I have seen many people develop their practice to the extent where legs go behind the head on a regular basis. Young people, old people, people with wide hips, narrow hips, people with inherent stiffness in the joints, people with hypermobility, light people, heavy people.
The common factor is they practice a set sequence consisting of many variations of forward folds and twists in combination with many jump-backs and jump-throughs to strengthen the upper body and pelvic floor. They practice like this 5 or 6 days a week for a few years and the body opens, becomes graceful, long and strong. The practice is called Ashtanga Mysore style.
You have to resist the temptation to use bone structure as a cop-out. You have to apply a proven practice for a few years on faith. You have to persist and develop optimism and discipline. You have to learn to resolve the whims of the body and the vicissitudes of the mind. You have to organise your life and manage your time.
Back bending (spinal extension) and leg-behind-the head (spinal flexion) are the two extremes of the human spine and nervous system. Alternating between these two states repeatedly has psychological and spiritual consequences. The latent power of the material aspect which exists at the base of our spine unfurls gradually, it rises up through the spine, piercing through blockages, transforming apathy into knowledge in a symphony of the highest order. Matter and consciousness unite, the feminine embraces the masculine.
Even a taste of it is overwhelming, it’s too much, and rare is the person with the nerve to hold this space for long. People can withstand it for a while, but eventually we shrink back into conditioned and distracted existence. We tend to stick to safe little self contained bubbles of self, where ego controls all which enters.
Through this practice the walls created by ego start deforming and expanding – it’s exhilarating, it is the greatest thrill that can ever be had, and also terrifying. The ego structures are the most familiar thing to us since we were first thrust out of the cosmic womb into separate existence.