The evolution of laziness: Why humans resist the gym

Why do many of us struggle with exercise when it’s essential for our well-being? Evolutionary biologist Daniel Lieberman says that it’s not laziness: it’s evolution. 

For most of human history, conserving energy was of utmost importance: The key to survival: motion without purpose would be a waste.

Lieberman explains why modern fitness feels unnatural, why guilt-driven workouts will always fail, and what hunter-gatherer lifestyles reveal about health today.

DAN LIEBERMAN: My name is Dan Lieberman. I’m a professor of human evolutionary biology at Harvard University, and I’m the author of “Exercised: Why Something “We Never Evolved To Do Is Healthy and Rewarding.” Chapter 1: How evolution shaped the human body. If you want to understand anything about human beings, from our behavior to our biology, right, there are sort of two ways of thinking about humans and the way we are. One is a kind of a mechanistic set of explanations, right? You know, how does my immune system work? You know, how do my muscles work? You know, how does my brain, you know, create memories, and how do I speak, et cetera. That’s the kind of bread and butter of most aspects of biology. But our bodies weren’t designed. They weren’t engineered. They’re not machines. They evolved. And, so, if you want to understand why we do what we do, why our brains work the way they do, why our feet work the way they do, why we run, you know, why our immune systems function the way they do, the only explanation for those sorts of questions is an evolutionary question, you know, ’cause evolution explains why things are the way they are. And so, you know, good biology combines both how questions, processes, with ultimate questions, you know, why explanations, which have to be evolutionary. And, on top of that, because we’re humans, I think you also have to add on anthropology because just as there’s an old expression, “Nothing in biology makes sense “except in the light of evolution,” I would say that nothing about human behavior makes sense except in the light of culture and in anthropology, and we need to understand the cultural component to our behaviors as well. So, a really kind of full complete explanation of anything, including exercise, but it could also be diet, it could be language, it could be anything, we really need to integrate, not just, you know, standard sort of physiology and, you know, other kind of branches of biology, but we also need to think about them from an evolutionary perspective, and it always helps to include an anthropological perspective. I started off my career as kind of a head guy. I studied fossils, and I was interested in, you know, when humans evolved and why we had sort of the shape heads we do. We have very weird heads, by the way. And I got very interested in the topic of how we stabilize our heads when we run. So if you ever like watch somebody running, and you see that they have a ponytail, right, that ponytail will do like this crazy figure eight, right, and it’s kind of fun to follow somebody when they’re running that way. And that ponytail is like an accelerometer on the head. It’s telling you the forces that are acting on the head. And yet, despite all those crazy forces, we manage to keep our heads really still. And most animals, the way they keep their heads still, is they have, you know, a neck that comes out the back of the head, and the neck comes out of the front of the thorax, and they can kind of flex and extend their neck and keep it still. But we can’t ’cause we have tiny little short necks that come out of the bottom of our heads. We’re like pogo sticks when we run. And so I did some experiments on how we stabilize our head when we run, and that led to the realization that we have these special adaptations that evolved around 2 million years ago that only only function to stabilize the head when you’re running. And, as I said, they showed up like 2 million years ago on the fossil record. And, all of a sudden, I had this interest in how we evolved to become really good long distance runners. And from there it just kind of took off. I’ve been working in Kenya for a long time, but I’ve been specifically working in the western part of Kenya, around the city of Eldoret. And it’s a wonderful natural experiment to study how bodies are changing as we go into sort of industrial lifestyles, urban lifestyles. So, because the city of Eldoret’s the fifth largest city in Kenya, it’s a very big, modern, sort of urban, sort of African city, and then, just a few miles out of the city, is a very rural area where there’s no roads, there’s no electricity, there’s no running water. People are living, are subsistence farmers but from the same group, the same Kalenjin-speaking population. And so we have a kind of a natural experiment. We can study how people’s bodies change when they go from the countryside to the city. And so, one of the things we were really interested in is carrying because people, until recently, carried things a lot. I mean, everything you wanted to have, you had to carry: you carried your babies, you carried your food, you carried your water, you carried your fuel. And people there carry a ton of water. And we wanted to do some experiments on how women, especially women, carry huge amounts of weight on their head. And they don’t seem to spend that much energy. And so our idea was to use a treadmill. ’cause it’s a lot easier to measure some of these things on a treadmill. And we’d have them carry the kinds of things they normally carry. We’d put on a respirometry mask to measure the oxygen and do some biomechanics to study how they do their gait, et cetera. So we bought this treadmill and schlepped it, oh, you know, these are like horrible roads, you know, to the nearest place we could plug it in, and then we brought the people from the area where we’re doing research to the treadmill and put people on the treadmill. And, you know, if you’ve never been on a treadmill your whole life, and all of a sudden somebody sticks you on a treadmill and you start walking, it’s kind of a weird experience. And we realized that, you know, we couldn’t really do the experiment because people weren’t walking normally on the treadmill. So, you know, we abandoned the treadmill after all that money and expense. You know, we gave the treadmill to a local school and did our experiments by having people walk on on ground as they they normally do. And, you know, to me it’s a perfect manifestation, it’s a perfect demonstration of the fact that treadmills are really weird, right, you know, they’re a strange, modern piece of equipment that we buy, we spend a lot of money on, and we spend a lot of money to go to a gym, you know, that makes you work really hard to stay in the same place. It’s the apotheosis of exercise, you know? And that’s why, in the book, I spend a lot of time making fun of treadmills. And, by the way, if you think treadmills are a form of torture, I think it’s kind of interesting that the kind of the modern treadmills’ origins are in the Victorian prisons where they were actually invented as a form of torture. They were invented to keep prisoners from enjoying themselves. They made them trudge for hours and hours on these early treadmills. I don’t know anybody who really enjoys being on a treadmill, right? Most of us, if, you know, we were forced to be on a treadmill, we either like listen to a podcast or some music or watch something on our iPhones or whatever to make it tolerable, but they really, kind of, to me, epitomize how so many modern forms of exercise are kinda like cod liver oil. They’re not really pleasant, right? We do them because they’re good for us, but it’s not fun. And so it’s, you know, it’s like taking your medicine. I study the human body and why it is the way it is, and I’m especially interested in the evolution of physical activity. And as I’ve been studying, walking, and running, and various other sort of physical activities, it’s become really clear to me that a lot of people are exercised about exercise. They’re anxious. They’re confused. They don’t understand, you know, what’s the right amount of exercise to do. They have trouble getting off the couch, and they feel kind of shamed and blamed for not being as physically active as they might like to be. And so I wanted to write a book to try to debunk a lot of myths about physical activity and about exercise using the lenses of evolution and anthropology. So the word exercise, you know, comes from the Latin exercisio, and it meant, you know, to train. So we still do math exercises, or soldiers do exercises to get fit. But eventually the term has changed its meaning, and it’s developed new meanings. So, on one hand, it means to do voluntary physical activity for the sake of health and fitness. That’s the kind of sort of fitness, physical activity kind of exercise, but, on the other hand, it’s also means, you know, to be exercised means to be upset, to be confused, to be anxious, to be kinda worried about something. And that, again, that comes from, you know, we get exercised by our math exercises, right, you know, and so, to me, it’s, you know, it’s part and parcel of this strange concept of exercise, right? It’s this modern idea of doing voluntary, discretionary, physical