When one gets to a certain level as a stage-combatant in the SAFD (I think also especially when one is looking to teach), one's stage combat instructors urge one to take a real martial art in tandem with one's continued stage combat training. I assume the reasons for this are something like the following: it's important to know how fights can go down in real time and speed for one to be able to create an effective staged illusion; one should always be in fighting trim; there are many film fights that require a martial-arty style to them and it behooves an actor-combatant to be versed in said style; it's a good idea to know what a real punch/kick/etc. feels like, again so one can create an effective illusion.
I have had a few SAFD-tied friends ask me for advice when they are told to embark on the martial arts journey. They ask me which martial art I'd recommend. I've answered them with the following, and I thought you lovely lurkers would benefit from hearing this question and answer as well.
First of all, I could never tell you what martial art to study. Beginning martial arts training is the start of a lifelong endeavor (or at least it should be), and is perforce a very personal choice. So I'd urge you to take a bunch of introductory free classes, talk to a bunch of teachers, and especially interview students to see what their experience at a school is like. Look to see what the credentials of the teacher are and what the tenure of the students is (do students study for a couple months, get a black belt and leave, or are there people that have been around for years?) and most importantly, listen to your instinct, young Padawan, and see if you dig the vibe.
That's advice for anyone. For actor-combatants in particular, I would add:
Find an art that will ameliorate your training, and challenge you. Find one that will add to your skills, not allow you to continue doing what you're already doing. Find what they call a "hard" martial art.
Why? Because by practicing stage combat, you are constantly going for safety, throwing punches and weapon strikes outside the body, and (we would hope!) never taking a hit full force, or really at all. If you go from this to a soft art like Aikido or T'ai Ch'i, you're just continuing the softness, the avoids, etc. Choose a hard martial art: one that will have you actually landing punches on bags and pads, one that has you defend against free-response attackers so you can experience speed, one that will teach you how to punch and kick (and/or cut, stab, and staff-smack) correctly when the strike is landing. This way, you know what happens in real life (at least, a school's close approximation) and can bring this new knowledge to your creation of illusions of violence. Having said that, make sure nobody's really getting hurt or you're not going to want to study there very long. There's a delicate balance between martial arts safety and combat realism that many schools have mastered, which will help you immensely in your theatrical combat pursuits. Don't take the easy path of just allowing yourself to continue to look cool. Choose something that will improve what you do.
I also personally feel that knowing how to fall and roll is the most important stunt/stage combat skill you can master. If the martial art you choose doesn't include ukemi, find something you can study along with it that does.
Finally, if you didn't get a chance to read this way back whenever I posted it earlier, I hereby assign it to you again: Tony Wolf's excellent article called "Ne'er the Twain," about the "martial arts/performing arts dichotomy." And read this post from August again.
~Jenn Images from the most recent two test nights at the Boulder Quest Center (2009).