Spacial placement of the body cannot be the determining factor of flexion or extension when it comes to the back. One must have an understanding of the basic structure of the spine as well as physical limitations todays athletes show up with in an effort to counter the repetitive actions as well as avoiding compromising the integrity of the body for the glory of the final pose.
In the womb we have but one curve, our primary curve which is still present in the thoracic spine. Then as a baby we began to lift up our head and form the lordotic cervical curve. As we began to get stronger and prepare for walking the lordotic lumbar curve was formed which is what enables us to walk upright on two feet.
So the spacial placement of the body cannot be the only determining factor as to whether you are in spinal extension or spinal flexion. I have some of my students who go into a spinal flexion simply by raising their arms up over their head. The restrictions are mostly muscular and with time they are able to open up and go further into a back bend. Occasionally they present with a pretty severe case of Kyphosis and they will never be able to safely go into a back bend. This is the result of poor posture and to much rounding of the back. The muscular tension and pull on the spine over time creates a shift in the structure of the spinal column and care must be taken to educate and modify.
Further practicing of spinal flexion should be avoided and support offered when doing asanas while lying on the back.
In a forward fold, one can maintain spinal extension simply by hinging at the hips and maintaining the natural lordodic curves of the neck and low back to avoid increasing the kyphotic curve of the upper back. Keeping your gaze forward to the wall will also prevent todays athlete from rounding the back, as each of the primary and secondary curves effects the other. The idea is not to round the back but to flex the hips and lengthen the hamstrings. It may mean your head is not going to be as close to the floor, but as that is not the intended action and function of the asana, who cares.
As you maintain the curve in the neck, the low back maintains a neutral lordodic positioning, if you exaggerate the primary arch of the mid back the secondary curves of the neck and low back shorten and the tail bone tucks under.
This is important for todays athlete to recognize in their practice and additional modifications and supports may need to be utilized.
This shows up as a restriction in down dog in some of todays athletes as well. The function of down (with the face) dog pose are many, to strengthen the upper body, open the heart while creating length in the hamstrings as well as a little reverse traction to the spine. An overall yummy pose, but by focusing only on the alignment and not taking into account limiting structural and muscular factors that todays athlete shows up with, you may lose the benefit.
Knowing the intention and the action as well as being mindful and watchful of limitation, there are so many different variations to help Todays Athlete receive the benefits of the asana with out actually having to express it by the book. Bringing in props such as balls, straps, chairs, block and even the wall can help create the action of the asana to allow for a safe progression. It also builds confidence to have other options as opposed to standing there avoiding the pose all together.
How might your expression of spinal extension change as you now look at the action of the asana as opposed the ideal form of the pose?
How might your yoga expression change if your intention of Downward dog were to feel the length in the hamstrings? Or to simply feel the benefit and release of opening up the heart?
See you, on the mat!