Every night before I go to bed I do an exercise which I think protects me from RSIs. I used to get them but this exercise and improving my posture has made it happen less.
The exercise is this:
1. Get a pole of some kind (not with weights like in the picture).
2. Do this (I call it rolling my wrist) five times forward with each wrist.
3. Do it again backwards, five times for each wrist.
4. Repeat. Remember to keep your arms straight and try to keep the pole as stationary in the air as possible.
In total I roll each wrist twenty times forward and twenty times backward. I think it helps me, but I would not say it has made my wrists thicker.