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RHR: Setting the Record Straight on Exercise, with Dan Lieberman


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Exercise is a modern phenomenon. We no longer engage in physical activity for immediate survival; we do so for health, longevity, and, sometimes, but rarely, pleasure. Why is that? In this episode of Revolution Health Radio, I talk with Dan Lieberman, professor at the Department of Human Evolutionary Biology and [the Edwin M. Lerner II Professor of] Biological Sciences at Harvard University, about the evolution of human physical activity. We cover the differences between physical activity and exercise; the impact they have on the musculoskeletal system, weight loss, and aging; as well as running form and the effect of shoes on biomechanics. Let’s take back the enjoyment of physical activity, exercise, and play.

Revolution Health Radio podcast, Chris Kresser

In this episode, we discuss:

  • Dan’s background
  • The relationship between physical activity and exercise
  • Setting the record straight: activity and aging in the Paleolithic Era
  • Cardiovascular exercise vs. strength training for long-term benefits
  • The impact of exercise on the musculoskeletal system—and why you should try running barefoot
  • The role of physical activity and exercise for weight loss
  • Is running bad for your knees?

Show notes:

Hey, everybody, Chris Kresser here. Welcome to another episode of Revolution Health Radio. This week, I’m really excited to welcome Daniel Lieberman as my guest.

He’s a professor at the Department of Human Evolutionary Biology and the Edwin M. Lerner II Professor of Biological Sciences at Harvard University. His research is on how and why the human body is the way it is and the relevance of human evolution to contemporary health. And one of his major focuses has been on walking and running and the effect of shoes on biomechanics and injury, and also [the] human relationship to exercise, which we’re going to be talking about today. He’s done fieldwork projects in Kenya and Mexico, and at Harvard.

He teaches a variety of courses on human evolution, anatomy, and physiology. He’s also published several books, including The Evolution of The Human Head, The Story of The Human Body, and then his most recent book, Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding. He is also an avid runner.

So I really enjoyed this conversation. I think you will, too. It’s a fascinating evolutionary look at exercise and, like I said, our relationship to it. So let’s dive in.

Chris Kresser:  Dan, welcome to the show. It’s such a pleasure to have you as a guest.

Dan Lieberman:  It’s my pleasure to be here. Thanks.

Dan’s Background

Chris Kresser:  So I always like to start with a little bit of background. How did you get interested in the how and the why of the human body being the way that it is? What led you down this path that you’ve been on for many, many years now?

Dan Lieberman:  Gosh, I’m not sure if I can answer that question. I think when I was an undergraduate, I was thinking about medical school. My grandfather was a pediatrician, and he was a big influence on me. And so I always had [an] interest in medicine. And then I got sidetracked by evolutionary biology. When I was an undergraduate, I took a class that sort of, I fell in love with the way of thinking about using evolutionary logic to think about problems and what happened in human evolution. And that slowly led me to a PhD where I became a head guy.

So I worked on chewing and chewing biomechanics for my PhD. But I was interested in locomotion. There’s a lot of stuff going on in locomotion. When I was a student here at Harvard, and Harvard has always been a center for locomotor research and physiology, so it was in the air. And then I focused my early career on heads. I actually wrote a book called The Evolution of the Human Head, and one of the subjects that I got really interested in was how we stabilize our heads during locomotion.

And that really got me interested in running, because we discovered that there were special adaptations just for stabilizing the head during running. In fact, we just published an article on that last week that got some press in the New York Times. But that got me interested in running, and then [I] eventually wrote that paper with Dennis Bramble, the Born to Run paper in 2004, and that kind of took over my life.

Chris Kresser:  Right, yeah.

Dan Lieberman:  So it’s been a long, nonlinear journey.

The Relationship Between Physical Activity and Exercise

Chris Kresser:  Great. I know one of the topics that you have spent a lot of time focusing on that I’d like to talk to you about, and it was the subject of your most recent book Exercised, is our human relationship with exercise and physical activity. What we might say a normal pattern is for human physical activity that we’ve discerned from studying ancestral populations, versus what our modern relationship with exercise and physical activity is and how they differ.

So maybe we could start by defining some terms that we’ll be using in a conversation. What’s the difference between physical activity or non-exercise physical activity and exercise?

Dan Lieberman:  Physical activity includes exercise, but physical activity is just moving, right? Anything you do that involves moving is physical activity, right? Washing the dishes, sweeping the floor, going to collect berries, walking to work, whatever, right? That’s all physical activity. But exercise is a special kind of physical activity. It’s discretionary, voluntary, planned physical activity for the sake of health and fitness. Going to the gym to lift weights or going for, like, I went for a five-mile run this morning, for no purpose other [than] going for a run. So that’s exercise.