activity for the sake of health and fitness, but we don’t do it often, you know. Most people don’t do it ’cause they want to. They do it because, you know, it helps stave off death and decrepitude. And in the modern world, of course, a lot of people are confused about it ’cause they find it hard to do, they’re not quite sure how much to do, there are all kinds of myths surrounding it. So, very much, people are exercised about exercise today, and, really, I think that by shining the light of evolution and using kind of an anthropological perspective, my goal really is to help people be less exercised about exercise. I would say that the definition I use of exercise is pretty much the bog standard definition that people in the sort of fitness, exercise science world use. It’s important to make a distinction between physical activity and exercise. So physical activity is just moving, right? When you do anything, right, go shop, you know, pick up your groceries and take them to your car, that’s physical activity. When you, you know, sweep the kitchen floor, that’s physical activity. But exercise is discretionary voluntary physical activity for the sake of health and fitness. So it can include everything from sports to running on a treadmill to, you know, going for a walk. I think the paradox of exercise is that everybody knows it’s good for them. I don’t know really anyone who says they don’t want to ever exercise, right, but the paradox is that most things that are good for us, we kinda want to do, you know, but exercise is kind of the reverse, right? It’s something that we all know we want to do, it’s good for us, and yet a lot of us have a hard time doing it. And, you know, the proof is, you know, in the data. According to the CDC, only about 20% of Americans get the very minimum levels of exercise that every health organization in the world thinks is the minimum for an adult which is 150 minutes a week. So 80% of us really struggle and fail to get the very basic amounts of exercise, but almost everyone says that they want to get enough exercise. The most common reason that people don’t like to do exercise, when you ask them, is that they don’t have time. You know, they find it stressful, and they’re busy, right, and that’s a legitimate concern for a lot of people. Imagine if you have to commute a long distance, you have a job that, you know, is very sedentary, you gotta, you know, deal with your kids in the evening, and, you know, or maybe you have two jobs, or whatever, you know, it’s very challenging for people to exercise and to find the time in the modern world. The other reason that people often give for not exercising is they don’t like to. They find it uncomfortable. They find it unpleasant. They find it, you know, they get hot and bothered, and they don’t feel like they get much reward out of it. And so, there’s a lot of inertia that prevents people from doing it. They have a hard time getting off the couch. And, you know, I think we need to be compassionate towards both of those reasons, right, because, yes, people are stressed for time, and, yes, it is often unpleasant and unfun, but we make them feel bad about that, right. We make them feel bad for being stressed. We make them feel bad for having that inertia when actually it’s completely normal. I mean, you know, nobody ever exercised in the stone age, right? People were physically active when they had to be, and they might dance or play, you know, do other things that were for fun, but volitionally going on a five-mile run in the morning or going to the gym to lift weights whose sole purpose is to be lifted, that’s a really strange, weird, modern behavior, and there are all kinds of instincts we have not to do it, and we shouldn’t make people feel bad for having those instincts. Instead we should help them figure out ways to overcome those instincts because we live in a world where we now, because we’ve mechanized everything, right, we no longer have to be physically active, we now, in a very strange way, have to choose to be physically active, and that’s not so easy. Oh my gosh, there’s so many myths about exercise, it’s hard to know where to start, but I would say that, you know, one myth is that our ancestors were sort of just natural, incredible athletes who’d just get up outta the bed in the morning and, you know, run, you know, ultra marathons at will without ever, you know, much stress or difficulty, that our ancestors were really incredibly strong, that there’s a trade off between speed and strength, that you don’t have to, you know, that it’s normal to be less physically active as you get older, that there’s a perfect type of exercise, perfect amount of exercise, you know, that sports equals exercise. I could go on. The topic of exercise is just laden with myths. A common view about our sort of evolutionary origins and about sort of the evolution of physical activity is that, you know, we evolved from these kind of super athlete kind of ancestors and that civilization has sort of contaminated us. So, if you wear shoes or you drink Gatorade or you have a fancy watch or something like that, somehow that kind of deprives you of the kind of natural talent that you have, and if only you had been born, you know, in some little village somewhere and, you know, didn’t have TV and didn’t have access to all these commercial goods, that you’d be a natural, incredible athlete and that you could just get out of bed and, you know, run an ultra marathon or something like that. A lot of these myths, to be honest, stem from, I think, this Rousseauian idea of the myth of the noble savage, right, that humans, uncontaminated by civilization, are also sort of naturally good and fine. And they also come from terrible, horrible racist stereotypes about, for example, you know, Africans not experiencing pain as much, and, you know, Asians having some kind of natural sort of proclivity to sneak around in the dark. You know, I mean, we all know these stereotypes and they’re pernicious, and they’re wrong, but they’ve been applied in various ways to hunter gatherers and to, you know, subsistence farmers in various parts of the world to make us feel that somehow they’re like these sort of, these kind of basically, you know, fundamental super athletes. And when you do that, I think you do harm to people all around the planet. You do harm to those populations because you kind of dehumanize them. I mean, when they run an ultra marathon, it’s just as hard as when, you know, I were to try to run an ultra marathon. They sweat, they toil, they get nausea, they get cramps. They do it, not because it’s easy for them. They do it because they value it, they think it’s worth doing. And you also make people in the West feel terrible, like somehow there’s something wrong with them, right, and they should, you know, throw away their shoes and, you know, eat a paleo diet or something like that. And, all of a sudden, ta-da! They’ll become this like amazing athlete. And that’s just not true. That’s just a myth. So it’s pernicious in a variety of ways. In 2012, I had the good fortune to be invited to go to the Ironman World Championships in Kona in Hawaii. It’s an amazing event, right? And if you don’t know what an Ironman, full Ironman triathlon’s like, you start off with a 2.4 mile open water swim, then the athletes rush out of the water, jump onto bikes with these like high tech helmets and stuff like that. They speed off, and they do a 112-mile bike ride across the desert. And then they come back, jump off their bikes, and then they do a full marathon in the heat. It’s like 90 degrees Fahrenheit, right? And it’s really amazing. And the elite athletes do this in a little bit over eight hours. They’re just like cyborgs. They’re not like human beings. It’s astonishing to watch. And then the lesser athletes, you know, take longer to do, and everybody has to finish by 17 hours, so by midnight, and it’s just astonishing to see people put their bodies to that kind of endurance to achieve something like that. And I was really impressed by that. I’d never seen a full Ironman before. And then, just a few weeks later, I was in a very rural part of Mexico, in Chihuahua, up in the Sierra Tarahumara, where I got to observe a rarajipari which is the traditional foot race that the Tarahumara Native Americans do. And it’s kinda of like, almost like a soccer game. There are two teams, and they have a little ball, a little round ball that’s carved out of wood that morning. And there are about five people on each team, and they kind of kick the ball with their feet and then chase it and find it and then kick it again and chase it and find it and kick it again. There’s like a little circuit they do. And there are two teams, and whichever team laps the other team wins. And the race I saw must have been about 40, 50 miles long. And so it’s another incredible endurance event. And on the surface you’d say, “Oh my god, “these events are totally different, right?” Iron Man is very commercial, and everybody’s wearing the fanciest latest gear, and they’ve got super fancy shoes, and they drink, you know, they’re using gel and goo and, you know, all kinds of specially formulated, you know, nutrition drinks, and their bikes cost like, you know, $10,000, $20,000, and it’s very commercial, right? And there