The only sport/excercise I have consistently done is cycling which means I look like a much less exaggerated version of this guy:

My upper body is the same as him (practically no muscle or strength) but quads & calves decent (similar to a soccer player)
The guy in the pic is called Jason Kenny, a british 20yrold track racer. His physique is paying dividends for him and I was thinking, if I mainly want to be faster at bike racing (sprint/track) would it be such a bad idea to focus mostly on my legs?
Id still be into developing core strength & stronger shoulders to improve stability & reduce injury. But I think im only motivated to try for huge gains in bulk & power on my legs. I am getting a little ahead of myself though, ive only just begun conditioning myself for training, probably be a couple months before deciding upon direction.
Anybody else got freakishly big specific muscles for their sport?