Simple answer in my understanding, yes. Much like with fat cells, you are intended to be born with a certain number your whole life. Hypertrophy occurs first. But once you supercede natural bounds, it isnt very reversible. The muscle cells eventually split, but at a rate that is very slow and too hard to be actively measured. Fat cells split much easier than muscle cells, but stretching, power exercises, long periods of bodybuilding, IGF, and theoretically test would all induce some splitting. The hypertrophy will probably be minimized later though, evening out the total compositional look. I read a study conducted on bodybuilders where oddly, they didnt have as much hypertrophy as hyperplasia (which is unique). But theoretically with proper diet and very intense training, the body will undergo a transformation.
Think about it like this. At 180 its easy to lose weight but hard to gain 100 pounds. At 300 pounds its easy to lose 50 but easy to gain 50. If you induce a massive amount of hyperplasia and quit lifting, id never recommend quitting without a running regimen. Because if that muscle converts into fat, you are in for a roller coaster.[/quote]
It’s not possible for “muscle to convert into fat”, as you put it.