I've been practicing for a couple of hours after work lately, and I spent about four hours on and off yesterday working on some new songs. Today, I woke up with a sore hand, and had to stop playing after just a few minutes. It's worst at the base of my thumb (on the palm side) and around my little finger; the latter I can probably chalk up to repeated practice of a fast riff where I'm reaching for one note with my pinky rather than shifting my hand. I've been stretching a little before practice with many of the same exercises I use in warming up for martial arts. Is there a particular set of stretches I should be doing? Or something to help my hand recover? I'm assuming that I should rest it and read about music theory instead tonight.