Just for starters, you might want to read some of Shioda's stuff on kokyu power and the way he attempts to break it down in his books (I feel pretty sure that Shioda had a more sophisticated understanding than is shown in the simplified writing in his books).
Also, this is pretty good, although it's so general I can't tell if the author understood much:
Here's part of an interview with Kenji Ushiro that I recommend you go to Aikido Journal to read: This "breathing," or kokyu, is not so much the kind of breathing that involves respiration by bringing air in and out through your nose and mouth; it's more the kind you do with your body as a whole. If you can cultivate that kind of kokyu, then energy (ki) begins to flow through your body and that flow of energy helps you develop abdominal and back strength. (Because this strength is created through the breath I refer to these as abdominal and back "power" instead of abdominal and back "strength.") This process leads to a kind of "zero power," that you can use, say, to neutralize the power of an incoming punch by just making light contact with it. Even if your opponent comes in with a strong, sharp attack, you simply absorb that energy. And if you absorb it with more energy than he is coming in with, he is suddenly and momentarily deprived of his breath, which immobilizes him there for a moment.
Striking using this kind of kokyu is also very different than striking that relies on the power of strength. A strike done with kokyu extends more than one done with muscle power, and it also doesn't incite any particular urge to block it in the opponent.
In Shindo-ryu karate we use kata to cultivate this kind of kokyu.
Moving from reliance on muscle strength into the realm of kokyu is an incredible turnaround, a wholesale change of method and effect. You could say that this is a kind of energy or potential inherent in traditional kata.