Paschimottanasana is practiced for extended stretch to the inner muscles of legs and the shoulders. It facilitates chest building with even distribution of energy between the upper and lower portions of the body. This is called Padaprasara Paschimottanasana.
After sitting with the legs wide apart, one has to interlock the fingers behind the back to begin with. Then turn the trunk to the right, raise the arms up behind straight and bend down to touch the knee with the nose. This position can be maintained for considerable duration after continual practice. In the reverse, trunk has to be raised and arms lowered.
The same movement is to be continued turning to the left and further to the centre. As seen in the picture bend forward so as to touch the forehead to the floor directly in front of the body while raising the arms as high as possible from behind. This completes one round.
Inhale while beginning, exhale while bending forward and make the breath slow and deep in the final position or keep it out(baahya kumbhak) for a while.
One precaution is that this asan should better be done after back bending asanas like bhujanga, chakra, matsyasana and when once a beginning is made, it should be with the paschimottanasana and not directly with this difficult one.
An extended and dynamically stretched posture of this ensures mental elevation and physical flexibility to the maximum extent setting aside all sorts of abdominal disorders.