Thank you! At any of these speeds there’s really zero excess tension because that’s a prerequisite for being able to play at them. You have to be able to relax all of your muscles immediately and continuously from the first note.
The best analogy I can give is it it’s like a machine gun turret in a video game. You keep firing the gun but you have to keep cooling down with another button as you do it to prevent overheating. That’s what tension control is for me on the guitar. Visualization is important, too.
I don’t think my technique changes whether it’s 100 BPM eighth notes or 300. So to answer your question in a roundabout way I think I’d need to test a few metronome speeds to see what is the fastest 30s-1min stretch I can maintain. The motion is this pseudo-knocking motion which is likely the extension to which you’re referring, which is also part of that circular motion to reset the pick. I believe it’s ulnar wrist deviation to clear the string, then a combo of radial deviation and extension to go back to square one. I don’t think my bicep is engaged here. It’s been a while, I’ll have to do another video.
The interesting thing is I have zero movement outside the wrist, or so it seems. This is now how my entire technique looks in general; even for string tracking my elbow almost never moves, and the picking motion for downstrokes/upstrokes is identical to Paul Gilbert, Anton, etc.