I spent about two years playing Unreal Tournament competitively. At the peek of my "career" I was playing 16+ hours per day. I was not one of the naturally amazing players, and to me it seemed that I had to work twice as hard to be half as good. There were days that I had to ice down both of my wrists and my right elbow as well. Personally, I had way more trouble out of my "mouse elbow" than I did out of either of my wrists. I played with a super low sensitivity... If I recall correctly, a 180 degree turn took like an 18" movement of the mouse. (Mouse acceleration was off, so moving faster didn't decrease the travel distance)
From my experiences, here are a few tips:
Pressing down hard on the keys isn't just bad for your body, it's bad for your game as well. You need to be fluid and use minimal motion. I used a
Saitek Eclipse Version 1 keyboard. To this day, I have never seen a keyboard that even compared to the feel and motion of the keys. There are others with much better features, but the feel just isn't the same. It is unfortunate that these are no longer manufactured. As long as the keyboard is comfortable, it should be fine. The most comfortable position I found for my left arm, was to have my left elbow resting on the arm of my chair and my left wrist on the palm rest of the keyboard. This required no tension to maintain arm position. You should also choose your keymapping carefully to avoid having to pick up the left hand.
For my right hand, I rested my elbow on the arm of the chair lightly, but with my low sensitivity, it was necessary to pick it up often to sweep the mouse. The trick to aiming is to use the arm and not the wrist, so it's basically impossible to avoid stress on this arm and wrist with so much motion.
My arm issues were compounded with being a music major (percussion) at the time and playing constantly. I didn't get into cubing until around the time that I retired from competitive gaming (and dropped out of college) so that didn't factor into my problems. I currently spend a lot of time on my computer and even more time cubing. I find that I still have wrist issues, but nothing like I used to.
Other than limiting your time with each activity, using the most ergonomic setup possible, and taking breaks, there really isn't much you can do. You can try icing your arms... it can be beneficial. Don't wait until there is pain, it is too late then. Ice them for a few minutes after finishing a long session of cubing or gaming. It can keep down the inflammation somewhat. If the pain gets too bad, ibuprofen based pain relievers are the best to use. (advil, motrin, etc) These aren't daily drugs and shouldn't be used to keep down the pain so you can keep cubing/gaming though, as they can cause stomach, kidney, liver damage over time if used in excessive quantities.
On a side note: What games do you play? I've been looking to get back into gaming somewhat, but I really only like PC FPS games, and there aren't many that I like. I'm really not into the COD type games.
Edit:
In response to the comments about muscle issues... with gaming/cubing, the chances that this is muscle related are extremely slim. Check out the symptoms of
carpel tunnel syndrome, this was the suspected culprit with both of my wrists.
