worth it to you that you can make that.

And I think, like, playing around with so many of these different recovery modalities and understanding, like, what effect. you and what doesn't. Like, it's an up to you, you know, like maybe getting a massage is great, but, you know, it's $100 each time. So do you want to make room for that in your budget? And there's so many kind of things like that. And, you know, we generally assume that like all of our athletes want to do what it takes, but it still is up to them. Like, whoop isn't going to make you a better athlete. It's going to give you the information to make yourself a better athletes. It's almost like, you know, and this has always been kind of one of the, I think one of the principles is once you understand the factors that influence your performance, performance

no longer becomes this guessing game. It becomes a choice, right? And I think that's where I think our insight is really powerful as you start to understand how your behaviors through the subjective, you know, we've got these user inputs that pop up across each one of our pillars and we're able to then take some of the feedback from the user and what you're inputting and correlate it to your metrics. So we're able to kind of give you some insight into, you know, how sharing a bed, for example, or drinking alcohol or taking new medication might correlate positively or negatively to your data. And then you can kind of take that information and then apply it to kind of how the choices

that you're making throughout the day. And I think that's where, you know, this data has certainly helped me make better choices. And, you know, I feel pretty confident at this stage that I have enough understanding of how these factors influence my performance that I can make a choice that's either going to serve to upgrade my performance or downgrade my performance. And to your point earlier, it just depends on how important it is for me to kind of do what I want to do. But let's just talk a little bit about water and nutrition.

And, you know, Emily and I, neither one of us are nutritionists. So we're going to speak broadly. But I think that those two inputs, I think, definitely impact heart rate variability. So maybe just briefly just talk about hydration and how critical water is, you know, and how that relates to HRB. Yeah. So basically, hydration determines your blood volume. volume. And so the more liquid in the system, the more, the less hard your heart has to

beat in order to kind of circulate the oxygen and nutrients that it circulates. And so what we tend to see is that when you are better hydrated, your stroke volume goes up. So you basically start looking like you're more fit. And so, you know, you never want to be kind of exercising dehydrated because you're just working a lot harder because you're circulating less blood per heartbeat, which means you need to have more heartbeats in order to sort of do something. And so you're basically like your total maximum load that you're capable of outputting goes down. And so that's just you're disadvantaging yourself for no reason. And for the most part, you know, water is one of the things that's democratically available, right? We all kind of have access to it

for the most part. We're really, really fortunate and privileged to have access to clean water, right? So we consider that for Lockford word. Just do it. Just do it. Just drink water. For the love of God, drink water because that is one of the biggest you just never want to go to bed dehydrated because that will absolutely impact your heart rate variability your resting heart rate which will influence kind of your preparedness for for tomorrow so yeah drink water throughout the day that's really critical and generally speaking depending on what you're doing from you know workout wise almost an ounce per pound I mean that's probably a little bit much maybe 0.75 per pound something like that certainly if you're traveling getting on a flight you know you

want to drink more? One of the great things about hydration is that we have this great little built-in system to know if we're doing it adequately just by looking at the color of your urine. And I know it sounds a little bit weird and it's definitely not sexy. But, like, if it's dark, hydrate more. If it's like perfectly clear, you're probably doing it right. And, you know, you can just sort of calibrate from that and just kind of be aware of things like air travel being on planes are way more dehydrating than people realize.

So like if you're going to work out, if you're going to travel, if you're even just like stressed, it's hot out, you know, you can increase it. And if you're sort of not doing any of those things, you can decrease it. And just kind of get in that habit of checking in with yourself and paying attention to that color and sort of adjusting there because it's, you know, for so many things, being hydrated is just going to make everything function more smoothly. High level nutrition, you know, obviously, you know, we could go down a three-hour podcast, just a nutritional loan. But I think as it relates to nutrition and heart rate variability, I think it goes back to, again, like sending the right signal to your body relative to what you're

going to be asking of it. So if I'm going to go into a weightlifting session, like I probably want to have some carbohydrates, right? I'm going to need that. I don't need a lot, but I probably need enough to be able to sustain the level of energy that I need. After my workout, I probably want to take on some protein and vegetables. But I don't want to have protein and vegetables prior to my weightlifting session because I'm going to be asking my body to do something that it doesn't want to do. When I go weightlift, I want to be sympathetic, dominant, right? I want to, you know, epinephrine, adrenaline, cortisol. I want to be, you know, that's what I want pumping through my system.

I don't want to be asking my body to digest protein. So I think, you know, just thinking about what I'm asking of my body and how that relates to my autonomic nervous system. And just trying to make that as in sync as possible is going to kind of help your HRV, right? Right. So what you were getting at is sort of not just nutrition, but the timing of nutrition is really important. Yeah, and content, obviously. Yeah, and content.

But the timing, as it relates to your autonomic system, I think the timing is really, because it's not binary, right? No. And I think we kind of tend to talk about and think about it like that, but it's a little bit more complex. And I think that one of the things that's so exciting about the whoop system is that sort of there are some, you know, things that you can pretty much assume are universal, right? Like nobody's going to exercise better drunk. Right. So like alcohol, as far as the nutrition stuff goes, has like a very predictable relationship. But then a lot of other things can vary a lot from person to person.

