In yoga practice, the hips, pelvic joints, and lower spine develop a new relationship with the earth through bearing weight directly on them in sitting postures.
If practiced with attention to the anatomy of the relevant joints,
muscles, and connective tissue, they can help to restore some of
the natural flexibility that people had in childhood, when sitting
and playing on the floor for hours at a time was effortless.
When the spine is supported efficiently by the pelvis and legs, the ribs are also free to move with the breath, rather than become part of the supporting mechanism of sitting.
The goal should be to find the position of the legs that allows the weight to fall most clearly from the spine to the pelvis into the sitz bones and the support of the floor.
Some people need to raise the seat a great deal or even sitting on a chair for ease in the spine until more mobility can be cultivated in pelvis and legs.
In a well supported seated asana, the intrinsic equilibrium of
the pelvis, spine, and breathing mechanism supports the body,
and the energy that has been liberated from postural effort can
be focused on deeper processes, such as breathing or meditation.