What is yoga? Part 6: Asana - Lightness in the body
The Third Limb of yoga is asana - body position. In the Yoga Sutras Patanjali says that the position of our body, while referring to the posture for meditation, should be "stable and comfortable." He does not mention any of the postures that we do in yoga classes in the modern world - they are described in other texts, for example, in Hatha Yoga Pradipika. Patanjali emphasizes that the yogi should use his body in such a way that it becomes a tool for further spiritual development and meditation.
Asana is not just the ability to sit still with a straight back in a meditative posture - it is the practice of the body, when we learn to be present, to check how our bodies are feeling, to be attentive to our bodies. When we focus on the breath and specific parts of the body (muscles, bones, internal organs) during yoga, we develop focused awareness. We bring our thoughts back to the body and breath again and again during yoga, and this "trains" our mind to be focused and present, which is critical to success in the following areas of yoga, such as meditation, as in our life in general. When we can control our body and mind, we can control our life.