Why Work Out Till You Puke?

Between Crossfit, P90X and the Tough Mudder races, extreme work outs (that sometimes cause participants to vomit or otherwise injure themselves) are growing in popularity. Julie Beck, senior associate health editor at The Atlantic, and Gretchen Reynolds, author of the "Phys Ed" column for the New York Times Well blog, explore the motivations behind this form of exercise and wonder if it's even healthy.