Shri. B. K. S. Iyengar loved backbends; they were his favorites. In his own words, he spent two hours everyday in the morning practicing them.
In an interview with his senior students way back in 1991, he had this to say about backbends:
In the asana system,the most advanced postures are backbends. Backbends can be felt more than expressed. They are meant to understand the back part of our bodies.The front of our body can be seen with our eyes. The back of the body cannot be seen, it can only be felt. That is why I say these are the most advanced postures. The effect of backbends is that our nerves which originate from the spine are very greatly activated by our will power, logic and reasoning in adjustments. The strength created in the nerves is enormous. Through the practice of backbends, by using the senses of perception to look back and drawing the mind to the back portion of the body, one day, meditation comes naturally.
Magadhi, (the girl in the photos above) a school girl and a tennis player, might be a little too young to understand Iyengar's philosophy on backbends, but she is a natural when it comes to doing them.
At the Shala, she demonstrates a few of the most difficult backbends, which call for not only extreme mobility and flexibility of the spine, but strength and balance too.
The first posture is Eka Pada Kapotasana (one leg pigeon pose) and the next is a variation of Eka Pada Raja Kapotasana (one leg king pigeon pose).
Backbends are like Rasayanas in Ayurveda; anti-aging medicines that keep us young.
So practice them.
Everyday.