WHOOP Podcast - The Science of Stress & Sleep For Optimal Performance with Dr. Bill von Hippel

Episode Date: June 4, 2025

On this week’s episode of the WHOOP Podcast, WHOOP Global Head of Human Performance Principal Scientist, Dr. Kristen Holmes, sits down with WHOOP Senior Scientist Dr. Bill von Hippel to discuss the science behind stress and sleep and its impact on performance. Dr. Bill von Hippel is a scientist, author, and renowned social psychologist and evolutionary specialist. In today’s episode, Dr. Holmes and Dr. von Hippel discuss cardiac responses to threats and challenges and the core 4 circadian behaviors that help sleep consistency. (00:36) Intro to Cardiac Responses and Daily Threats and Challenges(03:08) Using WHOOP to Conduct Studies(09:09) Stress Monitor: Understanding Stress vs Challenge(11:10) Stress + Sleep Data on Shiftworkers(23:27) Low Fit vs High Fit: Use Case for Strain Coach (32:26) Amplifying Effects of Exercise(37:18) HRV-CV as a Predictor of Strain Load(43:03) Behaviors That Improve Sleep(51:06) Core 4: Circadian Behaviors That Help Sleep Consistency(58:49) The Impacts of Social Jetlag(01:02:53) Negative Impacts of Oversleeping(01:07:2) High HRV Indications and HRV ImprovementsReferences:WHOOP Wear Frequency StudyShiftwork Biometric Analysis StudyDr. Bill von Hippel:LinkedInThe Social Paradox: Autonomy, Connection, and Why We Need Both to Find HappinessThe Social Leap: The New Evolutionary Science of Who We Are, Where We Come From, and What Makes Us HappySupport 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

Stress monitor, what it's telling you when you're stressed, is far more sensitive to challenge than it is to threat. And so when I look at my stress monitor and it says, Bill, you spent two hours in the high stress zone today. That could have been a great day. The only days that you aren't going to get any stress at all are going to be days where there's neither threat nor a challenge. And there's another word for days that have no threatened and challenge. And it's called boring. When you see a high stress monitor score, it could be that, yes, you were threatened about something. But it's very possible it was a day of high engagement.

A day we were excited. Challenge is what makes life exciting. And of course, that shows up in stress monitor. as a sign that you're stressed, but it's not a bad form of stress at all. Dr. Von Hiffel. It's great to see you. Senior scientist at Wu. I'm so excited for this conversation.

We have a paper that was just published, which is very exciting. Cardiac responses to daily threats and challenges during wakefulness and sleep. So why don't you tell us a little bit about what we found in this paper and why it's interesting? And I might stop you just to define some things as we go. This paper is part of a big project that we ran through Woop Labs, where about 11,000 people volunteered to measure their blood pressure and then answer some questions about stress that they experienced both in the evening and then they answer in the morning anticipating their day. So there's a really lovely data set that actually tells us lots of cool things, some of which we could come back to later in this podcast, like, for example, sleep concerns. But for now, the focus is on these ideas of threat versus challenge. Now, when we tend to think about stress, we think about things being bad.

Like I'm really stressed about the drive I have to do tonight and whether I'll get there on time or whether traffic will be too bad or maybe it's not even safe that the weather's bad, whatever. For over 40 years now, since the work of Lazarus and Folkman in the early 80s, we know that stress actually has two components to it. It has the bad side, which is what they call threat. And a threat is when whatever's going to be demanded of you is greater than what you're likely to be able to achieve, either because you don't have enough time or you don't have the skills or training or whatever. And so you're threatened when probably it's not going to go well. In contrast, challenge is the state when you're going to have some big demands made of you, but you're equal to those demands. And there's every chance that you're going to succeed.

And so when Mahomes goes out and plays the Super Bowl, he's not threatened. He's excited. He's challenged. And so it's a positive state. It's not, you know, life without challenge is a boring life. So stress really has these components, both the positive and the negative. And the key, what it really comes down to what Lazarus and Folkman, told us 40 years ago, is that it all depends on whether you've got the resources to achieve

whatever it is that's going to be demanded of you. And so the same thing could be threatening to one person but challenging to another. So what we did in our surveys, we thought, well, it's time that we started introducing threat and challenge, you know, into the kinds of things that would measure. So we asked people, we defined it and we asked people about it. And if you're one of the 11,000 people who did it, you know for a while, you remember this. Then we tried to look at how those states, whether you anticipated threat or challenge that day, whether retrospectively you experienced threat and challenged that day, actually predicted things about your cardiovascular state and about stress monitors. So that was what the project was about.

Amazing. So folks woke up in the morning. A little survey popped up and we asked them about how they perceive their day, if they perceive it as threatening or they perceive it as challenging. And then we were basically able to tie back their answer with things like sleep. So tell us a little bit about that finding. So the coolest thing in my mind, I think the most interesting finding, but it's up to you to decide, of course, you, the listener, the most interesting finding is that threat and challenge look a lot of like during the day, but challenge looks like threat light. And so when you anticipate or retrospectively experienced challenge doesn't make a difference, your heartbeat goes up about a half a beat for challenge and then about

a full beat for threat on average across the whole day. So you're, you know, that's your body gearing up to deal with the problem, right? And it gears up more for threat than it does for challenge, in part because threat is more stressful than challenge. Both are stressful. Both are more stressful than neither because, of course, you don't know a challenge is going to go well. You could fall in your face. But it's also exciting because you could really succeed. So it's still stressful, but threat you don't expect for anything except a bad outcome and so stress levels are higher and heartbeat accordingly is higher. But what's I think even more interesting than that is that at night before, so now this is the night I'm sleeping before. I'm going to face these threats and challenges. When I face a threat, when I anticipate a threat, again, my heartbeat goes up, but when I anticipate a challenge, it goes down. And that's really nice for sleep because you want parasympathetic dominance during sleep, right? And so you literally sleep better when the following day is going to be challenging than when it's just going to be dull and nothing's going to happen, which is really cool.

So cool. So we're asking folks in the morning, of course, when they wake up, whether they anticipate threat or challenge that day. But it isn't just according to them then, right? It's the night before you're thinking about, what do I have to do tomorrow, right? And that cogitating on whatever it is that they have to do tomorrow is actually influencing their sleep. Yeah. And for all we know, it could be a week ago, right?

Because you've got a big event coming up. You've got to make a pitch to the company, whatever it is you do. You got to travel. Like you have to, yeah, mobilize all the center. And so it's not even necessarily the night before, but that's when we tapped into it. Right. And so humans, you know, we're forward-looking species. We're the only one that is.

Yeah. And so it's really important that we gather together our resources and deal with the problem. And what's so cool about challenge, it actually helps us sleep a little bit better in preparation for something important that we think we're going to succeed at. So you and I think a whole lot about the interrelationships of our psychological processes and our physiological responses and vice versa. And that's really what this paper captures. I think in such a beautiful way. And maybe just as someone who has, you know, is in the field of psychology and works very closely with this obviously all this physiological data. Why should people

even care about these interrelationships? What makes it so special? They're special for a host of reasons. But if you look at the cardiovascular side of the equation, our mind evolved to do what it does in the context of our body. And so there's no dualism there. They're not separate systems that are running on their own. Our body responds to our mind and our mind responds to our body in the same exact way that if I get really poor sleep in one night, the next day I wake up and I'm groggy. If I work out really hard, my body's tired, all those things. But it also goes the other way. When, you know, here we are, I'm thinking about tomorrow and I've got this, let's call it a big softball game, right?

And I think I'm going to play well. I'm confident in my position. I'm first baseman. Things are going to go well. It went well last week. We're going to beat these guys. But it's not guarantee. That fact drops my resting heart rate an average of a half a beat all night long, right?