Chris Kresser:  And where would you characterize sports, and that’s a distinct form of exercise because it’s purposeful? But activities that are, let’s say, hiking or backcountry skiing, or something like that, which certainly involve greater amounts of physical activity, but seem to span a couple of different categories, especially if there is any kind of practical element associated with them.

Dan Lieberman:  There’s no need to come up with completely discrete categories, right? There can be a blurring between physical activity and exercise. And sports can be an example of that. There [are] some sports that don’t involve very much exercise, baseball being one of them, right? Or darts, or race car driving maybe. I don’t know; you can come up with some others. But others involve, there’s a continuum, right? There’s never going to be a simple clear dividing line between exercise and physical activity.

I like to go cross country skiing. It’s certainly a sport, it’s a pastime, it’s play, but it’s also exercise. I’m doing it solely for the sake of the fact that I enjoy it and it’s good for my health and my mental health and whatever. But I’m not skiing in order to chase reindeer so I can eat dinner.

Chris Kresser:  Right. Yes. So we seem to be in a historically unique situation, at least for the past several decades where in the past, and please correct me if I’m wrong, there was quite a bit of physical activity, and the exact amount differed from different populations and either zero or very little exercise. And then today, we have a situation where there’s perhaps a significant decline in physical activity and in varying amounts of exercise, sometimes none at all and sometimes quite a lot, depending on who you’re talking to.

Dan Lieberman:  Basically, the idea of going to do a physical activity for the sake of health and fitness is a completely modern concept. If you’re a hungry hunter–gatherer, you might play as a kid. You can debate whether you want to call that exercise. You might dance as an adult for social reasons, but most of the physical activity you did was to survive. To get food or to avoid being somebody else’s food, right? And so, we were physically active for, as I keep saying in the book over and over again, it’s the mantra of the book, until recently, people were physically active for two reasons and two reasons only. One was when it was necessary, and the other was when it was socially rewarding. So dance or play would fit into the latter category.

But nobody went to the gym, nobody had treadmills, nobody went for five-mile runs for the purpose of having a five-mile run. That would be crazy. And the reason for that is that until recently, people were calorie limited. It was very hard to get enough calories. People did get enough calories, but it’s extra work. And so, [if] calories are limited, then you have to engage in trade-offs. So the best example of trade-offs is with time. The time you’re spending listening to me is time that you can never get back and spend doing something else. So time is inevitably traded off in terms of what you do. But in most societies, until recently, calories were also traded off too. When calories are limited and you can either spend it on growing your body or maintaining your body or storing it as fat or reproducing or moving. And so [the] energy you didn’t spend on moving you can spend on taking care of your body and reproducing, which are the only things that natural selection care[s] about.

So doing needless physical activity that has no benefit, has no reward, like lifting weights, for the sake of lifting weights, is a completely modern idea. Nobody ever did it in the past, or if they did it, they did it very, very rarely. So that’s the basic argument of exercise, which is that exercise is a modern phenomenon. And we’ve increasingly industrialized it and we’ve commodified it. We’ve medicalized it, we prescribe it, we pay for it, [and] we sell it. But those are all very recent trends.

Chris Kresser:  So we could say that exercise was not only something that we weren’t programmed to do, it was something that actually could have presented [a] risk, survival risk to us. And so would you say that we were actually programmed not to do it unless we had to?

Dan Lieberman:  I’d stay away from the word “programmed.” Because we’re not programmed to do anything. But it’s maladaptive. So there’d be, perhaps selection against it. Look, here’s the way I think about it. All of us have this instinct. Like, I’m on the fifth floor of the Peabody Museum right now, which is this old Victorian building at Harvard. And every time I walk [into] the building, I pass by the elevator and I want to take the elevator to the fifth floor. I have this little voice always, every day, no exception says, “Take the elevator.” But of course, there were no elevators in the Stone Age. But it’s natural to try to avoid unnecessary exertion so I can spend those calories on something else. And I have to use my slow brain to override that little voice and take the stairs. Because otherwise, not so much because I don’t get enough exercise, because I do, but partly because if anybody sees me in the elevator, they’ll call me a hypocrite.

So, it’s just an instinct (I wouldn’t say it’s a program) to avoid unnecessary exertion. And we see that all the time in escalators. When there’s an escalator next to a stairway or you’re in the subway and you want to sit down rather than stand up. The list is very long. It’s just a basic instinct that we have to overcome because we never had to choose to do unnecessary exertion. That was just not an issue in the past.

Chris Kresser:  So we shouldn’t be surprised that in a society where we don’t have to work or move our bodies, in most cases, to secure our food or maintain our survival, and we’re not necessarily engaging in physical activity for social reward reasons, that we have this epidemic of [a] sedentary lifestyle.

