Most knitters I know who've knit for very long or who've reached a certain age start to worry about their hands. Obsessions have their physical price. For knitters, the biggy is hand problems.
I'm especially paranoid of hand pain. Before I took up knitting for the second time and as an all consuming reason for being, I had the same relationship with my garden. Several years of planting small bulbs one by one in a heavy clay soil (often with a flashlight in your mouth so you can get the last ones in without messing up the arrangement) will do things to your wrist you don't want to experience if you can avoid it. Let's just skip over the part where I tell you about brushing my teeth two-handed.
Ironically, two years of driving a stick shift 60 miles each way to nursing school and hefting a 1,000 page text book did their part, too.
I knit relatively slowly partly because I stop to reposition my hands often. I pick (AKA Continental) because I find it more comfortable.
I just learned to throw by pencil-hold at the Sally Melville workshops I took. (couldn't find a link on pencil hold - a topic for a future post, I guess.) This resulted in a plan to do a small project every now and then by this method. I have a baby hat going at the moment. The particular muscles used feel different -- good for not overworking and possibly also for still knitting when something hurts.
I also stretch my hands and 'exercise' them a couple times a day -- more often if they bother me. And I'll skip knitting or choose my project carefully if they are giving me grief.
My favorite hand exercises/stretches also show up the most often as recommended moves. Sally taught them in one of the workshops. The first just involves opening your hand and spreading your fingers as wide as you can, then clenching your fist. Repeat several times. Follow this with consecutively touching the thumb and each finger to your palm, working down and back up the digits a few times. To stretch, I start with my hands together in the classic pious/Namaste pose and push down gently. After my wrists tendons have stretch slightly, I turn my hands over so my finger tips point down while continuing to press them together.
I've done just these regularly for about two years, plus some effect from the Pilates lessons I take. I notice a big difference in the flexibility and comfort of my scarred muscles and tendons.
Some stretches I have to take care with. The one where you place your palm against a wall pointing backward and turn away from it often puts too much stress on the tendon running along my elbow.
The tendons of your arm are linked from your hands up to your shoulder. Problems with wrists will creep both up and down to affect the next joint. Bad wrist tendinitis will have the same effects as carpel tunnel syndrome as the swelling of the injured tendon presses on the same nerve.
(Note - I'm on the road back to Seattle until Tuesday night late, so I may not respond to comments and e-mails right away. Thanks in advance.)