Kriya Yoga is so effective because it works directly with the source of growth — the spiritual energy deep in our spines.
All yoga techniques work with this energy, usually indirectly. Yoga postures, for example, can help open up the spinal channels, and balance the energy in the spine. Yoga breathing exercises can help to awaken that energy.
The Kriya technique is much more direct. It helps the practitioner to control the life force by mentally drawing it up and down the spine, with awareness and will. According to Yogananda, one Kriya, which takes about a half-minute, is equivalent to one year of natural spiritual growth.
The technique itself is taught through initiation. As Yogananda said in his autobiography, “Because of certain ancient yogic injunctions, I cannot give a full explanation of Kriya Yoga in the pages of a book intended for the general public. The actual technique must be learned from a Kriyaban or Kriya Yogi; here a broad reference must suffice.”
You can learn more about the technique by reading “The Science of Kriya Yoga” in Autobiography of a Yogi.
“The Kriya technique will bring you to the source of inspiration and will give you answers, clear the brain and stimulate it, strengthen the medulla, and open the spiritual eye, as well as greatly magnetize the body.
”By this method, the blood becomes so oxygenated that gradually dependence upon mortal breath becomes less and less. In this way the student of Self-Realization lives more by the Word of God, or Cosmic Energy, and less by the bread of life, or breath and solid and liquid foods. When the current is sent through and around the spine, the higher perception of God in the spine and brain is felt. The spinal cells then become the whole body.
“These are control of prana exercises and not ordinary breathing exercises. Numberless students have practiced these Kriya techniques with the greatest benefit to their spiritual and moral growth.”
— Paramhansa Yogananda