In a comment to Chen Practical Method on Sore Knees, Rick of Wujifa outlines three basic components that can cause knee pains:
- Knees bowed out which the I.T. Band on the outside of the can be contracted and shortened which will contribute to mis-alignment
- Tight muscles on the inside of the leg contribute to bowing the legs in
- Twists and counter twists of the up and lower leg bones and these can be cause by tight muscles in the back down to the ankle
Rick notes that #3 above is the most common. I’ve noticed many instances in which there may be counter twists in my upper and lower leg bones, not just in taiji/standing practice but in everyday motion. Example, while sitting at my desk, I have a tendency to stretch out my legs and cross my feet at the ankles. I notice this adds a little strain to my left knee and creates a twist/counter-twist in my right leg. Solution: Uncross legs and place feet flat on the ground. The "tipping point": Notice when this type of thing happens.
Additionally, some light stretching can play a major role in loosening the tension. Check out Knee Mystery Solved | Get Fit Slowly for some stretching exercises.