I was wondering what the exact technique for metal rhythm guitar strumming was. More precisely I'm working on the tab of Blind Guardian - Born In a Mourning Hall, and the rhythm guitarist strums his open Low E (in this case it's actually a D#) string real fast, as if he was almost drumming with it. In the same song, and in many many other power metal songs fast single string strumming is pretty pervasive, so I really want to know what the correct way of playing it is.
I mean, I understand that it's all about playing it fast (duh..) but I'm more concerned about doing in "techically" right. For example, do I use my wrist only? Do I rest my palm on the bridge? Do I actually use my arm a little bit for that sort of motion?

It's probably palm-muted for that percussive sound, while using alternate picking to get it up to speed.
I find wrist only is much faster, and feels more comfortably. Palm muting, rest your hand on the bridge, have to mute the strings. Aside from that, I find its easier to strum/pick without resting my hand on the bridge.
When I pick fast I tend to just move my thumb and finger holding the pick, its less movement = more speed with less effort.
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