Canova appears both exasperated and amused. "What does she think to eat a breakfast like this?" he asks Lin. "She is missing out on good training."

Canova's newest athletes might be forgiven if they appear to be in over their heads. Despite being China's best young runners, their credentials are unimpressive in a town known as the Home of Champions, where thousands of Kenyan athletes—including Olympic gold medalists, world record holders, and past winners of Boston, New York, London, and dozens of other major marathons—can be found plying the dirt roads every morning.

Training between 6,000 feet and 9,000 feet helps stimulate an athlete's production of red blood cells

Overlooking the Kerio Valley, Iten has several attributes that make it an ideal spot for training: a temperate climate, soft dirt roads and forest paths, and an altitude—7,500 feet—that falls within the "sweet spot" defined in David Epstein's 2013 book The Sports Gene. Epstein argues that training between 6,000 feet and 9,000 feet helps stimulate an athlete's production of red blood cells, and therefore aerobic capacity, while still allowing for vigorous training.

The town also lies at the heart of territory inhabited by the Kalenjin, a community of several closely related traditionally pastoralist tribes renowned for its distance running prowess. Though the Kalenjin represent just 12 percent of Kenya's population, the group accounts for nine of Kenya's 10 all-time fastest male marathoners, and seven of its 10 all-time fastest women—a dominance that extends down through other long and middle distances in the world's most decorated endurance running nation.

Kalenjin, as a group, have several physical attributes that lend to biomechanical efficiency

Although no single factor is responsible for this success, studies have shown that the Kalenjin, as a group, have several physical attributes that lend to biomechanical efficiency, including thin lower legs and a high leg length to torso ratio. More likely to be born with frames conducive to distance running, Kalenjin children are thought to benefit aerobically by growing up at altitude and—because many live in rural locations—commonly walking or running long distances to school. Given the Kalenjin running tradition, and the prospect of financial rewards for those who make it to the top, many pursue the sport with the aim of escaping poverty—which is acute enough in the Kenyan rift to remain a motivating factor, yet not so acute that widespread malnutrition hinders the development of young athletes.