how do you alternate pick?
yeah i know its downstroke and upstroke alternatively, and its the basic knowledge u need for shredding, but one important question i'd like to ask here..
when u alternate pick, do you move your wrist, or move ur elbow?

and for sweep-picking, are u supposed to move ur elbow too?

which one is more confortable and natural to you? i dont think theres a right or wrong. I move my tumb and index when doing alternate picking. Im learning sweeps now and doing it with my wrist. I find pciking and sweeping with elbows weird.

i move my wrist....

alternate picking = all

you have to practice from fingers , wrist and arm ...

each of it has different sounding , dynamics , maximum speed..

be in control

Gapnap is right! (He always is... )

Thumb + Index = Maximum Speed, Least Dynamics
Wrist = Moderate Speed, Moderate Dynamics
Elbow = Least Speed, Maximum Dynamics

Of course, the above is just 'in general'. If you work on using a certain part of your arm/hand/fist/weapon hard enough, you can maximize both speed and dynamics just by using either part!

Example, I think Yngwie Malmsteen uses practically only his thumb + index, yet his playing is lightning fast with dynamics as well. Paul Gilbert is a wrist user, very fast with good dynamics as well.

As for John Petrucci, I'm not too sure, perhaps the hardcore John Petrucci fans can help me out on this one? He seems to be using his elbow a lot, yet he achieves insane speed with alternate picking.

And there are guitar players who combine all as well.

for me, use wrist for soloing, and mostly arm for riffing, that is until my arm get tired lah, then wrist.

malmsteen gets dynamics from his fretboard
you can break strings so easy on that if you're not careful

may b using all parts can divide the work to each part,
so u hav longer stamina

for alt picking i use mostly my wrist, sometimes i use thumb+index(comes naturally). for sweep picking i use my elbow.

Whatever is most comfortable will probably work best...

finger, wrist and arm will all move to a certain degree... like gaps says, be in control!

grab a copy of Troy Stetina's Speed Mechanics, lotsa good stuff there for learning how to practice speed.

Tips noted!

I use my wrists for everything but power chording