Since there's a lot of typists here, this book of Dr. Pascarelli about RSI - Repetitive Strain Injury is quite helpful and food for thought.
The faster you type, the higher risk you will be suffer from RSI.
(quoted from this book)
Download RSI - The Complete Guide.
No other piece of computer equipment has had more design research and gone through more style changes than the computer keyboard. Research has focused on key placement, size, adjustability, touch, key pressure, and technical design. Still, the keyboard that suits everyone has not yet appeared.
What kind of keyboard should you buy? Choosing a keyboard can be confusing, as there are so many available at a wide range of prices. When you buy a new computer, it comes with a standard keyboard, and if it is not comfortable or is causing you pain, you will want to get one that suits your needs better. As mentioned in chapter 2, the elbow carrying angle, which varies from person to person, will affect the way you place your handsas you hit the keys. The greater your carrying angle, the greater the likelihood that you will need a split keyboard. In any case, I believe a split keyboard is generally a good choice for everyone.
Virtually all keyboards now on the market have the cheaper-to-manufacture membrane cushioning for keys, rather than the more desirable individual spring loading for each key, which is best for good touch feedback. Basically, three types of keyboards are available: traditional, ﬁxed split, and adjustable split.
The traditional keyboard is supplied with most home computers and is usually what you will ﬁnd at your workstation. Some are available with a number pad on the right side, while others are alphanumeric or have a separate number keyboard.
The ﬁxed split keyboard has a split at an angle of about twenty-four degrees and a slight downward taper on each end, which takes the hand slightly out of the palms-down position. The number pad, on the right side, is ﬂat. The palm apron along the front edge of these keyboards is not ergonomically sound—don’t rely on it to support your palms. Small legs that prop up the far end of the keyboard should not be used, since they encourage extending your wrist, as when pushing a door open, a harmful posture. If you purchase this type of keyboard, make sure you have the right size of pullout tray.
There are several varieties of adjustable keyboards. These keyboards can be placed in the traditional position, angled, and even tented so the hands are no longer in the palms-down position but are held somewhere between palms up and palms down.
According to Dr. Alan Hedge, an ergonomics researcher at Cornell University, keying with the palms in a vertical position, as in playing an accordion, allows the forearm tendons, which move the ﬁngers, to work more easily. Since you cannot see the keys in this position, it is difﬁcult or impossible for a nontouch typist to use one, so vertical mirrors are installed on each side.
Many of the people who feel uncomfortable in the palms-down position at the keyboard have tight forearm pronator and supinator muscles, which need to be stretched. By placing the adjustable keyboard at a tented angle of approximately thirty degrees they might feel more comfortable during their retraining. See chapter 6 for details on exercises.