donīt think it has something to do with genetics, but defintely something with breathing technique (and obviously not having a gut). take a deep breath, then exhale as long and as much as you can, HOLD your breath now(exhaled position), lift your ribcage as much as you can and SUCK IT IN, BABY!
Ok, I'm a little lazy and don't feel like reading the whole thing to see if someone else contradicted you. If so, sorry for saying the same thing again. It's totally genetics. obviously if you have a gut chances are you won't be able to pull off a vacuum but if you think of Kevin Levrone, Priest, wheeler all bb'ers with mall waist that don't have a vacuum pose.
