“Working out your butt can be difficult, especially for women, because the hips and upper legs are common areas for body fat storage, which can make it tough to see the muscle you might be developing,” says ACE spokesperson CrisDobrosielski, owner of Monumental Results and author of Going the Distance. “And when results come slowly, many of us feel our efforts are not paying off.”

If you’re sweating it out at the gym each week and your booty still isn’t filled out, don’t give up just yet. Here are eight perfectly good explanations why your butt routine isn’t working—and how you can give it the encouraging kick in the rear it needs.

Bad Form

“I see this a lot: People think they’re engaging their glutes, but they’re actually not,” says celeb personal trainer Monica Nelson. “You’d be surprised at how often you can do a squat improperly.”

To make sure your squats are on point, Nelson recommends focusing on these body alignment tips first, and then worrying about how deep your squats are:

• Face your head forward (not down) and hold your chest up, open, and out.
• Keep your shoulders back (not rounded) and place your feet hip-width apart or wider.
• As you’re squatting, bend your legs as if you’re going to sit in an imaginary chair—with your back straight and your heels grounded.
• At the bottom of your squat, your thighs should be parallel to the floor, with your knees slightly over your ankles.
• Don’t let your knees buckle in toward each other on your way down, as tempting as it might be to do so.

Not Lifting Enough

“Women are sometimes a little hesitant to lift heavy weights because they fear they’ll get ‘bigger,’” says Janet Hamilton, C.S.C.S., exercise physiologist and lead running coach for Running Strong in Atlanta. “But in order to challenge a large muscle like the glutes, you should lift to the point of fatigue. That usually means heavier weights and fewer reps.”

The secret to these butt-blasting moves is to pound out as many as you can before you start to lose form. So if you’re doing a set of 10, then on your 10th rep, you should really have to focus and push yourself to finish it while keeping your alignment, says Hamilton. To see results, Hamilton says you should be doing three to five sets, fatiguing between six and 12 reps, and taking a one- to two-minute break between each set.

Not Mixing Things Up

Doing the same workouts day in and day out can also kill your progress toward a better backside. To get your bum into a round, perky shape, you have to work it from all angles—which won’t happen if you’re repeating the same moves.

“To develop lean muscle mass, routines should contain multiple exercises,” says Dobrosielski. “Three days per week of targeted resistance training—full extension squats, lunges, and hip hinging, for example—and at least two days of cardio work that focuses on glute engagement will help. Think stair stepping, hill climbing, or running.”

Forgetting All About Nutrition

“Putting in an hour of exercise five to seven days a week is only part of the equation,” says Josh Kernen, C.S.C.S., co-owner of Bridgetown Physical Therapy and Training Studio in Portland, Oregon. “You need to support your work and boost your results with a clean diet.”

To build muscle and melt any fat you might be packing in the trunk, Dobrosielski recommends sticking to vegetables, lean proteins, and good fats, while passing up on sugar, processed foods, and other empty calories. If you’re having trouble figuring out your diet, talk to a registered dietitian to find out how to get the right balance of nutrients that will keep you healthy and fuel your workouts.

Giving Up Too Early

“When starting a new weight-training program, the body is learning to activate and use as many muscle fibers as possible,” says Kernen. “It’s not until you have been training for six to eight weeks that the body starts developing muscle and shaping the glutes. People typically get frustrated at that point, which is the most critical point, and stop.”

Like all good things in life, achieving a bootylicious figure takes time and commitment. If you tend to get bored easily, Kernen says it’s best to know ahead of time what it will take to reach your goals. Try planning out your routine four to six weeks in advance so you’re not picking random exercises every time you hit the gym. Zeroing in on your target and wholeheartedly committing to it—no matter how long it takes—will get you exactly where you want to go