So, wild. So my body's responding to this sort of. happy, excited state by saying, well, let's get ready for this. Let's make it happen. I think to me, like what I love about investigating these questions in the way that we do is that there aren't a lot of good published data that showed these kind of relationships with the kind of numbers that we have. You might get 13 people, right, to participate in a study like this, but we have literally thousands of people who are able to participate in this study to tell us something really interesting about how our perceptions impact our sleep physiology. Yeah, it's a

real privilege to have data set of this size because it does something that you can never do otherwise, which is we're used to bumpy looking data whenever we look at changes across time or place, but the bumps are meaningless. All they're really looking for is what's the slope underlying the bump. But with the size of data sets we have at Woop, every bump has meaning. And so if it squiggles up a little bit before it squeakles down, I'm like, why is it doing that? Which I never asked before my life when I had a sample of 100 people in some experiment that I ran in the lab. Right. It's really cool to just to know that every single thing you're looking at is meaning.

And, you know, when I think about kind of translating these data and, you know, what would we advise people? How would we advise people to think about these data? I mean, from my perspective, is that your perception of kind of your day, your perception of tasks actually really does matter, you know, has a meaningful impact on your physiology that could have a downstream effect on things. like sleep. And so, you know, to the extent that we can, to be able to label am in a state of threat, I'm in a state of challenge, and then then be able to back up and be like, all right, what do I need to actually shore up in my life so I can put myself in this challenging state, right? We're going to be far more effective when we're in these states of challenge versus states of threat. So, you know, how is this practically useful? I think if people start to think more deliberately about which state

they're in, then they can kind of back up and take corrective action if they need to. I totally agree. And sometimes it's just not possible. Sure, sure. Sometimes I just don't have the resources to do. I don't have the math skills. I don't have the, and they're not going to transpire in the next 40 hours. You said, you know, Bill, have your resignation on my desk in the morning. And I'm like, oh, no, you know, and so I'm going to get fired and there's just nothing I can do about it. But most of life isn't that black or white. Most of life is in this gray zone. And so if you stop and step back and say, okay, what can I do about it to do my best chance to ensure

success. How can I engage positively with this? How can I go in with the best possible attitude? That tries to turn threats into challenges. Now, again, remember I mentioned earlier that we tend to think about stress in the negative way. But the same thing holds when we're looking at the relationship, the relationship between mind and physiology with stress monitor. Remember, stress monitors is that link between your resting heart rate and your HRV. And what we see is that stress monitor, what it's telling you when you're stressed, is far more sensitive to challenge than it is to threat. And so when I look at my stress, monitor and it says, Bill, you spend two hours in the high stress zone today, that could have been a

great day. The only days that you aren't going to get any stress at all are going to be days where there's neither threat nor a challenge. And there's another word for days that have no threat and challenge, and it's called boring. And so when you see a high stress monitor score, it could be that, yes, you were threatened about something, but it's very possible it was a day of high engagement, a day we're excited. Now, yes, we like relaxing days where nothing happens. They're not necessarily boring. They could just be pleasant vacationy. But as a rule, challenges what makes life exciting. And of course, that shows up in stress monitor as a sign that you're stressed. But it's not a bad form of stress at all. Stress monitor is more sensitive to challenge. So what

is really picking up is the activation. So it's less sensitive to that withdrawal state where you're in threat. Now, mind you, it can pick up threat too. And particularly it picks up threat better if you say, looking back on your day, was it threatening? Then stress monitor is more likely to get it. But when you anticipate threat, stress monitor can't really see it. Whereas when you anticipate challenge, stress monitor grabs that right away. Yeah. I think it's interesting. For people who focus or who are looking at stress monitor, I think it's a really important

bit of insight because I think we might have been interpreting the results maybe a little inaccurately that that stress isn't necessarily bad. It could actually just be, it's picking up a challenge. That's right. And so when it says you had three hours and you're like, gee, that was more than I thought, think to yourself, well, wait a minute. Was it a bad three hours or was that a high engagement? You know, the Moms is going to remember winning the Super Bowl and overtime.

for the rest of his life. He's going to keep going back to that and thinking how fun and exciting it is. That's what challenge is. It's fun and exciting. It's also scary, but it's fun and exciting. It's very cool. All right, shifting gears. We're going to talk about shift work data. We've done a lot of research in this area. This is a very interesting population and they have enormous demands. Physically, mentally, emotionally, their job is really, really hard. Let's talk about some of the work that we did with Denver Health, where we've published now, a third paper. So let's maybe just go in chronological order. Let's talk about the first paper. What do we find? Okay. So you're straining my brain, but I'll do it. What happens

on call doesn't stay on call. That's right. And so the first paper, this is a project that was run by some of our wonderful colleagues who are themselves emergency medical physicians. Acute care surgeons. Yeah, that's right. Mitch Cohen and Jamie Coleman. And they moved around a fair bit, but when the project started, they were both at Denver Health together. That's my understanding. And so they gather this amazing data set where they track hundreds of surgeons who are acute care surgeons who have to take call because, of course, that's her job. People don't only get in car accidents during the day. So now these emergency care physicians get called in at all hours. And everybody has to take call.

And in fact, in their sample, the average person takes two nights of call a week, where they're actually in-house, which is their term for in the hospital. So in the first study we found, look, these people love what they're doing, right? They love their jobs. They love putting people back together. And I remember talking to Jamie one morning on a call where she was saying how the person came in and basically all their ribs had broken from their backbone. And I was like, that's the most ghastly sounding accident I've ever heard. I mean, you're going to be in this pile of mush. And she's like, no, it was super interesting.

I was like, are they dead? She was no, no, no, I was able to fix them. I was like, oh, my God. It's a totally different way of being in the world. I've never put together somebody who was that broken. So obviously what they're doing is super exciting for them and super rewarding. But of course, doing it a night is really hard, right? Doing it in the day is what we've, that's how we're diurnal animals.

And so it's costly for them to do it at night, especially since they're typically then losing a lot of sleep. And sure enough, in that first study, what we found is that every episode of call that they do increases their feeling, their momentary feelings of burnout. Just that day, I'm feeling burned out. it increases their momentary feelings of exhaustion, and then those momentary feelings just accumulate over the course of the year such that they feel this emotional form of burnout. You can divide burnout into different components.

They don't feel unappreciated. They don't feel those things, but they feel just emotional exhaustion. After being on call, two nights a week, week in a week out. And the scale we use is the Maslik burnout inventory is what we use as our measure. That's right. It's actually each one of these episodes of acute care during the next. night and then if they they like I said the project was amazing they then broke it down well did anything particularly stressful happen while you're on call did you have to do surgery did

surgery go badly now of course having to do surgery was not a problem if they could if they were in house that's what they were there for but if it went badly then things looked even worse because of course sometimes when somebody's ribs are all broken from their backbone they die and they can't save everybody and and that seems to be really that too has a high cost to them and leads to burnout. Yeah. What do you feel like, you know, for, for, for doctors, Jamie and Mitch, you know, what do they, what do they take away from that? Like, what's the action item? What's the policy that hospitals need to think about, you know, if we're, you know, because we're doing this research for it to be useful. Yeah, exactly. At an individual level and, and hopefully at a

policy level, right? Like, we're trying to humbly change the world, you know? Agreed. A little bit at a time. A little bit at a time, you know, with these, with these insights. So how can we apply? What happens on call doesn't stay on call. So the good news is that the third paper that we've written, so skipping over number two for the moment, that just came out a week or two ago, actually addresses that very question. Great. And so in that study, we looked at differences between different call cultures, because remember, the doctors that they recruited were from all over the U.S. And so some of them worked in tiny hospitals, some worked in huge ones. Yeah, there's 27 different locations, I believe, across the state side. I've got to mean, I can't remember, but that sounds right.

There's 270 acute care surgeons across the country. And to Bill's point, They're in different regions of the country. So just to back up, so people heard you, call culture is important for people to understand. Every one of these kind of hospital systems has a different call culture. Right. And basically what that meant is that you could divide into two basic patterns of rules. They're way more detailed than this. But essentially, one type of call culture is if I was on call last night, so that means I'm in the hospital all night.

Maybe I slept in a cot, but I probably kept getting bugged and did surgery and things like that. If I was in the hospital all night in one type of call culture, that's part of my job. And so the next day I go about work as if it never happened. I still got to go to work. I still got to do everything else I was doing. And my day might segue to my night, which might segue right back to my day without me ever going home. In contrast, some other hospitals have the rule, well, if you're on call during the night, you go home as soon as it's over.

