There was a discussion about exactly this some months ago on Levnet. Coming from a mime training background, I call it what the Decrouvian mimes call it: a "biceps twitch." Mr. Pringle agreed that it must be the technique used by Ms. Rockmore on those very fast runs of notes in her performance of the Fuleihan. Thomas Grillo has mentioned, here in Theremin World, that the same technique would enable him to play, as a matter of fact, Flight of the Bumblebee. (Is that where you got the idea?)
I've been working very hard on exactly this method for about a year. First you have to learn to tense the muscles while moving the arm or wrist or fingers in a controlled way--and then you have to wean yourself from the tension to produce the same effect in a relaxed way. It's really a matter of establishing neural pathways, and that process is facilitated at first--so it seems to me--by the production of the fast series of notes through the muscle tension.
I've been very happy with the results of this work. If you heard my Lillibulero on Spellbound, that's the technique I used for the grace notes. I'm still ironing out some issues in Debussy's 1st Piano Arabesque. Carolina Eyck performed it with some orchestra--and you can hear her at it in a clip on her website--but at a snail's pace. With the biceps twitch, one can perform it at a more interesting tempo. I posted a version of this on Youtube some time ago, but my pitch accuracy left a lot to be desired, so I pulled it to work on some more.
As of now, I have more difficulty with slow notes than with fast ones. I have to practice long tones and slow passages with diligence--just as my flute teacher used to make me do.
