Santosha , the cultivation of perfect contentment, the result of which is tranquillity and equanimity of the mind under all circumstances. Svadhyaya , thorough and detailed study of Yogic literature and constant reflection over it so as to prepare the mind for the reception of real knowledge from within. Asana , posture. It should be steady and comfortable and maintained for a considerable period of time. All movements of any kind whatsoever should be eliminated.
Rigidity is definitely wrong.
What should be aimed at is the ideal combination of immovability with relaxation. In Hatha Yoga books it is said that a particular Asana is considered to be mastered when the sadhaka can maintain it steadily and easily for four hours and twenty minutes. But this has really no important significance. It gives merely an approximative idea of the length of time for which practice may be undertaken for gaining mastery. Since the Asana-anga is part of seven angas, physical exercises are not an end in themselves.