My local gym on a weekday evening doesn't just smell like a sweatshop. It sounds like one. Dozens of people on machines, whirring and spinning and pedaling -- to judge by the activity alone, you'd think it was a factory. (One with rows of twittering cable TVs).

There's a lot of human energy being applied to those repetitive motions on machines, and some entrepreneurs are devising ways to harness those spent calories on the exercise bikes to power the rest of the equipment.

The Green Microgym, when opened in September in Portland, Oregon, is the first American gym to use the energy generated by customers as they work out. Its owner has retrofitted workout equipment to capture the energy created by exercise and, using batteries, feed it back into the daily operation of the facility. New solar panels on the roof go even further to reaching the goal of using only energy that is created by its customers. If that works, its electric bill could be zeroed out. The concept has already been tested by a Hong Kong gym, California Fitness, although not on a gym-wide scale.

The problem is that so many people are trimming gym memberships from their tightening budgets. The Green Microgym's web page lists its monthly fee as $49, plus $100 to sign up. I called a few gyms in the Portland area, and almost all of them cost less (Bally's, for example, quoted me $30 to $40 a month, depending on the plan I chose). That leaves the Green Microgym at a competitive disadvantage, a predicament made worse by the fact that its name is apt: It's not very big.
Ten bucks is not a lot of difference, but it's still something of a sacrifice, particularly for a gym that's truly tiny and has no showers, sauna, or other perks. And that could be a problem.

Even though the technology behind self-generated power has the potential to slash your energy costs (you don't have to pay for what you generate yourself), we're currently at that delicate stage in which good ideas live or die by their ability to make money. But the technology is so new, customers have to pay more to access it until it matures into something that will actually cut our daily costs.

Solar panels, CDs, and home computers made it into our daily lives after years as super-luxury items, but not all strokes of genius are so lucky. This tenuous lag time (surely Malcolm Gladwell could write a book about this phenomenon, too) has killed a lot of juicy fruit before it had time to ripen.

Then again, people go to the gym because they want to feel better about themselves and how they look. It's not such a stretch to think some people would extend that to feeling good about their energy usage, and pay a little bit more for those warm-and-fuzzies, at least for now.