You don't even deal with your patients anymore. Somebody else will do rounds. Somebody else will cover all those things. And so that's kind of the two main types of culture. And the interesting finding from that paper was that if you're in a culture that doesn't take into account what you just did all night, then every episode of call has a bigger impact on your burnout than if you're in a culture that takes it into account and now tries to be kind to you in return. And so we don't know if it's the actual physical having to be up forever like that or if it's just my hospital doesn't really appreciate what I just did for them all last night. Or maybe it's a bit of both, probably both.

but whatever it is, there's greater burnout from the exact same experience if your hospital doesn't like pat you in the back and say, go home, you've earned it. Beautiful. I mean, for me, I think that's a really important data point that hospitals could learn from, you know, if they care about mitigating some of the dilatory effects of being up and working at night under very stressful conditions. No, that's exactly right. And in fact, Jamie talks about when she presented this work at one of the big conferences,

some of the old guys get up and say, what are you talking about? a privilege to be up all night and saving lives. How could you be complaining about this? And Jamie's not saying it's not a privilege, but she's saying, look, what you don't understand is that we live in a different world than we used to live in. And now there's a lot more attending physicians who have to be there. There's a lot more paperwork that's involved with it. It's not the same job it was 30 years ago. And so hospitals should respond to that fact and should treat you a little bit differently as a consequence. Yeah. Just because it was done 30 years ago. Doesn't make it doesn't make it good. Yeah. Exactly. So we need to evolve and recognize that. And I think the second

paper, we see the physiological cost so clearly in this job. And this is really sobering when we were able to kind of look at the physiology of these humans. So maybe just talk through what that look like, because it's quite shocking. Sure. So this final paper is actually not published yet. In fact, we haven't even really put pen to paper to write. All we've done is analyze it. And this actually came, you were the one who sparked my looking into this question. And basically, what we started I'd ask is, well, all right, can we see any consequence in their cardiovascular system? Because, of course, that's what who is really measuring is cardiovascular fitness. So can we see any consequence for this 10 years, on average, that they've been on call

two nights a week every single week, except for the few holidays they get for a decade, right? So for 10 years on call for two days on average per week. Yes, overnight, in the hospital. If you're either sleeping on a cot and getting up bugged or you're actually doing surgery all night long. And look, you can see the cost when you talk to Jamie and Mitch on Zoom anyway, right? You look at their faces and they go, I've been up for 36 hours and they're leaning on, you know, they're leaning on the computer screen. I don't know how they do it either. Those are two of the hardest working humans I've encountered.

They're just insane. But what we find when we do that is that HRV CV, which is the variability in your HRV over a longer period of time. Remember, HRV is just your moment-to-moment variability in your distance between your heartbees. So HRV CV is just literally the coefficient of variation. So we're looking at basically how much does HRV change day to day? Yes. And then we're measuring that variation. That's right.

That's right. Over a longer period of time. Over a longer period of time. A week, a month, a year, whatever you want. Yeah. And when we do that, we find that what you want is low variability. Right. So this is opposite of just kind of how we think about acute HRV where, you know, high

HRV is better. When we're looking at HRV CV, a lower CV, means that you're adapt. more functionally, a higher CV actually means you're not adapting as functionally. Exactly. So if imagine you somehow talked to me into going running with you, which you can't do, so don't even try it. But imagine you did. At the end of some heinous run that we did together, you would have almost no impact on any of your physiological metrics. And tomorrow I would look like I got kicked in the face by a horse. And so that's because my HRV CV is way higher than yours. So you're ready to take on any strain that you face, and I'm just not. And so what that means is that

An elite athlete has a really low H.RVCVCV. No matter what they do tomorrow, their body can, fine, I can deal with that. It's going to be down. It's going to adapt. It's going to be ready to go. And a 61-year-old schmuck like myself does not, right? They're going to respond very poorly to really hard. I can handle light things, but I can't handle hard things.

And so we can look at the H.R.V.C.V.V.C.V., which we did, basically, what they look like. So their average age is like 42 or 43. Forty-three. Yeah. And they look like there's 60-something. They've literally aged cardiovascularly two decades more than they really are by virtue of this decade or more of two nights a week. Yeah, it's huge. Now, remember, we haven't published these data yet. So it's possible that in peer review, which is a super important process, somebody will find fault with it.

And then I would say, oh, it turns out we're wrong. And so you cannot take that to the bank yet until it's published in the literature. But we're going to talk about a lot of new stuff today, at least I hope so. Yes. And so when they're not yet published, please take them with a grand assessment. salt, but take them as a strong hypothesis. Yeah, the first three papers we've talked about have gone through peer review and have been published. So this is the fourth paper that we're talking about that we're in the process

of kind of writing up. But we have analyzed and we've looked it over. We feel really good about it. So we'll see what happens. We can still be wrong, but it's, it looks very promising. I think one of the really exciting things that we're able to do here at Woop is, is measure the cost of certain behaviors. And understanding shift work is, it's a super important function in society, but it does create a lot of health problems for folks in this profession. So if we can, I think these kind of these learnings can help us make conditions safer and better for these folks. Right.

I mean, so the downside is like cult culture can help you not be burned out as much from what you have to do, but your body's going to do what it does, when it has to work all night. And so we've got another data set where we've been examining the same question where we looked of people on the Woot platform who are shift workers who do so much shift work that essentially 50% of their nights they sleep during the day and 50% of their nights they sleep at night. So these are people who in principle, day should be no worse than night because they do it half the time. But if we're diurnal species, which we are, and if we're not meant to go to sleep when the light is up, you know, et cetera, there still should be a cost. And sure enough,

in these folks, so now we're not looking at different people. We're all packed within the same people. We find that on nights where they sleep during the day, we don't get the characteristic rise and fall in duration and probability of slow wave sleep that we get when they sleep at night. And so what a proper night sleep looks like is early in the night, you get this big peak in slow wave sleep, and then it slowly dissipates, you don't do it very much anymore. These folks who spend half their nights working and therefore sleeping half their days, when they sleep during the day, they barely get any peak at all in the early part of the night in slow wave. Now, I have no idea, of course, if that's what's the problem in the doctors, but it seems highly likely

that that loss of early night slow wave is just something that accumulates in your cardiovascular system. That's when all the repairs happening. Yeah, I think changes in architecture are really interesting. And we see this in other data as well and can maybe shift to that data set where we look at folks who exercise and kind of are in the higher fit bucket have a fundamentally different sleep architecture than people who are in the lower fit bucket. So maybe we can segue and we'll kind of get into kind of strain effects. What I love, I think, in society right now is I think there is this acknowledgement that exercise actually really matters for our brain health, for our hormone health, for everything.

And it turns out that we actually see exercise really matters for our ability to get a quality night's sleep. That's right. And so maybe talk a little bit about how. we think about low-fit, high-fit, how we come to those kind of delineations, and then the data. Sure. So we've been looking at low-fit, high-fit, in one basic way, but then looking, splitting them to two types. So the basic way is, how often do you meet your strain targets? You know, easy to do you. You just get up in the morning, you see what it's asking of you,

and then what do you look like by the time you go to bed. Yeah. So folks, we have strain coach for people who are listening, and we're going to give you a strain target every day. So exactly. And so we divided the sample into people who almost never meet their strain targets, people who meet them, you know, about half the time, and people who basically always meet them. So you can think of the sort of lower third, and actually it's about thirds, lower third of the sample as far as activity levels, middle third and then the top third of the sample. And when you do that, you can then look at the long-term effects of what does it mean to be somebody who's always meeting strain versus almost never

meeting it. Then the second way that we're going to look at this exact same question is look at it within person. And so because our samples are so big, we could look for people who go for at least 60 days, typically when they first get the device, hardly ever meeting strain targets, despite wearing it. And then after that 60 days, these are people who, although they didn't meet it for 60 days, for whatever reason, they decide to get it together, and they start almost always meeting it for at least 120. So it's a very specific sample, right? But with so many people on the platform, we can find lots of those people. So now we can look at both the between-person effects of somebody who makes strain targets versus somebody who doesn't, and we can look at the within-person

effects, what happens to over time. And what we hope, of course, is that they tell us the similar story, and the good news is that they do. Not quite the same, of course, because somebody who's always been doing it has been doing it for longer than 120 days, but nonetheless, the story looks very similar. So if we start with two different samples, folks who basically always do and do and new never do. We can start with, for example, HRV. If we look at folks who basically almost always meet their strain targets, their average HRV is 70. Now, that might not seem super high. But remember, older folks tend to have lower HRVs, and so it all averages out. In contrast, the folks who almost never meet their strain targets, their average HRVs in the upper 40s. So it's more than 20 points

different. I mean, that is insane. So we just need to pause because I think, you know, we don't give enough air time to strain coach. Yeah. I mean, strain coach is so damn powerful. Strain coach knows what it's talking about. It knows what it's talking about. And I mean, just if you literally, if all you do is just listen to your strain target, meet your strain target, you are in such a good spot.

