The elliptical machines at my local Gainesville Health & Fitness Center are being used for more than health and fitness. They're being used to convert the energy spent exercising into something pretty darn useful: Electrical power.

Credit for this energetic feat goes to Hudson Harr, the 22-year-old who came up with the ReCardio system -- a patent-pending technology currently wired to 15 elliptical machines and working to convert the kinetic energy from pushing pedals into electricity. The power produced by the machines is plugged straight into the utility grid, which helps produce power for the gym and offsets utility costs. Each elliptical machine can produce one kilowatt of electricity every 10 hours -- enough to charge the battery for a 2004 Toyota Prius once or a cell phone up to 397 times. So far, 150 kilowatts of electricity has been produced.

Harr, the founder and CEO of ReRev LLC, a renewable energy company, is working with several large institutions and franchises to put this technology to work in other settings.