Sthira Sukham Asanam (Seated posture should be steady and comfortable.)
Most experts tend to agree with Julie Gudmestad, Yoga Journal's anatomy columnist and a physical therapist, who says the hips play a key role in proper sitting. "In order to sit comfortably, you need a lot of external rotation in your hips," she says; lack of external rotation prevents your knees from releasing down toward the floor. If rotation in your hip joints is limited, says Gudmestad, then your body will accommodate your attempt to rotate by moving at the next available joint. Unfortunately that joint is the knee, which is much less stable than the hip. The knee's main job is to flex and extend; it has no business twisting. When you externally rotate the leg at the knee instead of the hip joint, knee pain often results. And as any yoga teacher will tell you, knee pain is never a good thing: If your knee hurts in any cross-legged position, choose another way to sit.
According to Gudmestad, tightness in the hip will not only threaten the knee but can also "end up torquing the pelvis, causing it to rotate posteriorly." So in other words, you round your back. Put simply: If your thigh can't rotate, your shin or lower back probably will. And a rounded lower back pushes everything else out of alignment: The whole spine slumps, the head falls forward, and then the diaphragm compresses, all of which impedes the blood flow to the core of the body and restricts breathing. No wonder anyone sitting this way feels uncomfortable!
Of course, lack of external rotation isn't the only problem in cross-legged sitting. According to Anusara Yoga founder John Friend, another reason for such slumped posture is weakness in the paraspinals, the muscles running up along the spine. Tight hamstrings in the back of the legs and tight gluteal muscles in the buttocks can also contribute to slumping by making it difficult to tip the pelvis back toward alignment.
And while external rotation is crucial, some practitioners have plenty of external rotation and still cannot successfully execute a comfortable Padmasana or even Siddhasana. In fact, too much external rotation can also be a problem: Ballet dancers often complain of sore hips when they sit, not because their femurs can't externally rotate but because many of the muscles surrounding their outer hips—including the gluteus medius muscles in the buttocks and the illiotibial (IT) band on the outer hip and thigh are so tight from years of turnout. As Friend points out, the femur head (the top of the thighbone) needs to be able to do more than just externally rotate; it must move in toward the midline, toward the inner part of the hip joint. In addition, the femur head must glide back within the socket. To help with these movements, Friend suggests that some students can actually benefit from manually rotating their upper thighs inward first, so they ground the sitting bones and release the sacrum forward before trying to go into external rotation.
What's a Yogi to Do?