I've yet to find any of the classic Charles Atlas body-building ads, but this one is awesome in that it manages to attract boys by appealing to two of their aspirations - a muscle-bound hero, and an astronaut.
Incidentally, most ads of the time encouraged boys to use the program in order to gain weight (or muscle mass), not for the fatties to lose it.
Meanwhile, now I know the astronauts were tough, but I dunno if they were kick-sand-at-the-bully's-face-tough. At the very least they're no longer top of the list for aspiring boys and overbearing parents... at this point I think people honestly do think it would be easier for your child to be president than be an astronaut.
Appeared in Amazing Spider-Man #43, December 1966.