Did about ten years of Aikido, but it's waaaay back now... stopped when my first daughter came in...
Lot's of ladies there too, which is not a bad thing I guess.... actually it would REALLY do me good to start again...
And despite looking pretty harmless and faked at times, I can assure you that it's very efficient once you got it and it also was the most exhausting training I ever experienced... maybe you have seen some early Steven Seagal movies... then you saw some moves applied... ^^
There are simply put two ways to apply it... the no harm above all... just exhaust your enemy, which is VERY hard and implies a great deal of routine, or... apply as much damage as possible with the smallest amount of energy... which is used by the japanese police for parts (I think they name it Aikijutsu, but don't quote me on that...), mostly meaning very complicated multiple breaks at and around the joints by handles, locks and throws, sending the bigger parts off while holding some others locked... or just moving parts against there natural direction... you do the math...
also did some Shotokan karate first, but in a real bad school, which put me off....