That is not a big ribcage. If you're worried about presentation, I've found that a great way to counter the ribcage and better show your musculature is by working on your posture. Ive always looked much smaller in say, a bikini, than fully clothes- a sign of a large frame. Occasionally, children have the problem on 1 side. It is caused by a defect in the tough connective tissue cartilage that holds the ribs to the breastbone.