When I was teenager, I did my best to increase the size of my rib cage, because I wanted to look like an orindary man. Muscle exercise and playing on parellel bars. Nothing worked.
My height has been 6 feet (183 cm), but the perimeter of my rib cage has been just 31 inch (78 cm). At my height, it should be greater than 39 inch (100 cm). People said my body shape is deformed.
After crossdressing, however, my body shape suddenly became a kind of ideal one that many m2f transgender may envy.
After teens, I think it is difficult to grow rib cage. Except malnutrition during childhood, I think genes determine most of the variability in rib-cage size. My body shape resembles my mom's.
Barbie~~