OLIVIA WILDE HULA-HOOPING
WHAT IT IS: L.A.-based studio Hoopnotica capitalizes on the nostalgia and mass appeal of hooping by transforming the activity into fitness classes and DVDs that incorporate weighted Hula Hoops.
WHAT IT DOES TO YOUR BODY: The high-cardio, full-body dance workout "strengthens core muscles-but it's fun!" says founder Gabriella Redding.
STARS WHO LOVE IT: Enthusiast Olivia Wilde included the colorful handmade hoops in her online short film Free Hugs.
NAVY SEAL TRAINING
WHAT IT IS: For those in search of a rigorous mind and body workout, programs like SEALFIT, developed by former SEAL Mark Divine, take no prisoners.
WHAT IT DOES TO YOUR BODY: The intensive conditioning programs build strength and military-grade stamina.
STARS WHO LOVE IT: Vanessa Hudgens trained with Navy SEALs for five months to prepare for her role in Sucker Punch
. "It was the most intense thing that anyone could ever do," she says.
WHAT IT IS: The calorie-burning, Latin-inspired dance workout offers classes worldwide. "The moves and choreography are supereasy!" says Gina Grant, an instructor based in Portland, Ore.
WHAT IT DOES TO YOUR BODY: The dance routines build a lean, muscular figure, including, says Grant, a tighter lower body and toned abs.
STARS WHO LOVE IT: Singer Sparks dropped 30 lbs. by going to classes two to three times a week. "She loves it and is really good at it," says Nichet Smith, her instructor.
WHAT IT IS: Programs such as the Bar Method and Ballet Beautiful are based on the training principles used by professional ballerinas.
WHAT IT DOES TO YOUR BODY: The routines result in a "sleek, graceful shape," says Ballet Beautiful founder Mary Helen Bowers, Natalie Portman
's Black Swan trainer. Adds ballerina Alexandra Blacker, who worked with Kunis: "We created long, lean muscles."
STARS WHO LOVE IT: Mila Kunis says, "The best part is changing your body, the way you walk and hold yourself."