Okay, I'm a new MMA student, doing it more for recreation than anything else. Anyway, I do envy those that can do headkicks with ease. I am so stiff in my hamstrings, groin, and most of the rest of my lower body that I can only kick knee high. Even waist high gets the hip joints hurting. What is the best training material to make me incredibly flexible, enable easy headkicks, and add overall flexibility too? Thanks.