Nāsikāntarmadhyasaṁyamāt kimatra savyāpasavyasauṣumneṣu
नासिकान्तर्मध्यसंयमात् किमत्र सव्यापसव्यसौषुम्नेषु॥ (sūtra III.44)

nāsika – the energy of prāṇa, also known as prāṇaśakti; antar – inner; madhya – centre; saṁyamāt – intent awareness; kim – what else; atra – in this respect; savya – right; apasavya – left*; sauṣumneṣu – the middle one. 

The prāṇa, also known as the vital energy, that has been discussed in the previous aphorism, flows through three main nerve channels of the body viz. left (iḍā), right (piṅgalā) and central channels (suṣumnā). In the middle of intent internal awareness, the supreme ‘I’ consciousness is seated. The yogi always establishes himself in this inner awareness.

Irrespective of the channel through which prāṇa traverses, the yogi never allows his awareness to get distracted. The yogi, by experience has learnt to direct his prāṇa at his own will. He accomplishes this by his intent awareness and not by his breathing. His prāṇa is controlled by him. In other words, he directs his life energy at his own will. He now attains the supreme power of the Lord. This happens to him because he stays connected to the Lord at all times.

The difference between a perfect yogi and a mediocre yogi is that, the former activates kuṇḍalinī energy at his own will, without resorting to breath control. In the case of the latter, he could activate his kuṇḍalinī energy by breath control.

*Gabriel Pradīpaka clarifies on the two words savya and apasavya in his site http://www.sanskrit-sanscrito.com.ar which is reproduced below with his permission.  

“In order not to have a flock of Sanskrit students correcting my translation of "savya" and "apasavya" as "right" and "left", respectively, I need to say something: Yes, you are right! If you consult a dictionary, you will see that "savya" means "left" and "apasavya" means "right". Anyway, Kṣemarāja is fond of considering the meanings of "savya" and "apasavya" as if they were indeclinables always (whether or not they act as indeclinables). If you check the dictionary, "savya" and "apasavya", as indeclinables --i.e. as savyam/savyena and apasavyam/apasavyena--, mean "to the right" and "to the left", respectively. Now, you can easily understand why he interprets the meanings of "savya" and "apasavya" in an opposite manner to what one would expect. Yes, it is a little hellish and confusing... in fact, it makes me dizzy just reading savya and apasavya, it is like a tongue twister!... but we cannot help it, you know. Remember this in the future, please.”