Between perfect nutrition, supplements, steroids, and great technology made specifically to make one "big," I'd imagine we have a leg up on the famous soldiers like the Spartans and such, but how much of a gap was there? Or was there even one for some of the more famously strong in the past? On that note, what was common knowledge for getting tougher? I'm assuming most just became as strong as their job required, but then what was used to get beyond that?
I might can answer this question but I'm not sure what era you are talking about. Do you mean ancient strong men like Milo of Croton from Greek history? If so it is hard to say because their lives are intermixed with mythology, and that is outside my area of knowledge. If you mean strong men from the Strongman era of the 19th century it is easier to say since many of their feats and training methods were recorded and I happen to know a lot about them. Your comparison to Spartans makes me think you mean the more ancient variety.