Endure. Alex Hutchinson

in short races lasting less than a minute. But there are other hints that the finishing kick isn’t just physiological.

      In 2014, a group of economists from the University of Southern California; the University of California, Berkeley; and the University of Chicago mined a massive dataset containing the finish times of more than nine million marathoners from races around the world spanning four decades. The distribution of finishing times looks a bit like the classic bell-shaped curve, but with a set of spikes superimposed. Around every significant time barrier—three hours, four hours, five hours—there are far more finishers than you’d expect just below the barrier, and fewer than you’d expect just above. Similar but smaller spikes show up at half-hour intervals, and there are barely perceptible ripples even at ten-minute increments. The cruel metabolic demands of the marathon, which inevitably depletes your stores of readily available fuel, mean that most people are slowing in the final miles. But with the right incentive, some are able to speed up—and it’s only the brain that can respond to abstract incentives like breaking four hours for an arbitrary distance like 26.2 miles.

      A further curious detail from this dataset: the faster the runners were, the less likely they were able to summon a finishing sprint. Of the runners finishing near the three-hour barrier, about 30 percent were able to speed up in the final 1.4 miles of the race; 35 percent of those trying to break four hours sped up; and more than 40 percent of those trying to break five hours managed it. One possible interpretation is that, over the course of their long hours of training, the more committed runners had gradually readjusted the settings on their central governors, learning to leave as little as possible in reserve. Perhaps that’s another, slower way of achieving the run-in-the-present-moment strength that allows Diane Van Deren to race so close to her limits. I tried to trick myself into forgetting the last kilometer of my 5,000-meter races; Van Deren’s bittersweet gift is that she can forget without even trying.

      Right from the start, the central governor proposal was highly controversial. After his 1996 speech, Noakes recalls, “people got very, very angry.” There were rebuttals and surrebuttals in a cycle that is still continuing, more than two decades later. In a 2008 article in the British Journal of Sports Medicine, Noakes argued that physiologists’ focus on VO₂max had “produced a brainless model of human exercise performance.” Roy Shephard, an influential professor emeritus at the University of Toronto, shot back with an article in the journal Sports Medicine in 2009 titled “Is It Time to Retire the ‘Central Governor’?” Following a further exchange, Shephard concluded, “In the parlance of my North American colleagues, the time may now be ripe for proponents of the hypothesis to ‘Put up or shut up.’”

      If anything, the controversies swirling around Noakes have increased since his retirement from the University of Cape Town in 2014. His book on hydration, Waterlogged, accused most of the world’s leading hydration researchers, including former colleagues and collaborators, of selling out to the commercial interests of sports-drink makers. He is now a vocal proponent of low-carb, high-fat diets for both health and athletic performance, leading him to disown the chapters he wrote on nutrition and carbohydrate loading in Lore of Running and earning him a disciplinary hearing that threatened to revoke his medical license after he tweeted advice to a breastfeeding mother about weaning babies onto a low-carb, high-fat diet.

      As these other battles rage, the central governor controversy has to some extent faded into the background. With their own retirements on the horizon, it’s clear that the older generation of physiologists—Noakes’s peers—will never be convinced. On the other hand, says American Society of Exercise Physiologists cofounder Robert Robergs of Noakes’s influence, “most of the younger breed of exercise physiologists, in which I would group myself, recognize that, boy, some of his challenges are correct.” Whether the brain plays a role in defining the limits of endurance is no longer in doubt; the debate now is how.

      One way to answer that question would be to peer inside the brain during strenuous exercise—a task that, until recently, was completely impossible. With advances in brain imaging, it’s now just very, very difficult. Functional magnetic resonance imaging, or fMRI, allows researchers to observe changes in blood flow to different regions of the brain with great spatial precision, but can’t capture changes that occur in less than a second or two. You also have to remain perfectly still inside the bore of a powerful magnet—a restriction that presents serious challenges for exercise studies. During my visit to Cape Town, Noakes showed me video of a Rube Goldberg–esque contraption, developed by collaborators in Brazil, that allows subjects to pedal an externally mounted bike (you can’t have metal parts in the same room as the MRI magnet) via a 10-foot-long driveshaft, while lying supine inside the cylindrical bore of the magnet, with cushions jammed around their heads to keep them still. But the initial results, published in 2015, didn’t manage to push subjects to exhaustion and produced unclear patterns of brain activity.

      Other researchers have tried electroencephalography, or EEG, which uses a web of electrodes mounted on the head to measure the brain’s electrical activity. The advantage of EEG is that it can truly measure changes in real time; the disadvantage is that it’s highly sensitive to body or head motion—just blinking or letting your gaze wander garbles the results. Such studies are already yielding insights about the brain areas involved in fatigue, and (as we’ll see in Chapter 12) even being used to identify promising regions for electrical stimulation in an attempt to enhance endurance.

      But these approaches are unlikely to ever truly pinpoint the central governor. “One of the big issues with the central governor is that it was initially portrayed to be a specific point, as if there was going to be one structure that did all this,” Tucker told me. “And people were like, show me the structure.” But endurance isn’t simply a dial in the brain; it’s a complex behavior that will involve nearly every brain region, Tucker suspects, which makes proving its existence (or nonexistence) a dauntingly abstract challenge.

      Ultimately, the most convincing route to proving the central governor’s existence might also be the first and most obvious question that pops into people’s minds when they first hear about the theory, which is: Can you change its settings? Can you gain access to at least some of the emergency reserve of energy that your brain protects? There’s no doubt that some athletes are able to wring more out of their bodies than others, and those who finish with the most in reserve would dearly love to be able to reduce that margin of safety. But is this really a consequence of the brain’s subconscious decision to throttle back muscle recruitment—or is it, as a rival brain-centered theory of endurance posits, simply a matter of how badly you want it?

CHAPTER 4

       The Conscious Quitter

      Since the days of Marco Polo, no trip along the Silk Road has ever been straightforward—and Samuele Marcora’s 13,000-mile motorcycle ride from London overland to Beijing in 2013 was no exception. Unlike Polo, Marcora didn’t encounter any dragons or men with dogs’ faces along the route, but he and his trip-mates did spend seventeen hours crossing the Caspian Sea on a rusty Soviet-era freighter; navigate the crumbling roads and stifling bureaucracy of Turkmenistan, Uzbekistan, Tajikistan, and Kyrgyzstan (the ’Stans, as he refers to them affectionately); skid along endless soft sand and mud trails in the thin air of the Tibetan plateau, up to 16,700 feet above sea level, for two weeks; and splash through monsoon-drenched roads on the final leg of their journey through China. Oh, and he also broke his ankle in Uzbekistan and shattered a rib on the road from Everest Base Camp, making the bone-rattling corrugated roads of Central Asia even more painful than normal.

      In a sense, all of these stressors were part of the plan. Their inevitability was the reason Marcora, an exercise scientist in the University of Kent’s Endurance Research Group, joined the eighty-day expedition, which was organized by adventure motorcycling outfitter GlobeBusters. Packed on the back of Marcora’s BMW R1200GS Triple Black was his “lab in a pannier,” crammed with portable scientific equipment to perform daily measurements of the trip’s mounting mental and physical toll, with himself and his thirteen