The modern gym typically uses a lot of electricity to run the treadmills, the big-screen TVs that keep exercisers entertained, and the air-conditioning to cool them. However, not only are some gyms trying to use less power, but they are even putting some back into the grid.
In order to look good in a swimsuit for her upcoming trip to Hawaii, Cory Bilger hits the elliptical trainer at Portland's Green Microgym pretty hard these days. And she's not just burning calories, she's creating electricity - 4.19 watt hours of energy - by pumping her arms and legs. The elliptical trainer she exercises on generates electricity in the same way a windmill does.
"Wind turns the turbine, that kinetic energy is converted into electricity through a generator," says Aaron Bird, chief technology officer for Resource Fitness, which developed the equipment. "It then runs through an inverter to convert it to AC electricity, which goes into the grid."
In this case, instead of the wind, the power comes from an exerciser?s arms and legs. And all of Resource?s machines send that energy directly into the electrical grid.
Bird says that makes them a much more efficient power source than earlier generations of exercise equipment which stored the energy in a battery.
"The problem with a battery is when you charge the battery, and then when you drain the battery to get the energy back, there's efficiency loss in both directions," says Bird. "There's also efficiency loss when the battery's just sitting there because it doesn't hold the energy forever."
According to Bird, there's still some unavoidable loss in the conversion. But overall, energy-generating exercise equipment is pretty efficient. And it's cropping up across the country in gyms, college athletic centers and community rec rooms.
One company is getting ready to outfit an array of bikes at Edwards Air Force Base.
So how much power is created from an hour's worth of exercise?
"Generally people generate somewhere between 30 to 60 watt hours," says Adam Boesel, owner of Green Microgym. "Thirty watt hours can power an iPad for three hours. Sixty watt hours can power a stereo for an hour."
There are times when the Green Microgym actually generates more power than it draws, say when all the machines are going full speed during a spin class. But on the whole, the gym doesn't even create enough electricity to meet its own demands. Still, Boesel says, every little bit helps.
"The way we look at it is that you can choose to be in a gym with machines that waste a lot of electricity, or you can choose to be in a gym that's very energy efficient, where you're creating electricity."
For Microgym member Cory Bilger, reducing her carbon footprint is definitely part of the draw. And if she can do it while getting ready for a Hawaiian vacation, all the better.