are, you know, speakers and crowds, et cetera, whereas the Tarahumara, when they’re running, they’re just wearing the clothes that they normally wear. They’re running in sandals. It’s very uncommercial. And you think, “Oh my gosh! it’s so different.” You know, one is more authentic than the other, but if you stop and think, actually they’re very similar, right, because both involve rewards, right? So Ironman, there’s like, you know, the winner, and the winner gets a prize, et cetera. Well, the Tarahumara also have prizes. They bet huge amounts of stuff, right? They bet clothes and goats and corn and stuff like that. They don’t have Gatorade, but they make their own kind of form of Gatorade out of corn, and they cheer on their runners too, and, you know, there’s the joy of victory and the agony of defeat and all that. So, in some ways, they’re very different, but, in other ways, it’s kind of the same thing, you know, and it’s a personal journey that people undertake, a very small number of them. The vast majority of people are observers. They’re not participants. So really it made me realize that, oh, yes, there are some differences between sort of more modern, commercialized Western forms of endurance physical activity. This is something basic and fundamental that all cultures do, and actually I think what makes us similar is greater than what makes us different. You know, there are different kinds of training, right? You know, play is a form of training in a way, right? You know, children play, right, ’cause they’re learning skills, they’re developing capacities, and humans are one of the few species, dogs are another, that continue to play as adults, right? And that play helps us, you know, maintain our capacities. It helps us with social relationships. I mean, there’s all kinds of good things that happen with play, right? But exercise is kind of a very… I wouldn’t say exercise is generally play, although some play is exercise. And when you kind of exercise in order to, you know, or train for like an event, you’re doing something, you’re spending a lot of energy, you’re doing physical activity kind of to get ready for something, right, and, certainly, you know, for the kinds of things that we do, again, that’s a very modern Western behavior. So when I was, you know, talking to, and I’ve talked to Native American runners who participate in these long distance races, and I asked them how they get ready for the race, how they train, they would kinda look at me like they didn’t understand the question. There was, you know, “What are you talking about?” Like, and so, you know, I was working with the translator. The translator was saying, “You know, you know this gringo, “you know, he like runs five miles every day “to kind of get ready for a race.” And, you know, the question that I got was, you know, “Why would you run if you didn’t have to?” right, you know, ’cause their life is their training, right? You know, when I ask people there or ask people in Africa, in the places where I work, you know, “Like, when do you run?” The most common answer I get is, “Oh, well to chase a goat.” You know, that’s the most common answer I get. There are a lot of ways to quantify how physically active somebody is, right? And a very simple one, it’s not necessarily the best one, but a simple way of doing it is what’s called the physical activity level. It’s just a ratio. So it’s the total amount of energy you spend in a day divided by the energy you would spend if you were just in, you know, at bedrest, what’s called your basal metabolic rates, the energy you spend just taking care of the most basic essential functions of your body. And so, say if you’re in bed rest, you know, in a hospital and, you know, lying in bed with just like a clicker for the TV, and you’re doing absolutely nothing, not even digesting food, your PAL, or physical activity level, it would be about a 1.2. And if you’re like a Tour de France cyclist, it would be above 3. If you’re kind of a desk worker, it’d be like 1.6. So it’s kind of a way to compare individuals but also species because it’s standardized by your body size ’cause your body size essentially determines your basal metabolic rate. And it’s interesting that most animals have physical activity levels of about 2 to 3. So they’re, you know, pretty active. We evolved from apes, and turns out that primates in general, and apes in particular, have really low PALs, really low physical activity levels. Chimpanzees have physical activity levels about 1.4. And so their physical activity levels are actually lower than sedentary Americans. So your average sedentary American, who doesn’t really do much, and, you know, spends most of his or her time in chairs and, you know, et cetera, and takes elevators and all that, is still more physically active actually than your average chimpanzee whereas hunter gatherers, people who, you know, every day have to go out and get their food, their physical activity levels tend to be around 2, about, you know, 1.92, or if subsistence farmers who don’t have a lot of machines and tractors and stuff like that, they may be a little bit harder working, maybe 2, 2.1, 2.2, and, really, it wasn’t until the industrial revolution that people’s physical activity levels would be able to go down, like about 25%, to, you know, 1.6, 1.7, which is sort of typical of your average American. So it’s a useful kind of simple standard to help us compare just generally, how active different groups or different individuals are. So your basal metabolic rate is a really important number because it tells you kind of just how much energy you’re spending on just the essential maintenance of your body, you know, paying for your brain and paying for all the tissues in your body, and, you know, you have to turn over tissues all the time, like the cells in your gut are being replaced like every five days or so. I mean, your fingernails are growing. Everything’s happening in your body, right, and that all costs energy, and it turns out that a kind of typical say, adult male, my size, right, and I’m not all that big, but, you know, it spends about two thirds of his or her metabolism just on basal metabolic rates. So I spend about 1,600 calories a day just existing, you know, just taking care of my body. So the vast majority of the energy that we spend isn’t spent on running around and being physically active and moving. It’s actually spent on just maintenance, just basic total maintenance, and that’s one of the reasons why we kind of never evolved not to be, you know, all that physically active when it wasn’t necessary because, until recently, energy used to be limited, right? It wasn’t like, you know, 7-Elevens or Dunkin’ Donuts or Whole Foods or whatever your, you know, favorite place to get food is right around the corner. You know, if you wanted something to eat, you had to go find it. You had to either, you know, hunt it or gather it or dig it up, and so energy was limited, and when energy is limited, you have to engage in trade-offs, right? And so if you spend energy on physical activity, that means you’re not spending energy on taking care of your body or reproducing which is the only thing natural selection really cares about. And so the fact that our bodies are so expensive helps explain why we tend to avoid unnecessary physical activity because it prevents… Like, for example, this morning I went for a five-mile run. So I spent about 500 calories. Those are 500 calories that I could have spent on my metabolism, and if I were energy limited, that would’ve been a bit of a problem, right, which is why people who are energy limited and already physically active, it makes no sense for them to go for a needless completely pointless five-mile run in the morning. So technically a calorie is the amount of energy it takes to raise one gram of water, one degree centigrade, right? So it’s a unit of energy. And so we convert various kinds of energy into calories. There are other, of course, other units of energy like the joule, for example, but the calorie’s a kinda of a useful one, ’cause, you know, our food is labeled in calories. So calories is the most common one. But actually the calories that we mostly talk about that are on our food labels are actually kilocalories. They’re actually 1,000 calories. So when you look at a, you know, label for a chocolate bar or a can of beans or something, and it says there are 50 calories, it actually means that there are 50,000 calories, right? But anyway, that’s neither here nor there, but that’s fine. But so most of the time we’re talking about calories with a capital C or kcal, kilocalories, and, you know, our bodies use a lot of calories. Typical, you know, human body, you know, spends about 2,000 to 3,000 calories, or, in this case, kilocalories a day, you know, existing, that’s your basal metabolic rate, plus all the energy you spend, you know, running around, doing chores, making dinner, whatever it is you do for your day. When you go for a walk, you probably spend an extra 50 calories per mile. If you go for a run, you’re spending probably an extra 100 calories per mile for that run. So that kind of gives you, hopefully, gives you a sense of sort of what, you know, energy amounts we’re talking about.

– [Narrator] Chapter 2: Smarter sitting, smarter sleeping.

