The biggest difference maker for me in terms of alleviating repetitive strain was switching from a mouse to a trackball. Something about not having to tense my arm up and move the mouse all over anymore...
I never had pain on my right hand which I use for mousing. My mild pain is the left hand - two hypotheses: this hand is weaker, and too much alt-tabbing.
I suspect lifting weights already improves this generally, as I have periods of much less pain which coincide with being more active.
I had wonky, comes-and-goes knee pain which cleared up when I hit the gym and started doing squats.
If you have a body pain problem, "see if lifting doesn't help" is good advice, but you have to be careful, i.e., don't be a dumb gymbro and load on more weight than you know you can hamdle with good form.
Trackballs are amazing. The best one I ever used hasn't been made in years, and if you can find a Cordless Optical Trackman new in box it commands a pretty decent price.
I suspect lifting weights already improves this generally, as I have periods of much less pain which coincide with being more active.