I put in a lengthy legato practice session last night, but nothing out of the ordinary from my general practice routine. This morning I woke up with a lot of stiffness and a little soreness in the "thumb pad" area of my fretting hand. It's stiff/sore on kind of the heel of my hand, near where the thumb muscle connects to the rest of the hand. This has never happened before. Should i be concerned? How long should i avoid playing for?
Sounds like you've been using poor technique, and way too much force. You don't need to apply a lot of pressure to the strings. I think you've probably been using your thumb to apply the pressure instead of your fingers. It's a very fine line between them, but it can make a lot of difference. Plus you might have your thumb in a bad position. Take a few days off, go see a doctor, and when you've healed, try it again. If it still hurts, take some more time. Just make sure you're playing properly, or you may end up hurting yourself again.
Quote by Geldin
Junior's usually at least a little terse, but he knows his stuff. I've always read his posts in a grouchy grandfather voice, a grouchy grandfather with a huge stiffy for alternate picking.
Besides that, he's right this time. As usual.
I suppose when practicing legato stuff, you're fingers get tired and you probably compensated by increasing the pressure with your thumb. Probably gave those muscles a bit more of a workout than they're used to and they're a tad sore this morning. Maybe just take a day off from practicing if you feel it's necessary and then see how it feels tomorrow.