I know this is a biased source of info since most runner girls tend to like slimmer guys, but I thought it'd be better than nothing.
When I go to the gym, a lot of the big guys there do indeed have a lot of muscle, but they really just look like muscular fatties to me. I mean, they have very little definition. I'm wondering if girls actually think that's attractive.
Here's an example, though the guys I'm talking about are softer than this guy.