Your gym workouts might do more than just work up a sweat -- they also can help power the lights in your club. It's the latest development in the green revolution: Gyms that convert the kinetic energy produced by their members' workouts into electricity.

The technology that converts kinetic energy into electricity is relatively simple. Electromagnets in a generator turn mechanical motion into electrical currents. It's easy to apply to all kinds of activities. Dance clubs have started harnessing the motion of their dance floors to power audio systems. Kinetic backpacks from


use energy generated by hikers to power their


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Tremont Electrical Supply

has created a device called the PEG (personal energy generator), which transfers the kinetic energy generated by a person walking or running into electricity that can power any handheld USB-powered device.

The River Gym in New York City, which is in its planning stages, would include a series of floating, enclosed gyms navigating routes along the East and Hudson rivers.

Only a few energy-producing gyms are up and running now, but one might be opening near you soon -- so keep an eye out for clubs like these:

Ridgefield Fitness Center

in Ridgefield, Connecticut, is the beta-testing center for

Green Revolution

, which plans to install kinetic-to-electric energy converters in more than 200 gyms across the country by the end of 2009. Michael Curnyn, head of marketing for Green Revolution, estimates that over the course of a month, a gym with 20 energy-producing cycling machines could generate up to 300 kilowatts of electricity, preventing the emission of 420 pounds of greenhouse gasses.

California Fitness

in Hong Kong was the first gym to convert the kinetic energy produced by its members' workouts into electricity, which it uses to power lights and televisions. The


88 cycling, elliptical and


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Stairmaster machines are hooked up to generators. According to company President Steve Clinefelter, spending one hour a day on one of the gym's exercise machines could easily generate up to 18.2 kilowatts of electricity, preventing 4,380 liters of carbon dioxide from being released each year. California Fitness plans to equip the rest of its gyms in Asia and the U.S. with this technology in the near future. Fees (converted into U.S. dollars) are $30 a month with an enrollment and processing fee of $36.

Green Microgym

in Portland, Oregon, uses technology similar to California Fitness' to generate extra power. The gym's cycling machines produce 300 to 600 watts of energy an hour, which is enough to power a stereo, a 37-inch LCD television and a laptop computer. The


says this technology is just one component of a more holistic, environmentally friendly approach. Adam Boesel, the gym's founder, plans to install solar panels that will help power the rest of the facility. Most of the gym's members are within walking distance, which helps further reduce the gym's overall carbon footprint. Individual members pay an enrollment fee of $100 and a monthly fee of $39, while couples pay a one-time fee of $100 and a monthly fee of $58.

The River Gym

, a work in progress in New York City for more than four years, promises to be a truly

innovative take

on eco-friendly technology -- eventually. Architect Mitchell Joachim envisions a series of floating, enclosed gyms, which will navigate circuitous routes along the East and Hudson Rivers in Manhattan. The kinetic energy expended by the exercisers aboard the gyms will be converted into electricity, which will power the gyms' engines. Navigational computers will steer the gyms along predetermined routes, so members can enjoy panoramic views of the city as they sweat. Meanwhile, water purification devices installed on the bottom of each gym will help reduce pollution in the rivers. The gyms will vary in size: Smaller ones will require the kinetic energy of only a few people to power their engines, while larger floating gyms will require more power and will be reserved for peak hours. doMembership fees have not been announced.

Harper Willis graduated from the Gallatin School of Individualized Studies at New York University with a concentration in ancient theater and jazz guitar. He is a musician and writer, and lives in Brooklyn, N.Y.