Every week, it feels as if there’s a hot new fitness trend. The classes are full, there’s a line at the squat rack, and there’s a good chance you know someone with a stationary bike in a corner of their apartment. When it comes to how we choose to move our bodies, we have options. But our pilates (and barre and weightlighting) obsession did not come out of nowhere.

That’s where Danielle Friedman comes in. She’s a journalist and author of the book, Let’s Get Physical: How Women Discovered Exercise and Reshaped the World. According to Friedman, we’re living in a fitness golden age, but it wasn’t always this way. In the 1950s, people were actively discouraged from exercising. “For women, exercise was seen as especially dangerous,” she says. “There was a widespread belief that strenuous exercise would make your uterus fall out.” This week on Explain It To Me — Vox’s weekly call-in podcast — she tells us how the messaging around movement changed.

Below is an excerpt of our conversation with Friedman, edited for length and clarity. You can listen to the full episode on Apple Podcasts, Spotify, or wherever you get podcasts. If you’d like to submit a question, send an email to askvox@vox.com or call 1-800-618-8545.

When did we first start to see our ideas around exercise evolve in America?

The post-World War II era was actually a time when Americans were moving less than ever before that then helped give rise to what would come. After all of the hardships of the Great Depression and the war, Americans were really embracing what they called the “modern way of life,” which largely meant exerting yourself physically as little as possible, particularly in the middle and upper classes. Push button appliances became popular, ranch houses eliminated stairs, driving replaced walking, and TV exploded.

So the good life meant a life of little sweat, and it was at that point when the first real fitness influencers stepped onto the scene through TV. The message that exercise was both necessary and good for you was beamed........

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