The most common mistake people make with their ab workouts, according to a trainer

Whenever I’m working on my core, two things are going through my brain: What number rep am I on, and when will it end? But then, on top of that, I’m really supposed to be paying attention to my form. In a Pilates class, for instance, the instructor always emphasizes the fact that you’re to tuck your ribs under and make sure that your stomach is pulled in.

But when I’m simply doing crunches on my own time and I peer down at my core, I notice that I sometimes suck it in. This may be subconscious but it may also be for vanity purposes. Either way, I do it because I feel like it’s activating my abs more and, consequentially, giving me a stronger core. But then I spoke with a fitness trainer who told me that this is very very wrong.

“When people suck in their belly to supposedly deepen their ab engagement, it’s actually counterproductive,” says Erica Ziel, author, certified personal trainer, and founder of Core Athletica. “Sucking in can put unnecessary pressure on your pelvic floor and lower back, restricts your ability to breathe more deeply, and contributes to poor posture.”

It seems minor, but it’s really important to get it right—not only for a more effective ab workout, but because the issues that stem from doing it incorrectly can lead to issues. “Back pain and pelvic floor issues are among the top issues women suffer from and don’t need to, and a lot of times ab exercises are contributing since they aren’t engaging at a deeper level and connecting to their entire core,” says Ziel.

Instead, what you should be doing is “zipping up” your stomach, which, yes, sounds like it’d be a lot like sucking in, but there’s a nuanced difference. “Zipping up helps your body activate even more muscles through your core, improve your breathing, improve your posture—which can help you say goodbye to annoying lower back and neck pain—and strengthen your core in a deeper way,” says Ziel. “To do this, as you inhale, breathe into the sides and back of your ribs. As you begin exhaling, gently connect to your pelvic floor—think of it as a diamond shape, and gently draw those four points together then upward through your entire torso and the top of your head. Think of it as ‘zipping up’ from the base of your pelvis through the top of your head.”

Once all of those factors are in place, she says you’re ready to execute your ab exercise. “You can practice this even when standing or walking—just make sure you aren’t holding your breath,” says Ziel. “This can be common when initially retraining your body how to engage your core.”

One thing to note: While trying this, she says that you may not feel your abs so intensely. This is normal. “In the long-term, your body will learn how to connect on a much deeper level, leaving you feeling more from your ab routines,” she explains. And then you’re on your way to being a core master.

While you’re focused on that core, try these at-home Pilates moves via Karen Lord or the ab workout Kendall Jenner swears by.