Intrigued by the mingling of music and extreme sports, ENTERTAINMENT WEEKLY critic David Browne crisscrossed the country for three years to talk to competitive skateboarders, BMX bikers, snowboarders, and freestyle motocross riders. In ''Amped: How Big Air, Big Dollars, and a New Generation Took Sports to the Extreme'', he traces each X-sport from renegade beginnings to a growing (and increasingly lucrative) popularity. He found that up-and-coming extreme athletes often now face a quandary—to sell out or not to sell out?—which mirrors that of your typical rock band. ''I was interested in what amounts to the indie rock of sports,'' says Browne. ''They are to regular sports what Elvis was to big-band pop of the ’50s.''