What is the correct posture for the left hand thumb? I am double-jointed in the thumb, it bends backward to make a perfect "L" shape. No pain when I do that but I can feel it stretch the tendons at the base of my palm. Being self-taught, I always used that backbent thumb as an anchor so my middle thumb bone was perpendicular to the neck. As such I could put plenty of pressure on it and still be very loose in the fingers for very fast fretwork. Seemed like an unfair but welcome advantage. Worked fine until I got old, now I want to get away from that to relieve pressure on those tendons. Should the left thumb be used as an anchor or pivot at all? Is it best to wrap it over the top of the neck? This seems to limit agility on the lighter strings where I need it most. Is it best to lay the thumb down parallel to the neck always pointing at the headstock? This seems to mean using more bicep to change hand positions which is slower than just pivoting on the thumb. My best guess at this point is that it should be pointing toward the headstock, tip barely touching the neck just as a guide, and the whole thumb kept straight. I've made a brace with duct tape and popsicle sticks to train it to stay straight. Anyone with real expertise on this issue, I would greatly appreciate letting me know whether I'm on the right track or what you would recommend. Thanks!