From PEOPLE Magazine Click to enlarge
TAYLOR

LEAN BODY

WHAT SHE DOES

Running ("I don't like any other kind of exercise," Swift, 21, has said) and a healthy diet that includes salads and yogurt. Still, she's said, "it's nothing too regimented or crazy."

KATY

TONED ARMS

WHAT SHE DOES

Arm-sculpting exercises involving 5-to 10-lb. dumbbells and good-for-you snacks like whole-grain pizza with low-fat cheese. Perry, 26, "looks amazing in her outfits," says her trainer Harley Pasternak.

RIHANNA

TIGHT BUTT

WHAT SHE DOES

A workout of skater lunges, weights and her least-hated cardio exercise: cycling. The 23-year-old has "a strong lower body," says Pasternak (he trains her as well as Perry).

BRITNEY

SOLID ABS

WHAT SHE DOES

A five-day-a-week regimen featuring core-strengtheners such as sit-ups, planks and Pilates, and a 1,500 calorie-a-day diet. Now Spears, 29, "has more of a slimmer look," says her trainer Derek DeGrazio.

Beyoncé Knowles

HOT LEGS

WHAT SHE DOES

Lower-body exercises-such as stair-climbing, yoga and intense treadmill sprints-and a healthy diet (scrambled egg whites, salmon). "Her endurance is through the roof," trainer Marco Borges says of Beyonce, 29.