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

and his men, but it was still a perilously close call. Their ship had been instructed to wait until March 1; Shackleton and one other man reached a nearby point late on February 28 and lit a wooden weather station on fire to get the ship’s attention and signal for rescue. In the years after this brush with disaster, and with Amundsen having claimed the South Pole bragging rights in 1911, Shackleton at first resolved not to return to the southern continent at all. But, like Worsley, he couldn’t stay away.

      Shackleton’s new plan was to make the first complete crossing of the Antarctic continent, from the Weddell Sea near South America to the Ross Sea near New Zealand. En route to the start, his ship, the Endurance, was seized by the ice of the Weddell Sea, forcing Shackleton and his men to spend the winter of 1915 on the frozen expanse. The ship was eventually crushed by shifting ice, forcing the men to embark on a now-legendary odyssey that climaxed with Shackleton leading an 800-mile crossing over some of the roughest seas on earth—in an open lifeboat!—to rugged South Georgia Island, where there was a tiny whaling station from which they could call for rescue. The navigator behind this remarkable feat: Frank Worsley, Henry Worsley’s forebear and the origin of his obsession. While the original expedition failed to achieve any of its goals, the three-year saga ended up providing one of the most gripping tales of endurance from the great age of exploration—Edmund Hillary, conqueror of Mount Everest, called it “the greatest survival story of all time”—and again earned Shackleton praise for bringing his men home safely. (Three men did die on the other half of the expedition, laying in supplies at the trek’s planned finishing point.)

      Once more, Worsley decided to complete his hero’s unfinished business. But this would be different. His previous polar treks had covered only half the actual distance, since he had flown home from the South Pole both times. Completing the full journey wouldn’t just add more distance and weight to haul; it would also make it correspondingly harder to judge the fine line between stubborn persistence and recklessness. In 1909, Shackleton had turned back not because he couldn’t reach the pole, but because he feared he and his men wouldn’t make it back home. In 1912, Scott had chosen to push on and paid the ultimate price. This time, Worsley resolved to complete the entire 1,100-mile continental crossing—and to do it alone, unsupported, unpowered, hauling all his gear behind him. On November 13, he set off on skis from the southern tip of Berkner Island, 100 miles off the Antarctic coast, towing a 330-pound sled across the frozen sea.

      That night, in the daily audio diary he uploaded to the Web throughout the trip, he described the sounds he had become so familiar with on his previous expeditions: “The squeak of the ski poles gliding into the snow, the thud of the sledge over each bump, and the swish of the skis sliding along … And then, when you stop, the unbelievable silence.”

      At first, A. V. Hill’s attempts to calculate the limits of human performance were met with bemusement. In 1924, he traveled to Philadelphia to give a lecture at the Franklin Institute on “The Mechanism of Muscle.” “At the end,” he later recalled, “I was asked, rather indignantly, by an elderly gentleman, what use I supposed all these investigations were which I had been describing.” Hill first tried to explain the practical benefits that might follow from studying athletes but soon decided that honesty was the best policy: “To tell you the truth,” he admitted, “we don’t do it because it is useful but because it’s amusing.” That was the headline in the newspaper the next day: “Scientist Does It Because It’s Amusing.”

      In reality, the practical and commercial value of Hill’s work was obvious right from the start. His VO₂max studies were funded by Britain’s Industrial Fatigue Research Board, which also employed his two coauthors. What better way to squeeze the maximum productivity from workers than by calculating their physical limits and figuring out how to extend them? Other labs around the world soon began pursuing similar goals. The Harvard Fatigue Laboratory, for example, was established in 1927 to focus on “industrial hygiene,” with the aim of studying the various causes and manifestations of fatigue “to determine their interrelatedness and the effect upon work.” The Harvard lab went on to produce some of the most famous and groundbreaking studies of record-setting athletes, but its primary mission of enhancing workplace productivity was signaled by its location—in the basement of the Harvard Business School.

      Citing Hill’s research as his inspiration, the head of the Harvard lab, David Bruce Dill, figured that understanding what made top athletes unique would shed light on the more modest limits faced by everyone else. “Secret of Clarence DeMar’s Endurance Discovered in the Fatigue Laboratory,” the Harvard Crimson announced in 1930, reporting on a study in which two dozen volunteers had run on a treadmill for twenty minutes before having the chemical composition of their blood analyzed. By the end of the test, DeMar, a seven-time Boston Marathon champion, had produced almost no lactic acid—a substance that, according to Dill’s view at the time, “leaks out into the blood, producing or tending to produce exhaustion.” In later studies, Dill and his colleagues tested the effects of diet on blood sugar levels in Harvard football players before, during, and after games; and studied runners like Glenn Cunningham and Don Lash, the reigning world record holders at one mile and two miles, reporting their remarkable oxygen processing capacities in a paper titled “New Records in Human Power.”

      Are such insights about endurance on the track or the gridiron really applicable to endurance in the workplace? Dill and his colleagues certainly thought so. They drew an explicit link between the biochemical “steady state” of athletes like DeMar, who could run at an impressive clip for extended 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,