Fellow Travellers… why so gym-fit?

I’ve just started watching the series Fellow Travellers and I’m constantly being thrown out of the period of the drama by the muscularity of the cast. Surely this is anachronistic? I know there was a culture of men’s health magazines in the 50s and 60s but the fact that everyone is so ripped is very unperiod. Even the geeky politico journalist is toned to gay porn standards. Gym culture didn’t really kick in until… what… 2000? It really does feel a major fail. Or does anyone know any better?