I'm pretty sure I'm around 10% body fat, when I tighten my ab muscles, you can see my ab muscles and it looks like I'm in good shape, but when I'm relaxed, my stomach protrudes around 2 inches forward. I'm recently found out about the inner abs and doing "stomach vacuums" to strengthen them. I'm not getting much success out of it so far though. Is it possible that having tight muscles somewhere on your body can have an effect of lengthening the inner ab muscles and prevent them from being able to tighten up? I have pretty bad posture and am pretty sure my chest and back muscles are pretty tight... I'm been told before that I have a minor form of pectus excavatum by an x-ray person when I had some chiropractic work done on me. It's where your sternum sinks in a bit, I think its pretty minor and its only noticeable from the side view, it still sucks though, I try to develop my chest muscles and only the sides grow, the center of my chest is like skin and bones... Ever since middle school I've notice that problem about my abs and kept "sucking it in" so I wouldn't look "fat" though I always been skinny (just my stomach sticks out). I probably always had this problem though, and I just learned a few years ago that it was a bad thing to try to suck it in all the time like that...