i agree with father serb1389.
there is plenty of eastern mysticism in the martial arts.
of course there is also lots of hype and marketing, but i would not recommend any Christians to do it.
if you must, go to a self-defense class, but leave the 'clearing your mind' and meditation side of any exercise alone.
there is a similarity with yoga; the yoga positions are all hindu positions of worship (yes, they like to pray in these positions!).
i have had plenty of hindu friends and martial arts loving friends and read books on it too. also when i was a kid i used to go to this exercise class, and the teacher started to do 'relaxation techniques' after the class, and there was a definite spiritual aspect to it. we used to pray during this part, but got told off for not 'emptying our minds' as instructed. the teacher could tell we were not 'with her'.