The myth is If I don’t pull my navel inward while doing a crunch type movement, my stomach will become distended. I'm glad to say, that is simply not true.  Your stomach attached to your pubic bone at your pelvis and the bottom few ribs. Its job is to short these two areas. As the stomach contracts, it pull the rib case towards the pelvis. It's a straight line. No distention can or will occur. It's likely you will get a better squeeze and better focus on your abs if your focus on slightly pulling the naval inward. I hope this clears things up for you.