Miley Cyrus got her killer abs by doing 30 minutes of crunches a day.

The 'Wrecking Ball' singer has rarely been seen without a crop top exposing her slender midriff since returning to the spotlight with a controversial new image, and has put in a great deal of effort to look good in her skimpy outfits.

Mari Winsor, Miley's Pilates instructor, said: ''When we work out we don't just do a couple of moves. It's at least a half an hour of working out...

''You have to learn how to not just tighten up your tummy but actually pull your tummy in to your lower back as much as you can. Just doing 40 crunches a day isn't gonna do it for you.''

The Los Angeles-based fitness guru revealed Miley has recently installed a studio in her own home so she can sculpt her body every day, and is especially pleased with the result Mari's workout regime has had on her lithe limbs.

She told People magazine: ''I gave her those legs. She's always going to have those long gorgeous legs. We just toned and firmed in all the right places.

''She wants to be healthy, she wants to have good abs. It always makes her feel better and clearer when she works out.''