Let me take you on a tour of Eka Pada Sirsasana
By all appearances, the goal here is to place our foot behind our head. This action may inevitably occur, but by setting this as our chief intention, the yogi can become self-limited. In more extreme cases, straining of the cervical vertebrae may also occur, which negatively impacts our well being, that which we work day-in and day-out to cultivate.
As is the case with respect to most postures, it is best to approach Eka Pada Sirsasana in stages. My first aim is to position my knee in back of my shoulder while lengthening my hamstrings. Later, I work to close the gap between my waist and thigh, while drawing my femur back in its socket. By doing so, your foot may spontaneously approach the back of your head.
After threading your shin behind your neck, the next stage of this elaborate dance is to apply counter force between one’s inactive leg and the opposite shoulder. I find that doing this allows me to go deeper into the posture, enabling my shoulder blade to resist the brunt of the pressure of my hip’s counter rotation. As a final touch, I point my foot and place my hands in anjali mudra for maximal expression.
If you are looking to entertain yourself, you can always attempt to place both legs behind your back. In that case, I suspect that you will be quite pleased with the stability which a deep and methodical Eka Pada Sirsasana affords. I simply ask that the yogi enter and exit this posture slowly, especially until he or she becomes accustomed the stages therein. And be open to your own body’s unique pivots.