Once, we believed that the body was a machine, and the secret to optimal performance came from the muscles, the lungs, the heart. Then, we were told that it’s all in our head, and we just need to push through the pain. The truth is that “the brain and the body are fundamentally intertwined,” writes Alex Hutchinson, a fitness journalist (with a doctorate in physics) who competed for the Canadian national team as a runner. To understand the limits of the human body, you have to consider them together.
Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance, out this month from HarperCollins. In the eight years he worked on the book, he traveled to labs all over the world and spoke to hundreds of athletes and scientists about how the mind and body influence each other and the role that each plays in the “mystery of endurance.”
The Verge spoke with Hutchinson about the dueling theories of endurance, nature versus nurture, and what we can learn from Olympic athletes.
This interview has been lightly edited for clarity.
The book is about the limits of the human body and the role that the brain plays. In the first part, you trace the intellectual history of these attitudes toward endurance, from the notion that the body is just a machine to the “it’s all in the mind” saying we hear a lot today. Can you go over that with us?
Yes, though of course my attempt to trace the intellectual history streamlines and makes simpler things than they really were. In the 1920s, the Nobel Prize-winning physiologist A.V. Hill wrote all these ideas for Scientific American, talking about how the human body is just a machine, and if we could learn the parts and measure the outputs, we can really confidently predict the outer limits of human performance. And he introduced the concept of VO2 max [maximal oxygen consumption], which you hear a lot in exercise science. No one really thought VO2 max was the be-all and end-all, but the philosophical underpinning was that if we could know everything about how the body works, we could understand what the limits were.
That was the dominant 20th century paradigm. In the ‘90s, though, a guy named Tim Noakes gave some very controversial lectures saying, you got it all wrong, the brain is what determines human performance. I’d say the last 10 or 15 years, there’s been lots of talk about the role that the brain plays, and that’s where the interesting debates are now.
The caveat I’d add is that even A.V. Hill knew that the brain mattered, but this is how we’ve evolved from a focus on the muscles to a focus on the brain — to the point where we hear that it’s all in your head. But actually, all this time, there’s been a parallel stream saying “it’s all in your head,” and that’s positive psychology, which isn’t really within the realm of science. So now we’re looking at the scientific underpinnings of claims that sounded a little silly — like the idea that changing your internal monologue can really do something.
I think everyone can understand why and how the body limits us. What are some studies that stood out to you that showed how the mind does the same?
One of the most eye-opening experiments to me was done by Samuele Marcora using subliminal images. He had cyclists do a test to exhaustion, and on the screen in front of them, he flashed pictures of either smiling faces or frowning faces. These were flashed 16 milliseconds at a time. That’s like a tenth of the length of a blink, so the cyclists were totally unaware that there were any images. It wasn’t like a placebo effect or something to do with self-confidence. They weren’t even aware of this manipulation.
The ones who saw the smiling faces lasted 12 percent longer on the ride than with the frowning faces. These sorts of experiments are really controversial right now with the replication crisis, so I don’t want to overstate the significance. But if these results stand up, they’re a really nice demonstration of the complicated ways that the brain’s interpretation of the body signals is maybe more important than the body signals themselves.
Seeing smiles helps us create a sense of ease. You see someone smiling, it makes us feel more comfortable and somehow that bleeds into the idea that your panting breath and your aching legs aren’t quite as bad as they might otherwise seem.
What else interested you from talking to so many scientists?
Another line of research that I’ve found really interesting — but also a little bit worrying — is electrical brain stimulation, which basically amounts to taking a nine-volt battery, attaching a couple of wires to it, connecting to your head, and running a very weak current through your brain to change the excitability of the neurons. If you put the electrodes in the right place, you can enhance endurance.
It’s been around for three or four years, with conflicting results, though it seems to be getting more repeatable now. What seems to be happening is that you’re altering your perception of effort. You’re not changing your lactate levels or your heart rate, just changing how your brain interprets those signals.
So, for our readers who aren’t closely following the science, are there certain concepts and theories that are key to understanding how the brain might influence endurance?
There’s lots of debate about exactly how the brain controls endurance, but there are two key concepts that are dueling right now. One is that, fundamentally, your brain is just trying to protect you, and it does this by trying to anticipate what’s going to happen. So if you go running on a hot day, you go slower, not because your core temperature is at a dangerous zone, but because your brain is worried that it’s going to reach a dangerous zone and you’re going to overheat and cause damage. Fundamentally, all of these warnings and perceptions and feelings of discomfort are designed to save you from your own worst decision-making. And that requires your brain to be smart and anticipating the future. This comes out of Tim Noakes’ work, and he called this the theory of the brain as “central governor.”
The other main sort of tenet out there is from Samuele Marcora. He says, there’s no prediction of the future, there’s no really subconscious protective circuitry. Fundamentally, all endurance is is the balance between how hard it feels and how hard you’re willing to make it feel, between perceived effort and motivation. So everything that’s going on in your body — your core temperature, your oxygen levels dropping — all of that is important only insofar as it makes exercise feel harder to you, and at a certain point, it’ll reach the maximum you’re willing to tolerate and you’re willing to slow down or stop. That’s a conceptually simpler approach that doesn’t require any sort of anticipatory prediction of your future state. It’s just “this is harder than I’m willing to work.”
What surprised you the most?
