A friend of mine in med school said they did their autopsy on someone with sleep apnea and the man's diaphragm was unusually thick. I myself have sleep apnea and my allergist was surprised how hard I could blow into her breath measuring thing. Not off the charts but high enough that she noticed.

I guess there are other reasons to be on CPAP, but that's my personal datapoint.

(Imagine how strong your diaphragm would be if you spent a third of your life breathing through a crushed straw.)