Dan Lieberman:  Right. We’ve created a world where we have machines that do everything for us. You can even brush your teeth with a machine. You don’t have to do anything. But the reason I titled the book Exercised, is that I think people have become exercised about exercise. We’re confused, we’re anxious, [and] we’re nervous. And we’re very judgmental about it. And I think one of the things that we have to stop doing is judging people who don’t do unnecessary exertion as being lazy. They’re being normal. We’re asking people now to do something that we never evolved to do. Let’s be more compassionate, and help each other be physically active in a world where we now have to do something very strange, which is choose to be physically active. And that’s a hard thing to do. And we need to help each other rather than judge each other.

Chris Kresser:  Yeah, that makes a lot of sense. And there [are] lots of other examples beyond exercise where we’re acting out our instinct from an evolution. I think of technology, screens, smartphones, and things where we’re just, we were primed to be distractible for lots of different reasons. And those devices really take advantage of that instinctual response. And it’s not a personal failing or something we should be ashamed of.

Dan Lieberman:  Yeah. I think that, I’m not sure we have lots of just-so stories about these things and maybe they’re true. A simpler one would be if you put a bowl of potato chips in front of me, there’s no way I could not eat them.

Chris Kresser:  The old [Lay’s] ad, “I bet you can’t just eat one,” right?

Dan Lieberman:  Yeah, it’s really hard.

Chris Kresser:  Wouldn’t even win that bet.

Dan Lieberman:  That’s a basic instinct, right? And potato chips are not good for you, but I love them. So the only reason, the way I don’t eat them is that I have to exert some self-control and mostly by not buying them. But if there was a bowl of potato chips right in front of me, there’s no way I could.

Chris Kresser:  Right. It’s easier to control your environment and make sure that that bowl is not in front of you than resist eating them if it is, right?

Dan Lieberman:  It doesn’t mean I’m a glutton, whatever, everything is wrong with me. It’s just an instinct.

Chris Kresser:  Yeah. So I want to talk a little bit about how we work at overcoming this instinct. Starting with just let’s assume someone’s completely sedentary or mostly sedentary. Not only are they not engaging in distinct exercise, [but] they’re also relatively inactive physically.

Dan Lieberman:  So you’re talking about the average American then.

Chris Kresser:  Exactly. So what does the research say? Would that person, and this is not necessarily either/or, but let’s set it up as if it is, would they be better off increasing their physical activity, walking X number of steps a day, gardening, doing more general physical activity, or remaining relatively sedentary but going to the gym three or four times a week for a half-hour or 45 minutes?

Dan Lieberman:  Well, I think the question that you just asked me is a classic example of how people get exercised about exercise.

Chris Kresser:  Yeah, right.

Dan Lieberman:  Because you just phrased it as a prescription, right? Would they be better off? And I think part of the argument of the book is that we should stop medicalizing exercise and we should stop commodifying it. And we should start thinking of it in a slightly different way. And let me answer your question in the following way, which is that, there [are] plenty of epidemiological data, there [are] mechanistic data, there [are] biological data, there [are] all kinds of data that if you’re inactive, no matter, doing anything is better than not doing anything. And so, if you’re, for example, physically inactive and you start exercising or being physically active just an hour a week, that’s like eight minutes a day, that still can lower your rate of mortality, your rate of dying, essentially by about 30 to 40 percent.

So even just a small amount of physical activity can have enormous benefits. And if you do 150 minutes a week, you can bring that down to about 50 percent. And more gives you even greater benefit. So anything is better than none. And a little bit more is better, and then eventually, the benefits level off and then you get no extra benefits. You don’t need to run marathons to get the benefits of being physically active.

So the answer to your question is that for most people who struggle to be physically active, the most important thing is for them to do what they like doing, that they’re capable of doing. For example, going to the gym requires money. Maybe you don’t have the money to go to a gym or you can’t get there because you need public transportation, and right now we’re in a pandemic and you can’t get on a bus. So maybe just walking or climbing the stairs in your building or whatever. And furthermore, if you don’t like it, you’re going to quit, right? That’s why most people quit exercise because they don’t enjoy it. I don’t know about you, but I hate the gym. I go sometimes because I force myself and I am good at that, but I don’t enjoy going to a gym. So if you don’t enjoy going to a gym, of course, you’re going to quit.

So we need to, again, the mantra of the book is that people were physically active for two reasons and two reasons only. When it was necessary or social[ly] rewarding. I think what we should do is make exercise necessary and socially rewarding, right? And the best way to do that is to do stuff with friends. So dancing is exercise or going for a walk with a friend. And the thing I often make fun of in the book from the very first page, and it’s on the cover of the book, is treadmills. [When] we think about exercise, [the] treadmill is the number one thing most people think of, right?

Chris Kresser:  Yeah.

Dan Lieberman:  Do you know anybody who actually likes using a treadmill?

Chris Kresser:  Probably not. I know people who do it regularly, but [it’s] hard to imagine that they like it.

