I met several people whose have o had been RSI or SAD. They were two friend’s mother, they worked in a supermarket like cashier and they were a lot time in front of the computer and they did repetitive movement every day.
I think that I sit well almost always, but I know that occasionally I sit bad. I try that my chair is a correct position and my table is tidy, my screen is near for me (not to much), and my things are clasificated to find easily for me.
Sometimes I hurt my back, and this is very worrying. My wrists hardy ever hurt, and my knees are very good (when I was young , I played football and my knees are sore).
A Person with RSI or SAD must do specific exercises. There are several typical exercises for this. You can consult on Internet. (Touch your right shoulder with your left arm, Lower your head and look at your feet, Stretch your arms behind your back, Turn your head to the left, Hold your left elbow with your right hand…)