– All right, so I’m sitting here talking to you, but, other than that, I’m basically doing nothing. Maybe I’m gesticulating a little bit, moving my mouth, but I’m, you know, completely physically inactive in any other regard, right? But even now, I’m spending, you know, a fair amount of calories just existing, right, and for every five breaths, one of my breaths is just taking care of my brain, right? My brain is constantly consuming vast quantities of energy, right? I spend about just, you know, 300, 400, maybe 500, 450 calories a day just paying for my brain. My muscle, even if I’m not doing anything with my muscles, my muscles constantly require energy. My gut is requiring energy. My kidneys require energy. My liver is requiring energy. My heart is requiring energy, You know, my immune system, which is, you know, taking care of my body and making sure that I don’t die from some virus or bacteria, that’s taking up energy. So all of these processes are all adding up, and a typical sort of human is spending about 1,300, 1,400, 1,500, 1,600 calories a day just on all those basic processes even if they’re doing nothing else, right? So just existing is a fairly expensive prospect, and we have unusually expensive bodies in one regard, which is that our brains are really big. So brains are extraordinarily expensive organs. My brain is, you know, about 2% of my body weight, but it’s using something like, you know, a fifth of my metabolism at the moment because of all kinds of reasons. It’s because I have to, there’s lots of pumps. I have to pump energy in and out of the brain ’cause I’ve separated my brain from my bloodstream with this barrier, and neurons are very expensive, and I’m synthesizing all kinds of neurotransmitters. There’s a whole bunch of things going on that make my brain super, super expensive, and the thing about brains is that they don’t store any energy. So unlike my muscles and my liver and, you know, other organs which kinda have some energy on board, all the energy for my brain is constantly has to be delivered, and if I stop delivering that energy, even for just, you know, a short amount of time, I’ll die, right. So brains, human brains, which are so big require us to constantly have a little bit of extra energy on board. I decided to start this book on physical activity and exercise with actually discussing physical inactivity because if you understand activity, you need to understand inactivity, and there are as many myths about inactivity as there are about activity, and they illustrate, I think, how we make people exercised about health and about physical activity and other such things. And I think, for me, the most pernicious maybe is this idea that sitting is the new smoking. And, you know, it’s a well-meaning expression, right? You know, public health experts who are trying to help people be more physically active, they think that by saying, you know, trying to encourage people to get off the couch, get out of their chairs and be more physically active, that “sitting is this new smoking” is a kind of way of doing that, and it’s true that if you’re never physically active, you increase your vulnerability to a wide range of diseases, but I think that the idea that the concept kind of backfires because, look, I mean the chair that I’m sitting in right now, I mean, it’s not like a toxin like a cigarette, and it’s not delivering, you know, poison to my bloodstream. It’s just a completely, you know, harmless sort of thing. And, furthermore, you know, sitting is very normal. My dog spends most of her day just, you know, sitting around the house. If you go to any other part of the world, you go to villages all over the world, if you go to study hunter gatherers, you know, when they’re not physically active, and we’ve already talked about how they’re not physically active all day long, guess what they’re doing? They’re sitting. Now, they may not be sitting in chairs ’cause they may not necessarily have chairs. They’ll be sitting on the ground, or they might have benches or stools, but it turns out that when you measure amounts of sitting in, you know, non-Western, non high-income populations, they sit pretty much as much as we do, about 10 hours a day. So I think we’re not honest to people, right? Instead of saying sitting is the new smoking and making people feel bad about themselves, why not tell them the truth which is that there are better ways to sit and worse ways to sit. So it’s good to be active when you sit, to break up your sitting in bouts, you know, don’t sit for huge amounts of time, get up every once in a while, you know, make yourself a cup of tea, you know, scratch the dog, or something like that. And then the other is that there are kinda more active kinds of sitting where you, like, use some of your muscles. Like right now I’m sitting in this comfy chair, and it’s stabilizing my back, and, you know, I don’t have to spend any energy, but if I was sitting on a stool or I’m squatting on the ground, I would have to spend some muscles to kinda keep my body going. And all of that just turns on, you know, the cellular engine of our body, right? It’s like turning on the car engine, right? It causes you to use up some of the sugar in your blood. It uses up some of the fats in your blood. It turns on various kinds of genes. It’s all good, right? So you don’t have to exercise hugely to get some of the benefits of being a little bit more active. Just moving a little bit is actually kind of healthy. And, furthermore, when you look at the data on sitting, turns out that how much you sit at work isn’t really that much associated with health outcomes. It’s how much people sit in leisure time that’s associated with negative health outcomes. So if you sit all day at work, and then you go home and you sit all day, and you’re driving to work, and you’re driving home, and, you know, you basically never do any physical activity, well, yeah, then your risk of a wide range of diseases goes up, but if you have a normal desk job, but you also, you know, walk around and get some exercise and do various stuff, you’re fine. There’s no evidence that there’s any problem with that. It’s a completely normal thing to do. So I got interested in this, in the myths about sleep because, you know, we’re told all the time to sit less, but then we’re also told to sleep more. And like, like why is that? What’s going on there, right? And one of the myths about sleep, right, which is of course one of the most fundamental forms of physical inactivity, right, is sleeping, is that the modern Western world has robbed us of sleep, right? We have television and iPhones and electric light bulbs and all these sorts of things, and ever since Edison, nobody’s been able to sleep very much, right? And, yet, you know, I’ve spent time in various parts of the world where, you know, there’s no electricity, and people seem to be up all night. I’ve always wondered about that, and I was delighted to see that there’s been some research recently on that, this is not my research, where people have shown that in, you know, parts of the world, and we’re talking about multiple continents, we’re talking about Africa and South America and, you know, other, you know, in North America, places where people don’t have electricity, people don’t sleep eight hours a night. They actually sleep like, you know, five and a half, six, sometimes seven hours a night. And so there’s no evidence whatsoever that people sleep less in the modern industrial world because of televisions and iPhones and stuff like that. And then, furthermore, when you look at the epidemiological data, right, so you look at how much people sleep and not just like what they say they sleep, but how much they actually sleep using sensors ’cause, I mean, who knows actually how much they slept? How can you know that? You’re asleep, right? But if you measure like, sensor-based data on how much people sleep against their health outcomes on the y axis, right, it turns out it’s a U-shaped curve, and the bottom of that curve, so the optimal amount of sleep, turns out to be for most people around seven. Now it’s not like a law, right? There’s some people who do better with eight and some people better with six, et cetera, but seven turns out to be better than eight for most people. So where this idea that we all need eight hours of sleep is, I think, pernicious. Now it’s true, it is definitely true that if you don’t get enough sleep, you are compromising your health. If you’re getting like three, four hours of sleep, and you’re constantly exhausted, and you fall asleep all the time, you know, that’s an issue, and it’s worth paying some attention to that. But then just making people feel bad about their sleep if they’re actually getting normal amounts of sleep just makes them anxious. It makes them concerned. And, of course, when you make somebody anxious about sleep, what do you do? You arouse them, you elevate their levels of cortisol, which is a stress hormone, and guess what cortisol does? It keeps you from sleeping. So telling people, making people kind of nervous about their sleep sets in motion, or can set in motion, a kind of vicious circle where you make people feel bad about their sleep, and then, because of that, they’re less likely to sleep, and it kind of drives a positive, you know, feedback loop. And so, look, we should relax about sleep. We should help be a bit more compassionate. If people aren’t getting enough sleep, let’s help them figure out ways to get sleep, and do that by treating the cause, not the symptoms, of the lack of sleep, but let’s not make people stressed about it in ways that are unhelpful. You know, if you want to look at the power of culture and affecting biology, you know, sleep is such a great example because we have, you know, in places like America, you know, Western countries, we have such culturally prescribed ways of sleeping that would baffle our ancestors and baffle people in other parts of the world, right? We have this idea that sleep is this sort of solitary thing, and you do in a dark room with no noise on a super comfortable mattress. And we get upset if we hear a, you know, car honking or a dog barking or whatever, but, you know, for most of human evolution in many cultures, sleep was a very social thing, right? People sleep in groups, and, you know, you’re outside, and you hear, you know, animals in the distance. And actually hearing them in the distance is maybe a good thing ’cause it helps your brain realize that they’re in the distance. They’re not nearby. And, you know, people sleep on the ground. They don’t need sleep mattresses, and they don’t have fancy pillows and all that kind of stuff. And, you know, you can learn to sleep in all kinds of situations if you relax, right, if you allow yourself. And the fact that we kind of feel like we have to have this sort of special, you know, circumstances, and, look, I’m no different. I like a nice quiet room and a comfortable mattress and all that sort of stuff, but I do try to remind myself when I have trouble sleeping that, you know, you can sleep on an airplane, you can sleep in a chair in a lecture when it’s boring. I mean, I can sleep, you know, all kinds of crazy places, and I can certainly sleep in this bed tonight if I want to. It’s just a question of my mindset, not the environment that I’m in.