Dan Lieberman:  Nobody likes being on a treadmill. Think about it. It’s a weird, expensive machine that makes you work to get nowhere. It’s usually indoors in a nasty gym, and it’s smelly and whatever, or it’s in a basement or whatever; it’s totally unfun. And yet, I think for me, it’s the apotheosis of exercise. It’s how we prescribe it. We do unpleasant, unnatural, weird stuff. Yes, it’s healthy. But it’s like cod liver oil, right? We do it because it helps us from dying or feeling sick, etc., or whatever. But nobody enjoys it.

So if you’re not already an exercise addict, there’s no way you’re going to, and you’re sedentary, the probability that you’re going to the gym and using the treadmill is going to get you anywhere is pretty infinitesimal.

Chris Kresser:  I suppose another way of answering or asking the question that I asked earlier was are there unique harms from being sedentary that are not completely mitigated by a few distinct periods of exercise a week?

Dan Lieberman:  I’m not sure if I understand your question. Look, exercise is not a magic bullet. It’s not, there are people who don’t exercise who still live to a ripe old age. And there are people who exercise and die young and get all kinds of diseases. It doesn’t work that way. It’s not like a simple medicine. Like an antibiotic that kills the bug, right? That (crosstalk 17:36).

Chris Kresser:  Well, let me be more specific. Because I think this actually does come up for people who, and if they follow your advice in the book, this will be a moot point because the advice is, which I fully agree with, to find something you really enjoy, that’s socially rewarding, [and] do it with other people. So maybe you have some additional accountability there. But I’ve had patients in the past who really just, they’re not drawn to exercise and even physical activity for whatever reason. But they know they have to, they should do something, so they force themselves to go to the gym and use whatever, the treadmill or lift weights for 30 minutes a few times a week. But outside of that, they really do no other physical activity.

Dan Lieberman:  Remember, exercise in and of itself isn’t what makes us healthy; it’s physical activity that’s healthy. So the benefits of exercise or the benefits of physical activity, exercise just happens to be the kind of strange physical activity we do in the modern world where people have to choose to be physically active, right? So if you’re physically inactive and sedentary, and the only physical activity that you do essentially is exercise, well that’s better than not. But you can also be healthy by being physically active without exercising, like gardening or taking care of the house and running after [your] children. And that’s what people used to do, right? And we’ve just, again, we’ve kind of turned exercise into a commodity. And we’ve prescribed doses of it. And if that works, fine. But that’s not the only way to be physically active. There are plenty of other ways to be physically active. Is walking to work exercise or physical activity? I don’t know. It depends on who you are.

Exercise is a modern phenomenon. We no longer engage in physical activity for immediate survival; we do so for health, longevity, and, sometimes, but rarely, pleasure. Why is that? In this episode of RHR, I talk with Dan Lieberman, professor, researcher, author, and avid runner, about the evolution of human activity. #chriskresser #evolutionofexercise

Setting the Record Straight: Activity and Aging in the Paleolithic Era

Chris Kresser:  Right. Well, I know you’ve done field studies yourself; you’re very familiar with the literature on hunter–gatherers and physical activity. What can we learn from that? I know you point out that hunter–gatherers stay physically active for not just years, but maybe decades after they stop having children, and that affects how they age. So can you talk a little bit about that, how physical activity contributes to aging?

Dan Lieberman:  Well, there are [an] enormous number of myths about physical activity in the hunter–gatherers in the Stone Age and whatever. And so we need to be really careful. And furthermore, we also need to be careful about not misusing the data. Just, as you probably know, I’m no fan of the Paleo diet and I’m no fan of Paleo fantasy thinking because I think people misuse a lot of this evolutionary information. It’s not a blueprint for how you should use your body, right? But it tells us something about what we’re adapted for or what’s sort of normal. But it doesn’t necessarily mean it’s necessarily better for us or necessarily worse for us.

So hunter–gatherers, of course, have to be physically active, but they’re not crazy, physically active, right? Turns out that measurements of hunter–gatherers indicate that from different populations around the world, they’re actually [doing] like two to three hours a day of moderate to vigorous physical activity. But not really more than that. They do a fair amount of light physical activity. And guess what? They sit around 10 hours a day, just like you and me. So [when] people talk about sitting being the new smoking, ]that’s] just kind of outrageous nonsense, right? It’s completely normal to sit. We’ve been sitting for millions of years. My dog spends most of her day sitting. So, hunter–gatherers are sort of moderately active, but they’re not crazy active. They do a few hours a day of moderate to vigorous physical activity. Not that much vigorous, mostly moderate. And the rest of the day, they’re relaxing. But the key thing is that they do it throughout their life. They don’t stop doing it when they [become] grandparents. In fact, they actually become sometimes slightly more physically active when they’re grandparents, because they’re foraging and hunting and preparing food and helping out their children and their grandchildren, which I think is one of the keys to physical activity as we get older; physical activity becomes more important, not less important, in terms of preserving health.

The other thing about hunter–gatherers [is that] there’s a misconception out there that they’re really strong, and they’re not. They’re reasonably strong, but they’re not jacked up and they’re not doing huge weights. And you can’t do huge weights; there are no weights out there to [use].

Chris Kresser:  Right.

Dan Lieberman:  You get the sense from reading certain books that they’re out there lifting enormous rocks, and that’s not only wrong, [but] it also actually would be maladaptive because muscle is very expensive tissue. When you can bulk up, you need to eat a lot more to pay for all the extra muscle. And when calories are limited, having more muscle than you need is a bad thing. And that’s why we have this use it or lose it phenomenon. So hunter–gatherers mostly do light aerobic physical activity, occasionally do some sort of activities that involve strength, but not a huge amount. So they’re like 75th percentile strength compared to Americans and Brits and populations like that. But the key thing is that because they stay active, they maintain that strength longer in life.

So they’re not running marathons, they’re not sprinting fast a lot, [and] they’re not running like Eliud Kipchoge for four-minute miles and all that. They’re kind of tooling along 10-minute miles when they run. They’re walking five to 10 miles a day. That’s about it.

Chris Kresser:  Yeah. And how does this affect how they age versus let’s say, how we age in industrialized societies?

Dan Lieberman:  Well, remember, we don’t know exactly how it affects how they age because we don’t have those kinds of data. But we know that in modern industrial societies, people who remain physically active age a lot better. And of course, hunter–gatherers seem to age pretty well too, right? So it’s a misconception that hunter–gatherers die young. They tend to have high infant mortality, but if they survive infancy, they tend to live about seven decades or so, sometimes eight decades.

But the important thing is that they tend to have less morbidity. So they don’t get the kind of chronic diseases that people get in Western societies. And I’m sure your listeners already know this. But that’s also true of people in Western societies who eat sensible diets and remain physically active. They also age better. They’re less likely to develop hypertension, they’re less likely to develop atherosclerosis; they’re less likely to develop sarcopenia, which is muscle wasting [that] causes frailty and creates a kind of vicious circle. But I think everybody already knows that. You don’t need me to tell you that, right? This is kind of common knowledge.

Chris Kresser:  Yeah, I think it is. And at the same time, it’s a good reminder because I think, at least in the people that I work with, sometimes there’s a tendency for them to compare themselves with the standard American person who is not exercising, not eating a healthy diet because so much of the research that you hear about that’s published is studying that population. And so it is, I think, a good reminder that if you make better choices, I mean, it should be fairly obvious. But it’s a good reminder that if you make better choices about food and exercise that that’s going to have an impact and you’re going to age differently than people who are not making those choices. All other things, like, of course, there are things that are outside of [our] control. But in general.

Dan Lieberman:  Yeah, we’ve known this for ages. The first studies that showed that physical activity reduced heart disease back in, well, people have known this since Socrates’ time and before. (Inaudible 25:39) every continent on the planet, but we’ve had good epidemiological data for decades on this. This is nothing new. Of course, we debate about exactly what’s the right kind of exercise and what’s the right kind of diet, etc., etc., etc. But look, there are very few people who don’t know that being physically inactive and eating a standard highly processed Western diet are bad for you. I mean, that’s not novel.

But I think what people misunderstand is just what you should do and how to do it and how to, because we, again, we make people really nervous about exercise. And people want to know what’s the optimal exercise. And you can buy books [that] tell you what’s optimal. Like, anybody who uses the word “optimal” is, in my book, we are using a red-letter word because there is no such thing as optimal. There’s no optimal diet; there’s no optimal exercise regime. Everything involves trade-offs. Everybody is different. But again, it’s pretty simple. And hopefully, by the end of the book, you understand why I conclude the book the way I do, which is that after you read all this stuff, you realize that it’s not that complicated. It’s actually pretty simple. Some is better than none. Cardio is the bedrock of any physical activity regime, but strength is also important to some extent. And the most important thing is keeping it up as you age and do something that you like to do. And beyond that, it’s all icing on the cake.

Cardiovascular Exercise vs. Strength Training for Long-term Benefits

Chris Kresser:  So let’s talk a little bit more about that. There [are] lots of different options that people are evaluating when they’re thinking about physical activity or exercise. You just mentioned that cardio should be the bedrock of any kind of physical activity that people are doing. But what does that mean, specifically? I know you don’t want to be too prescriptive here, but what do you mean by cardio? And are there any specific targets in your mind that you’re thinking about? Or does it just mean anything that gets your heart rate up to some extent?

