Hey, those clips look great! That’s a very nice looking elbow motion and the escape looks to be the 10- or 15-degree kind of escape these motions usually produce. Why is the sound missing, is that how your phone records slow motion? What does it sound like in normal video? Because if the attack is smooth, that’s great.
Not only that, but I’m pretty sure you are doing a combination of wrist and elbow, not just elbow itself. In slow motion it looks to me like the wrist joint (i.e. the hand) is moving in addition to the elbow itself. That means you are basically doing the DSX wrist motion that we teach in the Primer, but like Brendon, you are doing it as part of a connection to the elbow joint.
Try taking that motion and slowing it down a very small amount and see what it looks like. Then go a tiny bit slower. Does it become more wrist or stay elbow?
Either way, I like what this motion looks like. Maybe it’s something you can experiment with to see if you can find a way of doing it that feels less tense to you. When a motion is new, we tend to “overdo” it by using muscles that aren’t totally necessary. Over time, very often without consciously thinking about it, these motions become more relaxed because you learn by feel that only certain muscles are necessary, or only a certain amount of effort is necessary.
As you experiment with this, don’t do anything that’s painful or causes fatigue. And don’t play for long periods of time. Just be casual and experimental with this motion, using it at different speeds and with different kinds of phrases, whenever you have time. See if you can find a way that works more smoothly.
You’re using the pronated form here, where the pinky is slightly lifted from the bridge. This is the form where elbow DSX links with wrist DSX. But if you want to continue to experiment with the wrist USX motion, that’s fine too. Just flatten out the arm so the pinky heel also touches the bridge. Keep everything else the same - same motion feel, same speed. These two forms are very similar, almost opposite sides of the same coin. If they feel too different, the form might be wrong.
However, the pronated form seems to be working for you. When it comes to pure alternate picking you can do a lot of what you need to from this arm position without switching to supinated. This is what @tommo does, for example. Tommo’s form looks similar to yours, and he also does the elbow-wrist combination movement. We have a great clip for Instagram which we’ll put up soon where he plays fours against a three-note-per-string fingering using this combination motion. The upstroke escape is achieved by “dart thrower” wrist motion, helping out the elbow.