For those who look upon the practice of Hatha Yoga as some kind of exercise program, the focus tends to be placed on the correct execution and form of the pose being adopted, and there is an ever-greater emphasis on taking on the next advanced pose. Sri Aurobindo reminds us however that the actual purpose of Asana, and thus, the perfection of Asana lies not in achieving new poses or forms, but in using Asana to bring a strong and unwavering power of holding greater energy without spilling it out either in nervous movements or in some kind of mental, vital or physical signs, such as a trembling of the body, which are indications of more energy moving through the system than it can easily hold.
“The body, accustomed to work off superfluous energy by movement, is at first ill able to bear this increase and this retained inner action and betrays it by violent tremblings; afterwards it habituates itself and, when the Asana is conquered, then it finds as much ease in the posture, however originally difficult or unusual to it, as in its easiest attitudes sedentary or recumbent. It becomes increasingly capable of holding whatever amount of increased vital energy is brought to bear upon it without needing to spill it out in movement, and this increase is so enormous as to seem illimitable, so that the body of the perfected Hathayogin is capable of feats of endurance, force, unfatigued expenditure of energy of which the normal physical powers of man at their highest would be incapable. For it is not only able to hold and retain this energy, but to bear its possession of the physical system and its more complete movement through it. The life-energy, thus occupying and operating in a powerful, unified movement on the tranquil and passive body, freed from the restless balancing between the continent power and the contained, becomes a much greater and more effective force.”
The power of bringing the body under complete control, able to hold whatever is brought to bear upon it, represents the perfection of Asana. In this case, it is not even really relevant which particular pose is adopted. The Hatha Yoga practitioner uses Asana as the first step in achieving capacities far beyond what we consider to be the normal human capacity, yet this is not the goal but just a first step in the process of liberating the consciousness from control by the physical body.
Sri Aurobindo, The Synthesis of Yoga, Part Two: The Yoga of Integral Knowledge, Chapter 27, Hathayoga, pp.. 510-511