Sometimes all of us feel stress with our knitting, such as, will I have enough yarn, or will the recipient like what I made for them. Other stresses come from learning a new technique, until you "get it" it can be very frustrating. The other most common stress from knitting is Repetitive Stress Injuries (RSI); it is the strain that comes from doing one motion over and over again without relief.
First, if you are already showing signs of RSI, which include any or all of the following pain - dull or sharp, tingling, numbness, pain, extreme stiffnes in your neck and shoulders, or swelling, STOP KNITTING NOW. Fight through the pain will just make it worse and the recovery will also take much longer. Use the RICE therapy, rest, ice, compression, and exercise (start the stretching exercises when the swelling goes away). Ibuprofen is a pain reliever that may help reduce the swelling and inflamation that comes with RSI.
The best way to deal with an RSI is to avoid one to begin with. The best way to avoid the RSI is:
To take a 5 to 10 minute break each 1/2 hour or hour of knitting and do some simple stretches to keep your joints flexible.
The American Society of Hand Therapists (ASHT) recommend these stretching exercises*:
Hold each stretch for 10 seconds and repeat each eight times.
Fold your hands together and turn your palms away from your body as you extend your arms forward. You should feel a gentle stretch all the way from your shoulders to your fingers.
Fold your hands together and turn your palms away from your body, but this time extend your arms over your head. You should feel the stretch in your upper torso and from your shoulders to your hands.
Extend an arm in front of you, making sure the elbow is completely straight. With your palm down, take the opposite hand and bend the hand on the outstretched arm down toward the floor. Then turn the palm up and stretch the hand up toward your body. This stretches the forearm and wrist muscles.
Open the hands and spread the fingers as far as possible.
The ASHT offers other tips:
Adopt a neutral grip that keeps the wrist as straight as possible, because bending the wrist can add to the strain.
Take a break! They're called repetitive motion injuries because they result from performing the same task over and over. Allow your hands to rest, or at least switch activities frequently.
Sit up straight. You are more likely to strain your elbows and wrists when you lean or slouch.
Many knitters have found that having different sizes of projects on different styles of needles helps also, since we hold straight needles different than circular needles or even double pointed needles. Different length needles will also help.
The Berroco site has some great illustrations that show some of these stretches and others at http://www.berroco.com/hg_workout.html
Remembering these simple things will keep you pain free while you knit.