Martin from the Internet writes:
“I am 72 with a very weak low back. Are there any forms or exercises in Tai Chi to avoid?”
I would be careful not to do anything which would hurt your back, including Tai Chi.
That said, I would suggest that you avoid getting too low in your stances because, while they strengthen the legs if you do them correctly, and take pressure off the back, if you do not do them correctly they can also tend to tense the back. In healthy backs this is not a problem. In problem backs this could cause a spasm.
Also, be wary of the kicks. This is because you think that you do them with your legs, but actually, you may be lifting your legs with your lower back muscles.
Beware of the spins in Tai Chi. When you spin, you need to stop. If your balance is not just right, you use your back muscles to catch yourself and nail the spin, and that could hurt a very weak back.
I would also not do the snake creeps up (down) postures (a.k.a squatting single whip). If you are flexible this would not be a problem. However. if your back is tight, it can pull your back out.
That said, for a very weak back as you describe, I would suggest physical therapy to strengthen the back and then begin, or resume practicing Tai Chi. Consult your doctor about what you can and cannot do. If he gives you the green light, first do physical therapy, and then on to the Tai Chi.
In Tai Chi,