All right. Talk about resting heart rate. So resting heart rate, we see a similar story. So the folks who basically always meet their strain targets, their resting art rates around 54. Okay. There's the folks who almost never meet their strain targets. It's up around 61 and a half. I mean, yeah, seven points difference in resting heart rates.

That's a big difference. It's so wild. Yeah. So these are big differences. We find sex differences within that as well. Yeah. On average men have lower resting heart rates and slightly higher HRVs. But basically, that's what the story looks like.

And age, obviously age differences. Age makes way. Age is massive. Way bigger effects than sex differences. And so people are super fit, but in their 50s and 60s, their HRV is in basement. like mine and hovers in the 30s almost all the time and if you're ever went to the 30s you check into the hospital and so but I'm going to like oh 38 I'm doing pretty good today so that's what happens but what's also interesting is when we look at their sleep and here we find that the folks

who always meet their strain targets you know you'd think oh well they're working hard they must sleep a lot no it's the exact opposite they're actually sleeping about five minutes less per night than the folks who almost never meet their strain targets yeah and so So their body just becomes more efficient or it started life that way. We don't know with certainty. But I'll come back to that point in the second because remember we're going to look at people who change themselves. From here, you'd either say, well, if you're genetically predisposed to really be full of

energy, then you exercise a lot and you don't sleep much. But that leads to, well, can you change yourself? What happens if you just pick up your game and start exercising a lot? So to answer that question, we turn to that kind of interesting sub-sample of people who basically never meet strain targets for at least two months and then do and then do for at these four yeah and when we do that we see the differences in hrv and our hr are not as big as the ones i just told you but they're very clearly there if we start with hrv basically when you never met your strain targets you start out life around 60 if you're male around upper 40s if you're female

and then and again there's age differences as well and then as you start meeting your strain targets your HIV rises about five points. And there it seems to basically flatten out what it would do over longer periods of time. I don't know. My guess is that it would slowly, slowly continue to rise, but we see less of a rise after the first few months of meeting your strain targets. And we see the same thing with resting heart rate. If your male again, it starts out pretty close to 58, tiny bit below that. And then as you start meeting your strain targets, it drops down almost to 54. So you gain almost four points. And then it kind of flattens out. The question, though, of course, is what happens to your sleep? Do you start to, you know, you're suddenly meeting strain targets

that you never used to meet? Well, sure enough, as you start to exercise more, for the first few months, you start to sleep a little bit more, but then you start to sleep less. So much so that by the end of that six-month period, you know, your first two months not working out, the next four months I'm working on, your sleep is actually lower than it was when you started. So you're sleeping less, you've become a more efficient machine. One of the things that I think is also really important to call out is strain coach. So how much strain you can take on today is based on your recovery, right? So how recovered are you to take on strain? And then we'll assign you a strain target based on that recovery. So what's really cool is that the people who are following strain

coach are basically you're getting assigned a strain that is appropriate relative to your recovery. Absolutely. It's not the same every day. Yeah. And it's going to be different. And that's where, I mean, this is the whole thing we're trying to solve as a coach for 13 years. I mean, This is the golden bit of information in terms of knowing how hard do I train my athlete, right? It's got to be based on their capacity that day, right? Because it stands to reason, if you're in a situation where you are, you've got a capacity and you are exceeding that capacity, that is going to lead to burnout, right? If you do it every day.

Yeah, and some days a little bit is functional, right? Like what I'm kind of getting at is that when you are kind of appropriately applying load relative to recovery, your sleep is going to kind of adjust in ways that are super adaptive, right? You're able to spend literally less time in bed, right? The more appropriate you train. You know, if you're under training, that is going to probably lead to sleep that is not as impactful, right? Whereas if you're, you know, really training in ways that are appropriate and functional, you get just this cardiovascular bag for your buck. You actually have to spend less time in bed and you become a more efficient sleeper.

I mean, the knockoff effects are just. Yeah, very clear. I remember having a conversation about these exact data with my nephew and his roommates. And they're all these ultramarathoners. And I was asking them, how do you sleep after a regular training day? Like when you're properly training, and they're like, oh, I sleep beautiful. I say, how do you sleep after a marathon? Oh, I sleep terribly, right? Because then you've over... You've ever trained. It's costly that night. The next night you're back and settle. But for them

on days where they do nothing, they feel like they sleep not as bad as after a marathon, but they sleep, their sleep is very poor. And that's where performance and health are orthogonal, right? Like, but it's worth it because you're sacrificing. Over time, that's, that also helps them build in the end, right? Of course. Yeah. You keep running marathons and eventually that's not a big deal. Right. Totally. What's up folks? If you are enjoying this podcast or if you care about health, performance, fitness, you may really enjoy getting a whoop. That's right.

You can check out whoop at whoop.com. It measures everything around sleep, recovery, strain, and you can now sign up for free for 30 days. So you'll literally get the high performance wearable in the mail for free. You get to try it for 30 days, see whether you want to be a member. And that is just at whoop.com. Back to the guests. Amplifying effects of exercise.

So this is not something that I was actually looking for. It was something I found on accident. And I can't even remember what I was looking for when I found it. It's a little bit like you're going through the attic looking for your skis and there is that tennis racket. Anyway, yeah, yeah. So somehow I accidentally ran across this. What I found was that on days that you exercise, if you've done something good, it has a bigger impact on you than if you haven't done something good. And I think I was actually looking at the time restricted eating data that you were

collecting. I think that's where it started. And you'd ask me to do something with that. And I can't remember what you even asked anymore. But I was noodling around. And I saw that on Daisy, you underreach compared to what strain coach says that you should do, that TRE, let's say, we'll look at the effects on HRV. That it gives you, if you engaged in TRI, you gain two points of HRV. And TRI is time restricted eating. Sorry, yes, that's right, which means, you know, just during the daylight hours, typically. But if you overreached, you gained three points of HRV by time restricted eating. So it literally had 50% more impact on you on days you exercise more. And the same holds with resting heart rate. You drop one point on Daisy underreach, but you drop a point in a half

on Daisy overreach. So it's like, well, that's pretty weird. I wonder if it emerges in other domains as well, right? Like this could be this weird thing that has to do with TRE. Because, you know, eating and exercise, they're obviously related. So I said, well, what's, what has been Kristen that been having me look at that has nothing to do with exercise at all? And I thought, oh, morning Sun. Getting a light on your face in the morning has no bearing whatsoever on your actual activity. Well, the effects aren't as large, but they're clearly there. So on days of you underreach, morning sun gains you about 0.65 of a point of H.RV. On days of you overreach, it gains you like 0.85 of a point of H.R.V. Same with resting heart rate. You drop about 2 tenths of a

beat on days you underreach. You drop about three tenths on days you overreach. It's like, okay, that's pretty weird. But, you know, morning sun exercise is all. So I thought, well, Let me do something that's completely irrelevant because it hasn't even happened until the exercise is done. Because you know, your morning, sun in the morning, your teary during the day. Yeah. So I pulled up blue light blocking glasses, putting them on at night. Yeah. And on days that you underreach, blue light blocking glasses gain you about two points of HRV.

