You know all those tools in gymnasiums? Often you have to set various levels of resistance and tension in them to fit the strength of your muscles, then you engage in all these repetitive movements. The thing that always bothered me is that, aside from building a healthier body, a lot of that energy is wasted. Why don’t we hook these machines to electric generators and batteries? Perhaps I am being naive about this but couldn’t we use a gearing mechanism and the force in dynamos to generate the resistance needed to build muscle tissue?
I remember when I was at the Exploratorium a few years ago. They had this bike hooked to an electric generator and a bank of lights. The faster you pedaled, the more the resistance in the generator fought back, forcing you to work harder and the more lights went on. Maybe gymnasiums could use this as a selling point–come in and exercise and charge your fuel cells at the same time!