Endure: Mind, Body and the Curiously Elastic Limits of Human Performance. Alex Hutchinson

the University of Kent for a brain-training boot camp, and then tried out the technique for twelve weeks while preparing for a marathon. Marcora has also run a series of military-funded trials of the technique—and the initial results suggest he’s onto something big.

      The studies described in this chapter make it clear that we can’t talk about the limits of endurance without considering the brain and perception of effort. But they don’t necessarily mean that Marcora’s psychobiological theory is right. In fact, not everyone agrees his theory is even new. Tim Noakes, when I asked him about Marcora’s ideas in 2010, dismissed them as a minor variation of his own central governor model: “The only distinction between our model and his model—and he has to differentiate, obviously—is that everything is consciously controlled,” he said.

      The distinction between conscious and unconscious has become a bitterly contested flashpoint between the two camps, but the differences aren’t as great as they appear. Marcora does indeed argue that the decision to speed up, slow down, or stop is always conscious and voluntary. But such “decisions,” he acknowledges, can be effectively forced on you by an intolerably high sense of effort. And crucially, they can still be influenced by any number of factors that you’re not consciously aware of, as demonstrated most clearly by his own experiment with subliminal images. Noakes and his colleagues, on the other side, don’t dispute the importance of effort, motivation, and conscious decision making. When you run a marathon, it’s not the central governor that prevents you from sprinting for the first 100 meters (a fact demonstrated by the enthusiastic souls who do, in fact, sprint at the start of marathons and later pay the price).

      It’s true, though, that there are some real contrasts between Noakes’s and Marcora’s theories, and they’re most obvious at the limits of total exhaustion—a state most people rarely, if ever, encounter. Imagine going to the gym, setting the treadmill to 10 miles per hour, and deciding to run for as long as you can. For most people, the decision to step off will be purely voluntary, a simple result of the effort becoming greater than they’re willing to tolerate. But if, instead, you’re running the final mile of the Olympic marathon, neck-and-neck with a rival for the gold medal, it’s harder to accept that the runner who slackens first does so because the effort feels too great or because she’s not motivated enough. Noakes would argue that the runner’s brain is overriding her conscious desires, reducing muscle recruitment in order to prevent damage to critical organs—and that process is not only unconscious, but is flatly contradicting the runner’s conscious decisions. To anyone who has raced seriously, it’s the latter explanation that feels right.

      Of course, the other option is that such scenarios of truly maximal effort and motivation push you to plain old physical limits—that, as A. V. Hill would have argued nearly a century ago, it’s muscle fatigue or the limits of oxygen delivery that hold you back in the final mile of the Olympics. When I first started planning this book, in 2009, it was going to be all about Tim Noakes and how his ideas had upended the conventional body-centric view of endurance. Then I discovered Marcora’s work, and realized that no explanation of endurance could be complete without considering the psychology involved. And then, as I dug deeper, I got to know some of the physiologists who don’t believe either of them, and whose views of human endurance are still rooted in the heart, lungs, and muscles—like University of Exeter physiologist Andrew Jones, who helped guide Paula Radcliffe to a marathon world record and whose Breaking2 lab data suggests Eliud Kipchoge is capable of a sub-two-hour run. And I discovered that they, too, have some powerful evidence to back their views.

      So who is right? The short answer is that scientists are currently fighting about it, strenuously and sometimes bitterly, with no end in sight. The longer—and to me, more interesting—answer is that, as the comparison above between running on a treadmill in the gym and racing in the Olympics illustrates, it depends. In Part II of the book, we’ll explore how specific factors like pain, oxygen, heat, thirst, and fuel define your limits in different contexts. We’ll encounter situations that seem to confirm Noakes’s view, like sports drinks that boost your endurance even if you don’t swallow them. We’ll explore whether it’s really possible for a panicked mother to lift a car off her child. And we’ll see what happens when an injection in the spine temporarily removes the limits imposed by the brain, allowing athletes to push their muscles all the way to the brink—a dream scenario that turns out to be more of a nightmare.

Two Hours

       November 30, 2016

      A homeless man is asleep in the doorway, his grungy brown sleeping bag zipped up to his nose to keep the drizzle off. Next to his head, stowed neatly out of the weather, is a crisp, spotless pair of brightly colored Nike trainers with fluorescent yellow laces. This, I tell myself, is peak Portland. I jog a few more blocks back to my downtown hotel, shower up, and head out with David Willey to the manicured mega-campus of Nike World Headquarters to find out how, exactly, the company plans to leapfrog a half-century ahead of my predicted marathon timeline.

      It’s immediately clear that the Breaking2 project isn’t just a passing whim cooked up by the marketing department. As we’re ushered through security into the Nike Sport Research Lab—an area, our escorts breathlessly assure us, that is strictly off-limits even to the vast majority of Nike employees on the site—we pass a massive mural at the end of a hallway that doubles as a two-lane rubberized running track. It reads, in pixelated scoreboard font, “1:59:59.” Some twenty people have been working on the secret project, more or less full-time, for nearly two years, with a total cost that the company won’t disclose but clearly extends to millions, if not tens of millions, of dollars.

      The barrier-breaking science behind the plan? You name it, they’re willing to try it. In a series of meetings that stretches late into the evening, we hear from the company’s top physiologists, biomechanists, and product designers about the lengths they’ve gone to in contemplating how to squeeze extra inches from exhausted muscles. Some of the crazier ideas have, perhaps mercifully, been left on the cutting-room floor—like pinning your arms to your sides to save wasted motion and energy. Tests on former elite runner Matt Tegenkamp using a specially designed elastic sling showed a measurable efficiency boost, but “he wouldn’t wear it,” Matthew Nurse, the lab’s director, tells us. “It looked like a Three Stooges