Can you punch through a sheet of newspaper?
Sounds easy, doesn't it?
Okay, smarty pants, have a partner hold a sheet of newspaper very lightly on the top corners. You stand in front of it and punch through it.
It's an eye-opening experience but it is a good test of your internal body mechanics. Are you able to maintain the mechanics as you "put on the gas?"
This is one of the videos on my membership website. It was shot around 2005 - maybe earlier. I was practicing with a student last night and he mentioned the video, so we got a sheet of newspaper out and tried this. He was not successful in breaking it, but I (fortunately) was able to do it with my first punch.
The secret is in applying all the internal mechanics -- ground path, peng jin, whole-body movement, silk-reeling, Dan T'ien rotation, and opening/closing the kua -- in a connected, relaxed way while speeding it up -- fajing.
Try it yourself. Let me know how it goes. And thanks to Nancy for being my partner, as usual. She is an ace at paper holding. :)