The most basic requirement for doing Tai Chi is song kua, or relax the hips, means that the muscles surrounding the hip joint, i.e. where the thigh bone meets the hip, should not be used to any great degree in supporting your structure. These hip muscles can then be used to adjust the angle of your pelvis so that your upper body can remain relaxed, or direct the jin if so required. If you haven't achieved a song kua, then everything else is academic. You will not be able meet the requirements for the rest of your body.