In Hathayoga Pradipike Paschimottanasana is described asPrasaarya paadau bhuvi dandarupau dorbhyam padaagra-dvitayam grihitvaa jaanuparinyasta-lalaata-desho vasedidam paschimataanamaaham28Iti paschimataanamaasanaargryam pavanam paschima-vaahinam karoti udayam jatharaanalasya kuryaadudare kaarshyamaroghataam cha pumsaam29
Meaning: Having stretched both the legs, like a stick, and having grasped the toes of both the feet with both the hands, resting the forehead on the knees, it is called Paschima-tana.This is most excellent of all Yogasanas. This Paschima-tana carries the air from the front to the back part of the body. i.e., makes the Prana to flow through Sushumna. It kindles Jatharaagni (gastric fire), reduces obesity and cures all diseases.
This Asana is also called as Paschima-tanasana. There is no difference between Paschimottanasana and Paschima-tanasana.
Procedure:
Sit on the ground. Stretch the legs in the front. Slowly do exhalation and hold the thumb of left leg with left hand and hold the thumb of right leg with right hand. Then slowly try to bend the face and body towards the knees.
