Not only the lungs.
Additional muscle means additional cardiovascular networks. Additional blood to pump, additional protein to process (stress for the kidneys).
No flame at bodybuilding (cuz I do it very hard myself). But most if not all athletes are invalids in one way or another long after their glory days.
Mentzers dead. Arnolds heart, lee priest heart, dorians biceps/triceps. Many hockey players got joint injuries. etc.