Physicist: A person on a bike can optimistically generate around 200 watts, and an average nuclear power plant generates 800 MW of power (although a big nuclear power plant generates many times more power than a small one).
Given those two “statistics”, it would take somewhere around 12 million people on bicycles for eight hours to equal the power output of a single nuclear power plant for a day. Based on schematics for Viking longships, which were essentially mobile motivation machines, we can reasonably say that a “spin class power plant” would take up about 6.5 square miles (not including walkways or bathrooms) and require about 300,000 task-masters to keep the power supply steady. This, it’s worth noting, exceeds the total number of taskmasters currently living in Norway (oppgave mestere i Norge unite!).
The take home point is: nuclear energy doesn’t mess around. Other than extension cords (a technology still in its infancy), there really aren’t any other ways to, for example, power a spacecraft on a 50 year mission beyond the solar system, or to run a submarine for a few decades without refueling, on nothing more than a bucket-full of fuel.