Americans are flocking to gyms and fitness classes. It wasn't always that way.

This episode was produced by Hady Mawajdeh, edited by Miranda Kennedy with help from Naureen Khan, fact-checked by Melissa Hirsch, engineered by Andrea Kristinsdottir and hosted by Jonquilyn Hill. Photo of an outdoor group fitness class by ANDREW CABALLERO-REYNOLDS/AFP via Getty Images.

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