While talking to my coworker about my Shape Up series, I mentioned I wanted to take a dance class. She swore by Grit Fitness’ step aerobics class, so I signed up for an evening session. I was pumped.

There’s no time capsule quite like an ’80s aerobics class. “Physical,” the Apple TV+ series starring Rose Byrne as an aerobics instructor whose punishing inner dialogue reflects an era before body ...