Board Thread:Warhammer 40k General Discussion/@comment-7699236-20150618150629/@comment-8881468-20150619140255

you'd really have to do tons of things to the female hormone output as they have little testosterone (muscle growth) and in general are ~ 10-20% weaker than men(only talking muscle mass and density here)...

then again I think in Scars there is a quote of Malcador telling them Empi to make the Primarchs women coz then things would be more civilised (at least in the audiobook version) ^^