Thank God this wasn't Doc Brown's idea, he'd never get up to 88MPH in that thing.
Man Converts Minivan Into 4-Person Mobile Gym

Tired of sitting in traffic wasting time with nothing else to do (I typically exercise my vocal muscles yelling at other drivers), unorthodox maker of things Handy Geng converted a minivan into a mobile gym, with each seat designed as a different workout station. Plus the energy they generate working out actually powers the vehicle’s slow crawl. I’d be lying if I said that looks like a good time. It would definitely be a time though, I will give it that. *stripping naked in backseat* Now I’m sore, where’s the sauna?

Keep going for the video, but turn the captions on if they aren’t already.