From forum #170108, it seems like the intent was for muscular to become a sort of umbrella tag for big_muscles, huge_muscles, hyper_muscles and other muscle-related tags (like muscular_male). But the wiki page was simply carried over from muscles and never substantially updated.
Is muscular purely an umbrella tag, or does it on its own imply a level of musculature somewhere between athletic and big_muscles? If it's the latter, how could that level be defined?
Prompted by forum #259802.
Updated