The Jewish Dojo Dilemma

When Ethan and I were playing tennis the other day, I started thinking about other activities I'd participated in at various times in my life. My mind focused in on Judaism and Jujitsu, for reasons having nothing to do (as far as I know) with the obvious pun.

Many dojos and martial arts studios I've been in - all I think, actually - have framed pictures of the main sensei's own sensei, the founder of the particular martial style, or some other guru.

Do orthodox Jews study martial arts? I assume they must. Krav maga?

When an observant Jew walks into a dojo with a framed guru picture towards which, according to martial tradition, he is obligated to bow, what does he do? Does this count as graven imagery? Obviously, these martial masters are not being venerated as gods per se, but I would imagine the bowing thing doesn't sit well. It freaks me out a bit actually.

I remember reading about a line of workout videos for orthodox men, but that wouldn't really bring up the same issues.

Does anyone know?