The next limb we'll explore, is the third limb, Asana...
This is a limb that you may know very well. The practice of "posture" and movement. The practice of putting our bodies in different positions, shapes, and contortions to cleanse and purify the physical and energy bodies as a preparation for pranayama (breathwork) and deeper meditation.
While asana looked very different hundreds and thousands of years ago, the roots of asana can be seen in many yoga classes today.
Asana as we know it today often includes a series of sequences, balancing postures, seated postures, backbends, and other therapeutic practices stemming from the tradition of yoga. The history of yoga and asana practice is said to over 2,000 years old, but what we do not know for sure is when the first formal teachings of asana practice began. We have many ideas and can trace the lineage of hatha yoga practices to specific practitioners and rishis (the great seers and sages), but the exact details of how (and even the exact locations where) asana begin are still being studied by religious and sanskrit scholars.
What we do know is that that the wisdom of Patanjali included Asana as part of the 8-limbed practice of yoga. Within the yoga sutras of Patanjali, there is no real instructions on alignment, nor does they offer suggestions for how to improve your headstand. Patanjali instead gives the guidance, "sthira sukham asanam," which encourages practitioners of yoga to find a balance between steadiness and ease.
From this perspective, the goal and practice of yoga is not about how "advanced" you might be in any given posture, but rather to center into the steadiness of the mind-body-soul as you develop greater ease within the body— so that one might sit in meditation free of ailments, tension, and restriction in the body. I would like to say that "ease" does not necessarily mean "easy," but rather is about locating that space within the mind-body complex where the breath meets the body fully, and ease-fully, meaning the breath is free from inner and outer blocks and is moving fully throughout the body without pain or tension.
So whether you are practicing gentle yoga class or a vigorous vinyasa, notice what is happening with the breath in each moment and in each posture — and this relationship of your body and the breath will guide you in what to do next to cultivate your inner wisdom and establish sthira sukham asanam, steadiness and ease.
Resources for further reading:
The Wisdom of Patañjali's Yoga Sutras by Ravi Ravindra
The Yoga Sutra of Patañjali: A New Translation and Commentary by Georg Feuerstein