periods of time without obvious signs of fatigue, and the capacity of well-trained workers to put in long hours under stressful conditions without a decline in performance.
At the time, labor experts were debating two conflicting views of fatigue in the workplace. As MIT historian Robin Scheffler recounts, efficiency gurus like Frederick Winslow Taylor argued that the only true limits on the productive power of workers were inefficiency and lack of will—the toddlers-on-a-plane kind of endurance. Labor reformers, meanwhile, insisted that the human body, like an engine, could produce only a certain amount of work before requiring a break (like, say, a weekend). The experimental results emerging from the Harvard Fatigue Lab offered a middle ground, acknowledging the physiological reality of fatigue but suggesting it could be avoided if workers stayed in “physicochemical” equilibrium—the equivalent of DeMar’s ability to run without accumulating excessive lactic acid.
Dill tested these ideas in various extreme environments, studying oxygen-starved Chilean miners at 20,000 feet above sea level and jungle heat in the Panama Canal Zone. Most famously, he and his colleagues studied laborers working on the Hoover Dam, a Great Depression–era megaproject employing thousands of men in the Mojave Desert. During the first year of construction, in 1931, thirteen workers died of heat exhaustion. When Dill and his colleagues arrived the following year, they tested the workers before and after grueling eight-hour shifts in the heat, showing that their levels of sodium and other electrolytes were depleted—a telling departure from physico-chemical equilibrium. The fix: one of Dill’s colleagues persuaded the company doctor to amend a sign in the dining hall that said THE SURGEON SAYS DRINK PLENTY OF WATER, adding AND PUT PLENTY OF SALT ON YOUR FOOD. No more men died of heat exhaustion during the subsequent four years of construction, and the widely publicized results helped enshrine the importance of salt in fighting heat and dehydration—even though, as Dill repeatedly insisted in later years, the biggest difference from 1931 to 1932 was moving the men’s living quarters from encampments on the sweltering canyon floor to air-conditioned dormitories on the plateau.
If there was any remaining doubt about Hill’s vision of the “human machine,” the arrival of World War II in 1939 helped to erase it. As Allied soldiers, sailors, and airmen headed into battle around the world, scientists at Harvard and elsewhere studied the effects of heat, humidity, dehydration, starvation, altitude, and other stressors on their performance, and searched for practical ways of boosting endurance under these conditions. To assess subtle changes in physical capacity, researchers needed an objective measure of endurance—and Hill’s concept of VO2max fit the bill.
The most notorious of these wartime studies, at the University of Minnesota’s Laboratory of Physical Hygiene, involved thirty-six conscientious objectors—men who had refused on principle to serve in the armed forces but had volunteered instead for a grueling experiment. Led by Ancel Keys, the influential researcher who had developed the K-ration for soldiers and who went on to propose a link between dietary fat and heart disease, the Minnesota Starvation Study put the volunteers through six months of “semi-starvation,” eating on average 1,570 calories in two meals each day while working for 15 hours and walking 22 miles per week.
In previous VO2max studies, scientists had trusted that they could simply ask their subjects to run to exhaustion in order to produce maximal values. But with men who’ve been through the physical and psychological torment of months of starvation, “there is good reason for not trusting the subject’s willingness to push himself to the point at which a maximal oxygen intake is elicited,” Keys’s colleague Henry Longstreet Taylor drily noted. Taylor and two other scientists took on the task of developing a test protocol that “would eliminate both motivation and skill as limiting factors” in objectively assessing endurance. They settled on a treadmill test in which the grade got progressively steeper, with carefully controlled warm-up duration and room temperature. When subjects were tested and retested, even a year later, their results were remarkably stable: your VO2max was your VO2max, regardless of how you felt that day or whether you were giving your absolute best. Taylor’s description of this protocol, published in 1955, marked the real start of the VO2max era.
By the 1960s, growing faith in the scientific measurement of endurance led to a subtle reversal: instead of testing great athletes to learn about their physiology, scientists were using physiological testing to predict who could be a great athlete. South African researcher Cyril Wyndham argued that “men must have certain minimum physiological requirements if they are to reach, say, an Olympic final.” Rather than sending South African runners all the way across the world only to come up short, he suggested, they should first be tested in the lab so that “conclusions can be drawn on the question of whether the Republic’s top athletes have sufficient ‘horse-power’ to compete with the world’s best.”
In some ways, the man-as-machine view had now been pushed far beyond what Hill initially envisioned. “There is, of course, much more in athletics than sheer chemistry,” Hill had cheerfully acknowledged, noting the importance of “moral” factors—“those qualities of resolution and experience which enable one individual to ‘run himself out’ to a far greater degree of exhaustion than another.” But the urge to focus on the quantifiable at the expense of the seemingly abstract was understandably strong. Scientists gradually fine-tuned their models of endurance by incorporating other physiological traits like economy and “fractional utilization” along with VO2max—the equivalent of considering a car’s fuel economy and the size of its gas tank in addition to its raw horsepower.
It was in this context that Michael Joyner proposed his now-famous 1991 thought experiment on the fastest possible marathon. As a restless undergraduate in the late 1970s, Joyner had been on the verge of dropping out of the University of Arizona—at six-foot-five, and with physical endurance that eventually enabled him to run a 2:25 marathon, he figured he might make a pretty good firefighter—when he was outkicked at the end of a 10K race by a grad student from the school’s Exercise and Sport Science Laboratory. After the race, the student convinced Joyner to volunteer as a guinea pig in one of the lab’s ongoing experiments, a classic study that ended up demonstrating that lactate threshold, the fastest speed you can maintain without triggering a dramatic rise in blood lactate levels, is a remarkably accurate predictor of marathon time. The seed was planted and Joyner was soon volunteering at the lab and embarking on the first stages of an unexpected new career trajectory that eventually led to a position as physician-researcher at the Mayo Clinic, where he is now one of the world’s mostly widely cited experts on the limits of human performance.
That first study on lactate threshold offered Joyner a glimpse of physiology’s predictive power. The fact that such an arcane lab test could pick the winner, or at least the general gist of finishing order, among a group of endurance athletes was a tantalizing prospect. And when, a decade later, Joyner finally pushed this train of thought to its logical extreme, he arrived at a very specific number: 1:57:58. It was a ridiculous, laughable number—a provocation. Either the genetics needed to produce such a performance were exceedingly rare, he wrote in the paper’s conclusions, “or our level of knowledge about the determinants of human performance is inadequate.”
By Day 56, the relentless physical demands of Henry Worsley’s solo trans-Antarctic trek were taking a toll. He woke that morning feeling weaker than he’d felt at any point in the expedition, his strength sapped by a restless night repeatedly interrupted by a “bad stomach.” He set off as usual, but gave up after an hour and slept for the rest of the day. “You have to listen to your body sometimes,” he admitted in his audio diary.
Still, he was more than 200 miles from his
