It was a little after noon on March 26, and Naomi Campbell was working out in her living room in New York City.

Disco music on blast, she crushed a set of squats, guided by her personal trainer, Joe Holder, who had tailored the 40-minute workout. As she started a grueling set of flutter kicks, Campbell stopped and glared at her trainer. “Oh my God,” she said. He couldn’t help but laugh.

Holder was not in the room, however. He was monitoring her on camera as she cycled through the circuit. Thousands of other people on Instagram Live were watching too — and participating — in what is normally a private workout between the supermodel and her trainer.

As America hunkers down during the coronavirus pandemic, free fitness workouts, many of them delightfully low-tech, are multiplying on social media platforms. They are being delivered by trainers and yogis and retired athletes. Holder calls these people the “player-coaches for the real world.”