Purva Pratana Kriya is the action of arching the spine backwards. 

In everyday life there are no movements like going upside down in Sirsasana.  Neither are there back arching movements like Urdhva Mukha Svanasana (Upward Facing Dog), Bhujangasana (Cobra) or Salabhasana (Locust). That is one of the reasons why yoga is so beneficial to the health of the body. It keeps the spine flexible. 

Backbends stretch the anterior and central portion of the spine symmetrically.  They increase blood circulation to the nerves keeping the nervous system invigorated and well-coordinated.  Backbends stimulate the nervous system and enliven a weary mind and rather than distracting the mind, this category of poses encourages introspection. 

Back arching demands a fair amount of physical flexibility.  It is important for the practitioner to avoid abusing their suppleness and direct it towards the working of the nervous system. In order to bend backwards the hips, shoulder and spine need tobe strong and flexible. This chapter focuses on strengthening the spinal muscles.

There are many categories of backbends and they can be done lying on the abdomen or the back, in a standing position or inverted.  The different positions and the intensity of the spinal action have diverse effects on the body and mind. 

Some of the benefits of Backbends:

• Effective in banishing fear and lending courage.

• Eliminating an inferiority complex

• Invigorating the mind.

• Bringing agility and tone to a body that feels heavy.

• Bringing alertness to an indifferent mind.

• Lifting depression.

• Controlling desire and anger.

• Enhancing memory.

• Sharpening the intellect.

• Awakening self-respect.

• Turning the ego inward and making the mind humble.

These effects depend on the intensity and sequencing of various backbends in one’s daily practice.

The practice of backbends is not merely a physical workout, but an exercise in culturing the consciousness.  In this chapter, BKS Iyengar explains how the physical practice of asana is like a mantra. Movement is the physical equivalent of sound.   You can read more about that here. 

In this chapter he gives us three simple backward arching asanas:

1. Salabhasana (Locust)  In this asana we only contract the superficial layer of back muscles

2. Bhujangasana (Cobra) – The back arching action of this pose penetrates to the middle layer of back muscles.

3. Urdhva Mukha Svanasana (Upward Facing Dog) This is the most intense of these three postures.  This pose has the potential to access the innermost layer of back muscles. 

These three poses complement each other and introduce the practitioner to their own back. 

These basic asanas prepare us for the more complex back bends.  In backward arching poses, it is not enough to use the flexibility of the spine to assume the asana.  It is also necessary to coordinate the movement with the shape of the spine.  The shape of the cervical and lumbar spine are naturally concave and bend backward easily.  The tendency is to overuse these parts of the spine which can disturb the balance of the spine.  The thoracic and sacral regions are naturally convex and are difficult to arch.  It is critical to work consciously on these areas so that the load is distributed evenly through all four regions of the spine.  It is especially important to arch the thoracic region because it elevates and broadens the chest, expanding the lungs and the regios around the heart.

When practicing backbends, it is important to remember to breathe normally.  Holding the breath while trying to force stiff back muscles to arch increases blood pressure and can cause headaches. 

You can read the techniques of how to come into each of these poses here.