If you watch a little further in that vid, around the 3 minute mark, he describes turning his hand “into cartilage and letting it go loose”. So that’s his way of saying he’s flinging his hand around, the forearm rotation doing just about all the work - the wrist would need to be flaccid.
I think he’s great at what he does, and admit I’m not super familiar with him, but I’m not seeing anything too fast here.
I’m sure there are people much faster than this, but it seems to be faster than Master of Puppets, and that seems fast enough to make most people happy. Now, that said, I’m not sure that CW could get a good metal sound, but that would be something fun for an interviewer to ask him, “can it chug?” (Yeah, Ola should interview him.)
Ah, but this doesn’t work out. If he’s alternating 16ths at 120bpm, this becomes alternating 8ths at 240bpm - Master of Puppets is only downstroke eighths at a bit over 210, which is much faster (in regards to movement frequency).
I’m sure that you’re right. So CW is 240 downstrokes/minute. Then it sounds, from what you explained, MoP is 420 downstrokes/minute! Quite a difference, I’d say! Thanks for pointing that out, I would have gone through life thinking the funk people were around the same speed as MoP.
Definitely looks more forearm-y but I think that’s more due to the large amount of supination. Look how flat the motion is! I don’t think the forearm alone is capable of creating such a flat motion, this looks like RDT wrist motion with a bit of forearm to me 
It’s incredibly curved. He’s like a mile away from the strings at the peak of the upstroke. lol
I agree that on the very end of the upstroke there is the most amount of forearm turning but the rest looks mainly wrist to me, I think it is more obvious when you slow it down.
Have you spent any time trying to develop I fast strumming motion? As soon as you want to hit more than one string I think it becomes obvious that you basically have to use the wrist 
Why do you think this is obvious? 
To me, it seems that the most natural motion is elbow, followed by forearm rotation and a ballistic hand (what funk looks like to my untrained eye), and finally, wrist, as the most unlikely. Of course one can use multiple joints, too. What am I missing?
Perhaps the question can be recast: Is strumming like sweeping, except faster?
I sure have, but my technique is not like Cory’s here.
This just isn’t true, as KGK points out. However, I’ll humor you a bit - there are times where I’d say that visible forearm rotation is a side effect of wrist motion occurring in certain positions. BUT, there are also times where visible wrist motion is a side effect of forearm rotation, and this is one of those times. Just let your wrist go pretty loose and use rotation to whip the hand around: this is what Cory says he’s doing, and that is very much what appears to be happening. Categorizing it as RDT is missing the forest for the trees, imo.
Have you tried elbow motion for fast strumming? As soon as you try it, it becomes clear that it’s too garage spiky (which slows you down) and makes the tone abrasive.
Okay I don’t think I’m gonna be changing any minds here! 
Lets agree to disagree? Unless @Troy wants to weigh in?
Well, I try to have a neutral slant, 45 degree edge, and use a forgiving pick (2.0mm Flow), so I don’t have that particular problem. But, I have lots of other problems!
I try to avoid terms like “natural” since it’s basically a value judgment. Instead I try to stick to more observational ways of describing things.
Are you asking if it’s possible to do elbow in a way where the attack sounds and feels really smooth? Yes totally. I can’t really do elbow, I never figured it out. I always get some type of wrist of forearm going. But my partner Reyenne has a great elbow technique that sounds butter smooth and goes super fast:
I was responding to the question downthread about elbow motion, but if I missed the point and what you are really asking about is dart thrower (non-reverse) motion for strumming, John Taylor’s lesson in Obsidian on chord tremolo is entirely DT. Lots of great shots in here of what this looks like:
There is nothing inherent to the wrist motion itself that makes the attack spiky, if you use John’s overall form and grip.
Awesome! Thank you!
For high speed strumming a la Guthrie Govan, Andy Wood, Joshco Stephan and Cory Wong are they using mostly RDT wrist motion with a bit of forearm or are they using primarily forearm rotation?
Guthrie’s technique is reverse dart wrist – the forearm doesn’t move significantly:
Awesome stuff, and the technique I use.
Specifically, how about Cory Wong here? Visually this very much appears to primarily be rotation to me, sort of flinging the hand about like a weight, which also aligns with what he says he’s doing, but there are some mixed thoughts in this thread.
It’s both. Hold your arm over the strings and rotate the forearm. It just spins, and doesn’t look like what Cory does. Do the same thing with the wrist flexed a little, but without actually moving the wrist. This also doesn’t look like what he is doing. The only thing that looks like what he does is to make a large reverse dart wrist motion while rotating the arm.
Edit: “Flinging” the hand is an apt way of describing it, and the only way to get that look – and feel – is by making a large wrist motion:
