Hi All:
Spinal breathing is the mainstay of the kriya tradition, of which Yogananda is an important a part -- the part that came west.
The various lines in kriya teach spinal breathing with different nuances, reflecting style and local culture.
Norman Paulsen, a direct disciple of Yogananda, teaches some deliberate breath suspension in his style of spinal breathing, though I do not believe it is involved in Yogananda's SRF style kriya. See Paulsen's book "Sacred Science" on this. Yoni mudra is a different story, which nearly always involves breath retention, and is part of the kriya lines also.
In AYP we don't use deliberate breath suspension in spinal breathing -- this is reinforced in the new Spinal Breathing book. But we do use it in other practices, as comfortable, like yoni mudra and chin pump, which is standard for these practices in the kriya lines and elsewhere.
So, except for removing the style and cultural add-ons, the AYP treatment of both spinal breathing pranayama and kumbhaka (breath suspension) is pretty standard. What is vastly different in AYP is the flexibility to independently integrate complementary practices (like spinal breathing and deep meditation) and self-pace as necessary. That is a big step forward, enabling highly efficient self-directed practice instead of having to run to "the guru" for every little thing, and then end up in trouble anyway due to the absence of ability to engage in self-pacing on the fly as needed.
With self-pacing, it becomes clear that slow deep breathing and kumbhaka are simply variations on the same principle of restraint of breath, and that we can regulate the application of this principle up or down according to the results we are seeing from our practice -- cause and effect. In this way we can maintain good progress with comfort and safety.
It should also be mentioned that AYP adds back some things that were down-played or removed from many of the teachings that came west from India in the last century. Kechari mudra is one example. A clear presentation of tantric sexual principles is another. Things like these were generally regarded to be "too much" for westerners at the time, and maybe for easterners too. Probably right. But times have changed, yes?
Make no mistake about it, we are standing on the shoulders of giants like Yogananda as we forge ahead into the 21st century. Without them, where would we be? If our successors can benefit half as much from our practical application of the principles of human spiritual transformation, then we will have done our job.
The guru is in you.