A gym in Portland, Oregon (where else?) claims to produce 36 percent of its electricity from a combination of solar panels and special exercise bicycles that transform patrons’ exertions into electricity.

The idea is straightforward: Exercise equipment that provides resistance turns your effort into waste heat, so why not turn it into usable electricity instead? So far, three different companies have applied this technique to stationary bicycles, elliptical trainers, and stair-steppers. The Green Microgym in Portland uses a type of custom-made stationary bicycle to produce power.

Other gyms have gotten in on the act, including the New York Sports Club on Eighth Avenue in Manhattan, and, most famously, Hong Kong's California Fitness gym.

Unfortunately, yuppies turn out to be a fairly inefficient way to turn quinoa into electricity. The average person, even one in reasonable shape, only produces energy at a rate of 50 to 150 watts when exercising, according to IEEE spectrum. That amounts to about $18 worth of electricity per machine per year, which means the technology will probably never pay for itself.

Gym owners who are serious about conservation would be better off paying for better insulation, but that would miss what might be the most important intangible benefit of these efforts: consciousness-raising. If we were all forced to think about how hard it is to make energy, maybe we'd be less likely to waste it by going to the gym in the first place.