– [Narrator] Chapter 3: Walking, running, and everyday strength.

– Humans really suck at speed. I mean, there’s just no way around it, right? I mean, as soon as we became bipedal, which was a great thing in some ways, right, about 7 million years ago, probably to save energy when we were walking, and, you know, maybe it helps us carry things, and we can have tools, and we can gesticulate in ways that quadrupeds can’t. Lots of great things about being a biped, but the second we get up on two legs, we lose half our horsepower, right? You know, we only have two legs to generate power as opposed to four, and so we’re about half as fast as a quadruped our size, and that’s true for the world’s best runner. So Usain Bolt, who still owns the world record in the 100 meters, he can run a little bit over 10 meters a second, right? He can run I think 10.4 meters a second. You know, your average goat, you know, from a pen just down the street, can run 20 meters a second and for a lot longer than Usain Bolt, right? So humans in general are slow, even the fastest humans on the planet, and so we have this idea that, you know, humans evolved for running but not for sprinting but more for endurance running. And so there’s this general idea out there that there’s a trade off between speed and endurance, and that you can either be really fast and not go very far or can be slow, and you can go forever. And we all know that’s kind of true, but at the elite levels, it’s especially true for if there’s a performance, but for most of us, actually, if you want to improve your endurance, one of the best ways to do that is actually to work on your speed, do what we call interval training, you know, occasionally get around, do some track work, you know, do 200, 400, 600 meter repeats. That’ll not only make you faster, it’ll also improve your endurance. But we often think about this trade off because of the world’s best athletes, right? And I think it shows how we get kind of off track by focusing too much on elite sports and professional athletics. So, Usain Bolt, right? He can run like 10.4 meters a second for like 10, 20 seconds, but he can’t run a marathon in that distance. The world’s record holder at the moment for the marathon is a guy named Eliud Kipchoge, fantastic runner too, and he can run, you know, a 4:40 mile, it’s like six meters a second, a little more than six meters a second for 26 miles, which is astonishing. I can’t do that for one mile, right? And so you look at Bolt and Kipchoge. You think, “Okay, you know, this guy’s running, you know, “almost twice as fast as the other guy, “you know, there’s a trade-off between speed and endurance.” But for most of us, actually, you know, we can run, you know, people who can run, you know, as I said before, if you want to run longer distances, one of the best ways to do that is to increase your speed, and people who are good at speed tend to also be better at endurance, you know, unless they’re elite athletes, right? So, if you look at decathletes, for example, you know, amateur decathletes, the ones who are really good at the speed events are also good at the endurance events, you know, so that trade off is true only for really elite athletes. It’s not really true for the vast majority of us. So strength is important, and there are misconceptions about strength too. So strength, you know, is the ability, how much force you can produce, right? And power is the rate at which you can produce that force. So, you can be really strong, but not actually necessarily all that powerful, right? And so people who aren’t all that strong, you know, if I were to get out of this chair, that requires power. I have to rapidly push my body up, right, and one of the problems that happens in the world today is that people get really frail as they get old. They lose strength. So hunter gatherers aren’t super strong. They tend to be about 75th percentile for sort of standard measures of strength, like, you know, grip strength tests. So, you know, they’re, you know, like 25% of Americans would be stronger than your average hunter gatherer, right? So they’re not super strong. They’re strong, but they’re not like crazy strong. But the difference is that as they age, they stay strong. So, Americans, as we get older, or Brits, as they get older, you know, the strength declines rapidly. By the time people are in their sixties and seventies, they’re pretty frail. But hunter gatherers remain fairly physically active as they age because they’re doing stuff, you know. They don’t have can openers. They have to, you know, they don’t have jars anyway, but they’re, you know, they have to lift things and carry things and do stuff that keep them strong. And the end result is that they maintain that strength, and that strength is important because one of the real serious most pernicious issues of aging is a disease, or it’s a problem, called sarcopenia. Sarco is flesh, and penia is loss, so it’s flesh loss. And as people get older, in the West, they tend to lose a lot of strength and power, and that makes basic tasks difficult like getting out of a chair, you know, going to the bathroom, you know, climbing the stairs, you know, doing chores, you know, going to the store. And when that happens, people become less active, and when they become less active, they become less fit. And it kind of sets in motion a really disastrous, vicious cycle, right? And so, as we get older, strength training becomes more and more important so that we can avoid those losses of vigor that are really important to maintaining your health and staying strong and staying healthy as we age. I mean, every culture engages in sports, right? It’s a human universal, and sports are important and they’re fun, and they’re kind of play, right? And they serve all kinds of functions. Sports are socially important, especially when you’re children. You learn good sportsmanship, right? You know, somebody scores a goal on you, it’s not appropriate to bash them in the face, you know, that sort of thing. You learn to be, you know, you learn hierarchies, you learn companionship, you learn how to cooperate. There’s a lot of wonderful things about being on a team in sports and all that. But some sports also have an another origin, which is, I think, to train warriors. It’s not coincidental that a lot of the sports, for example, in the Olympics, think about the ancient Olympics, especially, were skills that were really important for warriors, right, you know, javelin throwing and chariot racing. Well, we don’t do chariot racing anymore. You know, sprinting, wrestling, boxing, right? These are all very kind of physically demanding sports that they’re kind of combat related, right? So, sports have all kinds of different meanings, and, of course, the problem is that not everybody enjoys sports, and not all sports are all that physically active. I mean, take baseball for example, which is a perfectly wonderful game, but I call it a game, not a sport because, you know, you don’t really have to be that physically active to play baseball. You have to have incredible reflexes. I mean, it takes a lot of skill to be a great baseball player, but, you know, it’s not, you know, maybe if you’re stealing bases you have to be fast, but the vast majority of baseball players don’t really actually have to engage in that much physical activity, right? And that’s not a criticism of baseball. It’s just that let’s not equate all sports with physical activity. And I think that a kind of an interesting dimension of sports that we never really think about that much is that sports, I think, evolved also to help us learn not to be reactively aggressive. So there’s kind of two kinds of aggression. There’s reactive aggression. So like, you know, you figured, “Take my watch.” I’d be really mad at you, I might hit you, right? but, you know, that’s kind of an instant kind of non-planned, you know, aggression, but, you know, road rage is a perfect example of reactive aggression, but there’s also proactive aggression, right, which is when you plan something, you know, premeditate, you work it out in advance, right? And war is an example of a proactive aggression. I think sports are also kind of proactive aggression sometimes, and in a lot of sports we teach people not to be reactively aggressive. I mean, the extreme to me is tennis, right? You’re not even allowed to swear when you’re playing tennis, right? But it’s perfectly acceptable to be appropriately, proactively aggressive as long as you’re within the rules, right? And that’s what humans excel at. We excel at curbing our reactive aggression, and we excel in many cultures, and US is no exception at being really good at proactive aggression. That’s what we call war. I like to try participant observation, you know, I like to try what I study, right? You know, I like to try barefoot running, and I like to eat foods that other people eat. And when I was working on this chapter on aggression, I realized, you know, I’m a very unaggressive person and I didn’t want to like, you know, go participate in some kind of brawl in a bar or something like that, but I thought I’ll go to a mixed martial arts fight. ’cause I’d never been to one before. You see them on TV, but it’s not the same thing. So I went to a mixed martial arts fight not too far from Boston, and it was a fascinating experience to see, ’cause you know, mixed martial arts, there are really almost no rules. You know, you’re not allowed to kick somebody in the groin, you’re not allowed to bite them, you know, and if somebody’s wants to stop, you