This is a cool topic and one we discussed recently in the live broadcast. Pure forearm rotation, like EVH’s tremolo technique, even when done with small movements, and without the big gypsy-style wrist flex, really doesn’t look like this. The wrist and arm freeze, and the whole apparatus from the elbow on down rotates as a unit. It’s a cool movement and it’s certainly fast, but it’s not really representative of what most people do when they use forearm rotation for general purpose picking. So I’m going to suggest that we we’re seeing here really isn’t pure forearm, and thinking of it that way is more likely to confuse those of us (myself included!) who are still wrapping their heads around doing all these different picking motions.
One thing you can do, when you’re looking at picking movements and trying to figure out how they are generated, is to look at the movement of the pick itself, and ask what joints you have available in your hand and arm that could possibly generate that movement. This is roughly analogous to what we did in the lab test with @milehighshred, just without the stick-on infrared markers to measure the motion paths.
In this case, the pick appears to move mostly parallel to the pickups, i.e. perpendicular to the strings. Simply put, forearm rotation alone cannot create that motion path, since it operates perpendicular to the direction the forearm is pointing. In fact, there is no single arm or wrist motion that can generate a pickup-parallel / strings-perpendicular picking path.
So I’m going to suggest that this is, as you’ve pointed out, a blended movement. Yes, there’s a small forearm component to this. But there is also some other component, most likely either wrist (deviation, FE, or both), or thumb joint (CMC?) movement, that is chipping in, because those movements move in the correct plane to create the movement we’re seeing when blending with the forearm. In fact, during the 2nps descending part of this phrase, the forearm component appears to shut off entirely so I don’t even think it’s accurate to call that forearm at all at that point. Again, my vote is CMC or FE/deviation, or both.
Ironically, this type of arm / wrist/ finger blend probably is more similar overall to the classic Yngwie method, as he has never really looked like a pure forearm guy. And yes I am aware that there is a Volcano chapter that makes a rather detailed case for Yngwie’s forearm movement, and I have wanted to kill that chapter for a long time. In fact, I asked Guitar World to un-publish my corresponding article on that topic last year, which they were bummed to do since apparently it got lots of views. We’ll pull that Volcano Chapter at some point and replace it with something better.
Anyhoo, why does this matter?
It matters because it can be super confusing to players who are still trying to get comfortable with one or more picking movements, when we call different things the same thing, especially when doing them can look and feel pretty different depending on the blends involved. We’ve seen technique critique submissions from players doing fixed-wrist EVH-style forearm rotation, and we’ve seen submissions from guys like @Hanky_Pooh whose approach is perhaps more similar to what we’re seeing here, and involves wrist and finger components with relatively small, almost imperceptible forearm motion.
So… I don’t think you need to micromanage the exact blend of picking movements you’re making unless you want to. But it definitely offers a lot of clarity to know what those blends are, what they feel like, and why they may not look like the clips others are posting up for critique.