(from a letter to a friend)
You mentioned that you switch your legs frequently when you sit the lotus, because the posture seems unbalanced. It's true that the position of the legs twists the hips and the pelvis, and maybe even the lower spine.
If we look to breathe naturally and relax into the posture, action to absorb the twist takes place. All we have to do is to allow awareness to "fall where it may" with the breath and relax whatever activity is present, to have this happen.
When awareness falls to the abdomen and we relax, we discover a feeling of leverage in the movement of breath. The feeling is very similar to the feeling of leverage we have in the movement of a swing. On a swing, we grip the chains, then stretch the upper body and the seat of our pants against the fulcrum we've created to move the swing. If we relax as we breathe, we engage the fascia around the abdomen from the lower back, and we begin to stretch the upper body and the seat of our pants against this fulcrum to facilitate the movement of breath. The stretch that we realize as we relax is a stretch between the lower back and the pelvis, and just as the stretch on a swing changes as we change directions, so too the stretch between the lower back and the pelvis changes as our breath changes directions; even so, a feeling of leverage is always present.
The stretch between the lower back and the pelvis is the first in a series of stretches that occur in the movement of breath. You could say that as we relax into a particular stretch, we shift the activity in the movement of.breath from one spot to another, and we translate the motion of the body from one direction to another. Here's a fast summary of what we can observe, as we relax and "breathe into" each successive stretch.
If we relax into the stretch of the ligaments of the lower back, we bring forward activity in the muscles that connect the tail-bone to the pelvis, and we translate motion along the spine, sacrum, and tail-bone into a side-to-side motion of the pelvis.
If we relax into the stretch of the ligaments between the tail-bone and the pelvis, we bring forward activity in the muscles of the legs, and we translate the side-to-side motion of the pelvis into a forward and backward movement in the legs.
The forward and backward movement in the legs stretches the long bands of fascia that connect the lower leg bones to the pelvis. If we relax into the stretch of the fascia along the outside of each leg, we bring forward activity in the diagonal muscles from the lower leg bones to the pelvis, and we translate the forward and backward movement of the legs into a turning motion at the pelvis.
At the pelvis, the turning motion from the legs stretches ligaments that connect the pubic bones to the upper leg bones on either side. If we relax into the stretch of these ligaments, we bring forward activity in the muscles that rotate the pelvis and extend the hips, and we translate the turning motion from the legs into a rotation of the pelvis left and right.
When the pelvis rotates left and right, the fascia behind the sacrum is stretched; if we relax into the stretch of this fascia, we bring forward activity in the muscles that connect the upper leg bones to the sacrum, and we translate the rotation of the pelvis left and right into a counter-rotation of the sacrum on its diagonals to the right and to the left.
The sacrum rotates counter to the pelvis on its diagonal axes, lower left to upper right, or lower right to upper left. The sacrum shifts between the two diagonals across a forward-and-backward axis with the pelvis; as the sacrum shifts, the ligaments that hold the sacrum to the pelvis stretch, until the forward-and-backward axis drops slightly lower on the wings of the pelvis.
If we relax into the stretch of the large ligaments that join the sacrum to the pelvis, we drop the forward-and-backward axis of the sacrum, and as the sacrum shifts from one diagonal to the other across the lower axis the fascia behind the sacrum is stretched vertically. With this secondary stretch, activity in the muscles behind the sacrum comes forward, and we translate the counter-rotation of the sacrum into a motion of extension from the sacrum up the rear of the spine.
The action in the muscles behind the sacrum and the spine travels up to the skull just the way a bell-ringer's hand motion travels up along the bell-rope to the bell. When this action is taking place, the bone at the outside-rear of the eyes moves forward and backward slightly; the eyes turn naturally downward, and the jaw closes.
The action up the spine also moves the two bones on either side of the crown of the skull. The nerves that control the volume of spinal fluid are in the joint between these bones at the top of the skull; because the nerves respond to changes in pressure at this joint, the movement of these bones can affect the rhythm of change in the volume of spinal fluid. At the same time, the rhythm of change in the volume of spinal fluid can facilitate the shift of the sacrum from one diagonal axis to the other, as the movement of the sacrum forward and backward is reinforced at the lower axis on the pelvis.
As the rhythm of change facilitates movement of the sacrum from one diagonal to the other, the rotation of the pelvis and counter-rotation of the sacrum carries upward through the ligaments between the pelvis and the lower back into the fascia around the abdomen, and the placement of each leg can be felt in the fascia. The feeling of the placement of each leg guides support in the abdomen for relaxed length in the psoas muscles, from the lower spine across the pubic bones to the inside of the upper leg bones. The psoas muscles reciprocate with the spinal extensors, and the tilt and rotation of the pelvis occasioned by the motion of the sacrum receives impetus from the contraction and relaxation of the psoas muscles across the pubic bones, until the contraction and relaxation of the psoas brings the tilt and rotatation of the pelvis back into the extension of the hips and the stretch between the pelvis and the sacrum.
As the reciprocation of the extensor and psoas muscles in an upright posture is returned to the stretch of the joints between the pelvis and the sacrum, the stretch of the fascia from the pelvis to the lower spine in the movement of breath is made steady, even with the twist in the hips and the pelvis that the lotus posture occasions. Again, the key is to allow awareness to "fall where it may" with the movement of breath, and relax into whatever motion is present.
Although the particulars make it sound complicated, what I'm describing is not much different from walking at a regular pace. When the gait is relaxed, all the pieces fall into place; each part of the body comes forward as appropriate, our thoughts settle into themselves, and we just breathe in and out to ourselves as we walk along.
For the lotus, I would recommend a cushion high enough to allow the weight of the body to rest forward on the sit-bones. I would also recommend that you rock side to side and forward and backward when you first enter the pose, to help position the legs correctly.
I hope this helps you find more of a way into the posture, on those occasions where you feel moved to try it.
©2008 Mark A. Foote (revised 2009, 2012)