Endure: Mind, Body and the Curiously Elastic Limits of Human Performance. Alex Hutchinson
and receive a coveted finisher’s medal, you have to cross the line before the 12-hour gunshot is fired. Summoning their final reserves of willpower, the runners within striking distance began to urge their battered legs into a final, frantic sprint. As the gun cracked, one man staggered across the line in 11:59:59; mere strides behind him, another man bounced off the burly course marshals who had linked arms to barricade the finish chute, while vuvuzelas sounded a mocking raspberry of defeat.
I had come to South Africa on assignment for Outside magazine, to write about Tim Noakes’s contrarian ideas about the brain. The hook for my story was the Comrades debut of American runner Josh Cox, who was fresh off an impressive American record of 2:47:17 over 50K. I figured that if he conquered the distance, he (and Noakes, who was also in Durban to watch the race) would be able to offer vivid insights into the nature of the limits he’d had to overcome—and if the distance conquered him, the story would be even better. “The one guarantee in an event like this is the pain,” Cox told me, all too prophetically, when we met for coffee the day before the race. “You have to welcome it—say ‘Here you are, my friend.’” But Cox’s hopes fizzled just a few miles into the race, thanks to recurring bouts of stomach cramping and diarrhea that slowed him to a walk. As familiar as this debacle might be to marathoners, these were not the limits I was hoping to write about. (The story was eventually killed.)
Still, the race had given me a perfect excuse to make a pilgrimage to one of the temples of modern exercise physiology: the next day, I flew to the opposite end of the country to spend a week visiting Noakes’s lab at the University of Cape Town. At sixty, Noakes had graying temples, a near-permanent grin that expressed everything from disbelief to delight, and a habit of punctuating his sentences with the all-purpose interjection “ja.” His fourth-floor office had a postcard view of Table Mountain’s iconic ridgeline, and a museum’s worth of sports memorabilia—framed clippings, signed rugby shirts, battered old Onitsuka Tiger running shoes—covering the walls and filling a long trophy case. On my first day there, we talked almost nonstop for four hours (“I don’t normally have much lunch,” he said, a bit apologetically, when I proposed a break, “but you’re welcome to if you’d like”) as he recounted the origins of what has become known as the “central governor” theory.
In his keynote lecture at the 1996 ACSM conference, Noakes had argued that A. V. Hill’s concept of VO2max was fundamentally flawed: that physical exhaustion isn’t a consequence of the heart’s inability to pump enough oxygen to the muscles. Otherwise, he reasoned, the heart itself, and perhaps the brain, would also be starved of oxygen, with catastrophic results. He liked to point out a famous picture of South African marathoner Josia Thugwane, moments after winning the 1996 Olympic marathon, jogging around the track with silver medalist Lee Bong-Ju, whom he had outsprinted by just three seconds. “Do you notice he’s not dead?” he’d say, pointing at Lee. “What does that tell you? It means he could have run faster.”
But if Hill’s ideas about oxygen were wrong, what was the alternative? Noakes felt the brain had to be involved, and in a 1998 paper he coined the term “central governor,” borrowing terminology that A. V. Hill himself had used seventy years earlier. But the details remained unclear. Over the next decade, working with collaborators such as Alan St. Clair Gibson, then at the University of Cape Town, Frank Marino, of Charles Sturt University in Australia, and a succession of other students and postdoctoral researchers in his own lab, he began to assemble a coherent picture with two key planks. First, the limits we encounter during exercise aren’t a consequence of failing muscles; they’re imposed in advance by the brain to ensure that we never reach true failure. And second, the brain imposes these limits by controlling how much muscle is recruited at a given effort level (an idea we’ll explore in detail in Chapter 6).
The first point—the concept of “anticipatory regulation,” as Noakes and his colleagues refer to it—is subtle, so it’s worth pausing to unpack it. Long before Noakes, researchers had theorized that the brain might sense distress signals from elsewhere in the body and shut things down when the warnings exceeded a critical level. Exercise in the heat is a classic example: if you run to exhaustion on a treadmill in a hot room, your brain will stop driving your muscles when your core temperature hits a critical threshold of about 40 degrees Celsius. But Noakes takes this idea a step further, arguing that in real-world situations like running a 10K on a hot day, the brain gets involved long before you reach that critical temperature. You don’t hit 40 and keel over; you slow down and run at a pace that keeps you below 40.
The most controversial claim is that this pacing instinct isn’t entirely voluntary: your brain forces you to slow down, long before you’re in real physiological distress. In experiments led by Noakes’s student Ross Tucker, cyclists started at a slower pace right from the outset when the temperature was high—and crucially, the amount of muscle recruited by the brain was also lower within the first few minutes. At a conscious level, the cyclists were trying just as hard (as their reported level of effort indicated), but fewer muscle fibers in their legs were contracting thanks to their central governor’s inbuilt caution. The difference between the traditional and revised views of the brain’s role, Tucker explained during my visit in Cape Town, is that “they’re really looking at the off switch, whereas we’re looking at the dimmer control.”
It’s easy to get lost in the weeds of this debate. Over the course of my visit, I spent hours with various students, postdocs, and colleagues of Noakes, learning about the various tentacles of evidence that buttressed their brain-centered view of endurance. There were long-standing historical anomalies, like the puzzlingly low lactate levels observed when people exercise to exhaustion at high altitudes, contrary to what Hill’s model would predict. And there was a steady stream of new observations: an instant performance boost when you swish a carbohydrate drink in your mouth and then trick your brain by spitting it out; marathon runners setting world records despite supposedly crippling levels of dehydration; brain-altering drugs like Tylenol that boost endurance without any effect on the muscles or heart.
But when I asked Noakes for the single most convincing piece of evidence in favor of his theory, he said, without hesitation, “the end spurt.” How could the runners at Comrades, after pushing themselves through 56 miles of hell, summon a finishing sprint to beat the 12-hour limit? Conventional physiology suggests that you get progressively more fatigued over the course of a run, as muscle fibers fail and fuel stores are emptied. But then, when the end is in sight, you speed up. Clearly your muscles were capable of going faster in the preceding miles; so why didn’t they? “That shows that our understanding of fatigue is totally wrong,” Noakes said. It must be the brain that holds you back during long efforts, and then releases the final reserves when you’re nearly finished and the danger is past.
I always try to evaluate scientific theories dispassionately, based on evidence rather than anecdote. But in this case, my head was nodding involuntarily as Noakes spoke. This phenomenon wasn’t just familiar to me—it was, in some ways, my nemesis. In my mid-twenties, after a few injury-plagued years, I’d moved up from 1,500 to 5,000 meters. But every time I raced the longer distance, my pace would gradually tail off in the later stages of the race—and then I’d launch a sizzling last lap, leaving everyone (including myself) puzzled about why I had slowed down so much in the previous laps. At first I chalked it up to inexperience, and then to lack of concentration. And there may be some truth to both those explanations, but it felt like something deeper.
By the time I ran what would turn out to be my fastest 5,000, on a perfect evening in Palo Alto, California, in 2003, I’d decided I needed a new mental strategy: I would pretend I was only running 4,000 meters, and simply not worry if I had to jog the last kilometer. I wanted to run 2:45 per kilometer, and my first three kilometers were 2:45, 2:45, 2:47. The moment of truth: I knuckled down and vowed to run the fourth kilometer