know, if they’re in in peril, you have to stop, but that’s about it. There’s not a lot of other rules, right? And, you know, apart from a few, you know, fights when I was in school, when, you know, people, you know, bullies, you know, hit me and stuff like that, I mean, I’ve never really, you know, seen a lot of fighting in my life. I lived kind of cloistered life, so it was fascinating to go see these mixed martial arts fights and see how people can be, you know, how humans fight ’cause, you know, we’re, as a species, you know, we do fight hand to hand, but most of the fighting that humans do is with weapons, right. You know, we’ve invented weapons millions of years ago, and it’s kind of strange to see people willingly fight each other without the benefit of weapons, right? And what it really shows is just how bad we are as a species, how inadequately adapted we are for combat without weapons. You know, we really are adapted for fighting with weapons. You know, we don’t have claws, we don’t have fangs. We’re bipedal, so, you know, we have these big heads that are very vulnerable. So it’s really kind of fascinating to see how human fighting is really so different from the way animals fight. You know, going to see a mixed martial arts fight really kind of, at least for me, as somebody who’s thinking about it from an evolutionary and anthropological perspective, just how much weapons have changed the nature of human aggression. If there’s any one physical activity that humans evolved to do, it’s to walk. We are the walking champions among the world. I mean, we’re just, you know, walking is the most fundamental basic form of human physical activity. We know from studies of hunter gatherers in tropical environments, you know, there’s not just one group of people, but peoples from different parts of the world, that women on average walk about about nine kilometers or five miles a day, and men walk on average about 14, 15 kilometers a day, so 9 to 10 miles every single day, right? They do it seven days a week. There are no holidays, there’s no weekends, there’s no retirement. Walking is the way in which humans get around, get food, you know. It’s kind of fundamental to who we are as a species. We often carry when we walk. And today, in the modern sort of Western world with cars and escalators and elevators and, you know, Zoom and, you know, TV and all that sort of stuff, we just don’t walk very much. So, especially during this pandemic, people have been walking, you know, step counts have plummeted around the world from already pretty low level. So, you know, the average sort of hunter gatherer will take maybe, you know, 10,000, 15,000 steps a day. The average American before the pandemic was taking something like 4,700 and something steps a day. So a lot less than our ancestors. And, you know, my step counter, you know, when I’m not running, you know, if I discount running, I mean, my steps have decreased by about 50% during this pandemic, during COVID, because, you know, I’m not going anywhere. You know, I’m trundling to the bathroom and occasionally, you know, I go on a little errand here or there, and I walk the dog around the block, but that’s about it, right? And one of the misconceptions, and it’s a bit of a debate right now, but people often sort of discount how important walking is ’cause people think that walking really isn’t very good for weight control and weight loss, and I would disagree with that. I think it’s to be sure that if you walk only, you know, a few miles a day, you’re not gonna lose very much weight very fast. You know, you don’t spend that much energy walking. So, if you wanna lose weight, you know, not eating, you know, bacon or cheese or, you know, other things that are really, you know, sugary things that are full of calories, you’re gonna lose a lot more calories than if you walk for a few miles, right? But walking is important because if you do a fair amount, you still will actually lose some weight. You’ll just lose small amounts, and you’ll lose it slowly, but that’s still good, but, more importantly, walking turns out to be an important way to kinda keep your metabolism going to prevent weight gain, and there’s a lot of studies which show that physical activity, you know, it’s not the best way to lose weight, but it is an important component of preventing people from gaining weight or regaining weight after a diet. So if people go on a diet, and they lose weight, and then they stop the diet, they often regain the weight. It’s very common. But people go on a diet, lose weight, and then they stay physically active, they’re much more likely to keep that weight off. Again, one of the ways which we medicalize exercise in the Western world is we think there’s a certain amount you should do, right? We prescribe it, you know. You should take two aspirin, you should get eight hours of sleep, and you should walk 10,000 steps a day. You know, we like that, right? And there’s nothing necessarily wrong with a goal, right? Goals can be really helpful actually. But 10,000 steps is kind of arbitrary, right? The number actually came from when the first pedometer was invented in Japan before the 1960s Olympics. In the boardroom, they were trying to decide what to call it. It turns out that 10,000 is a very auspicious number in Japan, and they thought it kind of sounded good. It seemed kind of reasonable, so they called it, you know, 10,000 step monitor and that kind of stuck. And, surprisingly, it turns out that 10,000 steps isn’t actually a bad goal, right? If you actually look at what, you know, a lot of, you know, people in non-Western societies do, you know, 10,000 steps isn’t actually that far off. So it’s a perfectly reasonable goal to shoot for, but there’s nothing like special about it. If you do 8,000 steps, that’s fine. If you do 15,000 steps, that’s fine. The important thing is to get, you know, be physically active because some is better than none, and a little bit more is, you know, tends to be better than that, but, you know, it’s all good. You know, there’s no magical number. It’s not a u-shaped curve with a, you know, a bottom on it, right, where that tells you like where you should aim for. That does not exist. I’m especially interested in running. It’s actually one of my major areas of research. And I’m interested in how humans evolved to run long distances and what role running plays in our lives and in our evolution. And look, running is the most fundamental form of vigorous physical activity. As walking is the most fundamental form of moderate activity, running is what we do to be vigorous, right? You know, ’cause there were no ellipticals and, you know, other kinds of machines back in the stone age. If you wanted to get your heart rate up, you probably were running, right, and people ran long distances in order to hunt or scavenge, et cetera. But running today is kind of, you know, a very popular way to exercise, and a lot of sports use a lot of running. You know, a typical soccer player will run, you know, five, six miles in a game. So, there’s a lot of ways in which people run, but people are kind of exercised about running too like they are about so many other kinds of physical activity, and one of the biggest myths about running is that it’ll destroy your knees. And, like all myths, this is a but complicated because it is true that the most common injuries that runners experience are knee injuries, right? But there are kind of two kinds of knee injuries. Some knee injuries are caused by, you know, by your muscles being kind of outta whack and, you know, you kind of pull a ligament or your pull a tendon or something like that, or your IT band, et cetera. But those are injuries that you can recover from, right? And the other kind of injury are wear and tear injuries which you can’t recover from, the worst being osteoarthritis. And the idea that running too much wears out your joints is just wrong. It’s just fundamentally completely wrong. You know, it’s like if you think about your joints, like the shock absorber in your car, it’s just like, it’s just nonsense. There’s tons and tons of studies, more than a dozen randomized controlled perspective gold standard studies which show that people who run more are not more likely to get arthritis. In fact, lots of research shows, and research from my lab among them, that physical activities like running actually cause your joints to repair themselves and to stay healthy. So you’re not gonna destroy your knees by running, at least in terms of arthritis, but if you have arthritis and you run, it can be excruciating. You can exacerbate it. The other kinds of running injuries, I think that a lot of them are caused because people, we don’t learn how to run properly anymore. Like we, you know, I think running is a skill, right, like swimming or throwing or, you know, all kinds of other things that we do, and we don’t learn the skill that much of running anymore in the Western worlds. But the cultures I work in, like, you know, you ask people about running, they believe that it’s a skill, and that there’s like a right way to run and a wrong way to run. And how do they learn the right way to run? Well, they imitate people who are really good. They’ll actually follow them, like, in Kenya, a good runner will run in the front, and then people will run behind him or her and imitate the way they run. They’ll move their arms and legs, et cetera. They’ll imitate them to try to learn that person’s skill just as we do that for, you know, we watch, you know, Andre Agassi hit a backhand, you know, try to hit