Under the topic, “What is so special about the lotus?” (“The Dao Bums”), someone posted the following:
When ‘tucked in’ there is a deep release I experience in the legs, kua (pelvis), that emanates up into the abdomen and prompts a deepening of sung (relaxation) and full body release.
I second that, and I have some specifics.
The movement of breath in or out shifts the accent in support for the lower spine between the ilio-lumbar ligaments that run vertically from the pelvis to the 4th lumbar vertebrae (in inhalation), and the ilio lumbar ligaments that run horizontally from the pelvis to the 5th lumbar vertebrae (in exhalation).
The weight resting on the sit-bones shifts the accent in support for the sacrum between the sacro-spinous ligaments and the sacro-tuberous ligaments:
The stretch of the ligaments generates activity in the muscles of the pelvis that alternates to relieve stretch on the ligaments, and that activity can carry into the quads and hamstrings right to the soles of the feet. The quads stretch fascia between the quads and the ilio-tibial bands on the outside of the legs above the knees, adding stretch to the ilio-tibial bands and generating activity in the sartorius muscles:
Stretch in the ilio-tibial bands encourages reciprocation in the sartorious muscles, triggering activity in the tensor muscles (from the ilio-tibial bands to the front of the pelvis) and in the gluts (from the ‘bands to the sacrum and to the lumbodorsal fascia behind the sacrum and the lower spine).
The action in the tensors and gluts carries up into the muscles of the abdomen and into the lower back:
There are two mechanisms that stretch the fascia behind the sacrum and the lower spine to the rear, to support the lower back. The first involves the extensor muscles behind the sacrum: they’re enclosed by bone on three sides, so that when the muscles contract and bulk up, that bulk presses rearward on the facia and effects a stretch behind the sacrum. The second involves pressure generated by the abdominals in the “fluid ball” of the abdominal cavity: pressure from the “fluid ball” can push the fascial sheet behind the lower spine to the rear, and even a slight stretch away from the spine can allow the fascial sheet to carry load in support of the spine.
Of particular importance to me is the way that activity in the legs returns as stretch behind the sacrum and activity in the lower abdomen, activity in the lower abdomen that is connected with a pressure that stretches the fascia behind the lower spine to the rear. Or to put it another way:
… a deep release I experience in the legs (and pelvis) that emanates up into the abdomen and prompts a deepening of (relaxation) and full body release.