Posture Clinic - Downward Dog
Adho Mukha śvānāsana - Downward Facing Dog
Adho Mukha means having the face downwards. Svana means a dog. The pose resembles a dog stretching itself with head and forelegs down and the hind legs up, hence the name - B.K.S Iyengar, Light on Yoga.

Technique
Start the pose with your hands. The middle fingers of both hands point forward. Spread the rest of your fingers and push your hands into the ground. Your hands are the foundation of the pose. If the hands are incorrect the pose is compromised.
Bend into the knees to begin with and push your hips towards the back of the room straightening your arms in the process.
Feel like the base of your spine is being pulled back and your spine is getting longer.
If you can maintain a straight spine, slowly straighten the legs as much as you can. If the lower back starts to curve, bend into the knees
Make your spine your priority, not the legs.

The image above represents what happens to your spine when you focus on your hamstrings too much. If the hamstrings are tight, they will pull on your pelvis. This compromises the natural position of the spine and, in some cases, causes lower back discomfort.
The image below shows what the spine should look like. Try to make your spine a priority. Bend into the knees and, as stated earlier, visualise your spine being pulled from both sides.

Below: The complete downward dog pose.

B.K.S Iyengar in Light on Yoga, asserts that this asana stretches the shoulders, legs, spine and whole body; builds strength throughout the body, particularly the arms, legs, and feet; relieves fatigue and rejuvenates the body; improves the immune system, digestion and blood flow to the sinuses, and calms the mind and lifts the spirits.
