I have written before about the issues I have with my right hand due to some nerve problems that cropped up a few years back. It is not painful at all, but it means I can struggle to hold a pick for long. So I have been trying some exercises to get some strength back.
First is the D'Addario hand exerciser that should help with grip strength. You can work each finger individually and it has variable springs. They have changed the design a bit since I got mine.
It seems there are various types of finger exercise bands out there. I think mine came from ebay. They work different muscles.
I bought my Powerball gyroscope long before I had this issue as a fun little exercise device, but had not used it much recently. I need to take it easy with my weak hand, but it works various muscles in the hand and arm.
I am generally fit otherwise from all the running I do. It is just a bit frustrating that this hand struggles, but the body can go wrong in many ways and it could be worse. At least I can still play guitar.