Whats wrong with some classical postures?
There are a lot of poses that are not good for postures. I dropped this postures long ago.
Yoga Asanas tries to replace this various poses.
Some of the postures gives stress to the body and are not helpful to posture.
When you twist knees, sheer the spine when you compress the lower back, you run into problems.
These are very stressful and could lead to bio mechanical issues.
No one teaches to twist knees.
Deep back bend is another one.
Back bends are done minimally in human life.
Yet in yoga we venerate the deep back bends.
For some people whose not genetically given to them, hurt themselves.
People who presude back bend line up, getting a lot of compression on the spine causing irritation.
Instead of back bend, you can sheer your body side ways. The spine can accommodate the pull.
When you continue the body to move sideways you get into impasse which is definitely helpful.
Some positions causes rotation on the knees. This gives strain in the cartilage.
Cartilage are not good in resisting rotational forces.
Back bends causes compression on the lower back.
The ability to do deepen back bends comes from thickness of the disc in the spine.
Back bends can compress the disc and cause problems.
On evolution point of view, we did not evolve doing this kind of movements.
The spine is architecturally capable of combinating. We have side bending, forward bending which are architecturally supported by the body.
Humans should learn forward bending and learn to do it well.
And when you back bend a lot, you'll probably encounter problems.
You can do back bend slightly on the upper back and you don't need to worry about.