Thanks for posting this. I had not seen it before, and viewing it led me back to some fond memories of seminars led by Master Yang Zhenduo. I also see some pictures of some folks I know, including one of my teachers.
When you first linked to it, I thought it was just a documentary about Tai Chi and its history, but when I examined it more closely today, I realized that most of it actually deals with what Tai Chi is and its principles.
One place you may want to look at is at 22:18, where are famous cheng
are discussed. There Master Yang begins by alluding to the fact the movements have Yin-Yang opposites like opening and closing, large (?) and small (?), and leg thrusting and propping up (cheng
). He says that to balance the forward movement, you have to prop up or support the movement backward to avoid losing balance. He then shows the heel-to-ball-to-toe movement, ending with showing how the legs and arm/hands should arrive together.
You may also be interested in this video
, which I discovered after looking at Yang Zhenduo's video. It tells the story of a certain Taijiquan School near Microsoft's Headquarters in Seattle. I see several friends I have not seen for a while, but you might be most interested in 17:00 through 22:00, when Master Yang Jun goes through the basic push hands curriculum, focusing on applications of the Eight Jins.