Okay people, butts are in again. They're so in, they're better than abs, at least according to Women's Health. Although there shouldn't be a reason to choose either: why not have both?

It is, of course, easier to work on your abs than your buttocks. For starters, many women suffer from "gluteal amnesia," a condition where the glute muscles get lazy, due to the hours we sit in a day. Instead, the hamstrings and lower-back muscles take over the job of extending the hips and rotating the femurs in their sockets. This can lead to back, hip, or knee pain over time - and not to mention a flat ass.

"The booty is like the final frontier," says L.A.-based strength and conditioning specialist Holly Perkins. "As you reach your ultimate level of fitness, 99 percent of your body will reflect this, while the last 1 percent will linger in your glutes. The true test of a woman's commitment to strategic eating and intelligent fitness is the quality of her glutes and hamstrings."

So the next time you work out, remember to work on your backside. "The larger a muscle is, the more it can help you on a hormonal and body-composition level," says Perkins. Exercise plays a huge role in reversing insulin resistance and increasing the activity of glucagon, a fat-burning hormone. Building your butt also improves metabolism, helping you burn calories at a higher rate.