Hey yutao (Ginger) , I wonder if it's related to Gluteus Medius or even Minimus. They are hip stabilizers and thus they work hard to keep the grounded leg strongly connected to the the pelvis. Maybe we can lengthen them. Where is the pain ? D
i'm not great at the one leg standing postures but feels good to be trying them out again. think i have to be quite modest re how high the raised leg goes. ;)