Q: What areas do I need to work on to be able to sit in simple cross-legged position while maintaining an erect spine?
Sitting cross-legged is an important part of yoga practice and is commonly used for breathing and meditation practices. It requires flexibility in the back thighs, back of the pelvis, and inner thighs, as well as external rotation of the hip joints. These are all very strong muscles that can take a long time to stretch. Whether you sit in a simple cross-legged posture like Sukhasana or a more difficult pose like Padmasana (Lotus Pose), developing the flexibility to sit easily is a gradual process.
And it's important to note that everyone has a different anatomical structure in their hips, which may potentially inhibit this kind of movement. If this is the case for you, then trying to work up to Padmasana (Lotus Pose) is an inappropriate goal. I encourage you to try other poses that may be more comfortable, like Vajrasana (Thunderbolt Pose), sitting on your heels, Virasana (Hero Pose), sitting between your heels, or Gomukhasana (Cow Face Pose). You can also meditate sitting on a chair. The chair should be firm, your back straight, and your feet on the floor or supported on a book or cushion.
If you choose to sit cross-legged, it is important to have your knees level with or below your hips. If you are having difficulty maintaining an erect spine while sitting cross-legged, begin by sitting on the edge of a cushion, bolster, or rolled blanket. For additional support, place rolled blankets or bolsters under your knees. (You may find that with the knees supported, the inner groins relax and that when you take the supports away, your knees drop further easily.)
Tightness in the inner thighs and hips is often connected to tension in the deep muscles of the abdomen (like the psoas). You can begin to release your pelvis by practicing breathing deeply into your abdomen. Focus on the rise and fall of your belly as you inhale and exhale. In all of the poses that follow, imagine the exhalation releasing out of your pelvis and through your legs, helping the thighs to relax and let go.
Standing poses, especially Virabhadrasana II (Warrior II Pose), and Parsvakonasana (Side Angle Pose), will help open the hips. Leg stretches lying on your back, Supta Pandangustasana (Reclining Big Toe Pose), taking the lifted leg both up and to the side will also stretch your legs.
Raja Kapotasana (King Pigeon Pose) forward bend is also an excellent hip opener. Supta Baddha Konasana (Reclined Bound Angle Pose), lying on your back with your feet together and knees apart is a good resting pose that will allow your hips to gradually open. Put a folded blanket or a bolster under your feet, so that your back is resting on the floor. In both of these poses, allow yourself to relax into the stretch, letting gravity help you to sink into the floor as you exhale.
Sitting poses that will help are: Janu Sirsasana (Head-to-Knee Forward Bend), Baddha Konasana (Bound Angle Pose), and Upavistha Konasasana (Open Angle Pose). Learning to stay longer in these poses will help the flexibility in your hips; however, you need to be careful not to overstretch your lower back. Setu Bhanda Sarvangasana (Bridge Pose) and Bhujangasana (Cobra Pose) are good counter-poses.
See alsoSukhasana Isn’t All Easy