It's amazing to find the similarities between Aikido and ExtremeProgramming. Aikido is a very unique martial art, not only in the art itself, but especially in the way it is taught. The master of the dojo usually demonstrates a waza (technique). Then, all the students pair up. The pairing process is not assigned by anyone - it depends on you. Everyone tries to pair with as many different people as possible in one session.

Sometimes, a beginner pairs with a top black belt. Sometimes, a senior student pairs with a black belt. Sometimes, two black belts pair. This is very similar to the PairProgramming which happens on XP projects.

The instruction mechanism is flexible. Usually, in other martial arts, everyone cannot instruct. But in Aikido, anyone can instruct his pair. So, sometimes, senior students learn from juniors (apart from the normal case where juniors learn from seniors). 

''Traditionally, the above is considered a breach of etiquette - especially kohai instructing sempai (junior/senior), if paired with fukushidoin (assistant instr.) it might be ok for sempai to instruct privately in some dojos. -- JonGroff''

The master of the dojo is like the XP coach. He moves around seeing how each pair is doing. When a pair is stuck (two juniors pairing up), he triple pairs or demonstrates the technique.

''Actually, he comes over and kicks both your asses for a few minutes to help you figure it out.''

The pairing process also ensures that monopolization doesn't occur. One person is the attacker, while the other is the receiver (the driver, I'd say). This configuration typically lasts four times, and the roles are reversed. After each pairing (which lasts from 10 to 15 minutes), pairs are rotated.

At the end of a session, one learns from a large collection of individuals - top black belts, senior students, and juniors. It's a beautiful learning experience, and makes it fun to learn Aikido. The beauty of diversifying the instruction source, and letting everyone have fun, is probably why XP is liked by the people who follow it (apart from business profits).

There are metaphors (akin to SystemMetaphor) while applying techniques. Tenchi nage - is the Japanese name for the Heaven and Earth technique. It is a powerful technique for overpowering someone who has grabbed both your hands, by moving one hand up, and the other hand down, and causing the opponent to completely lose his balance. Hence, the association with Heaven and Earth.

-- SomikRaha

This teaching technique is also used in Ju-Jitsu and Muai Thai and (I expect) most martial arts. Muai Thai training also involves periods where the entire group repeats the same move over and over, and periods where each trainee shadow-boxes on their own to concentrate on the aspects of their own skills that they feel need improvement.

In my experience, the additional training techniques of Muai Thai are valuable because a martial art is both a mental and, unlike programming, a ''physical'' skill. Repetition helps transfer skills into the motor memory so that they become intuitive. Shadow boxing uses visualization and mental reinforcement to do the same for reactions.

There are no metaphors in Muai Thai but there certainly are in Ju-Jitsu. For example, the koshi guruma (hip wheel) throw spins your opponent (the wheel) around your hip (the axle) and onto the floor, or when grappling the kesa gatame (scarf hold) wraps your arm around your opponent's neck. I expect many of the metaphors are the same because Aikido was developed from Ju-Jitsu when it was illegal in Japan.