Continuing to experience fretting thumb pain. I have tried the exercises of not using the thumb so i am not squeezing…but i realized i am not squeezing. And i am holding it parallel to the neck, not perpendicular.
The pain occurs due to extension…i.e. making the hitch hiking gesture, not pressing down or squeezing. I feel like i have to do the hitch hiker thing to get my fingers across the fretboard. I can repruduce the pain even without my thumb on the neck.
Ideas?
Sounds like your stiffening up.
Feel the zen, try to relax a bit when playing.
Try practicing without caring as much,
Or get a teeny bit high, play, remember that feeling and do that. 
You can try some thumb stretches to see if they help, my favourite is the one below.
Usual disclaimer: I’m not a doctor, etc.
I’ve said it a bunch of times so sorry to repeat it. But you have to be very honest with yourself - is it sore or is it pain? If it’s sore it will improve with time as you get stronger muscles and tendons. If it actually is pain, as in oh shiznit something is wrong here, do not play through it. It needs time to completely heal, and you should probably see an ortho guy to confirm 
Sore like dull …not sharp
I think the issue is me playing too tense.
If only there were some substance that helps with that
Oh there is, it’s time.
I… uh… I don’t think that’s the substance he was thinking of. 
There are also other … substances
Time for what? A safety meeting?
It happens to me from time to time when there’s very little friction at the back of the neck. It means I have to put more pressure on the thumb in order to get the right fretting pressure.
It’s a catch 22 for me better grip I use less finger pressure but friction kills speed and also promote blister, not every bass will have this problems. That’s why I sanded down my favorite Squier with 800 grit satin smooth but not slick.
Yeah I really dislike glossy necks for that. Satin all the way.
I told the doctor “it hurts when I do this” and he said “well then don’t do that” 
Glossy necks are easily remedied in under 5 minutes with the magic of 3M.
Takes more time to tape off the sides and ends than it does to ‘fix’ the problem.
Two of my Japan Aerodyne have satin necks and they are just about the BEST satin finishes I have felt. So Fender knows how to do it. Why they don’t do it more is mind boggling.
