PRACTICE

You start out with a totally real axed arm and palm. As you thrust
forward with your rear foot, you twist your waist so that your shoulders
turn quickly thrusting out your right or left palm. Just before
impact you lightly close the fist and allow it to flick up at the end so
that the last two knuckles are forced upward into the object being
struck. You can gain this whipping action by pulling your fist backward
quicker than it was thrown out. See Photo No. 135 for starting
position and Photo No. 136 for end position. If you punch into a
heavy bag, a good way to test if you are doing this punch correctly is
to hit the bag into the general area that a face would be, (hard bony
area) and if you cause a large popping sound to happen upon impact
without much, if any movement of the bag then you are doing it correctly.
How To Use Tai Chi as a Fighting Art: Page
When punching to a face area and using the bag, there should not be
much movement of the bag. We are looking for shock value and not
pushing value. However, it is different when striking to the soft areas
of the body. Now we must look for a movement of the bag when
it is struck. We still do not allow too much follow through; we try to
put a lot of energy into the bag to cause it to move away with the
least amount of forward movement from the punch.