It strikes me as how the body gets used to calisthenics real easily, it could get used to slightly weighted calisthenics just as well.
Try that out as an experiment.
…..
Do high reps regularly, but do them weighted ever so slightly.
Then add a bit, but keep those reps in the stratosphere.
Eventually you’ll be doing pushups for sets of 50 with a person, even an impressively large person or two small humans, standing on your upper back.
Persistence & Tenacity