This article about Jack LaLanne describes him as The Founder of Modern Fitness. The most interesting part of the article is that in 1936 he opened a gym with weights and the medical profession was against him:
“People thought I was a charlatan and a nut,” he remembered. “The doctors were against me — they said that working out with weights would give people heart attacks and they would lose their sex drive.”
I wonder what things doctors are against today, but which we will later take for granted. Maybe some of the ideas in this awesome book.