Pranam.
A few years ago I was attempting to settle into a posture called "Wu Song Hits the Tiger" that I learned from a previous teacher. I ended up pulling at least one hamstring at the sit-bone. That was in the month of June. I spent the remainder of that Summer and into the Fall rehabbing the injury and doing a lot of introspection and work on my pelvic floor. There was so much tightness and "locking" in that area. I think that years of meditation and qigong practice where we're taught to clench the sphincter to keep qi from escaping probably contributed a great deal to that tight condition. I would certainly appreciate Sifu's thought(s) on this. Is it ever necessary to clench or lock there?
Namaste
JD