What kind of sports do you do besides Taijiquan?
I used to do a lot of external martial arts but had to give that up because I had to many injuries (mainly back injuries).
So now I am working on core stability and hip flexibility through push up + abs exercises and yoga. Below are some of the videos I like to watch:
Abs - Yoga for hips and lower back -
Doing these exercises aside from my Taijiquan training helps me a lot for building a stronger core and releasing tension in my lower back and hips. This is especially important in Level 3 where you will learn Key Principle 4 - Relax the Waist, Sink the Hips.
Please share any videos or training material that is useful for you!