So all this weight or bodyweight training with progressive overload is kind of just a way to communicate to our body and tell it to grow more muscles and strength?

Muscles are incredibly inefficient.

That's why people that work 12 hour days doing manual labor were "skinny strong".instead of jacked.

To get huge muscles, we need to trick our bodies into thinking we randomly have to move heavy weights every once and a while.

Part of that is slowly increasing the weight so they muscle rebuilds even bigger otherwise it would just stay the same. If you stop, your body stops wasting the energy for those huge muscles and they get smaller.

...and your body fighting back because its working under the design that calories are still very difficult to get on a regular basis. So its not going to use the precious calories you give it to build all kinds of calorie consuming muscle and bone mass unless you show it is necessary or that you'd eventually die without it the muscle.

Just muscles?

It tells your peripheral nervous system to grow and optimize wiring to increase recruitment and activation, attenuate signal noise, boost reflexes and responsiveness, and improve sensory feedback.

It tells your circulatory system to branch out with many small vessels and more limber large vessels, all with improved resource transmission and lots more oxygen.

It tells your connective tissues you need higher quality rigging with less friction.

It tells your bones they need to shape the fuck up and increase their density.

It tells your endocrine system to quit being cheap and give you the good stuff.

It tells your immune system to chill out and focus.

And much more. Ultimately the supply chain requirements for the additional work leaves no system untouched.

You are what you do. Your body will adjust to what your regular physical activity happens to be, combined with what you choose to feed it.

This is the wrong community for this