Reddening, a rivulet of sweat running across her cheek, Amy McCullough hunched over the stationary bike, pumped her legs like crazy and began producing serious power, enough watts to run a flat-panel TV and a ceiling fan.
She thrust her arms upward and exclaimed: "Oh, 180!"
And, with that, her electrical output drooped. The generator attached to her exercise machine slowed, and the digital readout from the device on the handlebars fell below 100W.
The transient burst was a personal best for the 43-year-old legal aid lawyer who works out five days a week at a storefront fitness centre in north Portland, US, where members on exercise machines fitted with compact generators can burn calories and generate electricity at the same time.
Their workouts satisfy a modicum of the electrical draw at the Green Microgym. More important, they satisfy a demand among its 200 members to be fit in a way that fits Portland's green-indie-local ethos.
The 279m2 gym aims for a neighbourhood trade. It features solar panels, recycled toilet paper, renewable-source flooring and many reminders on the wall about turning off lights, fans and TVs.
"I was really attracted to the idea that it would be green," said McCullough, who joined shortly after the gym opened in 2008. "I could go in and generate electricity. How cool is that?"
It has occurred to many exercisers during long stretches on machines that it would be cool to turn sweat into watts. In recent years, a few tinkerers and entrepreneurs have brought the idea to market.
So far they have but a teensy sliver of energy production. The two leading start-ups sell equipment to retrofit existing bikes and elliptical trainers, and each reports hooking up about 1,000 machines. An executive of one company estimates that American fitness centres house eight million to 10 million machines that could generate power.
They do not, though. Like much in energy that is efficient or alternative, from plug-in cars to compact fluorescents, initial capital outlays are steep. Absent a subsidy, or a quantifiable green marketing rationale, the returns on investment do not come quickly, if at all.
Kurt Broadhag, a Los Angeles consultant to health clubs and an advocate of greening them, said it appears the payback period for electricity-generating exercise equipment is about 15 years, two to three times the machines' life span.
"The only sense it makes is in educating people in taking care of the environment," he said.
When Adam Boesel opened the Green Microgym in Portland's artsy, gentrifying Alberta district, he figured on a market among people already educated about the environment.
The former teacher from Seattle, Washington, looked at Portland, a city that, when cut, bleeds green. It ranks regularly in top 10 lists for bicycle and mass transit commuting, recycling, composting, energy-efficient buildings and so on.
"When I was researching Portland businesses, they all were talking about sustainability; all the good ones," he said.
He has received a lot of publicity about the technology, helpful for a business that opened on credit card financing a few weeks before the US economy tanked.
But the machines, he said, are "just the shiny wrapper on a package, which is energy efficiency", something gym members such as Martha Jones take seriously.
"Whoops, I have to turn off the lights," she said at the end of an interview in the gym's basement studio, dashing back inside.
Prominent in the gym are signs that explain how to use the individual, adjustable controls for lights and fans. A wall-mounted button connects to a remote device that allows the cable boxes to be shut down, not just put on standby and using 29W when the flat-panel TVs are not in use.
Jones is an Intel engineer who likes seeing her workout quantified in watts. But it is not primarily the electricity that attracts her to the Green Microgym.
"It's just really supportive," she said. "If you have somebody who knows you, who knows your name, they will keep you moving. I know for sure I will cheat right and left on my workout without that."
She counts hoofing it to the gym as warm-up and cool-down. "And I do more shopping in Alberta because I'm walking here," she said. "It helps the local businesses."
Boesel sees opportunity in such thinking. Emerging from what he called scary times in the recession, he has franchised a second neighbourhood gym in southeast Portland and plans to open a third on his own.
With a Seattle partner, he is getting into the manufacturing end, selling machines whose plugs feed electricity from the machine into a gym's distribution system.
Theoretically, in states like Oregon with "net metering" rules, such machines could power the gym itself and feed excess energy into the grid, perhaps generating a utility bill credit.
But that level of output probably would be rare, especially in big gyms heavy on lights, heating, cooling and other energy draws. Most often, electricity-generating machines would supplant some of a gym's draw from the grid, a smaller savings.
Boesel said he doesn't try to calculate how many kilowatt-hours the Green Microgym produces. "The payback period is irrelevant to me," he said.
But the machines themselves and the potential they represent are "pretty cool", he said. "It's not inevitable that all the machines will make electricity someday. ... It's all going to have to be pushed along. That's what I think I'm doing." - (AP, April 2011)