As yoga has catapulted from an obscure Indian tradition to an exercise regimen of the overstressed masses, it's no easy task to find a teacher who stands out from the om-chanting pack. Give Amy Jin Schmelzer five minutes, and the Iowa-native will prove that she's no cookie-cutter yoga instructor. For her afternoon power-yoga classes, she throws on a little R&B — a live Mary J. Blige concert, maybe, or some old-school Destiny's Child — and, between poses, slips in some inspirational philosophy that will make you re-evaluate how you're going to handle that jerk boss. To make a point about mindless addiction to routine, she might tell her beginning students, "Maybe I won't have you kick your own ass in this pose" as they switch from one bent leg to the other. Her power-yoga sequencing, on the other hand, is no laughing matter; she will get your ass ready for bathing-suit season. Of course, you'll probably be too engrossed in the moment to notice that you're getting an incredible workout. Which is what those Indian sages were going for in the first place.