Originally Posted by Mister Meddle
What's so unrealistic about a bodybuilder sized Batman? The "big guys can't move around" mentality is a very, very bad stereotype. Look at football players and MMA fighters. Some of them are just as big, if not, bigger than Henry Cavill and they move around just as well as a lightweight. So no, it's not just a comic thing, it's real life too.
It's a bad misconception that big guys can't move. There are 100s of body building exercises, to be able to do them all properly and with form you have to exercise the full range of motion and be very supple and flexible.
This is Greg Plitt, he's the world's top fitness model (and supplied the physique for Dr. Manhattan in Snyder's Watchmen) and has a body builder physique but is very active and move really well and really fast, just see any video with him.
Scott Adkins has already been mentioned in the thread above and also has a body builder level physique and yet is supremely agile and quick and one of the fastest guys around.
The Stat gets body builder big for movies but remains amazingly agile and active.
So speed and size are not mutually exclusive. They together can lend you great explosiveness and momentum.