Becoming Batman

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.

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.

How long would Bruce Wayne have to train to become Batman?
In some of the timelines you see in the comics, the backstory is he goes away for five years—some it's three to five years, or eight years, or 12 years. In terms of the physical changes (strength and conditioning), that's happening fairly quickly. We're talking three to five years. In terms of the physical skills to be able to defend himself against all these opponents all the time, I would benchmark that at 10 to 12 years. Probably the most reality-based representation of Batman and his training was in Batman Begins.

Why such a long training time?
Batman can't really afford to lose. Losing means death—or at least not being able to be Batman anymore. But another benchmark is having enough skill and experience to defend himself without killing anyone. Because that's part of his credo. It would be much easier to fight somebody if you could incapacitate them with extreme force. Punching somebody in the throat could be a lethal blow. That's pretty easy to do.
But if you're thinking about something that doesn't result in lethal force, that's more tricky. It's really hard for people to get their heads around, I think. To be that good, to not actually lethally injure anyone, requires an extremely high level of skill that would take maybe 15 to 18 years to accumulate.

Dark Knight Shift: Why Batman Could Exist--But Not for Long (Scientific American)