"The whole spine is stretched back and is toned. This pose can be tried conveniently by the elderly and even by persons with spinal injury." -Light on Yoga, B.K.S. Iyengar
GROUND YOUR ANKLES: The foundation of this pose can be found in the press of the top ankles into the floor. For most of us the weight moves onto the knees in this pose. Instead, squeeze your outer ankles in (I could be doing a better job of this in the photo!) and press the tops of your ankles down, extending your toes back along the floor. If you have trouble getting your ankles down, use the fold of a blanket so you have something to push into. What is the effect on your hips and pelvis?
RELEASE YOUR GROINS: Having established your foundation in the ankles and legs, keep your lower back long and enable an extension of your upper body start by releasing the inner groins of the legs. I am self-adjusting the pose by using my fingers to spread my inner groins apart. Practicing going back this way a couple of times. Is one groin gripping more than the other? What is the effect on your lower back, knee and even on your neck and shoulder?
ENGAGE YOUR SHOULDER BLADES: One of my favorite ways to practice and teach this action of the shoulder blades in Ustrasana is using a chair. Kneel in front of the chair and "back it up" so that your buttocks or thighs touch the front edge of the chair (depending on your height). Your shins will now be underneath the chair seat. Practice the actions above with your hands now on your hips. Then, arch your chest up towards the ceiling and place your hands on the back of the chair seat, palms down. Pull the chair towards you with your hands to bring your shoulder blades into your ribs. Bend your elbows slightly and pull your elbows apart to create space between your upper shoulder blades that will allow your neck to extend back. Finally, hug your bottom, outer shoulder blades in towards the spine to create a doming lift in your upper chest. Now try this same action with your hands on your feet or if you cannot reach, a bolster over the ankles or two blocks on the outside of your ankles.
ASCEND UP: "The great rooted tree by the flowing river." If you look at a statue of the Sage Patanjali, the lower half of his body is a snake with three coils and the upper part of his body is human. The three coils of snake are think and solid and stable as his human form rises up. Can you embody these virtues in Ustrasana (camel). The hips and legs representing the "great rooted tree" while the spine and upper body "flows like a river". To uplift your heart, squeeze the vertebrate on either side of your spine right behind your spiritual heart and lift straight up towards the ceiling while extending the front of your throat and keeping the nape of your neck moving away from your ears.
Now, what other poses are these actions preparing you for?