Hi! Beni here.
I just wanted to check whether this motion I stumbled upon last week is indeed a forearm + wrist blend.
When I did the motion tests, forearm was my second-fastest movement (230–235 bpm), second only to my elbow motion (245 bpm). But as a lefty playing righty, even a slightly supinated setup has always felt a bit alien to me, so I never really tried that hard to get it going.
Hey! I believe it does look like it. Maybe with more wrist and less forearm. I am also a lefty playing righty and have a similar form.
Awesome! Thanks for the insight!
Do you have any advice on developing USX?
I can already do 180+ BPM tremolo, maxing out at 200 BPM for a bar but getting easier and progressively faster every day. I’m just not really sure where to go from here.
I would start working on lines that test your USX motions such as even numbers of notes per string. Working on 2nps lines, like pentatonics or 2 ups 7th arpeggios, are really helpful. Also making sure you can do the 2 string economy motion, both in isolation and within alternate picking lines.
Since you’re a Malmsteen fan (judging by your user name 
) I highly recommend @Chris_Brooks 's Viking Shred course. Its one of the most comprehensive studies in Yngwie’s playing, and thus USX vocabulary, that I’ve ever seen.