Are you seriously saying that tights weren't invented back then....spandex was invented in 1958 and tights have been around forever
And do you actually have knowledge on make up/effects or are you just making the assumption that hair couldnt be attached ...?
Re-watching that "muscle" jiggle I've come up with another explanation, could just be something in the dudes pocket under the costume like his wallet and keys etc also seems there's a crease at the top that bulges out could also suggest a pocket. But as I said the video is just too poor quality to say real or fake.