I have been studying the martial arts since I was eleven. I have studied numerous styles; I have belts and sashes and cords from many styles, the highest of which is my second degree black belt in karate. Suffice it to say I am an experienced martial artist. What's interesting to me about that is, after my turn to atheism, the amount of my martial arts heritage I've had to leave behind.
Chi, ki, xi, prana, axé... All of these are "energy" of a mystical type I've run into via the martial arts. In some cases these are viewed as merely the energy that you get when you gather together with a group of people; in others, it is a literal energy flow that can be harnessed for various skills and techniques.
In karate, I was taught that by flowing my chi I could punch harder, use my attacks to damage internal organs without bruising the skin, even make getting punched hurt less. In kung fu I was taught many of the same things, as well as that specific sounds made with the mouth had specific effects on fighting. In taichi I was taught that it was chi, internal power, that made taichi boxers strong rather than muscles. In each of these cases, what I was taught was either exaggerated or just plain false. However, few question these unscientific ideas and accept the anecdotes they are given as fact.
The only energy that I can't argue with is axé, the energy said to gather when groups of capoeiristas get together to play together. I've heard it said that this is some kind of mystical energy, though in my experience it's just seemed to be used by "the group has a lot of axé today". Feeling more energy in a group is some kind of a real thing, I think.
Capoeira, however, isn't free of religious trappings. A lot of the songs we sing are just fun songs that don't say much, like "Si si si, nao nao nao", which is, literally, singing "yes yes yes, no no no" over and over again. However many songs call upon saints, ancient gods, Mary, and indeed the christian God. These are all part of the history of Capoeira, so I'm ok with letting them slide I guess. No one has made religion an issue with me yet, so letting it be seems like the best choice.
Knowing what I do know makes me curious about other martial arts that I haven't tried, but there isn't enough time in my life to learn all the martial arts that I'm curious about.