But the vast, vast majority of people are _never_ going to develop "real" muscle mass in the meaning of the word used by weight lifters. It is much easier to ge

But the vast, vast majority of people are _never_ going to develop "real" muscle mass in the meaning of the word used by weight lifters. It is much easier to get someone to do a few push-ups/crunches every other day than it is to get them to go to the gym consistently. The benefits of simple calisthenics for muscle building aren't necessarily that great, but just doing them in the first place is already a big win. You will definitely get "fitter", but maybe not _that_ much stronger/bigger.