Yoga Sutra 2:46

Sutra 2:46

Sthira Sukham Asanam स्थिर सुखम आसनं

The posture (asana) for Yoga meditation should be steady, stable, and motionless as well as comfortable.

The western exercise regime believes in "no pain no gain", whereas yoga philosophy says, "no pain no pain". The asana needs to be steady and filled with ease. I believe this applies in the real life, no matter what the situation your mental state needs to be sthira and sukha. You learn it on the mat, practice with your physical body and then apply it off the mat.

This sutra in a way re-iterates 1:2, yoga chitta vritti nirodh. Yoga is control of the modifications of the mind. You control modifications of the mind by bringing steadiness and easy in your thoughts, words and actions.

Here's what B. K. S. Iyengar has to say:

Asana is perfect firmness of bidy, steadiness of intelligence and benevolence of spirit.


Performance of the asana should be nourishing and illuminative. In any asana the body has to be toned and the mind tuned so that one can stay longer with a firm body and a serene mind.


Usually the mind is closer to the body and to the organs of action and perception than to the soul. As asanas are refined they automatically become meditative as the intelligence is made to penetrate towards the core of being.


Each asana has five functions to perform:

1. Conative - conative action is the exertion of the organs of action
2. Cognitive - cognitive action is the perception of the results of that action. when the two are fused together the discriminative faculty of the mind acts to guide the organs of action and perception to perform the asanas more correctly; the rhythmic flow of energy and awareness is experienced evenly and without interruption both centripetally and centrifugally throughout the channels of the body. A pure state of joy is felt in the celss and the mind. The body, mind and soul are one. This is the manifestation of dharna धरना and dhyana ध्यान in the practice of asana. 
3. Mental
4. Intellectual
5. Spiritual

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Here's a link to the article in YJ on this sutra from Linda Sparrow

http://www.yogajournal.com/practice/893 

This is by Judith Lasater

http://www.yogajournal.com/wisdom/45