There are many ways that an occupation can harm a body. We are all familiar with tennis elbow and housemaid's knee. However, in today's modern age of sitting at a computer doing nothing more strenuous than moving a mouse and pressing keys, surely all we need worry about is morbid obesity?
This is not so!
Different computer games come with different dangers. For example, one of my favourite games, Patrician III, is real-time. It has no Europa Universalis-like facility to pause automatically on events: if you want to pause it, you have to hit the pause key. You want to do this a lot. Thus, after playing it for three hours every night for a week, you find you develop shooting pains running up the bones of the middle finger of your right hand.
Another game I play a lot is Football Manager. The interface here is characterised by having buttons you must click on successively in different corners of the screen, so you end up using the heel of your mouse hand as a pivot as you cover vast distances between selecting something and OKing it. This means that after a few days of heavy playing, you end up with a callous the size of a malteser next to your wrist.
Particularly bad in this regard are games that use WASD controls. I don't like these at the best of times, seeing as how they involve use of the left hand. Keeping your arm static for several hours and just depressing the fingers is a great way to make your entire hand go numb. It's not just the body that suffers, either — here's a photograph of what my desk looks like after an evening of playing World of Warcraft:
Those are scratches on the wood south of the shift key there. I suppose if I didn't have a metal watchstrap it wouldn't be so bad, but then all that friction would be against my skin instead. I'd be risking spontaneous human combustion.
Some games have interfaces that don't seem to have any overt physical side effects. I can play Baldur's Gate for hours at a time and a medical examination of my extremities afterwards wouldn't show up anything abnormal (well, except for my shoulder, but that's abnormal anyway at the moment). Things don't have to be the way they are.
That said, when I was writing my book I had to invest in a wrist pad for my left hand because the QWERTY layout was killing it. I suspect that some of these interfaces are going to be with us for rather a long time...