Endure: Mind, Body and the Curiously Elastic Limits of Human Performance
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For Diane Van Deren, the first warning signs came when she was just sixteen months old, when a prolonged seizure sent her to the hospital where she lay, packed in ice, convulsing for nearly an hour. There were no apparent aftereffects, and Van Deren grew up to be a star tennis player, got married, and had children. Then, when she was twenty-nine and pregnant with her third child, the seizures returned, and over the next few years they got progressively worse. Working with neurologists at the University of Colorado, she eventually decided to have a partial right temporal lobectomy, to remove the portion of the brain where the seizures were originating. The surgery went well, and the seizures stopped—but not without a cost.
Even before the surgery, Van Deren had found running therapeutic. When she felt an “aura”—the odd out-of-body sensation that, for her, signaled an impending seizure—she was often able to ward off the seizure by heading out the door and running, sometimes for hours. After the surgery, she kept running, and began venturing farther and farther into the trails near her home south of Denver. Soon she was covering distances that would have daunted even the fittest runners, and in 2002 she entered her first ultramarathon, a 50-mile trail run with only one other entrant. The 50-miler turned out to be just a stepping-stone to 100-milers, which in turn led to multi-day races like the Yukon Arctic Ultra and, eventually, the three-week assault on the Mountains-to-Sea Trail in North Carolina in 2012.
In the final days of the record attempt, Van Deren’s feet were so beat up that she had to start each day by crawling along the trail until, thanks to the familiar numbing of endorphins, she could stand up and start putting weight on them. Then she would resume clicking off the miles, one by one. By 12:20 P.M. on the twentieth day of the run, she and Millsaps were still four miles away from the crucial 1 P.M. Okracoke ferry—so they accelerated. They caught the ferry with just minutes to spare, and the ferry operator solved the mystery of the “airplane” that had buzzed them earlier: “You must have just come through those tornadoes back there,” he marveled. Two days later, Van Deren climbed an 85-foot sand dune in Jockey’s Ridge State Park to complete the trail in a new record of 22 days, 5 hours, and 3 minutes. “That,” she told a small crowd of supporters, “is the hardest thing I have ever done.”
In the Runner’s World profile, neuropsychologist Don Gerber, who worked with Van Deren at Craig Hospital in Denver, speculated that brain surgery might have made her a better runner. Thanks to the region of her brain that was damaged, he said, “Diane’s brain interprets pain differently than yours or mine does.”
Van Deren, for her part, rejects this suggestion. “They all think, ‘Oh, great, you don’t feel pain,’” she argued in a subsequent profile. “Well, shit—I don’t feel pain? I feel pain.I just push through it.” And indeed, her suffering during the run in North Carolina was evident.
Still, it’s hard to escape the sense that how Van Deren experiences a prolonged endurance challenge is inescapably different from how it is for most people. Unable to read maps or keep track of where she is on a course, she doesn’t focus on the challenge ahead of her. Hampered by poor short-term memory, she doesn’t dwell on the effort already expended, either. “I could be out running for two weeks, but if someone told me it was day one of a race,” she once joked, “I’d be like, ‘Great, let’s get started!’” Instead, she has no choice but to focus on the immediate task of forward motion, taking one more step, and then another. Semi-oblivious to the passage of time, she is also free of the cognitive challenge—the shackles, perhaps—of pacing herself. She is all hare and no tortoise—which, Aesopian morality aside, has its advantages.
To get a visceral feel for the struggle between mind and muscle, there’s no better place to stand than at the finish line of the Comrades Marathon, the largest, oldest, and most prestigious ultra-race (that is, any race longer than the standard marathon distance of 26.2 miles) in the world, as the clock ticks down toward its rigid 12-hour cutoff. By the time the runners enter the cricket stadium in the coastal city of Durban, they’ve covered 56 miles of relentlessly undulating terrain, the downhills shredding their quads as mercilessly as the uphills burn their lungs, under the fierce South African sun. (In odd-numbered years, the course runs in the opposite direction, finishing in the inland city of Pietermaritzburg.)