Dan Lieberman:  Cardio is any physical activity that requires increasing your cardiac output, right? So you’re pumping more blood around your body. And that could be running, or it could be walking; it could be swimming, [or] it could be biking. It could be playing a game of tennis, whatever it is, right? That’s all cardio. But those tend to be low-resistance physical activities. Now, strength training involves resistance where you’re contracting lots of muscles, either isometrically or eccentrically, etc., where you’re contracting a lot of muscles. That generates resistance so your heart is no longer trying to push high volumes of blood throughout your body. Instead, it’s trying to maintain pressure against that resistance so you don’t faint, right? So you can keep profusion for your brain so your brain still gets blood.

So lifting weights or something like that, or wrestling, or whatever tends to be a high-resistance physical activity. And those are the kind of two poles right? And of course, in between, there’s a continuum like cycling, and your feet are strapped in; it’s high cardiac output, but also you’re generating a lot of resistance with your leg[s] constantly. So there’s a bit of resistance constantly being generated. So there’s no simple this is this and this is that kind of exercise, but those are the two poles. And we know that both are healthy. But for maintaining cardiovascular health, that’s why it’s called cardio, right?

Chris Kresser:  Right, sure.

Dan Lieberman:  It’s really critical. It keeps you from developing hypertension, which is unquestionably the leading cause of death in the world today. And without regular high cardiac output physical activity, you don’t increase the capillaries in your periphery, you don’t keep your arteries supple, [and] you don’t have a strong heart. There’s a lot of reasons why cardio is really good for you. So people who don’t do cardio at all and only do strength training, don’t actually see a lot of health benefits. There are some benefits to, in terms of cardiovascular disease, there are, of course, health benefits to strength training, but people who do only strength training who don’t do cardio run into trouble.

Chris Kresser:  So, is there too much cardio exercise?

Dan Lieberman:  So, first of all, two answers to that question. The first is, it’s not a question that I think we should worry about very much. There [are] so few people out there that are at that end of the extreme; it’s just not an important topic from a public health perspective. But if you happen to be one of those very unusual people who run ultra-marathons or whatever, it might matter to you. And the good news is that although lots of people think that there might be such a thing as too much, there’s actually not a lot of evidence that there is. In fact, a study just came out from the UK Biobank, which is probably the biggest study so far on this topic, that confirmed studies that have been done in the United States on large samples of individuals, again, few individuals at the really high end of this activity range, which show that there’s really no significant increase in [the] mortality rate for people who are doing really ridiculous amounts of exercise.

So there’s no benefit to them doing that exercise. But there doesn’t appear to be at least an overall mortality risk. But that said, there [are] certainly trade-offs. One of the concerns that people have from very high levels of physical activity could be increased fibrosis in the heart, which could lead to an increased risk of atrial fibrillation. That might be the number one concern that people have. And of course, if you’re not maintaining energy balance, you’re going to run into some metabolic problems. But really, it’s not an issue that really anybody should, very few people have to worry about.

The Impact of Exercise on the Musculoskeletal System—And Why You Should Try Running Barefoot

Chris Kresser:  What about [the] musculoskeletal impacts of exercise? I know this is something you studied a lot in your career and worked on a lot. And particularly things like the effects of shoes on biomechanics and injury. So can you talk a little bit about that both in, I guess, specifically in the context of running, which is something you love and something you’ve looked at a lot in your research?

Dan Lieberman:  Well, obviously, physical activity affects every system of the body. And of course, one of the ones it most directly affects is the musculoskeletal systems. So surprise, surprise, it’s important. It has all kinds of benefits. But there are also risks, and people do get injured. And I think one of the myths out there about exercise, again, is that it’s a magic bullet and that if you just do it properly, you’re never going to get injured. And I think that’s a myth we have to, everybody who’s very physically active is risking injury. But there are ways to mitigate that. And I think one of the issues is that many physical activities are skills, right?

If you swim, it’s a skill, and playing tennis as a skill, and throwing is unquestionably a skill. And I believe that running is also a skill. And the problem is that we live in a world today where people aren’t taught the skill of running. And I think shoes are a contributor to that, because, of course, shoes enable you basically to smash into the ground however you want and it doesn’t hurt. And so you can do some really stupid things wearing a shoe and feel like you’re getting away with it, but over, step by step over thousands, millions, tens of millions of steps, that can create troubles. And so I think that’s one of the reasons why barefoot running is interesting because when you’re running barefoot, you simply can’t do that. There’s no way you can slam into the ground and hit hard. It’s just not, you can’t keep it up, right?

So barefoot running requires people to run lightly and gently. And of course, that’s how we evolved to run. I don’t think you need to be barefoot in order to run well, but I think it’s like a free coach and it can give us some information. But it can also be a liability because people think, again, with the way we commodify and commercialize everything, barefoot running was also commodified and commercialized. It’s people who sell minimal shoes and they sell the myth of barefoot running that it’s going to solve all your problems. If you read some things, some books, you think you have no problems in the world and everybody will love you, and you’ll be able to just get out the door and run ultra marathons. We know those myths. I call this the myth of the athletic savage. But this idea that you can, if you just go back to being uncontaminated by civilization, all problems will disappear and that’s just nonsense.

