What is Shiva? Shiva is a representation, an archetype, of the primal force of transformation that is found in Life: nature, animals, plants, weather, humans, stars, galaxies. He is not called Lord of the Worlds for nothing! This power of transformation has a mysterious existence in all of this moved creation around us, endlessly partnering destruction with creation so that something new can continually emerge. It is a dance of infinite birth; Shiva is Lord of this Dance.
Infinity is symbolized by a circle, which is what the leg behind us should ideally form in the final-end pose as foot meets head. "Ideally" as this is an advanced pose that you can do for years and years and still not quite accomplish. Within the imagination, 'a circle within a circle' picture forms. Your leg not only begins rounding, but the top half of your body too as the back becomes more elasticized.
Shiva's power bestows the transformation of the body in all yoga poses. Again, he is not called Lord of Yoga for nothing! This fiery power on a metaphysical level also provides the gift of ego-destruction so that the infinite consciousness of an individual can be born; that the forever-solo dancer you might find yourself one day can reach its true self, shed of false constructs and facades. The OM symbol that you see above in Move Within Yoga represents this acknowledgement of the higher self layered deep within, the OM from an ancient mantra for this god.