Dhanura refers to the bow of an archer and in this pose the spine is curved like a bow. The challenge is to avoid compression in the lumbar spine and pressure on the knees.
Precede with other “belly back-bends” like cobra (bhujangasana), locust (shalabhasana) and frog (eka pada bhekasana).
Begin dhanurasana by taking hold of a strap that you loop over the lower shin region. Even if you are able to grab your ankles, try this preparation. Hold the strap firmly and at the same time drive your shins back away from your head. Simultaneously lift your shins and feet.
Then clasp your shins with your hands while resting your head to the floor. Before lifting up, draw the shoulder-blades back away from the collar bones. As you lift up avoid rocking to either side. The head and feet should be on the same level if possible.
Practice gripping a block between your inner thighs as you rise. This centralizes the support into the inner groins and can take pressure off the knees.
Lastly take both feet into the strap and catch the strap with your arms reaching upward and backward over your head. Keep your feet symmetrical, avoid one foot moving above or behind the other. Pin the inner edge of your feet together. In this last version the arms externally rotate.Dhanurasana puts pressure on the small intestine, the stomach, spleen, liver and pancreas thus helping to irrigate blood and lymph through the gut. It tones the muscular flap of the diaphragm due to the direct pressure on the upper abdomen.