Flexibility and knee strength

Practicing Taiji - specially Chen style - as well as slik reeling exercises requires a great deal of strength and flexibility in legs, hip joints and knees.  Most of the exercises involve sitting low in a horse stance, shifting the weight from one side to the other in continuous spiral movements.  There's also more of transitioning into empty stance from different low-height postures in Chen style.

Standing meditation helps a lot, and should be practiced in different forms.  Horse stance and one-leg standing meditations would increase the strength of the muscles and joints.