If you’ve ever taken a barre or Pilates class, you know how tough the toning workouts can be. They're famous for micro-movements that target many of the smaller muscles we don't often use in our everyday lives. The payoff includes a lifted butt, lean legs, and strong arms—that is, if you’re doing the exercises correctly.

“I’ve met students taking five barre classes a week who still have weak glutes and hamstrings, and a very sore lower back,” says Julie Erickson, a Boston-based Pilates instructor. The reason? They're tucking their pelvis.

“For many students, tucking the pelvis into an unsafe posterior tilt, and keeping the hip flexors flexed during exercise can render movements ineffective,” she explains. A posterior pelvic tilt occurs when the front of the pelvis rises and the back drops, so it’s slightly tucked beneath the hips. 

According to Erickson, most barre and Pilates exercises require the use of the lower abs and glute muscles to keep the pelvis stable in its natural position, with the pubic bone and tailbone in line with each other. Movement in the hip flexors (on the front of the body) and the hip extensors (on the back of the body) should initiate from the the femur bones in the upper thighs rather than the pelvis.

If the body isn’t in proper alignment, your workout isn't doing much good, says Erickson. Even worse, it could cause injury. "Tuckers" often struggle with lower back pain, compromised posture, weak glutes and thighs, and a “pooch,” since a tilted pelvis can encourage the hip flexors to take over the work of the lower abs, weakening the core as a result.

To get the most out of your barre and Pilates sessions, make sure your pelvis is in a neutral position. "If standing, make sure the pubic bone and tailbone are level with each other, and the 'underbutt' is squeezing to lift the tush," says Erickson. "Keep the lower belly engaged as if you were zipping up a tight pair of pants, from the pubic bone to the belly button." And don't forget to lift the rib cage off the hips to lengthen the front and back of the body, and create space in the torso, she adds.

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When you lie down on your mat, keep the tailbone heavy and the sit bones pressing away from it. "Think of wrapping a corset from the top edge of the pelvis to the bottom of the rib cage," says Erickson. By using the lower abdominals and glutes to hold your pelvis still, you'll be well on your way to a stronger core and firmer booty.