On days you overreach, they gain you about four points of HIV. I mean, that is just wild. It's bizarre. And same resting, all right, you lose about one beat on days you want to reach. You lose about two beats on days you overreach. So the days that you are exercising, positive behaviors are going to, have almost a double the positive impact. One and a half to two times the impact on your cardiovascular system. So then, of course, I thought, well, what about if you're naughty, right? Noddy behaviors.

Not everybody does just good things, right? And so what's our classic naughty behavior that we have in our data set is alcohol. We know that has a bigger negative effect on your resting physiology than anything else that people do. And so I looked at one dataset and the effects were so clear, I just double-checked in another dataset. Same exact thing. Except to in the opposite direction. So now, on days of you underreach, alcohol's not as bad for you as on days of you overreach. Now, again, most people are drinking alcohol in the evening, so the underreaching or overreaching are over. Nonetheless, on days of you underreach, I coded these days, whether you drank or not. Right. It's totally binary. Yeah, it's just binary.

Did you drink? On days you drink, on average, your HIV drops six points. On days your overreach, on average, it drops nine points. As far as resting heart rate's concerned, on days that you drank, you, your resting art rate goes up about four beats. That's when you underreach. When you overreach, it goes up about five and a half. And so alcohol is worse for you when you exercised more. And blue light glasses are better for you when you exercised more. It's wild.

Do you think with the alcohol and the exercise, so if I, you know, work out and like I feel like during the day, I was really good, I drink more at night. That's possible. And I need to go back. We can. Remember, this is too hot off the press. Right, right. It's not published. We haven't written it up yet.

I just know that this is what people will be thinking, right? It's a great question. We'll try to disambiguate. We'll try to basically figure out how many drinks people are having just so we can be more clear on that. We need to do exactly that because I don't always have drinks in the dataset, but I've got data set with drinks. And I can ask that exact same question, which I need to do. It's a great point. In principle, what ought to be happening is that every drink is worse for you when you've exercised them when you haven't.

Now, if that holds, there's two temptations. One is to say, well, what's going on with alcohol? What's going on with blue light glasses? What's going on with the sun? What's going on with Tiri? And you can come up with a different story every time. in science we don't like that though we like parsimony yeah and so in an ideal world there's one explanation that basically says exercise does something to you that causes good to get gooder

and bad to get badder right yeah i have no idea what that might be this is such an accidental finding yeah as you can tell i haven't fully analyzed it yet yeah and we haven't even started trying to write it up but it raises a very interesting possibility which is if you're going to be virtuous do it on days you exercise if you're going to be naughty do it on daisy you're lazy right Yeah, yeah, wild. Let's talk about HRV-CV as a predictor of load, so cost of strain. So remember, we were talking earlier about how HRV-C-V is this long-term fluctuation in your HRV. And if you're very fit, when you take on additional load, you don't get a big change in your HRV as a consequence because your HRV-CV is low.

So somebody like you has a low HRV-CV-V-CV, somebody like me has a big one. So obviously the goal is to be as fit as possible with a low H.RV.C.V.C. Well, that raises the possibility. In principle, what that means is that when Kristen takes on athletic load, she doesn't pay as big of a price as when Bill does. So we just wanted to answer that exact question. So what we did is we look back at the data and we categorize people who have very low H.R.V. CVC. down below 10 on our metric, all the way up to people who have quite high, one over 30 on our metric. And it works differently depending if you measure during the day or night. But that's how we measure it. And what we found is that take zones two and three and add them together and then just call them sort of zone two three

for every minute of zone two three so just one minute at a time if my hrvcvcv is really low so i'm very fit every minute of it costs me in rhr so every minute if i'm i have a very low hrvcvccc cost me one one hundredth of a point in resting heart rate every minute cost me three and a half one hundredths of a point in resting art rate if i have a hrbcvcv over 30 so i'm paying three times, more than three times the price for every minute of exercise when I'm, when I have a very high HIV-CV-CV than I want to have a very low one. My body's just very reactive to it. Yeah. We had a really- This is again, listen to Strain Coach. Yeah, exactly. And you would just like incrementally get fitter at appropriate pace. Exactly. And so then we even had a very clean

data set where the problem is that sometimes zone four and zone five, those really high heart rate zones are a byproduct of some artifact of movement and stuff like that. So we wanted to take a look at only when we knew they were actually exercising, not when something else might be going on. And it turned out we had a data set where people were logging their activities really religiously. And so we looked at just those folks. And then we could see that goes all the way up to zone four. Now, zone five, I'm not quite sure what's happening because people do so few minutes of zone five a day. But the same story holds with zone four. When you've got low HRVCVC, you pay much less of a price for it than when you have a high HRVCB. Yeah. Yeah, it's interesting. Again, I think for

people to understand these dynamics really does validate our coaching that we have, you know, and in it sounds, we're talking about, you know, a hundredth of a point. Like, it's, it sounds small, right? But for every minute. It's a minute. Yeah. That's what I'm saying. For every, like that adds up like really, really quickly. And so, you know, I think that's, yeah, I mean, I think it's just, this is just a, a great plug for, you know, this for daily. Beautiful. Yeah. Like, meeting your strength coach. If you meet your strain coach every day, your HRV CV slowly drops. And then you get to the position where when something on tour is asked of you or you decide to do it of your own accord, either way, you blast right back to the next day like it's nothing.

And what's great about the strain coach? And I think for folks, if you're an elite cyclist or, you know, are working with sports scientists on teams, like strain coach might in fact not be as valuable for you because there's just different goals. You know, just the programming is very different, right? So Strain Coach might not hold for those folks. I think it's important to say that. But for the regular kind of Jane and Joe who are focused on longevity. And feeling their best. And feeling their best.

And being able to recover and sleep and, you know, repeat that day in and day out. I mean, listen to Strain Coach. Yeah. If you do, all of our data are showing us and that it helps you enormously. And the beauty is, remember those data where you were at Slack for 60 days and then you turned it on and you. hit you know those folks start to look like the really fit folks like they it's not that hard if you're conscientious and do it it's not better to get there and and i think the thing to also remember is like look i i have to admit this i shouldn't in public but i hate aerobic exercise

where i know i'm exercising yeah it just feels like torture to me if i get on an exercise bike or go for a run you might as well punch me in the face i hate it but like i can i love to play squash yeah and then i'm trying to beat the person i'm not thinking about the exercise i'm getting but it doesn't even need to be high-intensity stuff. The Zone 2-3 stuff is really, really good for you. And for lots of people, that's a really brisk walk, it's going up a hill, it's things like that. We're not saying, go out and do hit training every night, right? We're saying, you know, set yourself reasonable goals that are very achievable.

You just have to carve out the time to do it. And from my perspective, let's say that you're somebody who's never meeting your strain targets. The perfect way to start is go for a brisk walk after your meal. It's doubly good for you, right? Helps you digest that meal and feel better. And at the same time, Rupos levels and at the same time, you're starting to build your strain, you're getting closer to meeting your strain targets.

Yeah. And this is why, you know, we're working hard to introduce HRVCVCV into the platform. And we're just kind of slowly letting people know what it is. And because it really does play ball in our analysis over and over again. So we want to be able to leverage it, right, to help people understand or get a sense of this longer term view of fitness, which is HRVCV is an amazing, you know, measure for. Yeah, it's a wonderful tool. I have to admit, when you first talk.

me about it, I didn't poo-poo it. Yeah, you're skeptical. I was skeptical, exactly right. And I thought, well, we'll see. But I'm totally converted. I'm a sold. It's a great measure. Yeah, we've been using it in sports science, you know, for years, you know.

Just looking at HRV acutely has so much utility and is really important, right? And helpful. You know, and we're just trying to kind of zoom out and look at trends. HRV-CV-V-CV is just such a wonderful, wonderful tool. So I love that. Okay. Let's talk about, we alluded to it, behaviors that have improved sleep. You mentioned blocking glasses.

