I've been reading through Chris Li's excellent translations of Morihei Ueshiba's writings. I know practically nothing of internal training practices and I'm quite fascinated by the implications of all this stuff.
Cutting to the chase, Mr. Li writes "So to sum up - the Floating Bridge of Heaven, also known as Heaven-Earth-Man, consists of creating a state within yourself by which you connect opposing forces and express that connection in spirals through the body."
Well I about did a spit take as I had stumbled across a video a while back known as the Slinky Drop. In it an everyday garden variety slinky is held up so that it stretches to its full length, then it is simply let go. Difficult to observe what happens with the naked eye, slow motion video reveals that the slinky just hangs in space for a moment, floating between the upward tension of the demonstrator's pull and the downward pull of gravity. Here's a quick vid of the demonstration and an explanation.
Now again, I plead complete ignorance on the subject in internal strength training. And this video may be completely off base with the subject and just an unrelated but interesting phenomenon, in which case I apologize for wasting bandwidth. But... just look at that thing! Between two equal and opposite pulls, balanced and floating. I know humans can't literally hover off the ground, but to generate that sense of balance between the forces internally, that gets my attention.