How effective are calisthenics in gaining muscle?

Question

Someone once told me that Herchel walker gaind all of his muscle from nothing but pushups? is that true?

How much muscle gain can you expect from calisthenics?

Answer 1

Yes that is true,

Jean-claude van dame never touched a single weight until he was weell into his late teens

Answer 2

I gained quite a bit in High school by doing isometricis, which is almost the same thing. I was very toned, but did not build much bulk.