This posterior pelvic tilt exercise, when done on your stomach, actually challenges your core to focus on engaging and activating the lower abdomen to maintain a neutral spine.
So, this is how you do it. You’re gonna get onto your stomach and your focus is to compress your ribcage down towards your pelvis. As a matter of just squeezing those abs versus sucking in, and what’s gonna end up happening is that your pelvis will actually end up tilting up towards the ceiling, so you’re going to have your hands up by your side, you’re going to have your head down, and your focus is pulling your pelvis up into the ribs. So contracting, and then relaxing. Another way to think about it is as if you were on your back but you’re having your hands up above your head so you’re focusing on engaging your core and then back up. Be careful to not arch your back because that’ll actually cause more pain. Your goal is to actually pull those ribs towards your pelvis as you relax.