To get rid of a pigeon chest, or a protruding breastbone, as defined by Dictionary.com, a person must build the muscle tissue in the chest and shoulder areas to compensate for the bulge of the sternum. An attempt must be made to expand or grow the ribcage, as well.
Building the muscles of the pectoralis, or chest, muscles and the deltoids, or shoulders, will give the upper body a filled-out, balanced look, taking the focus off a protrusion of the sternum. According to Bodybuilding.com, basic chest and shoulder exercises are the best for growing a stable base of upper body musculature.
For chest, barbell bench press, incline dumbbell press, flat dumbbell fly, bar dips, and push-ups are the recommended exercises. Shoulder movements to work the entire deltoid area are dumbbell press, lateral, or side, dumbbell raise, frontal dumbbell raise, and bent over rear dumbbell fly.
Attempting to expand the ribcage is another solution to reduce the appearance of a projecting sternum. However, ribcage expansion is often considered a myth, as the ribcage may not actually expand due to the structure of the skeletal muscles holding the ribs together, as stated on Natural Bodybuilding.com. However, by performing deep breathing squats and carefully performed dumbbell pullovers, the skeletal muscles are strengthened and grow giving the appearance of expansion.