Activating your core means creating “a brace, by drawing your belly button into your spine, as if you’re about to get punched in the stomach,” said Anatolia Vick, assistant director of fitness and wellness at Rice University

To truly activate your core, you need to breathe both in and out, said Jill Miller, a yoga teacher and the author of “Body by Breath.” A mistake people often make when trying to activate their core is simply holding their breath, then disengaging when they exhale, Miller said.

To start, inhale and expand the area below your ribs that includes your belly, waist, low back and pelvic floor, and let all of your muscles relax, she said. Then, as you slowly inhale and exhale again, hold in your stomach muscles slightly, gently pulling your belly button toward your spine. The goal is not just to breathe, but to maintain a slight tension in your core after you exhale.

“I liken it to a human blood pressure cuff,” Ms. Miller said of the sensation of properly activating your core, “but it’s from the pelvic floor through the waist, and even into the ribs.”