Well, there's a discussion on Socknitters about "how do I prevent pain and stiffness in my hands from knitting?"

and my first, bitter, thought on it was: become a college professor. Then you won't have enough time to knit so your hands get stiff and sore.

Seriously. If you're knitting six hours a day and your hands hurt? Doesn't take an exercise physiologist to figure out what you need to do.