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What is the fastest possible marathon time? This debate began in 1991, perhaps improbably, with the publication of a paper in The Journal of Applied Physiology by anesthesiologist Mike Joyner, who estimated the fastest possible time to be exactly 1:57:58. For a group of biologists and psychologists, trainers and scouts, shoe company marketers, and the world’s best runners, the fantasy of a marathon run in under two hours suddenly seemed attainable. The world record has been slowly approaching 120 minutes; since 1960, it has fallen by at least one minute and as much as five minutes every decade. By 2013, the record was only 203 seconds away. Then, last year, the gap fell to 177 seconds. So intense is the fixation among professional marathoners that their best-ever racing times function as names. They are a two-oh-eight guy, or a ­two-oh-four guy. A difference of minutes is the ultimate existential marker. “Two-oh-two or die trying,” writes Ed Caesar of one runner. “Nothing else could satisfy him.”

This obsession is the principal subject of Caesar’s Two Hours: The Quest to Run the Impossible Marathon, but his new book is also a tribute to elite runners themselves—their childhoods (mostly in East Africa), their strategies during a race, their moment-by-moment inner struggles to run faster and faster. Caesar meticulously describes the Kenyan runner Geoffrey Mutai’s performance at the 2011 New York marathon, where he ran the twenty-first mile in a mere 4:31. “He doesn’t brake at all, or strain for forward movement,” Caesar explains:

There is no tension in his arms. It’s as if he is on wheels, not legs. ... Because of this impeccable form, it’s sometimes hard to tell when he decides to push the pace. Only the speed of his turnover and the attitude of his head—cast down and bent forward as if at the prow of a clipper—betray his intentions.

Caesar calls this “pure athletic expression”; Mutai knows it as “the Spirit.” He has experienced the Spirit only a handful of times. It is, nevertheless, a central motivation of the rigorous training he undertakes every week. Caesar sees a counterpart to the Spirit in the French cyclist Jean Bobet’s concept of “La Volupté”: “It arrives, it takes hold of you, sweeps you up and then leaves you again,” wrote Bobet in his book Tomorrow, We Ride. “It is for you alone. It is a combination of speed and ease, force and grace. It is pure happiness.”

Compared to this spiritual appreciation of athletics, the arbitrary two-hour mark can only seem trivial, raising the question—amid so much discussion of grueling training schedules and practices runs and races—of whether the statistics of record-breaking can ever represent the glory of sports.

Marathon running has never been more popular than it is today. What began as a novelty in 1896 at the first Olympic games—one in which two leaders collapsed and had to be hauled off the track—is now an annual event for amateur runners in some 1200 venues worldwide. According to the running industry promotional group Running USA, about 550,000 people completed a marathon last year. And although the race has inspired many other tests of mettle and strength, such as the Ironman Triathlon and the Tough Mudder obstacle course, the marathon itself holds a special place in popular imagination. It is, in the memorable phrase of marathon official Chris Brasher, “the great suburban Everest.” Brasher’s quip suggests the demographic of laymen marathoners: the average household income of a reader of the magazine Runner’s World is $113,118.

Most professional marathoners, on the other hand, hail from rural East Africa: Of the 100 all-time best marathoners, 90 are either Ethiopian or Kenyan. The very speediest runners are ethnically Kalenjin, a tribe from Kenya’s western highlands. Despite making up only 0.06 percent of the world’s population, Kalenjins have run all but two of the ten fastest marathon times ever recorded. There are many explanations for the unusual success of Kalenjin runners. Kalenjins tend to have long, slender legs ideal for distance running. Born at high altitudes, members of the tribe develop large and powerful lungs as well as high levels of oxygen-carrying hemoglobin in their blood. Kalenjins tend to grow up walking and running barefoot, so their feet and arches become unusually muscular and elastic. The men endure a painful circumcision rite that includes a long period of seclusion, which is thought by some to prepare them for the suffering and solitude of running a marathon.

Caesar focuses much of his book on Geoffrey Mutai, a Kalenjin who holds the course records for both the New York and Boston marathons. Mutai was born in a small Kenyan village called Equator. He grew up poor and was frequently beaten by his father. He worked as a rock breaker, smashing big rocks with a sledgehammer to form little stones used to fortify cement. He did not start running seriously until he was 18 years old, and then he ran on his own, with little recognition or encouragement, for years. As a professional, he seems to have succeeded in races through superior acts of will. In the 2011 Boston Marathon, Mutai’s best, he ran his twentieth mile in 4:32, faster than the pace needed to complete all 26.2 miles in two hours.

