I injured my right thumb. I learned to touch type in HS, so been using that thumb to hit the space bar for 65 years.
Yesterday started trying to use the left thumb. You might think that would be easy enough, but you’d be wrong!
I go along slowly for a while, then OUCH, used the damn right one again. I now begin to question my intelligence, that can’t seem to overcome habit.
Oh well…
I’m like you; I’m going to need surgery on my right thumb eventually, which will render it useless for at least three months. I use a computer to earn my living, so being able to type very, very quickly is vital to my earning power. So I periodically try to use my left thumb, after having used my right for over 40 years. It’s hard, isn’t it? I’ve resorted to using a rubber band to tie my thumb against my right hand so I can’t use it, but even then I forget and try, or else I just get so tangled up in when I should hit the space bar with my left thumb that I can’t type any more.
Retraining the brain after so many years is not an easy task. I wish you luck, and I need it myself!
Habit is Goliath to intelligence’s David.
which thumb you use on the space bar is a near perfect handiness test. even people who have been switched when writing, will use dominate side on the space bar.
that makes it very difficult to switch sides. it will take dedication to swap. pain will work eventually!
?? They taught you to use one and only one of your thumbs for the space bar when they taught you touch-typing?
I’m pretty much ambithumbrious myself.
I thought I used the left thumb, but it is the right. Humph.
I write left-handed, but have always used my right thumb when typing. I guess it’s because that’s how I was taught back in school. But in any case, it wasn’t difficult for me to learn, and I never felt inclined to use my left thumb instead.
I am 100% left-handed but have always used my right thumb only. That’s how I was taught, and after all these years it doesn’t really matter if it’s contrary to handedness theory, it’s definitely channeled so deep in my brain that switching is not easy.
I was very proud of myself, though – after my first post in this thread, I spent about half an hour using only my left thumb. I was only typing at about half speed, at best, but I was able to hang in there very well and only tried to use my right thumb once or twice.
I suspect it’s going to take months of practice before I’ll be ready to have that surgery. 
I was absent during the typing class where we were taught which finger was to strike the “b” key. I’m still very inconsistent with which one is right.
I’m almost hamstrung trying to use my left thumb for the spacebar. What’s that about old dogs and new tricks?
Now get offa my lawn…
Odd. When I took typing, they taught us to use the thumb on the hand hand that hadn’t just been striking a key. I think I generally go to the right thumb, these days, but I’m fairly certain I learned to use both. checks typing Yeah, I use both, but I favour the right a lot.
Huh?
I’m right handed and the left side of my space bar was polished long ago.
Never had a typing class.
Good work, Mama Tiger. Since my OP, been working at it. Like you, I now find I can do it, with only an occasional lapse, but definitely at half speed or less. I’m determined to beat the damn thing, and obstinately, will continue with the left thumb.
The wear pattern on my space key shows that I certainly use the right thumb far more often that I might ues my left thumb. In fact as I typed this post, I find that I haven’t used the left thumb onece.
Odd, as I don’t remember being taught this, but as I look at my hand placement, it’s clear that my left thumb isn’t in a position to even hit the key. There is a nice worn spot just below the space bar where my left thumb must hit fairly often, but it’s well below the space bar.
I hope I never have to retrain my hand, just as I hope I never am forced to change to a DVORAK keyboard. I can do my QWERTY keyboard without thought.