Ask most people about RSI or carpal tunnel syndrome, and they'll tell you it's caused by spending too much time at your computer keyboard.

But before we blame your keyboard, let's ask the question - where does it hurt?

Is it one hand or both hands?

Which hand is it?

For most people, it's only one hand. And that hand is - their mousing hand.

The truth is that in most cases it's your computer mouse, not the keyboard, that causes RSI.

(If your problem is not your mousing hand, jump to the next paragraph where I'll cover the rarer problem of keyboard-related RSI).

When mice were first invented, most commands were still keyboard shortcuts. You used your mouse rarely - grab, move and click. There was no temptation to rest your hand on the mouse between moves, because you needed it to type! So it's no wonder the mouse is not designed to be ergonomic for continual use.

Take a look at the picture on the right. Can you see the angle between the wrist and the hand? That's the root cause of the whole problem. Holding your hand at that angle takes work, so doing it for a long time causes fatigue. Muscles can go into spasm, and stay that way. The angle can also pinch nerves, which causes inflammation and pain.

To avoid the problem, you need to set yourself up so that the back of your hand forms a straight line with your arm. A wrist rest will help a bit, but it's much better if you can arrange your workstation so your mouse is lower and closer, and your arm falls naturally into that position.

If you have pain in your non-mousing hand - or in both hands - then your problem is more likely related to your keyboard.

Many people try to solve this by buying "ergonomic" keyboards. That's not just unnecessary, it won't solve anything if you don't also change the position of your keyboard and your posture.

The keyboard has been around for over 100 years. Generations of typists have used the same design of keyboard in typing pools all over the world, and only a miniscule percentage of them ever developed RSI.

RSI suddenly became an issue among secretaries with the introduction of word processors, and flowed into the general working population as computers became an essential piece of equipment for almost everyone.

Once again, it's the angle between hand and wrist that is the culprit.

With manual typewriters, there was nowhere to rest your hands on the machine itself. Electric and electronic typewriters had super-sensitive keys, so you would never rest your hands on the machine for fear of accidentally typing something - the process of erasing a mistake was too laborious! If a typist needed to stop and think, she would drop her hands into her lap or rest them on the desk, away from the keyboard.

Computer users frequently rest with their hands on the edge of - or worse, on the desk in front of - the keyboard, creating that dangerous angle. Some even manage to type in this position, putting even more stress on their wrists.

In the old days, typists were trained on proper posture at the keyboard. It simply wasn't possible to attain the speed and accuracy they needed for their jobs, unless they had their arms and hands in the right position. Like a concert pianist, they had to get their fingers at an angle where they had optimum control.

Computer users don't need that accuracy because mistakes are so easy to correct. They're also likely to multi-task, so it's much more convenient to push their PC to the back of the desk and stretch to use it, than to keep it front and centre. However, if you want to recover from RSI - or avoid getting it - there is no other way.

Take a look at the desk on the right. You can see the keyboard and screen are pushed well back. The user has bought a wrist rest, but to get his wrists onto the rest, he still has to reach forward - so the rest will do little or nothing to ease the tension that's causing his RSI.

If you're going to have any chance at all of recovering from RSI, your shoulders and upper arms must be relaxed while you type. The only way that can happen is if your arms are hanging loosely from your shoulders.

Try it now. Stand up and let your arms hang by your sides. Now leave your shoulders and upper arms exactly where they are, and raise your hands in front of you at a 90 degree angle. You should feel your elbows lightly touching your body near the waist. That's the correct position for keyboarding. As soon as your elbows lose contact with your body while you're typing, you're putting yourself at risk of RSI.

To achieve that position at your desk, you're going to have to remember how to sit up like your Mommy taught you, and have your keyboard right on the front edge of your desk.

I know, I know - sitting up straight doesn't look nearly as cool as an artistic slouch. But trust me, once you've experienced the pain of RSI, you'll be prepared to look uncool to avoid it happening again!

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All text copyright Marisa Wright. Desk photo courtesy RossJamesParker on Flickr