Depends
When I first studied Tai Chi, I had no idea what it was. I thought that Master Choy’s way was the only way. As I continued my studies I became aware that there was so much more to Tai Chi than I had thought. At the time there were no books, no video, no internet, just the words and demonstrated movements of the instructor.
So after 50 years, I have come to the conclusion that it doesn’t matter “what” you do. What matters is “how” you do it. There are a few hard and fast rules, mostly about how to keep the body safe, the emotions smooth, and the Tai Chi philosophy expressed at all times.
With fundamentals, some instructors say the stance “should” be hip width, others say shoulder, while still others call for a narrower or wider. The rear foot angle “should” be 45 degrees to the front foot. Others say 60 or even 80 degrees. If there was really only one way, we would all be doing the same form in the same way.
My answer to most questions about the form is “depends”. The way a movement is done depends upon, mostly, the application. How can I express what I am trying to demonstrate. The how also depends upon my physical body with its structure and history. We have students who do their Tai Chi with a walker! With the proper mind set and enough desire, it can be done with plenty of positive results.
Speaking of Structure – Knees
The knees are the most challenged joints in the body when playing Tai Chi. Many people who practice Tai Chi experience knee problems. So to limit the possibility of doing any harm to your knees, follow these simple rules.
The knee always moves in the direction the toe is headed. Be careful not to let the knee collapse inward when moving the weight onto it. When sitting on the rear leg, be sure to still keep the knee headed in the direction the rear toe is headed. The rear foot should be approximately a 45 degree angle to the front foot direction.
The knee just covers the the toe when moving forward. If you move the body so that the knee extends past the toe, you will place a burden on the knee joint. If you do not cover the toe with the knee you might not be getting all the exercise you are looking for. If you have pre-existing knee conditions, don’t lower the body as deeply and don’t move the weight as far forward.
Never lock the knee. The knee always maintains a very slight bend when it extends. Try not to let the knee move in a lateral direction when doing any movement.
Be careful, practice with mindfulness, and your knees will end up being strengthened and opened.