Ardha means half. Matsyendra was a sage or Siddha who spreaded the teachings of Yoga, which is mentioned in the medieval Yoga text the Hatha-Yoga-Pradipika. This posture is also called the Spinal Twist because the spinal column is twisted gently.
1. Sit on floor with straight leg.
2. Bend the left leg and keep the heel under the pubic(buttock) bone.
3. Cross the right leg over the left and place its ankle near the left knee.
4. Cross the right hand against left knee to touch the lf big toe.
5. Turn your body to the left and take the left arm behind your back.
6. Do not put much strain and follow breathing effortlessly.
7. Repeat the posture for the other side by reversing directions 2-6.
It is one of the best Yogasana for cultivating flexibility and strength in the spine. It is useful as preparation and counter pose to more extreme movement of the spine, like forward bends and back bends. It softens the back and spine, release the neck, quietens the nerves and internalizes the mind. It soothes stiff necks and upper back tension caused by stress, poor posture, or prolonged periods of sitting in one position. All kinds of backaches are cured by its practice. It tones up the pancreas, liver, heart and lungs.
People suffering from peptic ulcer, hernia and hyperparathyroidism should practice this under expert guidance. People with sciatica and slipped disc may benefit from this, but great care should be taken.