Dude...go to your nearest rehab center or physical therapy office...a lot of them in strip malls...tell em you want to buy some OPTP exercise putty...tell em you want the blue or extra firm variety...It works like a charm....BUD
Actually there is an outstanding video devoted to injury-preventive piano playing that is very much worth viewing. It is Freeing the Caged Bird. You may be surprised when it argues for a different focus on control than you would expect, but study it. First rate stuff and VERY well demonstrated.
After attending one lecture with this teacher, my dexterity improved measurably and instantly.