As a classically trained guitarist with about 40 years of experience I can say with confidence that I’ll never have a bad case of carpal tunnel syndrome. It’s all a question of understanding how the body functions best.
When the elbow bends in, the wrist should not bend out; rather, both should form a graceful arc. I think it’s best to have your headstock at eye level or close to it, as well. Guitar should be angled up so the right hand can reach low and the left can reach high (for left-handed guitarists). As a rule of thumb, the closer the left hand is to the face, the less the wrist and elbow will have to contort to get the fingers where they want to be.
As for computerin’, when sitting at the keyboard, the wrists should ideally be closer to the ground than the elbows, and the keyboard should be low enough that the wrists can bend down slightly while having an angle something at least slightly greater than 90º at the elbow.
Try this: sit without the computer or guitar in front of you, and close your eyes. Put your hands where your body says they should be. Feel that it’s comfortable and natural, with posture erect, back of the head as if pressed up toward the sky. Then open your eyes and make it a goal to make the guitar or keyboard land where your hands want it to be, not making the arms contort to where the guitar wants them.
I hope these tips are helpful and as always I welcome comments.