Chris Kresser:  Right.

Dan Lieberman:  But again, there are better and worse ways to run. And I think we can learn from barefoot running how that works, and then if you want to wear a shoe, that’s fine. You can run well in a shoe and you can run badly barefoot. I think that’s what really matters.

Chris Kresser:  Do you think for many people doing some, especially if they haven’t learned how to run or ever been taught by anybody or paid much attention to it, that some period of barefoot running or at least feeling their feet on the ground is helpful to get the proper biomechanics, even if they go back to wearing shoes?

Dan Lieberman:  I think so. Also, it’s just kind of fun to use your body, right? People are scared of it, which is kind of interesting. Look, for millions of years, everybody was barefoot. My dog is barefoot, and most animals are barefoot. And the fact that people are scared of [being] barefoot means that we’re so out of touch with our bodies, we don’t even know how our bodies work. And you can, I get students to do this all the time. But I get them to take the shoes off at the end of a run and run down the street. And they’re so scared; they’re apprehensive because they think it’s going to be immensely painful. And then they take the shoes off and then they start running, and they quickly get off their heels and start landing on the ball of their foot, and they break into this, and it happens every time, they break into a big broad smile. And then they realize this is actually fun and it feels nice. And of course, if you do it too much too fast, you’re going to injure yourself. But the point is that people just don’t know how their bodies work because we live in such a bizarre modern world, right?

So, whether you run barefoot or not, I think there’s some value for everybody trying it just so you learn how your body works.

Chris Kresser:  Right. And most of us did it as kids without even thinking about it.

Dan Lieberman:  Of course.

Chris Kresser:  So, yeah.

Dan Lieberman:  I had a referee on a paper recently who said, “We’re no longer adapted to barefoot running.” And I was like, I almost hit the roof when I read this ridiculous statement, because first of all, there are still millions, hundreds, maybe billions of people on the planet who are still barefoot running. So don’t tell me they’re not adapted. But also, our bodies haven’t changed in the last few [hundred] years. I mean, this is just ridiculous. But we are so conditioned to the world that we live in, we think it’s normal to fly in airplanes and eat breakfast cereal from a box and wear cushioned shoes. And some of those things have benefits. I like [flying on] airplanes and I wear shoes most of the time. But that doesn’t mean that you have to do that and we can’t learn from other conditions.

So just because some of our ancestors did something doesn’t mean it’s necessarily good for us. But just something that we do today in the modern world doesn’t mean it’s necessarily bad for us either or vice versa. We just have to get away from this very simplistic way of thinking. It doesn’t help anybody.

The Role of Physical Activity and Exercise for Weight Loss

Chris Kresser:  What about exercise and weight loss or physical activity and weight loss? You mentioned earlier that there are tremendous benefits from even a small amount, going from being mostly sedentary to adding a really small amount of physical activity. What does the literature say about physical activity and weight loss? How much do you need? Does it even contribute to weight loss? Does it contribute to weight loss maintenance?

Dan Lieberman:  If you want to start a fight in the room of exercise.

Chris Kresser:  Exactly.

Dan Lieberman:  You just ask[ed] that question.

Chris Kresser:  Yeah.

Dan Lieberman:  There’s a vigorous debate going on. Let me try to summarize what is known, and then I’ll tell you what I think. So what’s known is that for sure if you want to lose weight, exercise is not the most effective way. Dieting is more effective than exercise for weight loss. And that’s for two simple reasons. Well, there’s maybe a third. But the two simple reasons are that exercise actually doesn’t spend that much energy. If I scarf down a doughnut and have a drink, I’m going to get 600, 700 calories just right there. It’s going to take me running six or seven miles to burn off the same amount of energy.

So exercise just doesn’t, it’s just not that expensive. So if you want to go into [a] negative energy balance, which is what dieting is, you’re taking in fewer calories than you’re spending, then dieting is more effective, simply put. Secondly, if you go for a five- or six-mile run in the morning to lose weight, when you come back, you’re going to get hungry. And so you’re going to eat some of that back, right? So, fortunately, studies show that, depending on the intensity, you don’t tend to eat all of it back. So, you can actually still lose weight [by] exercising. But the thing is, you can’t lose a lot of weight fast. But let’s get back to that point in a second. The third thing that everybody agrees on, is that exercise is beneficial for preventing weight gain or weight regain. So numerous studies show that people who exercise, a lot of diets, for example, when people lose the weight, then they get it back again. But if you combine exercise with a diet, you’re more likely to keep that weight off. And I think that’s pretty, pretty sound.

