When you're at the gym, does your mind ever drift off to ponder the perils of the planet? Do you feel a bit of remorse as your legs pound away on an electric machine that goes nowhere, while the ice-cold air conditioner blows down on your neck? OK -- so most likely, you're probably thinking more about the amount of calories you're burning. But if you're one of the more eco-conscious athletes out there, you may soon be able to let those concerns melt away with the pounds.
Several innovative gyms are popping up that convert human energy into useable electricity. One of them, in Hong Kong, has exercise machines that look perfectly ordinary from the outside, but have generators inside that create energy from movement. So while you're busy sweating it out, your efforts are creating electricity to power the exercise console and supplement the electrical juice it takes to keep the overhead lights on. The owner of the gym maintains that the average person can generate about 50 watts of electricity per hour on the machines [source: Blume]. So, unless you like running in the dark, you better get moving.
Pedal generators like the Pedal-A-Watt bike stand operate on a similar concept but are more powerful. A person in top condition can generate 500 watts of power, while someone in couch-potato condition could generate around 150 watts. Although that may not seem like much, that's enough to power two laptops, two fluorescent light bulbs and a cell phone -- as long as you maintain that pedaling [source: Treehugger].
The Pedal-A-Watt bike stand, which works by powering a generator with the movement of the bike's rear wheel, comes with an optional PowerPak that stores the energy you create for later use. The PowerPak has an outlet where you can plug in and power any appliance that runs on less than 400 watts of electricity. For a frame of reference, a large television uses around 200 watts, a stereo 20 watts, a desktop computer 75 watts and a refrigerator 700 watts [source: Convergence Tech, Inc.].