Re: "Conventional Muscles" and Internal Power
Even in traditional athletics, it's well known that the body can use different sets of muscles, or a different balance across sets of muscles, to accomplish the same movement.
Going back to my weightlifting days, a bench press can depend primarily on the pecs, anterior delts, triceps, or lats. A common limiting factor is depending too much on delts and tris and not getting the pecs engaged. The common fix for this is imagery: "Imagine there's a rubber band connecting your elbows. As the bar comes down, you're stretching the band. Then as you raise the bar it's pulling your elbows together."
Similarly for squats, depending too much on quads and not enough on hams and glutes. There's a set of visualizations to help lifters get the posterior chain involved.
So I don't see the IS imagery as magic or particularly unusual. Any time you want to get the body to move differently, it seems, people use visualizations to help create the new movement patterns. And the visualizations rarely have anything to do with physics.