The reality, as always, is quite more nuanced than that. Simply mechanically turning the legs in, which in my opinion has little to do with the muscles of your inner thighs (also known as the adductors), produces a bunch of unintended consequences.
It leads to overuse and tension in the tensor fascia lata and the gluteus minimus (two muscles on the outer thigh and hip) that medially/internally rotate the thigh bone/femur, among other movements. To feel what I am talking about, take your fingertips just below and outside of your hip point (ASIS) at the front of your pelvis and turn that knee in toward the other leg. Regardless of your position, you will feel the muscle jump into your fingertips and engage. If you do it more forcefully, you will most likely produce gripping, which will also move along your hip crease and deep into the groin. Now, imagine doing that faithfully and enthusiastically in your yoga practice on a consistent basis. In essence, you are creating a pinch in the front of your pelvis, in that emotionally charged site of sexuality, digestion, survival, to name a few.
Further, simply turning the legs in like that, from the outside if you will, strains and compresses the femoral triangle--home of the femoral nerve, femoral artery, femoral vein, femoral ring/canal (lymph nodes, drainage). The femoral triangle is basically the armpit of the thigh. Its boundaries are: the inguinal ligament (your hip crease from hip point to pubic bone), adductor longus (one of inner thigh muscles), and the upper portion of the sartorius (from the hip point to where it meets the adductor longus on its way down and in to the inner knee). Here is a visual:
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| Femoral triangle (boundaries discussed above pictured with dotted line). From http://home.comcast.net/~wnor/antthigh.htm |
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| Femoral triangle with psoas, iliacus, and pectineus. From http://www.massagetherapy.com/articles/index.php/article_id/417/Danger-and-Excitement-in-The-Femoral-Triangle. |
As you can see, there isn't much space for the vascular and nerve contents of the anterior thigh. They are bunched up between the pectineus (the shortest of the inner thigh muscles, which runs from pubis to the lesser trochanter on the inside of the thigh) and the psoas tendon as it crosses over the lip of the ilium (the pelvic bone) in front of the hip joint on its way to the femur where it attaches close to the pectineus. It's Singapore-style population density with prime real estate in there!
Mechanically turning the legs in like this also displaces whole muscle compartments from their intended locations and functions. It basically takes everything in this area in one direction only (down and in), unintentionally taking the quads, especially the rectus femoris, towards the midline of the body, which is not where they are supposed to be. Thus, indiscriminately turning the legs in serves to create less differentiation, and therefore less freedom, between the front of the pelvis and the front of the thigh, which is, in essence, another way of sitting on your desk, in your car, or slouching in front of the TV. I've noticed, for example, that when trying to sit "properly" in my work chair with my thighs parallel to each other (which in a sitting position basically means internally rotated thighs) that I feel much worse (as in tight-groined and tight-hipped) than when I am sitting in my chair with my thighs in a V shape (not too turned out and definitely not turned in).
I do realize that I might be exaggerating a little bit. Some of you will say that it's not about turning the legs in (and it definitely isn't), but about taking the inner thighs back. I don't disagree. But I would venture to say that when most people hear the instruction to take the inner thighs back, they will turn their legs in from the outside like I described above. In other words, they will simply internally rotate their legs.
It's quite a bit more subtle than that. The inner thighs activate from the ground up, more specifically from the lift of the inner arches of the feet via the tibialis posterior muscle (which starts deep in the foot, goes up the back of the shin bone and connects to the inner thighs), which is another way of saying that the inner thighs are part of the deep core line of the body. When the inner arches activate, the inner thighs, especially the adductor magnus, hug to the femur/thigh bone, only this doesn't adduct the thigh bones (i.e. bring them closer to each other), it actually creates abduction of the thighs from the inside (i.e. moves thigh bones away from each other laterally, which is not the same as rotating them) and creates space in the pelvis and hips.
These days, I rarely, if ever, tell my students to turn their legs in or take their inner thighs back. I tell them to lift the inner arches of the feet up towards the core of the pelvis to activate the inner thighs. To make it more subtle, I tell them to draw from the big toe balls of the feet back towards the high point of the arch (just in front of the heel bone) and lift that energy up into their inner thighs, literally activating the core line of the body. When the inner thighs are activated in this way, then you can tell them to "go back and apart," without actually having to rotate the thigh bones. This feeling of the inner thighs going back and apart is a function of the anatomy of the adductor magnus, which looks like the mainsail of a boat (see image below). Then the armpit of the leg softens, deepens, and feels more open.
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| Adductor magnus: as seen from the back (left most image). You can see its mainsail shape and its role in stabilizing the pelvis. The sketch in the middle schematizes the magnus and shows you how the muscle twists. The right most image shows you the thigh from the front. From Grundy, John Hull (1982). Human Structure and Shape. |
Let me know what you think and if this prompted any questions. I think my next post will naturally focus on external rotation of the legs, which is equally misunderstood but very under-appreciated in the world of yoga asana.