So the big debate really is how much weight can you lose [by] exercising. And I think, and here, I will engage in debate with some friends and colleagues. But I think that the studies, when people say that you can’t lose weight [by] exercising, they’re looking at really mediocre studies that are short-term and/or very low doses of physical activity. And there are plenty of studies [that] show that higher doses of physical activity, higher doses of exercise sustained over long periods of time, do help you lose weight, but you’re not going to lose it super fast, and you’re not going to lose a lot. It’s going to take a while for you to lose that weight. So if you want to shed 50 pounds, diet. And exercise! Exercise is important, too. And I think the other thing is that we tend to view everything, so many things through the lens of obesity and weight loss. And obesity is a big issue, and weight loss is important. But health isn’t only about weight. Weight is important, obviously. And there are plenty of other benefits to exercise independent of weight loss that we shouldn’t overlook. So don’t discount exercise, even if it isn’t all that effective for losing large amounts of weight rapidly.

Is Running Bad for Your Knees?

Chris Kresser:  I want to go back to something that I meant to ask you when we were talking about the musculoskeletal impacts of exercise and shoes and barefoot running, things like that, but didn’t get a chance to. There’s an idea that running is really bad for your knees. We all know people who have had knee problems from running. What’s your take on that?

Dan Lieberman:  So there [are] two different kinds of knee injuries. And yes, knee injuries are the most common injuries that runners experience, no question about it. But there [are] two different kinds. So there’s the kind that occurs from tissue overuse that lead[s] to pain like patellofemoral pain syndrome, and things like that. But then the other kind of injury is [to] wear and tear degradation. And we can strike the second off the list, right? The idea that running causes arthritis, which is the major kind of wear and tear, is disprovable. There are plenty of studies, prospective randomized controlled studies, long-term studies, retrospective studies, there [are] lots of data plus mechanistic data plus lab experiments on animals that show that the forces involved in running do not cause you to get arthritis. If you have arthritis, it will exacerbate it and make it painful and make it difficult. But we can banish the thought that running causes arthritis.

As for the other forms of injury, I believe, and again, this is a debate to be had and more research is needed, that a lot of those injuries come from bad running form. So forefoot striking versus rear foot striking, landing on the ball of your foot versus the heel of your foot, among the various trade-offs, and again, remember everything causes trade-offs, is the trade-off of how much work you’re doing around your ankle versus how much work you’re doing around your knee. So if you’re a forefoot striker, you’re really working your ankle a lot and you have to use your plantar flexors, your calf muscles a lot, and your Achilles and the foot muscles a lot. But that reduces the amount of and the rate and the loads that act around the knee. And furthermore, it reduces the shock, the impact that travels up and hits your knee.

So we have some data, and other people have published data, which show that running form does affect the other kinds of knee injuries. And so I think that we can really reduce running injuries considerably by teaching people to run properly so that they’re less likely to get those knee injuries. Will we eliminate them completely? No, but those are injuries that you can recover from. You can’t recover from arthritis. When you have to get a knee replacement, that’s the only treatment we have. So people should be less scared about running and their knees. Because if you do get a knee injury from running, chances are you can recover. But remember, treat the cause of the problem, not the symptom. So often, people go to the doctor’s office with knee problems. The doctor doesn’t even look at how the person runs, [and] instead treats the symptom, and you just keep the cycle going, right? Until you fix the way the person runs, you’re never going to solve the problem.

Chris Kresser:  Well, this has been really fascinating, Dan. I appreciate you taking the time to come on the show. If people are interested in the book, where can they find out more about it?

Dan Lieberman:  Well, get it on any bookstore, all the online places including Amazon, whatever is available. I think it’s got a website. If you Google it, there’s a website that we created for the book. I can’t remember that URL.

Chris Kresser:  Yeah. So it’s called Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding. And hopefully, now you understand after listening to this episode why that title was chosen. It makes perfect sense.

Dan Lieberman:  Thanks. And the book deals with inactivity, sitting, [and] sleeping. It also deals with strength, speed, aging, fighting, sports, running, walking, dancing, everything. And the final section of the book is really about how that all applies to health in the modern world in terms of dose and getting people to exercise, and there’s a final chapter, which is like a compendium of every scary disease you ever care about or worry about and how physical activity affects it.

Chris Kresser:  Yeah, I will also say it’s entertaining to read. I enjoyed the stories of the field research, and [it’s] funny, too. So a lot of books on, science books can be kind of dry and not very fun to read. But this was a refreshing example of how it can be entertaining to read a book about science, which I really [appreciate], I know the listeners will, as well.

Dan Lieberman:  I figured who wants to read a book about exercise that isn’t fun, right? It’s just like exercise itself.

Chris Kresser:  Exactly. You’ll be exercised if you do that, right? Okay, thanks for listening, everybody. Keep sending your questions into ChrisKresser.com/podcastquestion, and the book is Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding by Dan Lieberman. Go check it out. I think you’ll enjoy it.