The idea that the "earth" is pushing anything up - is incorrect. The Earth "sucks," literally.
That pushing up is not occurring. What is occurring is the releasing of the temporarily-stored positive energy. If you squat down, and then jump up - the power is not coming from the earth. It's coming from the stored energy in your legs that you compressed when you did the squat. And the energy is not released up. It's released down. That why we go up. The energy is drained - most effectively - and "in as pure a form as possible" through the decoupling of the body and the earth - through the inverted cones created by mainly the toes. And out of the toes - mainly at a point on the bottom of the big toe.
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.