How to Shape a better Butt

"If you're willing to spend the time on it, you have a lot of possibility to change the shape of your buttocks," Topp says, when I ask her if there's any hope of nonsurgically plumping my flat one.

In general, the gluteus maximus is a combination of fast-twitch muscle fibers -- that is, rapid-firing fibers, which are tapped for bursts of speed or power -- and slow-twitch muscle fibers, which are the workhorses during aerobic activities. Some studies suggest that the glutei medius and minimus consist primarily of slow-twitch muscles. This means theglutes can benefit from both strength training with high load and low reps, like heavy-weight squats (to work the fast-twitch muscles), and with low load and high reps and endurance exercises, like runningand stair climbing (to work slow-twitch muscles). In fact, EMG studies have been done to find which strength moves get each muscle firing, and our Sculpt Your Backside routine puts those principles to work; one flat-fannied tester added a quarter inch to her behind within four weeks.

Of course, a big part of your butt's appearance is dictated by the layer of fat that covers those glutes. "Much of the female posterior is adipose tissue," Reed says. "The actual muscles are shaped like men's, if a little different in orientation because the pelvis is slightly wider."

If extra flab is obscuring yours, your surest bet to uncover its true shape is to follow a healthy 1,500-calorie-a-day diet and add regular cardio on most days to lose fat all over, including around your lower half.

This mix of diet, cardio, and toning will give you the best butt you can have. And that should be the goal -- not J.Lo's or the one belonging to that woman putting her head behind her ankles in yoga class. "People say 'I want her butt,' but you can't have it, and you shouldn't want it," Dr. Marango says. "Instead, within your own structure, maximize what you have." And that's something any of us who is willing to get off her butt and move it can do.

Originally published in FITNESS magazine, January 2012. http://www.fitnessmagazine.com/workout/butt/exercises/butt-sculpting-exercises/?page=3