Yoga Sutra 2.50 the fixating operations become long and fine

Sūtra II.50

The external, internal, and fixating operations, practised in terms of place, of time and of number, become long and fine

Of this, of the three kinds the external, internal and fixating operations, practised in terms of place, of time and of number, become long and fine. There is an external operation, an internal operation, and a fixating operation. Of these stopping the flow after (a full) inhalation is the external operation. The operation in which the air from outside is taken in is the external operation, so it is called ‘external’, and others call it ‘filling’ (pūraka). Next, stopping the flow after (a full) exhalation is the internal operation. When the internal air is expelled away to the outside, it is the internal operation. Because it is internal air here, it is called internal, and others call it ‘expulsion’ (recaka).

But the third is the operation of fixation, not preceded by either of the other two neither the drawing in nor the exhaling and effected by a single effort. As water thrown on a heated stone shrivels up on every side so from a single effort, the operations of prāṇa and apāna simultaneously shrink to nothing and as he says, the flow of both ceases.

All three are practised in terms of place: in the external operation, the current drawn in is felt going through the space from the tip of the nose to the toes, and with the internal operation the expelled air is felt going through the space from the toes to the tip of the nose. In the operation of fixation it is felt pervading the body from the head to the soles of the feet. And again, its pervasion is measured by its range (the effect of breath on a hanging thread at a distance) of so many spans etc.

(They are) practised in terms of time – how many moments each can be maintained, how many moments the prāṇāyāma can be extended; and in terms of number – how many inhalations and exhalations it takes how many moments are counted to have passed till the first upstroke. The first up-stroke is when the held-in and excited airs first (rise up and) strike the head and cease there. This is the mild practice. Then, when the restrained air has risen in the up-stroke the first time, he counts how many exhalations it takes till the second up-stroke, and the prāṇāyāma taken to this point is said to be medium. Then the third one is practised by counting the number of inhalations and exhalations it takes till the third up-stroke. This practised to a third up-stroke is intense. Practised in this way by place, time and number, breathing lengthens out to extended periods, as the stages are mastered. The holy texts say that sages (ṛṣi) could prolong a breath for years. So it becomes long. And as the breathings become long and slow, they also become fine.