Calisthenics is the oldest form of resistance training using only body weight. It was practiced in ancient Greece and contributed to the Spartans' strength and endurance in battle. While calisthenics experienced popularity in the 1800s and 1950s, the 1960s-70s saw a shift toward bodybuilding focused solely on muscle size, often using steroids. Calisthenics was then seen as only for vulnerable groups and its advanced techniques were lost, though it created some of the strongest humans ever.