This is a good little stretch for you hamstrings. My own invention... My intention here is to draw your attention to any imbalance you may have between the inner and outer hamstings and begin to balance them. Many, if not all clients have a difference between in tension on the inside of the leg to the outside and it is commonly the opposite in the left to right leg. This imbalance acts as a pully system to your pelvis putting it in a torsion which upsets your whole structure often resulting in aches or discomfort in our back and or knees.
Follow my instructions and slowly feel where you may have an imbalance. Slowly rock your pelvis and body left to right. Try to not let one side of your pelvis, creep forward, keep it level with the opposite side, this will isolate the shortness in your hamstrings and make the stretch effective. Move slowly, not fast. Moving fast with only engage elasticity, moving slowly will start to change your tissue.
Who this exercise is not for