“One should move the spine as you would inhale and exhale.”
– TKV Desikachar

“Is it a misdirection within Āsana from talking
about effects on the body as if on the spine?
Thus too much focus on talking about effects on the body
and not enough on looking at the actual effects on the spine?”

“Bṛṃhaṇa Kriyā and Laṅghana Kriyā as expansive and contractive activities are two potentials actualised through the Breath and Āsana.
Within the practice of Āsana, Mudrā and Prāṇāyāma they are actualised through an understanding of the primary principles that inform Haṭha Yoga and Āyurveda.
The alchemical process underpinning this understanding is the relationship between the two primary principles of Prāṇa and Agni in order to influence Haṭha Yoga concepts such as Prāṇa, Apāna, Nāḍī, Cakra, Agni and Kuṇḍalinī.
In terms of Bṛṃhaṇa Kriyā and Laṅghana Kriyā, the viniyoga of Bṛṃhaṇa affects a dispersion of Agni from the core to the periphery and the viniyoga of Laṅghana affects a withdrawal of Agni from the periphery to the core.
Understanding the application of this particular process facilitates access, through the Merudaṇḍa, Prāṇa and Agni, to energising, cleansing and aligning potentials in the practice of Āsana, Mudrā and Prāṇāyāma.”