Hour 2: Yoga has quickly become a big part of the go-fast, ego-fueled U.S. fitness business, but what might American yogis be missing in their quick study of a practice that’s actually thousands of years old? We’ll talk this hour with New York Times senior writer, two-time Pulitzer Prize winner, and yoga practitioner William J. Broad. His new and thoroughly-reported book is “The Science of Yoga: The Risks and the Rewards” (Simon & Schuster, 2012).