What happens if some guy hits the air/wall 5000 times every day

You get arthritis.
You also get broken bones, if you don't work up to that physical stress over time.

>>841649
Not a great deal because you don't know what you're doing wrong.

>>841649
You burn calories. that's it.

Don't try punching or kicking anything solid at full strength either, as this anon >>842407 said. You will break your bones if you do all that training and then expect to be able to break boards.

>>841649
you get strong as frick and all the sweet babes think you're hot and smart and funny and cool