First, to establish some context for this question: I’m wondering about single-string tremolo playing, which is generally, and rationally, regarded as the ideal environment for maximum alternate-picked note speed. Second: among the different muscle groups responsible for picking motions, as documented here on CTC, it seems that pure elbow motion is the fastest single muscular axis for generating that tremolo speed. That is, maximum attainable speed seems to consist of a cycling pattern of elbow downstroke, elbow upstroke, repeat.
Here’s the premise that I can’t get out of my head: would it be possible to surpass that single-joint elbow speed with a combination of muscle group movements, in sequence? That is to say, to blend two motions together: for example, elbow downstroke, elbow upstroke, then wrist downstroke, wrist upstroke. Coordination issues aside, it seems plausible; anecdotally, it seems that the maximum speed between just two notes on the same string–downstroke upstroke–is about the same regardless of which picking motion you use.