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 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, plié squats, which are very effective for shaping and toning your butt.