This is a video of my forearm and elbow picking blend motion, or at least in this video the picking hand part. In the video I play a tremolo for a while and then, annoyingly off camera with the fretting hand, play a run notes which start on an upstroke to show it’s not only elbow motion on its own. You’ll see I bend my wrist to the right but I don’t think there is any wrist motion involved in the picking itself although I may be using the wrist to help to angle across the various strings.
I should add the view I think of Troy’s is this motion is rare and is not one which can be learnt. If you want to try it should be able to get it immediately or not at all. I feel it as a forearm rotation which I shove along with the elbow. In this clip after the tremolo I’m playing B minor pentatonic on strings three and four, so two notes on each string starting on an upstroke, and then on the fifth and sixth strings I’m playing three notes on each string starting on an upstroke (i.e. economy) which you can hear in the clip has no gap in the picking which you would get with an elbow motion.