Just as a warning for all of us: undue tension may be behind a lot of these aches and pains. You can, perhaps, deal with the pain with reduced playing time, ice, physical therapy, etc, but playing with tension will degrade the musicality of your playing--even when you're playing pain free.
Watch good guitarists play, particularly noticing the fluid and easy motion their hands make and the balanced posture they have. Then, play for yourself in front of a full-length mirror. If your hands don't have that fluid motion, you may have a tension problem. And, if they look stiff, like lobster claws, then you definitely have a problem.
Tension is one of those things that is very common among musicians and something that usually goes unnoticed. So, keep an eye on it, along with reducing any pains that you might have.
(US) (GER) The greatest good you can do for another is not just share your riches, but to reveal to him his own - Disraeli