RSI is one of those things (ADHD, autism and dyslexia are other examples) that start as a label some scientist puts on a specific set of symptoms that cannot (currently) be linked to a specific condition [1], becomes popular and then get used for a zillion things with more or less the same symptoms (Wikipedia lists edema, tendinosis, tendinitis, carpal tunnel syndrome, cubital tunnel syndrome, De Quervain syndrome, t…
For anyone reading here, if you’re regularly feeling any level of pain while typing, take an immediate break to figure out what’s wrong. If you let it persist it can do you serious damage.
There are a number of ways you can relieve your symptoms. Scale back your typing and keep trying ideas until the pain goes away. If pain persists or if it is acute/severe, go see a doctor right away. A doctor can much better diagnose you than internet commentary.
(1) Make sure your wrists are in a straight and neutral position while typing. This is in my opinion (having talked to many people with RSI and watched their typing style) the #1 contributor. Other arm/hand/finger position problems can also contribute, but keeping the wrists relatively straight and relaxed is the first most important step to take. Try to pull your keyboard in close to your body and tilt it so that its top is parallel to your forearms (the right tilt to use will depend on the height of your desk and chair and the shape of your body) and stop resting palms, wrists, or arms on a palmrest whenever actively typing (leave your hands “floating” above the keyboard, with just fingertips resting lightly on the home row). If the keyboard’s flip-out feet won’t let you get to the appropriate angle, try propping books or something under the near or far side, as needed.
(1a) More generally, pay attention to your body, and try to notice any muscles/tendons which are statically loaded while you type. Ideally you should be able to be in a position where your muscles are mostly relaxed, and only being used to actually press the keys.
(2) Try to avoid typing for too many hours a day, or for too long at a stretch. (Take a break to stand up and walk around a bit once at least every 45m or so. Go to the bathroom, make yourself a coffee, walk around the block, whatever.)
(3) Examine your seat and desk. Try to make sure your back is as straight as possible and your arms are in a relaxed position. Consider switching seat positions at least a few times throughout the day. Most office workers have their desks set too high compared to their torsos (this is because standard office furniture was designed for medium-tall European males to write with a pen on paper, not for people of arbitrary size/shape to type on a keyboard). You can either lower your desk or raise your chair to compensate. Consider alternative types of chairs (e.g. saddle seats) or an adjustable-height (e.g. sit–stand) desk.
(4) Try to eat a balanced diet, get enough sleep, exercise a few times per week, and avoid too much stress in your life. Obviously you should try to do these things anyway, but they can absolutely contribute to typing pain.
(5) If those changes don’t help, consider changing your physical keyboard/mouse hardware. A split keyboard with sufficiently “tented” sides eliminates the need to pronate your wrists, as is required for one-piece keyboards. This allows the elbows to be brought closer to the body, the shoulders to be relaxed, and generally reduces static load on several tendons/muscles. Consider an “ergonomic” mouse, a trackball, a roller mouse, or similar, or try to eliminate extraneous mousing. Consider changing the keyboard layout to avoid awkward stretched chords (“emacs pinky”), or even get a Maltron or similar row-oriented keyboard. Get a keyboard with switches that actuate halfway through the stroke (not a standard rubber dome keyboard), and try not to smash the keys hard into the bottom of the stroke while typing – aim for a light, fluid “dancing” style of typing.