One of the biggest surprises came when I was looking into limits of hydration and heat. Alberto Salazar, one of the greatest American marathoners, very famously almost died a few times after races. People always say it was because he didn’t drink enough, and I was looking back at debates in medical journals in the 1980s. After the 1982 Boston Marathon, the so-called “duel in the sun,” his body temperature was something like 88 degrees Fahrenheit [instead of our normal 98.6 degrees Fahrenheit]. Everyone had assumed he didn’t drink enough and he got heat stroke, but the link between hydration and heat stroke was different than expected when you look into the details of these famous collapses.
Generally, I came at this from the perspective of running, and that involved thinking broadly. In running, you breathe hard and you think that oxygen is a limiting factor, so I also looked into these free divers to see how long you can go without oxygen. The record for holding your breath is almost 12 minutes! From a physiological perspective, when I hold my breath I reach a point where I physically can’t anymore because my breathing muscles are contracting. It turns out that that’s not because I’m out of oxygen, it’s because my carbon dioxide levels are too high and are triggering a warning system in me. But these guys are able to ignore that warning system and just keep holding their breath until they’re literally out of oxygen.
“There’s no lab test that will tell you why he was always able to get to the finish line.”
To what extent do people’s bodies and genetic gifts give them an advantage? Take the free divers, for example. How much does it help that they probably have bigger lungs?
The lungs probably helped in some respect, but it’s not fundamentally the key limiting factor. If you want to be a world record-holder, you need to check a hundred different boxes. You need to have psychological and physiological and morphological characteristics. But think about it this way: I can hold my breath for two minutes, and he can hold it for 12, but I’m nowhere near my limit. My lung size makes no difference whatsoever until I’ve already learned to push my limits a lot more.
Yes, there are physical differences for sure, and they are absolutely crucial. The strongest mind in the world is not going to win the Boston Marathon unless you have all the other physical characteristics. It’s like the nature-nurture question in the sense that it’s almost impossible to separate the role of nature and nurture. And similarly, you have a total kind of synergy between psychological and physiological and physical characteristics that go into defining your limits.
One of the phrases I’ve heard at conferences when people talk about great athletes is that there’s probably some degree of benign masochism that the people who love to go out and run 100 miles a week are not just physically capable but mentally capable of doing that. For whatever reason, their brains are wired in a way that they get more of a kick out of it than the rest of us. Whatever brain chemicals make you feel satisfied, we don’t all get them in the same way, some people are inherently more eager for new experience or novelty or risk.
Is there a way to quantify the effect of the brain versus the body in endurance?
To answer that question, you have to think about what population you are looking at. Let’s say I ask, how important is height in the NBA for in basketball success? If you take the general population, well height is almost everything. If you’re not well over six feet tall, your chances of making it to the NBA are almost zero.
But how important is height to scoring success in the NBA for players who’ve made it? It’s not better to be tall and height is essentially irrelevant at that point. If you want to know who’s gonna be good at a marathon and just talking about in the population of the United States, send everyone to an exercise lab and have them do a bunch of physiological tasks. Those tasks will tell you almost everything you need to know. It really is the human machine. It’s VO2 max, lactate threshold, the running economy. You’re going to pick with very, very high accuracy who’s going to be good and who’s not.
But if you go to the Olympics and you do the same physiological test, that’s going to tell you nothing about what’s going to win the race. Everyone has the physical tools, and it’s not everything.
Look at Paul Tergat and Haile Gebrselassie, the two greatest distance runners of the ‘90s and 2000s. They had all these amazing duels, and they’re both amazing physically, both record-setting runners.
But Gebrselassie always beat Tergat, and that’s not physiology. There’s no lab test that will tell you why he was always able to get to the finish line. That’s mental. We’re born with certain physical characteristics and we can change them and get fitter, but if I want to know whether I’ve gotten the most out of myself, if I look back at my running career and say, did I run as fast as I could have? The key variable there is the mental aspect.
What trends do you see in fitness science as a result of this research? What can we learn from these new insights?
I spent a lot of time looking at Nike’s attempt to break the two-hour marathon. Everyone who covered that race came away sort of blown away by [the runner] Eliud Kipchoge’s presence and confidence. I came away from that saying, science doesn’t have anything to teach Eliud Kipchoge on how to push his limits. What science is doing is trying to figure out how the rest of us can take some baby steps in the direction of his mental approach.
There are a lot of people who have used a lot of different approaches in sport psychology, for instance, to try to get more out of people. I think science is starting to understand and systematize what some of these approaches are and how well they work, but there’s no new silver bullet.
In terms of forecasting trends, I hope we will see an attempt to take this whole huge genre of wishy-washy self-help positive psychology and start to recognize that there’s some really useful and powerful techniques in there — and also a lot of crap. And hopefully scientists can identify the techniques that are useful and winnow out the puffery that has surrounded the field.
You start the book talking about your own running career and goals. How has writing this book helped you put your past success, or failures if you see it as that, into context?
It really helps crystallize some questions and doubts and thoughts that I had for a long time. I got into the book fundamentally because I was still sort of wondering. I spent a lot of time trying to be the fastest runner I could, and thinking a lot about what would make me faster and what was holding me back. I had some experiences that made me confident that it wasn’t really just my muscles or my heart that determined how fast I ran, but I didn’t understand how it fit together. I don’t have a three-sentence answer to go back and tell my 20-year-old self. But I have a more solid sense of the reality of the mental impact on endurance, on the brain’s role in endurance. It doesn’t mean that I would do everything differently if I could go back in time.