Coughing is the body's way of expelling
something from the air cavity which doesn't belong ~ fast.
that break ribs?
The diaphram's action is to contract, thereby drawing air into the lungs.
On exhalation it normally relaxes...
unless you are coughing.
The diaphragm contracts when you cough. (Okay
Germs, everybody OUT!) So do your abdominal muscles, which could push the guts - stomach,
intestines, etc. - up into the diaphragm.
These contractions, combined, causes the ribs
to bend inward and down.
the cough is violent enough, all these sudden opposing actions will strain the ribs to the point of breaking. Yikes!
most common breaks happen on ribs 5 through 9.