the backhand in the same way. And the other thing is that we also use these cushioned running shoes, et cetera, and we run in different ways, and I think running shoes enable you to slam into the ground so you don’t learn to land more lightly and gently. And we overstride, and we have overly slow cadences. And the other thing is that when people run in other cultures, especially in the stone age, you know, they didn’t run every day, and they weren’t running, you know, they didn’t stand on one line and run 26.2 miles to another line as fast as they could on a regular basis. And they’d probably go running maybe once a week or something like that, you know? So the idea that you go running five, six times a week, which is what I do, you know, and for long distances on pavement, et cetera, these are all kinda weird with strange Western things, and there’s nothing necessarily wrong with them, and there’s nothing necessarily harmful about them. You have to learn how to do it properly, and you have to build up enough strength and learn the skills of running, but let’s not scare people off running. I think the most pernicious, the most serious, the most problematic, the most concerning way in which we think about exercise in the Western world, is that as people get older, it’s kind of normal to be less physically active, and I think that maybe the most important argument that I make in my book is that that’s actually really problematic because, you know, we evolved, we’re a unique species. We evolved to live long after we stopped reproducing. We evolved to be grandparents basically. And the reason we evolved to be grandparents is that grandparents in foraging societies and also in farming societies are active. They go out, and they hunt, and they gather, or they work in the fields, and they help get food for their children and their grandchildren. And that physical activity helps their reproductive success, right, because they make it more likely for their children and grandchildren to survive, and to make it easier for their children to be parents, right? But there’s another benefit, right? And the other benefit is that that physical activity is important because it turns on repair and maintenance mechanisms. You know, when you’re physically active, you stress your body. You produce like what’s called reactive oxygen species, which cause like, you know, cellular damage throughout your body. It causes mutations, it causes inflammation, it causes, you know, cells to get kinda cruddy, you know, proteins to get kinda cruddy, but because that’s normal, our bodies turn on all kinds of repair and maintenance mechanisms that counter those. We produce antioxidants. Our muscles produce all kinds of molecules that turn down the inflammation of our bodies that causes a wide range of diseases. We repair our muscles, we repair our bones, we repair our brains. We turn on like hundreds, maybe thousands of genes that get turned on by exercise that they’re involved in repair and maintenance. And as we get older, that repair and maintenance becomes really important because it prevents senescence, it prevents our bodies from decaying. So when people become physically inactive as they get older, they’re no longer turning on those mechanisms that we evolved to use, right, that help us age better, and it makes us more vulnerable to disease, and we age faster. So we evolved to live long in order to be physically active, and that physical activity helps us to live longer and stay healthy because there’s an important distinction health span and lifespan, right? We often think about the effects of physical activity on lifespan, how long you live, but really, before the invention of, you know, before modern medicine, what determined how long you lived was actually how long you were healthy, your health span. And so health span is really the key thing. And what physical activity does is it increases your health span, and your health span therefore increases your lifespan, and until recently that was what it was all about. And so, as we get older, let’s not cut back on the physical activity. let’s maintain it, do some strength, do some endurance. and the evidence is incontrovertible. There’s tons of data which show that, as we get older, the more we age, the more physical activity is really beneficial. The most famous study that kinda started all this was actually done at Harvard University. It’s called the Harvard Alumni Health Study, and they did it because, you know, universities are really good at keeping track of their alums. You know, they constantly ask you for money, right? And so they never lose track of alumni. And so a fellow named Ralph Paffenbarger, who was at the medical school at Harvard, got the Harvard alumni office to let him find out from alumni what kind of physical activity they were doing, and he asked them health questions and find out, you know, how healthy they were, and also find out when they died. And what he showed was that younger alums, and one of the advantages of this study is that it kind of controls for socioeconomic status, right, ’cause these are all Harvard alums back from the old days when they were all basically, you know, rich white people, right? So, the younger alums who were physically active were, you know, they had like 20% lower death rates. So that’s good, right? By the time they got to their seventies, the alums who were more active had like 50% lower death rates. And other studies have found the same thing, that physical activity as you get older is more important, not less important for preserving your health.

– [Narrator] Chapter 4: Exercise as medicine.

– Well, I think there’s two issues about the medicalization of exercise. You know, so look, exercise is very medicalized, and it’s also very commodified, right, and there’s nothing wrong with either, right? There’s nothing wrong with having, you know, fun sports clothes and gyms, and there’s nothing wrong with doctors telling people to exercise and all that, but the problem is that it doesn’t really work too well. It doesn’t get a lot of people motivated, and the proof of that is that, you know, 80% of Americans don’t get minimum levels of physical activity. And the other problem is that, you know, exercise doesn’t really fit a medical prescription in a very simple way. There’s like no optimal dose, right? You know, people want to know how much to do it exactly, and there is no answer to that question, right? And then, finally, in a way, it’s not so much that exercise is medicine, which is what we often say, it’s really that the absence of exercise or the absence of physical activity is harmful, and so you’re kind of just basically restoring to the body what it kind of essentially needs. And although that sounds like a kind of a trivial distinction, actually, I think it’s really profound ’cause it helps us understand on a deep level, you know, the kinds of dosages of physical activity and their effects and how they affect our vulnerability and susceptibility to various kinds of diseases and why it’s not really a magic bullet. I mean, people can look at, there are lots of people we can think of like the last president of the United States who is, you know, doesn’t exercise, right? And he’s in his seventies, and by all, you know, looks like he’s doing just fine, right? So, you know, you don’t have to exercise to live a long life, and that makes people kind of, I think, suspicious about the medicalization of exercise. We like to be told what to do. We like to think, you know, you should take, you know, you should take X milligrams of this medicine, et cetera. So you should exercise, you know, this many, you know, hours a week, right? We want to know what the optimal dose is, but there is no optimal dose, right, because, first of all, we’re all experiments of what, right? You know, you might be young, you might be old, you might be male, you might be female, you might be fit, you might be unfit, you might be living in a suburb, you might be living in a city, you know, you might be previously injured, you might be worried about heart disease, you might be worried about Alzheimer’s. There’s no one outcome, and there’s no one nature. It’s impossible to prescribe one dose for everybody. So that’s one thing. And then the other thing is that everything involves trade-offs, right? Exercise is no exception, right? You know, if you exercise more, that’s great for some things, but you also could have some negative effects on other things, the most common one being injury, right? You’re more likely to hurt yourself, right? So for the vast majority of people, what they’re trying to figure out is how to just get enough exercise, right, and I think the important message that often is missed is that if you’re physically inactive, and you’re struggling to be more active, anything is better than nothing, and you don’t need to run marathons. You don’t need to do a couch to 5K. You don’t need to even do necessarily 150 minutes a week, right? Even an hour a week will be better than nothing, right? It can actually lower on average somebody’s rate of mortality about 30%. If you can get up to 150 minutes a week, on average, it would lower somebody’s mortality rate by about 50%. More is better, but eventually it kind of tails off. And so there’s no one perfect dose. There’s no one perfect type. And I think helping people understand that, I think relieves them of some of the stress. There’s a big debate about whether you can exercise too much. And the answer is that most people think it’s true but we actually don’t have a