In 2010, I joined thousands of other spectators in the stadium counting down the final seconds as the race director assumed his position on the finish line, his back to the oncoming runners and his starter’s pistol pointed skyward. To be recorded as an official finisher of the race 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 as hard as I could—but little by little, I drifted back from the pack I was running with. My next split was a disappointing 2:53. That was as fast as I could move my legs, and my pace slowed even more as I entered the final kilometer. I’d bitten off more than I could chew and was paying the price.
At most track races, officials mark the start of your final 400-meter lap by ringing a cowbell in your ear. It’s a handy Pavlovian cue that tells you that your suffering is almost over. And on that night on the Stanford track, I once again felt the curious and familiar transformation in my legs as the bell rang for me. I passed ten runners while running the last lap in around 57 seconds, a full 10 seconds faster than my average pace for the race. My last kilometer, at 2:42, was my fastest even though I only started sprinting with a lap to go. And—I can’t emphasize this enough—I was trying as hard as I could right up to the penultimate lap. A friend who’d come to watch asked if I was trying to impress her by slowing down late in the race so I could finish with a flourish. No, I said, I just … But I didn’t have an explanation. I didn’t understand it myself.
As it turns out, it’s not just me. Noakes showed me a study that he, Tucker, and Michael Lambert had published in 2006, analyzing the pacing patterns of almost every world record set in the modern era in the men’s 800 meter, mile, 5,000, and 10,000 meter races. For the three longer races, the pattern was startlingly consistent: after a quick start, the record breakers would settle into a steady pace until the final stages of the race. Then, even though they were running faster than they’d ever run before, and their oxygen-starved muscles were presumably awash in a sea of fatigue-inducing metabolites, they accelerated. Of the 66 world records in the 5,000 and 10,000 meters dating back to the early 1920s, the last kilometer was either the fastest of the race or the second fastest (behind the opening kilometer) in all but one. I was willing to attribute my own uneven pacing to incompetence—but these were the finest runners in history on the best day of their lives, which suggests that the pattern is more deeply ingrained than a mere pacing error.
In fact, there’s good reason to think that pacing is driven as much by instinct as by choice, according to Dominic Micklewright, a researcher at the University of Essex. Micklewright followed an unorthodox route to academia, going straight from high school to the Royal Navy, where he served as a diver on nuclear submarines for seven years, and then spending nine years as a police officer in London before studying sport and exercise psychology. His interest in pacing dates back to his training as a military diver, when he and the other trainees had to swim submerged to the other end of a 1,200-meter saltwater lake on Horsea Island, on Britain’s south coast, without using up their supply of air. “If they caught you breaching, you would get clobbered over the back of the head with an oar, or they’d throw in one of those underwater scare charges,” he recalls. With that incentive, you inevitably thought very carefully about the challenge of spending your energy—and oxygen—as frugally as possible.
World records in long-distance races are run with a strikingly consistent pattern that includes an acceleration in the final stages, according to a 2006 analysis in the International Journal of Sports Physiology and Performance. This finishing kick is notably absent in shorter 800-meter races, for reasons we’ll discuss in Chapter 6. The intermediate splits above are every 400 meters for the two shorter races, and every 1,000 meters for the two longer ones.
In 2012, Micklewright had more than a hundred schoolchildren ranging in age from five to fourteen complete a battery of tests to assess their cognitive development, in order to slot them into one of the four developmental stages proposed by Swiss psychologist Jean Piaget; then the kids ran a race lasting about four minutes. The younger kids in the two lower Piaget stages opted for the unfettered sprint-and-then-hang-on-for-dear-life approach, starting fast then steadily fading. In contrast, the kids in the two higher Piaget stages had already adopted the familiar U-shaped pacing profile that world-record holders use: a fast start, gradual slowing, then a fast finish. Sometime around the age of eleven or twelve, in other words, our brains have already learned to anticipate our future energy needs and hold back something in reserve—a relic, Micklewright speculated, of the delicate balance between searching for food and conserving energy deep in our evolutionary past.
Not everyone buys Noakes’s argument that pacing patterns like the end spurt reveal the workings of a central governor. For example, it could be that you speed up at the end of a race because you finally tap into your precious but limited reserves of anaerobic energy, the high-octane fuel source that powers you 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.’”
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