Of course we can rule out drug use? Yate and Colemen are good example of how the internal organs can also grow along with the muscles of the body. Over use of GH and related test injections, I've been told by a couple of sports doctors. Growing larger, the organs tend to push the ab wall outwards. Usually getting ready for a contest, this can occur. Even with massive pec's, that flaw can still be noticed.
A shallow or narrow rib box could be root cause. With a deep & wide rib box foundation, unless your are very obese, the problem should not arise. Genetic influence at birth. Thinner & smaller types tend towards this. You might notice a few black boxers in the lighter classes have a protruding belly, Winky Wright comes to mind.
Might try heavy breathing exercises (squats, DL's, cleans, etc) followed immediately by a set of light pullovers, working for a full stretch of 20 rep's or so. Breathing squats are ideal for an increase in chest size. The cartilage is being stretched between the ribs. Some people are mistaken and think the the bones are growing, not true. If your young enough (mean average is 24-25 years old) the cartilages is still in a state of flux and will still stretch/grow a bit. After that average age (24-25) the cartilage matures and becomes harden. An increase from 2" to 3" is not that uncommon. Think how much more impressive the whole chest would look.
I, and a lot of other people, have gotten excellent chest/rib box growth from the bent arm pullover. Either DB or BB. Feel free to use heavy weight on this one. Can also SS these with the straight arm pullover followed by the bent arm version with a heavier weight. Not only hit's the chest/rib box but also is an excellent lat and tricep builder. Bent arm pullovers are my favorite exercise for upper body mass. Can also include the press from the chest to make it even more effective. Good Luck.
