There are quite a few in early stages of development right now.
Gina's Gym, Bayshore Academy, and Strong Girls FMG are probably the best three at the moment.
Although I think it is abandoned A Growing Romance is pretty good, lots of unique images at several different stages of growth.
Bodybuilding Academy has promise, but it only has the initial release and no further updates.
The problem I find with FMG games is that they all suffer from being pretty grindy while also rushing through the growth and transformation. The other big problem with most of them is that there is also very little story involved, but that is true of FMG in general; boiling down to guy likes muscular women, woman guy knows somehow magically grows muscles rapidly, guy and muscular woman fuck, and there isn't any characterization or plot outside of that incredibly basic premise. I'd love it if anyone has something with more substance.