I sprained or strained by middle back muscle on the right side last month. The pain's mild, but like some tough old piece of gristle, it just won't give up and go away.
I've taken to alternately icing and heating it for ten minutes every hour, as consistently as I can manage. I've got an electric body massage pad that I use as well. Whenever I hit the gym, I take some time afterward to soak for a good ten minutes in the hot tub.
But in the meantime, I'm having to figure out which exercises are safe and which make the injured muscle angry with me, so I can't really lift to full capacity on anything except perhaps legs.
It wouldn't be so bad, except that the muscle no longer jangles in pain immediately. It likes to wait a good 3-5 hours and THEN let me know I was a bad wolf. So all I can really do is stick to lightest weight possible and use trial-and-error, slowly building on the weight, sets and reps as the muscle heals.
It's not all bad, though. Less intensity in the gym means less food I need afterward, so my bank account is breathing a sigh of relief for the time being.
Pray to the gods of healing for me, boys! And watch that form when you lift!