The first pose that indicates a readiness for Wheel isCaturanga Dandasana, or low push up. This pose requires arms strength and it activates the muscles in theback which have to contract to lift your body up into Wheel. It is important totone the muscles that lift the body into Wheel, otherwise the flexibility willinvite weakness and pain for which beginners “have to pay heavily”, accordingto Geeta Iyengar. 

Then the back bends, in order of learning:

Prone Position:

Back arches are introduced in the prone position first:  Up Dog, Bow and Locust.  These poses are done from the more externalspinal muscles.  If the back hurts inthese positions, it indicates a defect in either the spine or spinal musclesand it is necessary to correct these problems before moving on, or the problemscan cause pain especially as the poses progress.

Upward Facing Dog

There are two ways to position the feet in both Caturangaand Up Dog.  One is to be on the balls ofthe toes and one is to be on the tops of the feet. The first way tones the legmuscles and the second way tones the spinal muscles.  This is important because back bends are donefrom leg strength.  If the leg musclesare not strong enough to hold, that translates into pain in the spine,particularly the lower back.    Therefore, one should tone the legs and thenlearn to adjust the spine by making the leg muscles strong.

Bow

In this pose, the body rests only on the abdominal area.  Keep a firm grip on the ankles and useresistance between the legs and arms to raise the legs and chest further.  Try to raise the knees and shoulders the sameamount.  Often it is easier to raise oneor the other more.

Locust

In Locust, learn to work on the thighs and chestsimultaneously to keep them above ground and, as in bow,  give them an equal amount of lift.

Locust and Bow act to strengthen the back and exteriorspinal muscles.

Camel

This is the first pose where you are lowering yourselftowards the floor rather than lifting up away from it.  In the beginning the knees and feet are hipwidth apart.  As you progress in thisposture, it is harder and more advanced to have the knees and feettogether. 

Up Dog and Camel are preparatory poses for the more advancedback bends such as Wheel.  IN performingthese postures, the student is asked to reflect on the curvature of the spineand the evenness of the spinal muscles. Does the spine bend more easily in one area than another?  The work here is to create an evenness in thespine and muscles.  

Often, while doing backward extensions, students experiencebreathlessness, hyperventilation, nausea, and headache in addition tobackache.  They feel nausea and dizzinessas if they are having an attack of vertigo. It is mainly because of the stiffness of the spinal muscles andsluggishness of the liver.  These twoasanas prepare the student, not only at the physical level but also at themental level, for removing such obstacles.  

Wheel

Once you are proficient in Up Dog, Bow, Locust and Camel then Wheel will come easily.