I have also heard speakers use beefy to refer to fat people, Lukas. In the context you provided, beefy seems to refer to muscularity rather than obesity.Can the words "muscular" and "beefy" be used interchangeably?
Well, you could call a woman beefy. It'd more than likely be taken as being insulting, however. I suppose it may just be me but calling a woman beefy would kind of be like calling her mannish. Or just fat, as other have mentioned.A woman could be muscular. A woman would not be called beefy.