Muscled bros might act like they own the modern gym. But in his new book, Lift: Fitness Culture, From Naked Greeks and Acrobats to Jazzercise and Ninja Warriors, Daniel Kunitz argues it was feminists who popularized organized fitness. In the mid–20th century, exercise was a fringe hobby; men were more likely to play casual games of tennis or basketball, while women tried to slim down through dieting. But the rise of feminism, Kunitz writes, encouraged women to pursue “strength, self-confidence and camaraderie,” which led to fads like aerobics and Jazzercise. Soon, women were training for marathons, attending kickboxing classes and signing up for co-ed gyms–which enticed men to sign up too. Now in the age of SoulCycle, CrossFit and Bikram yoga, Kunitz concludes, men and women alike are able “to assert control over their bodies and experience euphoria in doing so.”
This appears in the July 11, 2016 issue of TIME.