Re: Palm muting: wrist or elbows?
I use my wrist for precision palm muted tremolo picking. I always perform standing up and use the stubby picks (the insanely thick ones, generally meant for bass) with sharp tips. I find this gives me absolute control over the attack and pick flex isn't a factor. Even with the aforementioned techniques generally thought to be required to pick softer, I still manage to get the attack to be quite hard and loud. I haven't had any wrist issues so far.
Turn the pick very slightly sideways, just off parallel to the strings and practice this with a clean channel and even unplugged and get used to what your natural brute-mute really sounds like. This will also make you very, very precise as well as doing wonders for your tone. You'll actually start to really enjoy just how brutal you can sound starting literally at the pick to the string before distortions even come into it.
If there's crunchy muting in a slower more crushing song and speed isn't involved, then getting a bit of a wind-up by adding a bit of elbow (think of it as a flicking motion but with a full follow-through of the target strings) can add a lot of power and punch. Especially if you're like me and love clear, lower-output pickups running almost under-gained it's awesome for dynamics and lets your tone breathe.
It's like tee-ball. You want to go through the strings, not stop at them.