Paschimottanasana and Halasana bend the spine forwards. Dhanur, Bhujanga and Salabha Asanas are counter-poses to bend the spine backwards. This is not sufficient. It must be twisted and bent from side to side also (lateral movements). Then only perfect elasticity of the spinal column can be ensured. The Matsyendrasana serves this purpose well in giving a lateral twist to the spinal column.
Place the left heel near the anus and below the scrotum. It can touch the perennial space. Do not allow the heel to move from this space. Bend the knee and place the right ankle at the root of the left thigh and rest the right foot well on the ground close to the left hip-joint. Place the left axilla or arm-pit over the top of the vertically bent right knee. Push the knee now a little to the back so that it touches the back part of the axilla. Catch hold of the left foot with left palm. Then applying pressure at the left shoulder-joint slowly twist the spine and turn to the extreme right. Turn the face also to the right as much as you can do. Bring it in a line with the right shoulder. Swing round the right arm towards the back. Catch hold of the left thigh with the right hand. Retain the pose from 5 to 15 seconds. Keep the vertebral column erect. Do not bend. Similarly you can twist the spine to the left side.
This Asana increases appetite by increasing the digestive fire. It destroys terrible diseases. It rouses Kundalini and makes the moon-flow, Chandranadi, steady. Above the root of the palate the moon is said to be located. It drops the cool ambrosial nectar, which is wasted by mixing with gastric fire. But this Asana prevents it.
It keeps the spine elastic and gives a good massage to the abdominal organs. Lumbago and all sorts of muscular rheumatism of the back-muscles are cured. The spinal nerve-roots and sympathetic system are toned. They draw a good supply of blood. This Asana is an adjunct to Paschimottanasan