The erector spinae, quadratus lumborums, longus colli, and scalenes opi'rat to keep the general orientation of the spine in a straight line, and in prii ciple this could mean a spine that is leaned forward, that is perpendicuk to the floor, or that is tilted to the real-. It falls then to the psoas and iliaci: muscles to maintain the rear axis of the tetrahedron at a 90° angle from th base triangle. The individual actions of the psoas and iliacus muscles difie however, even though they share an attachment site on the upper part i the femur, and these separate roles are significant. Specifically, the iliaci muscles sit you up by pulling forward on the ilia and favoring sacroili. counternutation, while the psoas muscles sit you up by pulling forward 1 the lumbar lordosis and favoring sacroiliac nutation (see chapters 3 and for more background).
The iliacus muscles are the simplest to understand because they a solely across the hip joints, from the femur to the ilium, fanning up and oi to the inner surface of the ilium on each side and acting as a pair to crea an anterior pelvic tilt. You can feel these muscles in action if you sit uprigl in a straight chair and think of pulling the ilia forward to the exclusion the sacrum. You want to leave the sacrum behind in a position of countc nutation (fig. 6.2a), or at least in a neutral position between nutation a; counternutation. The actions of the iliacus muscles are subtle. You'll f, the idea if you feel a sense of lifting along with a sense of controlling tl angle of the spine with respect to the floor. But try to avoid a direct pulli 1 forward on the lumbar spine. And even more to the point, avoid creating lateral spreading of the ischial tuberosities. Just to make sure of the latt squeeze the hips together—and with the hips the ischia—to affir counternutation.
The two psoas muscles have a more complex action than the iliacus muse I because they each act across three joints—the hip joint, the sacroiliac joir and the lumbosacral joint—rather than just the hip joint. Since the pst-muscles attach to the lumbar spine, they not only act with the iliacus muscl' to flex the two hip joints, they also place tension on the lumbosacral joii between L5 and the sacrum, and they support nutation at the sacroili. joints (fig. 6.2a).
To feel the effects of the psoas muscles over and above those that are characteristic of the iliacus muscles, lift the posture as much as possible with the iliacus muscles alone (which also produces a slight anterior pelvic tilt, as mentioned above). Next, w ithout releasing the iliacus tension, think along completely different lines and pull the lumbal- region frankly forward. Look for a deep and peculiar feeling—an internal tension that is directed specifically to the lumbar spine from the femurs, a tension that ultimately pulls the promontory of the sacrum forward in relation to the pelvic bones. This is nutation. Also look for the other components of nutation—the squeezing together of the ilia and an even more obvious spreading apart of the ischial tuberosities. Full sacroiliac nutation is what to aim for and hold in a classic meditation pasture because it permits the lumbar lordosis to be maintained and even accentuated without depending so much on the iliacus muscles and an anterior pelvic tilt. And it's also helpful that spreading the ischia apart from one another during nutation shifts the origins of the adductor muscles laterally. That is practical and significant for everyone who is struggling with tight adductors, which we'll soon see are the muscles that protest meditative sitting postures the most.
The lumbosacral joint and the sacroiliac joints are the weakest links in the classic sitting poses, so be watchful. In the absence of good hip flexibility, trying to perfect these postures forcefully by ratcheting the promontory of the sacrum forward with the psoas muscles may strain one or more of these weak links. And if this happens, pain emerges near the site of the strain— lumbosacral pain close to the midline in the lower back, and sacroiliac pain at the rear of the pelvic bowl (chapter 6) just an inch or so lateral to the midsagittal plane of the body. To avoid problems with all of these joints, you must work patiently with the exercises suggested for freeing up the sacroiliac joints in chapter 6. You are less likely to hurt the hip joint because it is designed for flexion.
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