I do four versions. . .
1. very slow - very soft - breathing through nose. Feel as though your body is moving "on its own", no stress or tension. Emphasis is on accuracy of movements and posture without trying to "control" the kata. (difficult for me to explain but students seem to pick up the intent fairly fast although maintaining this "emphasis" throughout the kata takes awhile.)
2. Slow with dynamic tension using "uechi breathing". Emphasis on soft breathing (exhale through mouth - inhale through nose).
3. What I refer to as "middle" speed: Medium speed movements with thrusts that are "not" thrusts, but "touches" that are just below the speed of a full-out punch/thrust. Uechi breathing again. . . emphasis on soft breathing along with the powerful dynamic tension and smooth movements of the kata.
4. Full speed Sanchin: Emphasis on strong body, soft breathing and smooth techniques. Uechi breathing with "konling-breath-release" accompanying thrust focus. (grunt-like release many boxers use when punching pull force)
I use this formula for teaching Sanchin, starting with #1 for new students and adding 2,3 and 4 up to Shodan. Once a student reaches black belt they have a good understanding and method for breathing under stress. We still do #1. . . simply because it feels good and is a great way to begin class. Advanced students will do all kata then at #4 speed and at least once a month all kata using all four methods.
The test to see if students are breathing correctly ---- you should not be "out of breath" after completing any kata at any speed. (Which is also my test -besides accuracy of technique- for advancing a student to the next performance method)
Purpose for using these four methods: To get student into a natural breathing tempo - at all times - not just when they are punching - something that is very difficult to accomplish when students are taught only to breath when performing an "action" move. . . especially when they are tense and stressed. Using the four methods of movement provide an excellent template for "all" types of movement and non-movement.
Shana - hope this gives you that snapshot of my method of teaching Sanchin, active meditation through full out power moves.
I'll post a clip of my Sanseiryu #4 version to give you an idea what I'm talking about. Sanseiryu Clip: http://uechi-ryu.com/gem/gem-ssr-kata.wmv