But this was part of our threat challenge paper. We also looked at sleep concerns and sleep anxiety as questions. So from that data set, we were able to glean a lot of really interesting insights in terms of what behaviors really promote slowy of sleep, REM, sleep consistency, reduced awakenings. So this was really like such a cool, I think, source of insight that we're excited to share. It's a great data set. We really appreciated the 11,000 of you who are so conscious. I'm so grateful, and continuing to journal your activities.

And so what we did is we said, all right, well, let's take a look at behaviors that improve sleep consistency and that enhance sleep duration. And you might think, well, how could a behavior increase sleep consistency? Why would it matter, for example, if I dim the lights, why would that cause me to go to bed at the same time and wake up at the same time? And the answer, once you step back and think about it, is that just because you got in bed doesn't mean you fall asleep. So I could be super conscientious to get in my bed at the exact same time every night, but still

of a poor sleep consistency score if I struggle to fall asleep some nights and not others. And just to be clear, sleep consistency is measuring, you know, when the time point that you drop into physiological sleep. So it's not the time that you get in bed. It's the time that you actually fall asleep. What really matters is what helps you fall asleep once you're in bed. And things that help you fall asleep once you're in bed are naturally going to enhance both sleep consistency and sleep duration. Because once you fall asleep quicker, for most of the days of the week, your alarm is still going to go off at the same. time tomorrow morning, but also your sleep consistency score will improve as well. So we looked at a ton of

different behaviors. Again, same caveat. None of this stuff is peer reviewed yet. This is just things that we found. But, and this one has one more caveat, which is even though our sample was wonderful with 11,000 people, because not everybody does all these behaviors, our sample sizes are much smaller with the different behaviors. And what that meant is that we haven't yet asked a really important question, which is, I'm going to give you a list of behaviors that help. I don't yet know if doing two of them is better than doing one. It's three better than two, right? Probably for some of them, you can keep adding them together and for others not so much. And by way of example, earlier in our other research, we found that if you take melatonin and magnesium, does you no harm, but they don't

benefit you individually as much as if you do either melatonin or magnesium, because they seem to kind of work together. And so you get the benefit of interaction effect. Exactly. You get the benefit of one when you do the other to some degree. It still is good, but it's not as good. So I don't know if that happens with these data. I don't know if you can just do them all. Furthermore, it's also important to keep in mind whenever we tell people items like this that not everything works for everybody. In fact, to the contrary, most things that we study have wide variability and how well they work. For some people, if they give you an average of, let's say, three points of HRV, that's the average. Some people get six and some people get zero. So on all these things

that we're telling you, you should check yourself whether it really benefits you or not. And don't, you know, just go invest in all these things without trying them out. Right. Remarkably, and kind of really cool, if you ask me, the best thing for sleep consistency and the best thing for sleep duration is free, which is really nice, right? It's totally democratic, and that's dimming the lights in the evening. Demming the lights in the evening gains you three points of sleep consistency, and it gains you 19 minutes of sleep duration. I mean, that is, it might not sound a lot, but that is actually, it's a ton.

It's clinically meaningful. Yeah, that's every night, 19 minutes. I wouldn't turn my nose up at that at all. I mean, I say just even 14 more minutes of sleep has a meaningfully impact on next day alertness. And of those 19 minutes, in fact, nearly eight of them are REM and slow wave. Do you mean the lights is anyone can do it? Yeah. Well, not anyone.

Sometimes you work in a very well-lit place till bedtime. That's unfortunate. But basically, it's a free thing that most of us can do. And I think it's important to note that, you know, everyone has different sensitivities to light. And in fact, you know, the amount of light that you view during the day actually impacts how sensitive you are to light at night. So the more light you're seeing in the morning and in the day and at dusk, the bigger buffer that it creates in terms of your light sensitivity at night. So just something to note. But most humans, or all humans, the only way to release melatonin,

that hormone of darkness, is in the presence of dim light. That is the only way you're going to get that melatonin onset. You know, not surprising, right, that dimming the lights is signaling. to the brain and the body that it is time to sleep and it deactivates and the data show us, boom, helps regulate your consistency but is also helping you drop into these deeper stages of sleep. And that's just really nice. And it's cool that it's something free and accessible for almost everybody is our winner. A very close second place is blue light blocking glasses.

They do almost as much for sleep consistency, but they don't help you sleep quite as long, or not anywhere near as long, in fact. I don't have any idea why that is. So dimming the lights helps you fall asleep and stay asleep. Blue light glasses help you fall asleep, but they don't do as much for staying because you get about half the benefit, about 10 minutes of additional sleep out of them. I wonder if those filters just aren't quite. You may people who are like, you know, if you look at my screen right now, so bright,

so the filters might not actually be able to filter out all of the blue light. It's possible, but the fact that it gives you almost identical sleep consistency tells me that it's just about as good at getting you to fall asleep. My guess is that maybe people who dim the lights, dim them for longer. Well, that's what I'm saying. It's not just melatonin might be released at the same rate with blue light blocking glasses, but we know that there is an impact of light on the depth and quality of your sleep. Yeah, that's a very good point.

That's very possible. Once you go beyond those two as are kind of winners, you see things like weighted blankets are a big one. They give you almost two points of sleep consistency and 12 minutes of additional sleep. But my guess is not everybody likes those things. To me, it sounds a little bit squishy, but I've never even tried it. So what do I know? I mean, it kind of goes back to, you know, some people, you know, who have experienced trauma, you know, like the weight. It just makes them feel safe. So yeah. So it could be the very individual. It could be that in fact, oh, and by the way, I should mention this is super important.

All these effects I'm telling you about are not between person. They're within. So what I'm comparing is nights that somebody who does this on nights when they do it versus when they don't, which means it's the same person. People might are probably not familiar with that analysis. So it's really important to call out that these aren't just between effects, you know, population level. This is literally looking at. Susie, when she wore it versus when she didn't. Exactly. When she didn't light and when she forgot to or couldn't.

Right. So the within person effects, which pretty much. Yeah. They're always more valuable to us because there's lots of difference between me and you and you and you want to wait a blanket and I don't. And that could be just one of many things. And I don't really care what Bill is doing. I want to know what's happening within me.

Yeah. Yeah. No, everybody cares what Bill's doing. I know what I follow. So anyway, once you get beyond weighted blankets, you start to see some interesting things, too, like reading in bed. Reading in bed gains you almost two points of sleep consistency. It only gains you six minutes of overall sleep. I suspect but don't know that reading in bed is clearing your mind of the day's concerns, right?

And just making it a bit easier to fall asleep, but then doesn't have as much impact across the night. Sound machines gain people a couple of points of sleep consistency in almost 10 minutes of sleep. morning sun, your favorite, gains you a little less than a point of sleep consistency and about five, six minutes of extra sleep at night. You know, it's a super easy thing to do, so it's worth doing even if it's only five minutes. Time restricted eating, which is a bit more demanding, gains you one and a half points of sleep consistency and about 12 more minutes of sleep at night. And, you know, the list goes on, melatonin's on there, sound machines are on there, those sorts of things. What's good about this data set, but in some way it's limited, is that

These are all behaviors that are kind of in the immediate lead up to bed, which is really important. Our core four paper, so circadian behaviors that improve cardiorespiratory fitness through sleep consistency, this data set actually was able to show some behaviors during the day that actually influence sleep consistency in quite a meaningful way, which then in turn impact cardiorespiratory fitness and parasithic activity. So maybe just kind of talk through. We've mentioned some of these behaviors already, but it raises the importance of daytime behaviors and how they impact our ability to fall asleep at night. I just want to say, you know, we know at this point that sleep regularity and sleep consistency really matter, right? When we look at, you know, a paper was just

published that we talk about a lot in January of 2024 by Windred, Daniel Windred, and his colleagues. And they basically found that sleep regularity is a greater predictor of all cause mortality, then sleep duration does not mean that sleep duration doesn't matter. It very much does. But the regularity of your sleep, your sleep consistency is really what we need to kind of go after if we're interested in optimizing our longevity. This is really tight. And it's not just what you're doing before bed. And I think the typical sleep advice is, you know, dim the lights. And all these things are really, really important to help facilitate sleep consistency. But if we really want to nail it, it actually begins the moment that we wake up.

