Suddenly yoga is on the outs. “For many people, a number of commonly taught yoga poses are inherently risky,’’ according to a new yoga-bashing book excerpted in the New York Times Magazine last month. The book’s author, science writer William Broad, described his own experience where his back went out while engaged in an extended-side-angle pose “hailed as a cure for many diseases’’ and said that led him to lose his belief that “yoga was a source of healing and never harm.’’