The absorbing, definitive account of CrossFit's origins, its explosive grassroots growth, and its emergence as a global phenomenon.   One of the most illuminating books ever on a sports subculture, Learning to Breathe Fire combines vivid sports writing with a thoughtful meditation on what it means to be human. In the book, veteran journalist J.C. Herz explains the science of maximum effort, why the modern gym fails an obese society, and the psychic rewards of ending up on the floor feeling as though you're about to die.    The story traces CrossFit’s rise, from a single underground gym in Santa Cruz to its adoption as the workout of choice for elite special forces, firefighters and cops, to its popularity as the go-to fitness routine for regular Joes and Janes. Especially riveting is Herz’s description of The CrossFit Games, which begin as an informal throw-down on a California ranch and evolve into a televised global proving ground for the fittest men and women on Earth, as well as hundreds of thousands of lesser mortals.    In her portrayal of the sport's star athletes, its passionate coaches and its “chief armorer,” Rogue Fitness, Herz powerfully evokes the uniqueness of a fitness culture that cultivates primal fierceness in average people. And in the shared ordeal of an all-consuming workout, she unearths the ritual intensity that's been with us since humans invented sports, showing us how, on a deep level, we're all tribal hunters and first responders, waiting for the signal to go all-out.