E. Paul Zehr has a book coming out in October called Becoming Batman: The Possibility of A Superhero, about the physical and mental training one would need to become a superhero without any supernatural powers. Zehr, a professor of kinesiology and neuroscience at the University of Victoria in British Columbia, is also a karate expert. Over at Scientific American, JR Minkel interviews Zehr about how one might train as the Dark Knight. From SciAm:
What's most plausible about portrayals of Batman's skills? You could train somebody to be a tremendous athlete and to have a significant martial arts background, and also to use some of the gear that he has, which requires a lot of physical prowess. Most of what you see there is feasible to the extent that somebody could be trained to that extreme. We're seeing that kind of thing in less than a month in the Olympics.Batman and science (Scientific American), Pre-order Becoming Batman (Amazon)
What's less realistic? A great example is in the movies where Batman is fighting multiple opponents and all of a sudden he's taking on 10 people. If you just estimate how fast somebody could punch and kick, and how many times you could hit one person in a second, you wind up with numbers like five or six. This doesn't mean you could fight four or five people. But it's also hard for four or five people to simultaneously attack somebody, because they get in each other's way. More realistic is a couple of attackers.