What I am about to say is vain from every angle. Every. single. one. Regardless, it's the honest truth.
I would never want to become an expert in some fields of sports solely based on the expanse of muscles that are developed as a result.
Speed skaters for example. Huge, gigantic muscular thighs. I don't want them. As far as I know, most women already think their own thighs are thunderous, so I don't see how getting bigger ones would help anyone's self esteem. Well, maybe if you won a gold medal. But that's pretty much it.
Weight lifters are next. Big, thick necks. I like separation from my head and my shoulders to be visible.
Then come the swimmers. Really muscular, broad shoulders. Are swimmers cool? Of course they are. But if I had those shoulders, I would look like those shrunken head people from "Beetlejuice".
That being said, I will go ahead and swap bodies with Gabby Douglas. That, I can live with :)