Before I attempt the pike stretch I like to stretch each leg individually first. My goal is to be able to do it with a straight back using just my hip flexors. I used to grab my feet and try to pull myself in, but I feel like this is forcing the stretch and my legs get feel really sore the next day. So yeah my problem is that my left leg is more flexible then my right. when I try to stretch on my right leg its harder to keep my back straight and my quadricep contracts really tight when I try to lean forward. Heres a video of me stretching both legs.
http://www.youtube.com/watch?v=ua2nEpgdfcc&feature=youtu.be
Heres another video of me stretching my left leg. Is it more effective to bring your shoulder to the ground or forehead to your shin? Other leg in front or facing back? Feet pointing forward or facing up?