Why does it make sense to Ethiopian runners to get up at three a.m. to run up and down a hill? Who would choose to train on almost impossibly steep and rocky terrain, in hyena territory? And how come Ethiopian men hold six of the top 10 fastest marathon times ever? Michael Crawley spent 15 months in Ethiopia training alongside (and sometimes a fair way behind) runners at all levels of the sport, from night watchmen hoping to change their lives to world-class marathon runners, in order to answer these questions.

Writing from both the cutting edge of scientific discovery and the front-lines of elite athletic performance, National Magazine Award-winning science journalist Alex Hutchinson presents a revolutionary account of the dynamic and controversial new science of endurance.

New York Times best-selling author and ultramarathoning legend Dean Karnazes has pushed his body and mind to inconceivable limits, from running in the shoe-melting heat of Death Valley to the lung-freezing cold of the South Pole. He’s raced and competed across the globe and once ran 50 marathons, in 50 states, in 50 consecutive days.

Deena Kastor was a star youth runner with tremendous promise, yet her career almost ended after college, when her competitive method - run as hard as possible, for fear of losing - fostered a frustration and negativity and brought her to the brink of burnout. On the verge of quitting, she took a chance and moved to the high altitudes of Alamosa, Colorado, where legendary coach Joe Vigil had started the first professional distance-running team. There she encountered the idea that would transform her running career: the notion that changing her thinking - shaping her mind to be more encouraging, kind, and resilient - could make her faster than she’d ever imagined possible.

Quenton Cassidy's first foot races are with nature itself: the summer storms that sweep through his subtropical neighborhood. Shirtless, barefoot, and brown as a berry, Cassidy is a skinny, mouthy kid with aspirations to be a great athlete. As he explores his primal surroundings along the Loxahatchee River and the nearby Atlantic Ocean, he is befriended by Trapper Nelson, "the Tarzan of the Loxahatchee", a well-known eccentric who lives off the land.