Down Dog very clearly puts you in touch with the inherent isometric or push-pull dynamics of yoga asanas, where a movement in one direction is balanced and enhanced by an action in the opposite direction. This has deep philosophical and spiritual significance, corresponding to the meaning of hatha yoga as the union of the sun and moon, the masculine and feminine. The practical benefit of this yogic principle is that in any pose, Down Dog included, you are simultaneously creating strength and flexibility, extension and stability.
The first thing about Down Dog is learning to ritualistically place your hands in alignment with your shoulders and hips. As you lift your pelvis to the ceiling and draw your hips back, look at your feet. They should be hip-distance apart, aligned with your pelvis. Beginners will often walk their feet towards their hands to prematurely bring their heels to the ground. Have patience, grasshopper. Your heels may or may not touch the ground, but you want to feel that you have room to continuously grow in this pose.
What is the farthest vertical point from your hands in Down Dog? Your hips. What is the farthest point down from your hips? Your heels. Assume your Down Dog now and work those opposite points away from each other. Press into your hands and stretch your hips back from the tops of your thighs. Try to ground your heels. (Even if they don’t touch the floor, imagine roots growing from your heels down through the earth.) This movement starts to stretch your spine while evenly opening your hamstrings, hips, and shoulders.
To get the blissful feeling and benefits of Down Dog, you need to shift your weight back into your hips. Again assume your best Down Dog. This time bend your knees so that you can really stretch back into your hips by simultaneously pressing into your hands, extending your arms, and drawing your belly slightly in. Imagine that someone is pulling back on your hips. When you get that “Aha!” it will feel as if your weight is centered in your pelvis, and your arms will feel light. If your hamstrings are very tight, you may need to practice like this for a while, gradually straightening your legs as if a strong wind were pressing your thighs and shins back. You can also place a block between the middle of your inner thighs to learn how to work your legs and develop the inner rotation of the thighs. Grip the block and press it back to feel greater extension in your spine.
Learning how to both internally and externally rotate your arms at the same time to connect to your inner wrist, open your shoulders, and broaden your upper back is a key Down Dog trick. Start on your knees again with your hands in position. Typically the inner wrists start to peel off the ground, causing stress on your joints and a subtle disconnection. To ground through your inner wrist, internally rotate your arms towards each other from your elbows down. Thanks to the anatomy of your arms, your upper arms are naturally going to move in the opposite direction (external rotation). To witness how this happens naturally, when you press back into Down Dog, bend your elbows to the side in a diamond shape. Now rotate your elbows under and straighten your arms, maintaining the internal rotation from your elbow to your inner wrist. You should feel your shoulders broadening.
If this seems confusing, just try rotating your arms in the opposite direction and see how compressed the area around your neck feels. Are you starting to feel any sukha arising as you find relief in your shoulders and neck?
Often humans aren’t sure what to do with their necks in Down Dog. The general tip is to align the crown of your head with the natural line of your spine. If you tilt the crown of your head up, you crunch your cervical vertebrae. Dropping your head forward gives you a nice stretch, but over time can stress your neck. When you are in Down Dog, try aligning your ears with your upper arms. That should connect your head with your spine, simultaneously supporting your head while lengthening the sides of your neck.
Now is the time to breathe life and vitality into your Down Dog. On the inhalation, emphasize the broadening of your shoulders and extension through your arms to bring more space into your lungs. As you exhale, focus on the movement of your legs back and down through your shins and heels. As you relax, you will start to feel how nourishing this stretch is.
Excerpt from Yoga Journal Article Adho Mukha Svanasana by Shiva Rea