So like, you know, some people are gluten intolerant and others aren't. And so for some people reducing or eliminating gluten from their diet, it's going to have, you know, a positive effect on HRV and other people it's going to have none. Kind of same for dairy, same for, you know, so many other things, right, like starchy foods and different things like that. And so you can start to use a system like this to sort of say, like, well, what happens to my HRV if I cut out this thing that, like, you know, is trendy to be eliminating right now? You know, there's all these, like, low FODMAP diets, there's keto, there's, you know, paleo, all these things. And, like, you know, I think a lot of people end up on these diets because, you know, somebody on Instagram had a lot of success with it. And, you know, that person very much, like, could have legitimately had a lot of success with it. But it doesn't mean that you will because all of our bodies are so different.

And so kind of playing around with when I do this thing and try this thing, what does it do to my HRV and then actually paying attention to that data for the next two weeks. Right. And sort of seeing, like, okay, like eliminating this was helpful, eliminating that wasn't. Like, I heard of somebody doing an elimination diet and they found it like almonds were like messing with them. And it's just like so random, right? And it's such a healthy food that like very few diets tell you to like eliminate all right. Right. But like if you have that sensitivity, like that that's helpful. And so, you know, you can kind of play around with these different things. Because for the most part with nutrition, like there's some general rules like don't drink a ton of sugary soda. Right. That's probably safe. Yeah. You know, a lot of, you know, you want to eat real food. I'm all about, you know, if it grew on a farm, it's probably good. Yeah.

And so if it's if it's real food, you know, that's like a great starting place, but then sort of where to go from there, you know, it is highly personalized. Yeah. Yeah, definitely. All right. So water, sleep. Meeting your sleep need is obviously huge and getting good quality sleep. I think just some behaviors throughout the day that can help with the quality of sleep, building in some mindfulness, some meditation throughout the day. So you're not building that negative stress accumulation can be a really powerful way to improve HRV training, thinking about your recovery and strain and kind of mapping those. close together will maintain a higher level of HRV. Again, understanding your physiological intent is really important because it doesn't always mean, you know, low HRV is not always a bad thing, right? You're putting stimulus on your body. You're going to expect that. It's just making sure that that's not a trend that's happening over long term because that can lead to being run down or kind of overtraining syndrome. Is there anything else just behaviorally, Emily, that we've kind of left out that might be good for listeners to dial in on? Well, I mean, the thing

is I guess that like it's everything right and it's just like how much you're doing these different things so like and a lot of it's like sometimes modulated through things like sleep so like if you're getting a lot of like screen time at night you're not going to sleep as well and so then if you don't sleep as well you don't recover as much and so you're going to see this effect on HRV right sort of anything that's going to harm sleep is likely going to harm HRV psychological stress throughout the day right psychological so we've seen like you know people who meditate and can kind of like deal with that in a very healthy way that, like, you know, you can handle that and then it doesn't show up in their each other because it's being sort of positively handled.

Healthy relationships. Healthy relationships, right. I mean, but then it's also little things, like just having, like being physically comfortable, right? Like, we work hard to, like, compensate for that when we're not. So if you're itchy, you have, like, a whole bunch of, like, little stimulus. So it's like, you know, if your clothes are some, you know, material that, like, your skin doesn't like, you know, that's not going to, that's going to, like, cause irritants. that's going to make you like hypersensitive to that and you have all these little like neurons firing

that you should just be not focused on when you're trying to work out and you know obviously when we're hot we take a tremendous amount of energy to thermo-regulate and so there's something called like the thermo neutral zone which is like when we don't use any energy to either warm ourselves or cool ourselves and so if you're sort of in that zone then your HRV is going to be like as high as possible but it's really really hard to sleep for example when you're hot because it's such a sympathetic activity to thermo regulate which is sort of obviously counterproductive to sleep, which is a parasympathetic activity. Right.

So we see stuff like that. So the answer is, is like pretty much everything can affect your HRV either for better or for worse. Cool. So in short, hurry variability is important to track. It's important to understand. And obviously, at whoop, we feel like taking it during sleep is kind of the answer in terms of really understanding, you know, your next day capacity, both mental and physical. So it's a powerful marker.

I think, as always, if you have any other questions that we weren't. to kind of address here. Let us know. We'll do our very best to answer those. But that's pretty much all we've got for today. Thanks so much for listening. We really appreciate the WOOP community and your feedback is always welcome. So Emily, thank you so much for all your insight and expertise. Thank you. Big thank you to Kristen and Emily for the in-depth look at HRV and its impact on performance. If you enjoyed this episode of the WOOP podcast, be sure to leave a rating or review. Subscribe to the Wootle podcast. You can check us out on social. at WOOP at Will Ahmed.

If you have a question you want to see answered on the podcast, email us, podcast at WOOP.com, or call us 508-443-4952, and it might just be answered on a future episode. New members can use the code Will WI-L to get a $60 credit on WOOP accessories with a new membership. All right, that's it, folks. I wish you all a great week. We'll be back next week and stay healthy and stay in the green.

Thank you.