Caesar’s interest in top African runners extends to their lives off the track, which are often fraught with danger and disorientation. During a disputed presidential election that provoked both random and targeted ethnic violence in Kenya in 2007 and 2008, former world champion Luke Kibet was knocked unconscious by a rock thrown at his head. Later, he had to defend himself from another attack with a pistol. The marathoners Lucas Sang and Wesley Ngetich were both killed, Ngetich by a poison arrow. Sammy Wanjiru, Kenya’s gold medalist in the marathon of the 2008 Olympics, evaded the turmoil only to be undone by his own success. Wanjiru grew up in a mud hut unable to afford shoes, but by the age of 21 he had earned a Nike sponsorship and over a million dollars. He spent his money quickly, and started drinking and gaining weight. He failed to finish the London Marathon in 2010. In 2011, he died drunkenly falling off his bedroom balcony. Caesar visits Wanjiru’s grave soon after his death. A group of the runner’s cows, now emaciated, are wandering around the site. Caesar reports that they would die of neglect only a few months later.

Over the course of his career as a magazine journalist, Caesar has written on a wide array of firsts, greatests and bests. His previous subjects include Witanhurt, “London’s most mysterious mansion”; Alain Robert, who climbs “the world’s tallest skyscrapers”; Phil Taylor, “the finest darts player of all time”; foreign correspondents who report from places like Syria, “the most dangerous warzone in recent memory”; Roger Federer, “the greatest tennis player of the modern era”; the 2010 contest between John Isner and Nicolas Mahut, “the greatest Wimbledon match of all time”; and Mark Rylance, “the greatest Shakespearean actor of his generation—maybe the greatest actor regardless of category.”

The two-hour “impossible marathon” is a typical subject for Caesar, allowing him to speculate on the limits of human potential and, conveniently, to quantify that potential. The time stands at the edge of plausibility. Runners such as Derek Clayton and Bill Rodgers have doubted whether anyone will ever approach two hours. Ross Tucker, a Professor of Exercise Physiology at the University of the Free State in South Africa, argues that marathon runners have already nearly perfected pacing, and that the current gap of 177 seconds, slight thought it sounds, puts us some nine record-breaking runs away from two hours. Caesar, on the other hand, thinks we might be a lot closer. He points to a history of inaccurate suppositions about human ability; it was long thought, for example, that a mile could never be run in under four minutes, until in 1954 the British doctor Roger Bannister famously finished in 3:59.4. Caesar proposes that two hours has been out of reach so far because of “the structure of races,” and supports the idea of a race with perfect record-breaking conditions—in the woods, in the cool evening air, with clocks that run deceptively slow to motivate runners.

For Caesar, the reasons to stage such an event are self-evident. “As a species,” he proclaims, “we are interested in outlandish feats, and our brains cleave to landmarks.” He asserts, without explanation, that “the two-hour debate is irresistible, inevitable” and that “the two-hour marathon will not leave us alone.” To those interested in the human reality of a sport, in the specificities of its many individual races or games, these assumptions are bound to seem misguided. Caesar prizes barrier-breaking extremity for its own sake, in the mode of the Guinness Book of World Records. As a result, he seems to assume that most people won’t be interested in running unless there are sensational times and sums of money involved. He sympathizes with marathon organizers who resort to publicity stunts, such as the New York Marathon’s offer in 1992 of $1 million to any runner who broke two hours. “The two-hour play was a gimmick,” Caesar writes, “but so what? The sport needed gimmicks.” This sensationalism leads to the omission of some significant aspects of competitive running: the success of Paula Radcliffe, a British woman who has run the top three fastest women’s marathons, is not mentioned in Two Hours.

Caesar hits on a more convincing explanation of the meaningfulness of records when he writes about the pain that extreme athletic performance entails. Running a marathon, he writes, puts your body “at war with itself.” Mutai says that, in a brazen push forward at the 2012 Berlin Marathon, “I sacrificed myself.” The violence of marathon running is illustrated by Caesar’s slang: When one runner decisively pulls ahead of another, the first has “killed” the second; to have been beaten badly is to have been “murdered.” The two-hour mark exemplifies a general situation of runners coming up against and trying to go beyond their limits—even humanity’s limits.

But for all his focus on the record, Caesar never shows how it will clarify the elusive source of Geoffrey Mutai’s beauty and power as an athlete, what he calls “the Spirit.” Caesar compares the Spirit to “flow,” the popular term of psychologist Mihály Csíkszentmihályi for “optimal experience” that is often used to describe a certain athletic mindset. But he does little to explain how this state of “delicious agony” actually works. When does it arise, and how? Is it available only to the most gifted athletes? Do all of them experience it in the same way? The almost automatic shot-making of basketball players like LeBron James or Stephen Curry shares with Mutai’s best running a zoned-in grace, but not its overwhelming pain. Such distinctions would help to illuminate the mysteries of the Spirit, which is, after all, what would enable any future 1:59:59 run.