David Kirsch shares the inside scoop about celebrity workout routines, including his effective butt workout routines.

When Anne Hathaway, Heidi Klum and Liv Tyler need to get fit fast, they go to David Kirsch. Find out how the stars shape up and what you can do to see A-list results.

Q: What butt workout tips can you offer from your booty-sculpting manual, Butt Book?

A: [Supermodel] Karolina Kurkova coined me the "Master of the Ass." The idea was whether you had a flat bottom or too large a bottom, whether it was wide or narrow, I was able to focus on your specific issue and give you a nice, round, hard butt. So I have a variety of exercises in the Butt Book: sumo lunges, platypus walk, plie squats, which are very effective for shaping and toning your butt.

Q: Here’s another butt workout question. How do you work the backside without building up the quadriceps?

A: If someone is worried about bulking up their quads, they're not going to do a traditional squat. They're going to do a wide-stance squat or a plie squat, which is second position dance, opening up your legs and bringing the focus to the inner thighs and not to the quads. Don't use excessive weight and keep repetitions high. I use body weight or a medicine ball or light hand weights.