lot of evidence for that. So there was a study that actually just came out from the UK Biobank, huge study of just about everybody in England, large numbers of people in England, along with genetic data, by the way, and, of course, there’s very, very few people who are doing a huge amount of exercise. It’s a tiny, tiny number of individuals at the end of the curve there. But there was no evidence from that study that the people doing ridiculous amounts of exercise, you know, 30 hours a week or so, had actually any negative effects, and the same is true of some studies that were done in the United States. So, yes, it’s possible, but there’s not a lot of evidence, but, you know, I’m not really worried about those folks. There’s so few of them, you know. The vast majority of people we’re worried about are on the other end of the extreme, who are not getting enough, and let’s worry about them. We’ve medicalized, and this sounds like a strange way of speaking, but we’ve medicalized disease, right? We’ve medicalized health, right? For a lot of people, health is the absence of disease, and it is true to a large extent, but health, you know, can also be just vigor, vitality, the ability to do what you want. Somebody can have, you know, a disability and still be healthy, for example. So what’s really important about physical activity and exercise is that it reduces our vulnerability to a wide range of diseases. So, you know, you can not exercise and still, you know, live a long and healthy life. You can exercise and still get, you know, cancer and heart disease and all kinds of other diseases. It’s just that physical activity lowers your risk of most of those diseases, and we know that both epidemiologically, we know in terms of the probability that you’ll get those diseases if you exercise a certain amount, but we also know how that works based on a wide range of mechanisms, and the most important benefit of exercise is that it decreases inflammation. So inflammation is when your immune system essentially starts to attack you, yourself, right? So, you know, if you get a bacterial infection or a viral infection, your immune system kicks into high gear, and, you know, you attack those invaders, but your immune system can also can go on the offensive at such a very low level, that’s called chronic inflammation, that you can’t really detect it, but it’s still there, and it’s still kind of attacking things, and it can start attacking your own body, and that leads to heart disease, it leads to diabetes, it leads to Alzheimer’s, it leads to, you know, a wide, you know, osteoarthritis. It leads to a wide range of diseases, and one of the huge benefits of exercise is that it lowers those levels of inflammation. It does through a number of mechanisms. One is by getting your muscles active, those muscles actually turn down the inflammation with various molecules. The other way is that it reduces the fat around your belly, visceral fat, belly fat, which is very pro-inflammatory, and so the combination of these various consequences of exercise have enormous implications for just lowering people’s chances of getting a wide range of chronic diseases that are very debilitating. We spend so much time thinking about how exercise, physical activity is so good for physical health, for, you know, for diseases that range from heart disease to cancer, et cetera, and that’s all true, not in any way, you know, want to minimize that, but I think we often undervalue just how important physical activity is for mental health. You know, when you’re physically active, your brain turns on a whole, you know, cocktail of chemicals that are really good for you, right? It turns on dopamine and serotonin, which are important for anxiety and depression and mood. You produce opioids, which of course can make you happy, and even, in extreme cases, endocannabinoids, which can make you high and make you feel really good, right? And, you know, study after study after study shows that physical activity has important immediate benefits on people’s mental health. And so one of the crises, I think, of the pandemic has been as people’s physical activity levels downed, I think that’s partly responsible for some of the stress and the anxiety and the depression that’s on the rise recently today. And, you know, one way to help, you know, simple way to help folks, I mean, it’s not a magic bullet, it’s not gonna cure it overnight, but it’s certainly a potent part of our tool to help people, is to help people be more physically active. It has enormous effects on people’s mood and mental health. We think so much about exercise in terms of elite athletics, right? You know, the fastest, the highest jumping, you know, the strongest, et cetera ’cause, you know, you turn on the TV, and that’s where we see, you know, amazing athletes do amazing things, and it’s wonderful, right? It’s great entertainment, but that’s actually kind of what it is, right? It’s actually entertainment. I mean, what the world’s fastest runners are able to do, or the world’s best, you know, basketball players are able to do, have almost nothing to do with what most of us do, right? I mean, I can run, I’m a pretty good runner, and I, you know, struggle to run like a six minute mile, right, and like the world’s best marathoners are running 4:40 miles for 26 miles. I mean, I can’t even dream of that. I can’t run one mile that fast. I can’t even run a half a mile that fast. And so we get this kind of, I think sometimes a perverted idea about what’s normal from elite athletics because we’re looking at the extremes, the best of the best of the best, of the best of the best, right? And while that’s amazing and impressive, these are people who’ve spent years of their lives training to do just one thing and one thing really well. That’s not what most of us do. And they’re also, you know, they’ve gotten lucky in the genetic, you know, in the genetic, you know, lottery, right? They’ve got a lot of genes which I don’t have which give them certain kinds of capabilities, and I do worry that sometimes our focus on elite athletics can actually be offputting rather than inspiring. I think that one of the things that people really struggle with when they, you know, when I talk to them about the research that I do, is that they struggle to understand both the nature of research in general, but also sort of evolutionary research in particular because research is a process, right? You never know the truth, right? And so when I pick up a paper written by somebody else or my own work, or when I do an experiment, I’m not trying to think, “Oh, can I prove this?” What I’m trying to actually do is say, “Can I disprove this?” you know? And I’m trying to be really critical about it. So when we think about, for example, the effects of physical activity and exercise on the body, I’m not trying to prove that exercise is good. I’m actually trying to test the hypothesis. I’m trying to reject ideas about how exercise has effects on us. And the thing about evolution is that we can’t really directly test evolution. I can’t do evolution, you know, I can’t study human evolution in a lab, right? I can’t, you know, grow little humans and sit and do selective experiments on them and see what happens. I mean, first of all, it’s not possible, but also it’s not ethical and, you know, whatever, you can’t do that, right? So what we do is we try to look for kind of natural experiments. We kind of compare people. And the reason I look, I go to the field, and I don’t just work in my lab in Cambridge, Massachusetts, but go to Mexico and Kenya and Tanzania and other places like that is not because I want to study the other, right, you know, non-white people. It’s because I’m interested in people who don’t live urban Western lifestyles. I’m interested, for example, how do shoes affect your feet? And, you know, I can go and find, you know, Americans who’ve decided to throw away their shoes ’cause they’ve gotten, you know, gotten kinda hippie and think that, you know, shoes are evil or whatever, or they just prefer being barefoot, but that’s not the same thing as somebody who’s grown up being barefoot, right? If I want to study how sitting in chairs affects your back strength, which is something we’re working on, you know, yeah, I can find some Americans who don’t sit in chairs too much, and we do do that, but I also wanna look at people who’ve never sat in a chair in their life, right, and how that affects the way. And also it’s important to do that in the context of their culture and their environment, right, and because the world that we live in the United States is very WEIRD, and WEIRD in the sense of it’s Western, educated, industrialized, rich, and democratic, WEIRD, an acronym coined by my colleague Joe Henrich. And most of the world isn’t WEIRD. Most of the world is very different from us, and if you really want to understand human beings, you’ve just gotta get out of our little bubble, and you have to travel, and you have to look at how different peoples live, and when you do that, not only does it expand your, at least my, expands my perception of sort of what’s normal and what’s appropriate, but I think it also forces me to question what I do in my life because I’ve learned a lot from people in other parts of the world and other cultures, and it’s caused me to change my life, and it’s caused me to question my ideas, just as a scientist, I’m always questioning, you know, whether I’m right, and that’s kind of, I think, what I’m really lucky to do, and that’s what I really enjoy most about my research.