There is a tai chi, qigong and daoyin exercise that people often teach and do to “warm up” or “loosen” the knees. And it is the absolute worst thing you can do to your knees. It will “loosen” them alright – to the point that you may need surgery in a few years. WHY this exercise has been perpetuated on like this in taijiquan, no one knows. Some teachers, as I too, believe that this originated from other leg exercises that slowly became misunderstood.
I don’t wish to put down anyone or any teachers that do this, I just wish to see people benefit from tai chi instead of getting hurt. Let’s not concern ourselves with what a human teacher says or does – let us look to the greatest teacher of all – the Tao. Look at how nature works. How is your knee put together? What kind of joint is it? What actions damage it? How is it made to move?
Here’s a video about this. It also shows some beneficial alternative ways of doing this exercise – ways that I believe were the *original* way this tai chi exercise was done before it became “lost.”