How to build a practical household bike generator

It's a small thing, but I really appreciated the optimism of this sentence:

Athletes could produce more power, while couch potatoes would (initially!) generate less.

I always enjoy reading this author's work, but this one is almost cheating because I enjoy reading technical writeups about things people have built. I'm a little disappointed that they didn't experiment with a supercapacitor, though.

I think I'd rather buy a bike than make it at home