I've contributed to a few interactive stories at writing.com over the past two years and now I've started my own Female Muscle Growth story there.
The story is called The Big Mean Green Muscle Machine and it's about a machine at a shopping mall kiosk that builds muscle and strength. For some reason it works particularly well on females. I've started one thread on the story involving Superboy and Lana, which this board may find particularly interesting.
You can read it and contribute to it at
www.writing.com/view/1661052
Mark