The Flow of Prāṇa
Prāṇa flows through channels called the nadīs. Nadī translates to river. This gives us some insight into the qualities of Prāṇa, since that which flows in the river is…water. So, from an Āyurvedic perspective, it is the guṇas (qualities) of water which are close to those of Prāṇa. This is an important distinction since Prāṇa is often incorrectly translated to mean breath, which we associate with air. Air is dry and light and are thus the opposite qualities of water and therefore also Prāṇa. If we think of Prāṇa this way where it is closer to the qualities of air, we’ll end up using āsana to do the opposite of the goals of yoga.
The way Prāṇa flows is called the Gati. It is the rhythmic nature as well as the direction of flow of Prāṇa. This is the Vāyu system which many of us are familiar with. Prāṇa can flow up, down, laterally, circularly, and all around. Āsanas are built to both direct the direction Prāṇa flows as well as the way it flows. When both these things happen simultaneously, the goals of yoga are easier to reach. When they are lacking or are unclear, then the goals of yoga are usually difficult to reach.