Soorya Namaskar or  Sun exercise

"This exercise is called soorya namaskar because it is practiced in the early morning facing the sun. The sun is considered to be the deity for health and long life. In ancient days, this exercise was a daily routine in the daily spiritual practices. One should practice this at least twelve times by repeating twelve names of the Lord Sun. This exercise is a combined process of yoga asanas and breathing. It reduces abdominal fat, brings flexibility to the spine and limbs and increases the breathing capacity; it is easier to practice asanas after doing soorya namaskar.
Before students practice the more complicated and difficult postures, the spine should acquire some flexibility. For a stiff person, the sun exercise is a boon to bring back the lost flexibility.

There are twelve spinal positions, each stretching various ligaments and giving different movements to the vertebral column. The vertebral column is bend forward and backward alternately with deep breathing. Whenever the body is bend forward, the contraction of the abdomen and diaphragm throws out the breath. When the body bends backwards, the chest expands and deep breathing occurs automatically. This way, flexibility increases and breathing is corrected; moreover it mildly exercises the legs and arms, thus increasing the circulation."

in CIBY by Swami Vishnu-devananda