Can you give me a little more context? What, specifically, are you trying to accomplish?

Excellent questions. Let's address them in order. 1) Thumb always on the curve of the neck? No. This is a starting point. As you play different musical passages in different positions you may find that you need to adjust the placement of the thumb. That's totally find; I do it all the time. 2) Same for electric and acoustic? Basically, yes. The principle is the same but adjustments may be necessary to compensate for the difference in neck thickness. 3) There could be many reasons for continued strain. If we address the "U Shape" you refer to, yes, my wrist is bent slightly and does bend from time to time. Generally, it's best to keep the wrist as straight as possible when playing, but there's probably about a 20 degree margin for flexibility. It depends on the material you're playing. Intricate scalar passages will generally require a straighter wrist and a smoother path for the tendons than strumming along on open chords. With that, you may feel more comfortable gently flexing your wrist. Try not to make that flexion too extreme though because it will likely cause problems down the line. It could also be that too much pressure is being applied to the string. This is a very common problem if the action on the guitar is too high. It could be that the thumb is not quite in the right place for the passage you're playing. Like in answer number-one, the exact postion of the thumb behind the neck may need to change to perform certain passages. For example, I put the thumb on top of the neck when I bend notes. If you've seen my other videos you'll know that I always advise against that. It's an exception I've yet to discuss in a video. It may be that the palm of your hand is too far forward or back. As you can see, there are a lot of variables to explore when finding the proper orientation of the fretting hand. I wish there was a fool-proof method of finding that orientation but since everyone is shaped just a little differently from everyone else, personal exploration and adaptation is necessary. I hope that was helpful. If you have any more questions feel free to hit me up. Good luck!

@@KevinOShaughnessyGuitar thank you so much! Awesome information! Also, when I am strumming my right hand hurts. Can I email you a video of my strumming to see if I’m doing it wrong?