I use to teach fitness classes even before the iPhone was a thing. Even then I used a 30 pin to 1/8" adapter so I could get line level output. I also had a cassette adapter with a 30 pin connector for my car. I could hit fast forward and rewind on the cassette player and it would fast forward the audio on the iPod. When I took the adapter out or stopped the car, the iPod stopped. Of course these days even my cheap low end car has Bluetooth.

I would just carry a lightning to headphone cord (not adapter) if I were still teaching.