Yes. And that's a great point. I didn't believe you when you first told me this. The idea of sleep hygiene starts the second you open your eyes, right, in some sense. And so when you told me about Morning Sun, that was the first time I ever encountered that idea myself. And I bet you a kale smoothie, if I remember, right? But it wasn't going to do anything. I was like, yeah, that's just not going to replicate.

We have a big sample. Somebody found that, admittedly, but it was random chance it emerged. But you were right. And I still owe you that case. And you're here. So I could actually. So if humans drink those things, I will dig one up for you. But yeah, the core four was a really lovely data set.

It was one that you basically pushed me into looking at with you. And in that data set, basically what you did is you started with that challenge that was run in, if I remember in the month of August in 2023. Yes. Yes. Yeah. And so in that challenge, people were told to do any one of the following, or all of them, to get morning sun to zone to do some. do some zone two training, breath work, do some breath work, and do teary. Yeah, time and they could do any of those that they want or all of them. It was many thousands of people

did these things. I mean, we had 34,000 people participate in the challenge. Which is really wonderful. And then because whoop is such a great platform, we could then match them to 34,000 people who looked like they did before the challenge. And the lovely thing about doing that is that we could see that the challenge increased sleep consistency, the challenge increased sleep duration, but really sleep consistency was the key thing that we're going after there. And the nice thing was that controlling for sleep duration, what the data showed is that if you engaged in any of those four, but the more of them you did the better, then you had increasing sleep consistency, which in turn led to better HRV, to better RHR, respiratory rate even, and then even to better

HRV CV. Remember, we were talking about that earlier, this longer term variability in HRV. And so these effects weren't huge, but they're just reliably there, and they were there within person. The person who did this looked better by September than they did in the beginning of August. And the nice thing is, I think people could kind of sense that because mostly they kept up their habits. Which is really cool. So we analyzed September data, and people kept journaling these things, which is so awesome. It was really nice. And we really had, what's great about these challenges is we have baseline data.

So we were able to look at July and kind of compare that. And we're able to then even dig further, you know, deeper and looked at people who were not journaling and who did the challenge and people who were already journaling did the challenge. So it was just, it's just a nice way, you know, very thorough way to be able to look at the data. So I think with a lot of things that we're talking about, there's a compound effect. Yeah. You know, and any one of these behaviors by themselves might not be as powerful as if you combine them with, you know, some of these other ones.

And I think what's also really important and I hope what. people take away is that what we're doing here is we're able to bubble up to the surface, the behaviors that you get the most bang for your buck. We're looking at a lot of behaviors, right? And some just don't really move the needle as much, right? Exercising appropriately really moves the needle, stabilizing sleep wake time via these behaviors that we're talking about, restricting light at night, viewing some light in the morning, getting exercise during the day. These have meaningful impacts on facilitating sleep consistency and then, you know, getting really beautiful restorative sleep at night. So hopefully folks feel like this is a conversation

that is reducing the noise because this is a very noisy industry, right? The health and wellness industry. Of course. What we have here is a data set that no one in the world has. Yeah, we have two huge advantages. We have a data set that nobody has and it's very long term. And so if you watch the medical literature, you're constantly seeing them change their minds. Eat oats. Oh, no, oats don't do anything. Eat this. No, no, don't bother eating that. Seattle's fine. Oh, it's not fine. It's, yeah. And the problem is that it's always between persons. They're going, oh, we're looking at humans who took this diet and humans who don't. And there's a million differences between people. Yeah. And so what we can do is we can just say, well, what did you look

like before you started the challenge? You. Yeah, exactly. And then you can do it to yourself. Because just because morning sun helps, some people, doesn't mean it'll help me. And everyone's biology is a bit different. We're not like, we're not physics. We're biology. And once you went to biology, there's huge individual differences. Whenever you're going to take something on, Well, if it's easy, like morning sunlight, it's almost not even worth worrying about. Just do it, right? But if it's expensive or difficult, like TRE is a little bit difficult and weighted blankets and blue light blocking glasses, those kinds of things cost money.

Then it's worth testing them on yourself and seeing if they really were. And a note on Tarmor's eating, you know, a person like, it's not hard. But it's really just, you know, consolidating all your calories between the hours of, you know, 10 to 12 hours, you're eating all of your calories, hopefully during the day when we're in the active phase of your kidney. when we're most primed to metabolize food and digest, and all of our enzymes are ready to absorb the nutrients and utilize them. And again, that's the time frame when you're generally most active. So you're going to use the fuel, actually, as opposed during the inactive phase,

which is basically when the sun is down, when your body is in the opposite state, not primed to kind of digest and metabolize food. So, but time restriction to eating, I think I'm really very bullish on that. I'm very bullish on it, too, but I don't think it's for everyone. There are some people who get hungry very easily. They need to constantly eat. And then they get woken up by their hunger. And I would say those are generally people who are under-fueling during the day. They could be under-fueling during the day or they could have a crazy fast metabolism.

Then they're under-fueling generally during the day and not distributing their macronutrients appropriately. So that said, for sure. There are people who are doing triple sessions during the day. You know, they're athletes in college. You know, they have really fast metabolism. There are foods that you can eat that don't disrupt sleep. you know, high in case in protein, you know, yogurt with walnuts and raspberries before bed, big ball so that is not going to harm your sleep. But for most humans, though, you should

be fasting for 12 hours. And I can go days without eating. So that's not me. I've got a lizard's metabolism. And so I don't need to eat when the sun goes down. And once we did these data, I just stopped doing it. And it doesn't bother me. It's really nice. I can see a clear effect on my resting heart rate. Yeah, it's just wild. Same. The winter's hard, you know, just because it's I live in Australia. Yeah, I know. The winter's 70 degrees there, and it's not that hard. All right, this one's fun.

Social Jallag. Examining the influence of weekend sleep extension and consistent wake times on recovery, insights into social jallag and circadian health. So we're writing up this manuscript right now, but this one's a fun one. Yeah, so circadian rhythms in principle are something you should follow every day. But it turns out that they're differentially predictive of your recovery, depending on what day of the week it is. And that struck me as really weird when I randomly ran across that.

And so then I was asking, well, why might that be? And of course, it turns out that when you think about it, staying up late doesn't mean the same thing on Tuesday as it means on Saturday. And so if I stayed up late on Tuesday, I'm probably working late into the night for a project or maybe I'm helping my kid with their homework or something like that. But if I stay up late on Saturday, I'm probably out being quite physically active late at night, maybe dancing or something like that. And I may well be drinking as well.

And so when we took a deep dive into these data, what we found was that sleep consistency matters more on the weekends than it does in the weekdays, which immediately tells you that it's correlating with something else. And what's that something else? Well, alcohol is a biggie. And so people are more likely to both drink on the weekend and have sex on the weekend than they are during the week. Now, sex actually has a positive overall effect on recovery, but alcohol has a huge negative effect. And so once you control for the effect of alcohol, which covariies with sleep consistency, on nights that people drink a lot, they tend to stay up late and have poor sleep consistency. Once you control for that effect, then you can see the sleep consistency effects are still there. But the social jet lag, this notion

that it's really bad for you to stay up late on the weekend and then sleep late, the data are not so clear on that anymore. Once you control for the alcohol and misbehavior, it's probably that we don't necessarily measure, but things like dancing very late before bedtime, where it's very physically active, very exciting. What we really see is that you kind of gain as much out of that increased sleep duration by sleeping in the next day as you lost by messing around with your sleep consistency. Yeah. And the advice is mixed out there, you know, but I think this helps clarify what we should be telling folks is that extending your sleep, even though it kind of messes with your sleep, consistency actually is probably the right

