The Wheel(Chakrasana also known as Urdhva-Dhanurasana)

The Wheel is an advanced and one of the most dynamic whole-body postures in Hatha Yoga. In this asana the body is arched back and supported on the palms and soles of the feet.
Do not be discouraged if you are not able to accomplish this pose right away as it is a very challenging and difficult asana. Before fully attempting this inverted pose know the strength of your upper body and your spinal flexibility. Even attempting this pose without successful completion gives great benefits.
If you have limited strength but plenty of flexibility you can easily come up into this asana.
If you have lots of strength but limited flexibility you will be able to come up into the Wheel using the force of your strength.
If your strength and flexibility are limited the Wheel pose will be quite a challenge.

The Chakrasana has an overall tonic effect for the entire body. It tones the spine by stretching it fully. It strengthens the spine, upper back, arms, shoulders, wrists, buttocks, thighs and abdomen. It stretches the chest and the lungs.
It stimulates the cardiovascular system, thyroid and pituitary glands.
The Wheel gives a boosts of energy, great vitality and feeling of lightness. It counteracts depression.
By practicing this asana the glandular, digestive, respiratory and nervous systems are enhanced.

Although the Wheel is a very healthy and safe asana to perform for some people, the same may not hold for other people. There are many health conditions in which it is suggested that Wheel posture is not recommended.

Three important reasons (out of many) not to do Wheel:

1) Any person with weak wrists should not attempt this powerful pose.

2) In case of back injury avoid this posture.
3) During pregnancy this asana is not to be performed.

Issued in the interest of people practicing Hatha Yoga by Subodh Gupta, Yoga Expert based in London.