I lifted yesterday. It was good. My arms didn't hurt in a bad way during the workout. My left shoulder felt weirdly sore today, but for some reason, running on the elliptical trainer (3.13 miles in 30 minutes on resistance level 7 = w00t) seemed to help that a lot. I also did some more rotator cuff exercises. It appears that the owies are going away.
I have to get back into regular piano practice. My right hand is quite adept at finger gymnastics, but my left is not. I think I'm just used to thinking of the left hand as filling out the chord and the right as the one that provides variety. I just did some experimentation with using my left hand to lay down a bass line of sorts for one of my in-progress songs and then incorporating some of that motion into the standard left-hand arrangement for said song, and I really liked the results. If I keep playing around like that and practicing sequences that my left hand tends to stumble over, I think I'll make some great progress, and it will help me bust out of my songwriting rut as well.