- sthira = stable
- sukham = comfortable
- aasanam = Posture
Patanjali does not prescribe difficult, unstable methods of sitting. The need and use of aasanam is - to ensure that the Sadhaka is able to sit comfortably and in a stable manner – for the length of his meditation.
If you practice Soorya Namaskaar in early morning hours for a few days – and continue it thereafter – slowly, your bones and muscles will allow you to sit stably and comfortably for sufficient time. Never force your body into painful exercises. It is not advocated by Patanjali. Body is an implement. It is unique for each Individual. Each Individual can therefore choose that aasanam which is suitable and satisfies the twin conditions of stability and comfort.
All that can be said is – wherever possible, sit on the floor – on which you can erect a slightly raised, firm platform / pedestal, for sitting. If sitting on floor or pedestal is not at all possible for you – choose a comfortable chair. The back of the chair must however be erect. The back bone needs to be erect, stable and comfortable for meditation. But, do not keep backbone also stiff and rigid.
There are also some highly supportive environmental supports for aasanam and meditation practices. If the Sadhaka can arrange such environmental support, he can perform the aasanam and meditation near a river bank, or in a beautiful garden under a tree, or in one's own house in an exclusive room reserved for such meditation pactices.
The room should be clean, bland, but may have pictures of one's ishtadevata, which can be decorated in a simple manner with flowers, and can have mild fragrance. Those who are accustomed to performance of Pooja or Prayer - can also complete the same, and start asanam - after that for meditation.
If a slightly raised platform / pedestal is used, the platform / pedestal must be sufficiently wide to cover your sitting are, must be of small height (of just a few inches) to prevent any insects from reaching your body, and must not make you dizzy because of the excessive heights.
One must not be taken in by some movies showing meditations being performed at the end of a cliff of a mountain and in other risky places. These are not at all desirable for Sadhakas of Ashtanga Yoga. Aasanam must be STABLE and COMFORTABLE. It is the simplest prescription from Patanjali.