advice. And just social jet like just as a definition, it's basically how much your weekday sleep consistency varies relative to the weekend. that's right essentially is that yeah yeah that's exactly right and i also completely agree with your prior statement that basically what we're seeing is that people sleep 20 minutes maybe more 10 it varies by person but they sleep a bit more on the weekends and they achieve it they go to bed later but they wake up even later still and that seems to be that gain in sleep over the weekend seems to be really useful and it makes up for the cost that they've got in sleep consistency now of course the funny thing about that is that sleep consistency scores, you don't want them to be high on Sunday night

because you were up to no good Saturday and Friday. And so you're a high sleep consistency now means you're staying up late. And so there's the one night when you want your sleep consistency to be lower is when you're getting back onto your weekday schedule. Yeah. That's where you're like light hygiene is like so critical. Because if you, because there is a point where extending your sleep is no longer beneficial. So we're not talking about extending sleep by three hours. no you're where you're literally want to be kind of within an hour of your normal wake time because if you go beyond that you're going to fudge up exactly what bill is saying is you're not going to be able to fall asleep at a decent time right because if you wake up at 11 a.m. and you typically

wake up at 7 a.m. So that's a three hour extension, sleep extension. You are not going to feel sleeping until 1 a.m. 16 hours after 17 hours after that. And the good news is that on average people don't do that. Of course that does happen. Right. Right. But on average, you know, sample, people are more in the 20 minutes extra sleep range on the weekend. Yeah, okay. So that's right. That's right. But I would say just as a rule of thumb, try to keep that window within an hour or so,

preferably a little bit less. And then once you wake up, get some light on board so you can, you know, tell your system that's time to be awake and alert and ready to roll. Okay. So over sleeping. One of the things that I'm obviously very interested in, I'm very interested in sleep. And I, you know, in understanding it, it is, you know, I think that it is like the brain. Like, there's so many things about it that we don't actually know.

So I always feel like it's kind of, you know, Christmas. We get to like dive into these data and see what we see. But, you know, one of the things that I always thought that more sleep was better as a rule of thumb. That is simply not what we see in the data. No, it's not. And it's a complicated and confusing issue. And I don't pretend to know the answer. But I can tell you what we're seeing.

So on the one hand, when you look out in the lab, laboratory work where if they keep the lights dark for very long periods of time or they give you nothing to do, people start sleeping these crazy long hours. But that's not 100% obvious to me that that's what we evolved to do or this meaningful sleep. It could just be a sign that it's boring, right, or might as well not get up. So in my mind, the more interesting question is what happens during people's everyday lives, not when they're put in a cave with no light, right? Although putting in the cave and the light has value too. But that's less valuable to me. Those are good experiments, but they're not. They don't answer the questions that I really want to know.

Yeah. And so what we've been doing is we've been looking at everybody's sleep compared to their own individual amount of sleep that they usually get. And let me caveat this by saying if you get on average less than six hours a night, that's your average. All these relationships fall apart. And so our data suggests that most people should be getting more than six hours. There's probably exceptions to that rule. For sure. But I would say probably 95 to 99% of humans cannot get by on less than six hours a night. Yep. And so their body only responds properly when they're getting more than six. So that's my caveat here. But we can then say, all right, let's again look within person. And we can do that by saying we can divide them up into what are called standard

deviations. And a way of standard deviation works is that your own variability is taken into account. And so if you go one standard deviation less than usual on whatever the domain is, to one standard deviation more, you're capturing 66% of all your activities. If you go two, you're capturing 95 between those two. Now four, two down and two up. And if you go through, you're getting 99. So that's how we think about it. When you do that within person and you say, all right, how good you feel or what's your resting heart rate? What's your HRV? Whatever metric you want. And then we look at how much you slept compared to your own usual amount. And when you go from like two standard deviations less to one less to your average, once you hit one standard deviation more than you

typically sleep, you no longer see benefits. And so sometimes you even see costs, but at the very least, you no longer see benefits. And we've done this a million different ways till today. We said, all right, let's make sure that they were not ill in the last week. Right. We've controlled for everything that we could possibly control for. Yeah. And no matter which way we do it, the story looks the same, that when you're sleeping less than usual, if you add sleep in until you get to your average, you look better and better. And then you even look pretty good when you get one centivision more than your average, but it's not clear anymore. And once you get above one sanitation more than your average, there's clearly no benefit. Sometimes it costs. And so somewhere between your average and a

tiny bit more is where oversleeping lies. For most people, I suspect that, you know, we have jobs, we have set alarms. We're probably on average getting a little tiny bit less sleep than what we really want. And so everything's a little nicer when you get a little bit more than that, but not a lot more. And what it suggests is that, you know, let's say, I sleep seven hours a night. Somebody else might sleep eight and somebody else might sleep six and a half or whatever. What these data suggests is that your body knows what it's doing. And so you shouldn't be going, uh-oh, the consensual statement of the NIH is eight. I should be doing eight. That's just nonsense. You should not be doing eight. You should let your body tell you where you belong. And it depends

on the exercise during that. We talked about that. How fit you are. Like, I mean, there's a whole host of variables that we are seeing impact how efficient of a sleeper you are, therefore how much time you need to spend in bed. Exactly. And that time in bed is just, it is simply going to vary. And that's where technology like Woop is so damn helpful to really, everyone is going to have a different sweet spot for sleep. Yep.

And we kind of help you suss that out. You find the answer. And the journal is super valuable for that. I love the journal now because it helps me do great research. Yeah. But I also love it on my own whoop because then I can say, well, what does happen when I smoke weed at night and I tell myself fall asleep or whatever, right? It just, it gives you the answer after a month or so. Yeah. Yeah. It's very exciting. All right. Final question. I think this is on a lot of people's mind. Really high HRV. What does it mean? So look, we're seeing the very same thing with high HIV that we see with oversleeping. The picture looks the same. these curvilinear effects, whereby when your HRV is about a standard deviation above your

average, so it's in the realm of common, not really, really high, but just a little bit high, everything's good. Right. You know, that's probably a great day for you. Yeah. Once you get above that one standard deviation line, so you're now in the top, your top third scores, those are no longer good things, or they're not better. Right.

And sometimes they're maybe even worse. So if we look at your resting heart rate, once you hit that one standard deviation above, it doesn't get higher again, but it doesn't keep going lower. Right. If we look at what your sleep duration was, those really high H.RVs come out of nights where we were actually sleeping a little bit less. Yeah. When you look at sleep consistency, again, once you get above one centivation of H.RV,

your consistency is actually going down. Talk about artifact real quick, just to make sure people understand how you think about that in the analysis. Well, so the really high H.RVs are probably anomalous for one of two reasons. One is it may be that something happened to your sleep that caused it to to measure high when it's probably not actually that high. And otherwise, really high H.RV could be a sign that your heart is actually struggling in some kind of a way.

And so the latter would be a bad thing. And the former is just a neutral. You're getting a high score out of whoop that's not true because when it happened to measure. I mean, it's true for you that night, but that's not really reflective of your H.R.V. And so in my own case, about once a month, I'll get an H.R.V. score in the 50s. and I believe it in the sense that that's what my body did as the way I slept, but I also know it was not meaningful. I'm not ready to go.

In fact, if anything, if it means anything at all beyond my usual medium high 30s, it's probably bad news. Yep. And so what really we need to be thinking about is maybe HRV shouldn't be treated linearly, and we've been talking about that as a team a lot. Yeah. And with data science, we've been working with us, how do we find the sweet spot that people ought to really be looking for? Yeah.

I love it. Well, Bill, thank you so much. This is such a fun conversation, and I love jamming on all of these interesting questions every day with you. Yeah, it's such a fun. This is my favorite job in the world. I really enjoy doing it. Good. If you enjoyed this episode of the Whoop podcast, please leave a rating or review. Check us out on social at Whoop at Will Ahmed. If you have a question to what's answered on the podcast, email us, podcast at Whoop.com. Call us 508-443-49-2. If you think about joining Whoop, you can visit at whoop.com, sign up for a free 30-day trial membership. New members can use the code will, W-I-L, to get a $60 credit on W-W-A-Ccessaries when you

enter the code at checkout. That's a wrap, folks. Thank you all for listening. We'll catch you next week on the WOOP podcast. As always, stay healthy and stay in the green.