I've been trying to get my body very flexible to the point where I can do splits, touch my hands behind me back at shoulder level and put my chest to my knees in a pike all without effort or pain. I've been working at it for a few years now, sometimes regularly and sometimes not so regularly, and it does hurt and everything, but I haven't gotten the results I've wanted. I hold these positions for thirty seconds, usually two times (one for warm-up and one with more intensity) and to the point where it causes a noticeable amount of pain. It seems to make no difference if I do some cardio, just something to get the blood going, before stretching. What am I doing wrong? Please let me know if I need to supply any additional details.