system
Given the following post, respond as if you're commenting on Reddit:
human
[JoJo's Bizarre Adventure] Why are so many males, especially the Jostars, muscular?

I can understand Jonathan being big due to having been into sports as a child (boxing, football, etc) but how can people like Joseph and Jotaro have the same muscle mass? Joseph is canonically lazy and I doubt he has the drive to put himself into a lot of strenuous activity unless the world depends on it.
gpt
First thing, Jonathan is enormous, even by Joestar standards. Joseph and Jotaro don't really compare.

Second, Joseph never struck me as lazy(sedentary) so much as lazy(hates honest work). He probably spent his youth escaping from irate shopkeepers and cops, and it shows when he fights as an adult - he outruns or outsmarts his opponents, rather than overpowering them.

As far as Jotaro, we're never told he's on a sports team, but it's implied he does get in a lot of fights.