If you use a muscle alot, it will grow larger. I didn't lose my big bum until I quit

hiking up hills
running
skating
cross country skiing
steppers - or running up stairs
leg kick backs (on all fours, bend leg at knee, push foot towards ceiling)
squats

...and instead just started WALKING. NOW it's toned and not overdeveloped (bubble butt or J'lo butt) as people call it. All these women with rears out to there on the stairmaster, honey, you are only making it GROW in strength and SIZE and stick OUT even more.

Now if a FAT BUTT is your problem, any cardiovascular exercise, low carb diet and a little weight lifting should decrease the FAT content there and lift it, but don't over-do it or you might become your own worse enemy -

The gluteous maximus (butt muscle) is one of the largest in the body other than the quads...use it...and it WILL grow even larger...so when you exercise, think of using exercises that use your whole body pretty evenly - if your BUTT does most of the work, then THAT is what will get BIGGER. Work a bicep - build a bicep...same goes for that butt.

N (I ran for 15 years and highcarb/nonfatted it...now walk and atkins and NO MORE BIG BUTT. no kidding. Okay, now you can tell me to BUTT OUT>!