Well, I just started getting into guitar, so I was playing for a while last night, and then when I was trying to fall asleep a little later, my thumb on my fretting hand was killing me! It feels like I'm pressing it too hard against the neck, but it is supposed to be hyperextended, right? And I don't know how else I can "ground" my fingers on the fretboard without applying some pressure from the back!

Is this just beginner's pain? Or am I doing something wrong? Now I'm scared that if I practice, I'll get some repetitive strain injury before I'm even mediocre! Please help! What am I screwing up?
Notorious S.I.G.
i'm not sure what you mean by hyperextended, but that's never a good thing to do with any joint. When playing barre chords, your thumb should be near the center of the back of the neck. This is when you will need the most pressure from your thumb and over time, you won't feel any pain anymore. It also helps to keep your thumb near the center cause this gives your fingers plenty of clearance of the other strings when you're playing scales and such. But there certain chords where it will simply be easier on your whole hand to let the thumb wrap around the neck, like a D chord, this may not be technically correct, i don't know, not an expert, but i know it sure makes it easier to play a D/F# chord when you get your thumb on that top E string. Just throwing out some ideas....
By hyperextended I just mean like how you sort of make your thumb when you're pushing in a tack, you know? Should I be touching the back of the neck more with the middle of my thumb or the tip? Thanks
Notorious S.I.G.
you should try to keep the pressure towards the middle of your thumb. if you push in with the tip it will hurt more and can cause problems
Ah okay I was probably shoving the tip of my thumb into the neck. Thanks a lot guys! ;p
Notorious S.I.G.