This might be a primary disconnect, then - since if you're not understanding how the ground provides a counter force to gravity - without you having to do anything, flex any muscles, etc. Internal strength at it's baseline takes advantage of that when you push on the ground, the ground pushes back - how purely you've trained your body (to cite your example of the legs above - there's much more than that going on) to capitalize on this will affect the effect you have when you move/hit/throw with internal strength.
I agree with - - without you having to do anything, flex any muscles, etc.
Because, there is absolutely no "pushing" involved. At all. In any way. Ever. There is only releasing/draining.
And you'll come around on the rest. : ) This is simple physics. Jet propulsion. Even bottle rockets - fueled by carbon. What's carbon? Stored energy from the sun. The bottle rocket doesn't go up - or in your neighbor's wife's beehive hairdo - because it's pushing or being pushed. It's being propelled ( <--- note that word ) by the release of the energy in the carbon.
When you make a campfire, what makes the wood burn? Where does the energy come from to produce the fire? The earth. bzzz. Sorry, wrong answer. The tree. bzzz. Ooh, sorry again, wrong answer. Contestant number three... The sun. ding, ding, ding, ding. Hal, we have a winner, tell him what he's won.