Milo of Croton is often cited as the earliest recorded examples of a progressive resistance training program: "He would train in the off years by carrying a newborn calf on his back every day until the Olympics took place. By the time the events were to take place, he was carrying a four-year-old cow on his back. He carried the full-grown cow the length of the stadium, then proceeded to kill, roast, and eat it."
https://en.wikipedia.org/wiki/Milo_of_Croton