Harnessing the untapped power of breast motion.

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June 23 2008 4:10 PM

Victoria's Circuit

Harnessing the untapped power of breast motion.

Illustration by Rob Donnelly. Click image to expand.

As a woman who loves sports, I've always found the concept of breasts bothersome. If all goes according to plan, they will fulfill their intended function for about three of the 70 years that I have them. The rest of the time, they alternate between getting in my way and embarrassing me. They are a favorite target of Frisbees and soccer balls. Finding sports bras is a chore. Shirts don't fit.

And these are just the physical discomforts. I am still tortured by the memory of three cousins standing in a circle around me, at the impressionable age of 10, mocking my early development and telling me that I was going to be the Asian Dolly Parton. Fortunately, that never happened, but the possibility haunted my late childhood.

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Then one day recently I had an idea. As I rode public transportation to the office, my messenger bag slung uncomfortably across my chest, I thought, "Why not put the girls to work?" Human-powered devices are showing up everywhere, from Rotterdam's sustainable dance floor to human-powered gyms in Hong Kong. The time seemed perfect—perhaps even overdue!—for a bra that could harness the untapped power of breast motion.

The idea of an energy-generating bra isn't as crazy as it might sound. A company called Triumph International Japan recently unveiled a solar-powered bra that supposedly will generate enough energy to power an iPod. But I live in foggy San Francisco and prefer not to walk around in my underwear in public. Could someone design an iPod-powering bra for me?

I decided to run the question past some scientists. It turns out that the physics of breast motion have been studied closely for the last two decades by a gamut of researchers, most of them women. LaJean Lawson, a former professor of exercise science at Oregon State University, has studied breast motion since 1985 and now works as a consultant for companies like Nike to develop better sports bra designs. Lawson was enthusiastic about my idea but warned it would be tricky to pull off. You would need the right breast size and the right material, she explained, and the bra itself would have to be cleverly designed. "It's just a matter of finding the sweet spot, between reducing motion to the point where it's comfortable but still allowing enough motion to power your iPod," she said.

Lawson explained that breasts move on three different axes: from side to side, front to back, and up and down. The most motion is generated on the vertical axis. Naturally, the bigger the breast, the more momentum it generates. "Let's face it—if you're a double-A marathoner, you're probably not going to get that iPod up and running," Lawson said. Measurements compiled by Lawson and her colleagues show that a D-cup in a low-support bra can travel as much as 35 inches up and down (35 inches!) during exercise, while a B-cup in a high-support bra barely moves an inch.

Fabric and design are also important factors in distance traveled. Elastic fabric allows the breast to move more. Choosing between an encapsulation design, in which the cups are separated, or a compression design, where they are hugged close to the body, can also affect breast motion. An encapsulation design further reduces motion because two smaller masses are easier to control than one large one. "Also, if you have a really high neckline, the breasts won't fly up," Lawson said. So I was in the market for an elastic, compression-style bra with a low neckline. Sexy!

Of course, even a bra that perfectly maximized motion (without sacrificing support and comfort) would be useful to me only if there were a way to turn that motion into energy. For a primer on how to do that, I turned to Professor Zhong Lin Wang of Georgia Tech, who is currently working to develop fabric made from nanowires that will capture energy from motion. Wang's wires are about 1/1,000th the width of a human hair. When woven together in a fabric, these nanowires rub up against one another and convert the mechanical energy from the friction into an electric charge. According to Wang, the fabric is cheap to produce and surprisingly efficient; his team hopes to use it to create energy-generating T-shirts and other articles of clothing. A square meter of fiber produces about 80 milliwatts of power, which is enough to run a small device like a cell phone. Wang expects to have a shirt available for purchase within five years.

Many bra patterns call for about a meter of fabric, which would probably mean that a regular bra would have enough energy to power an iPod. But the fabric could also be layered, doubling or even tripling the amount of energy produced. I asked Wang whether his fabric could be used to make a bra. "Bras would be ideal," he said. "There is a lot of friction and movement in that general area. And the fabric would be thick."

"So you can generate enough energy to power an iPod?" I asked.

"Definitely," Wang said.

I asked Wang if this bra would be machine-washable.

"You don't need to wash a bra!" he said.

I disagreed. Wang said his team has been working on the washing problem for a while. Nanowire technology can generate electricity only if the space between the wires is maintained, and that space might be affected if the fabric were agitated by washing. One solution would be to layer the fabric so that the parts that directly touch the skin could be washed, leaving the nanowires in between untouched.

There was one more approach I wanted to investigate, one that might supplement Wang's technology. Was there a way to capture the energy of the bra strap, which bears the pressure of holding up the breast mass? To answer this question, I called Larry Rome, a biology professor at the University of Pennsylvania and the creator of Lightning Packs. The Lightning Pack, intended for long-haul hikers and for the military, generates kinetic energy from the vertical displacement of a heavy backpack. Would it be possible to use the kinetic energy generated from a breast's vertical displacement?

"The backpacks we've built are intended to carry between 40 to 80 pounds," Rome said.

I cited the D-cup numbers given to me by Lawson. "Well, that's not normal, is it?" Rome asked.

I said that it probably wasn't. Yet after a moment's thought, Rome came up with an idea. The Lightning Pack uses a rotary generator, which converts motion into energy by winding a rotor as the backpack moves up and down. Rotary generators produce up to 7 watts of energy, enough to power a compact fluorescent light bulb. Rome said it might be possible to insert a linear generator into the bra. A linear generator is a lot smaller and creates energy by moving a piston up and down. Rome conceded that with the right body type, this just might work, though he warned it "probably wouldn't be very comfortable."

Still, if someone were to engineer a kinetically powered bra, even one that isn't quite as comfortable as the old-fashioned kind, I'd be intrigued—and I might just start looking at my breasts in a different light. Maybe it's not very sexy to see breasts as a pair of batteries, but oil prices are so high, people are jogging to work. It may be time for breasts to start pulling their own weight.

Adrienne So is a freelance writer based in Portland, Oregon. Find her work at adrienneso.com.

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