Lessons From a Toad: How to Lighten Your Load

He never expected to become an inventor, but Larry Rome has created a backpack for the 21st century that could take a huge load off your shoulders. Or it could charge your cell phone and all those other dandy gizmos that we have to have today.

And it's all because he wanted to know how the lazy toad fish could suddenly lunge forward and grab a tasty morsel that just happened to be passing by.

If that sounds confusing, it's one of the reasons Rome feels these days as if he's stumbled into a "Lethal Weapon" movie. Even his colleagues sometimes wonder what he's up to.

"It seemed like a good idea at the time," he says. And it was.

Rome has invented two different types of backpacks. One runs a tiny generator, fueled by the mechanical energy produced by the movement of the wearer. The other reduces the force of a backpack's load on the wearer by a whopping 82 to 86 percent.

"It's like carrying an extra 12 pounds for free," says Rome, a professor of biology at the University of Pennsylvania.

Rome's ergonomic backpack uses common bungee cords to suspend the load at a constant distance from the ground, thus virtually eliminating the costly ups and downs that result from simply walking forward.

The research that led to his invention was funded by the Office of Naval Research and the National Institutes of Health, both of which hope to see the backpacks produced commercially for use by everyone from firemen rushing to a disaster site to young children who wear backpacks to school that are so heavy they could cripple a kid for life.

But for now, you can't buy one of his backpacks. He hasn't even thought about such consumer-oriented necessities as color and style.

So how does a biologist get into a project like this? For that, we have to go back to the fish.

For years Rome has studied muscles, trying to figure out which types of muscles do which types of activities. Humans have three types of muscle fibers, but it's hard to determine the precise properties of each type because even under a microscope, they're just so close that they blend together.

"It's extremely difficult to study them because they are all mixed up," he says.

So he started spending his summers at the Marine Biological Laboratory at Woods Hole, Mass. They've got lots of fish there, and it turns out that fish are great subjects for studying muscles.

"If you go to the local supermarket and look at a swordfish steak, you'll see all this white muscle, and in some cases a circle of red muscle, and these are different types of muscle fibers that are anatomically separated," he says. That's a great natural lab for studying muscles, and Rome's research caught the attention of the Navy.

At the time the Navy was interested in building a submarine that would "swim" through the water like a fish, and thus would be much more difficult for an enemy ship to find. Rome probably knew more about fish muscles than anyone else in the world, so he spent six months talking with the Navy about a fishy submarine.

But one day Navy officials told him they didn't have any money for a sub. But the war in Afghanistan was getting under way, and the Navy had a different problem.

"A typical military pack weighs in excess of 80 pounds," Rome says. And today's Marine, or soldier, has to carry all sorts of electronic devices, like GPS and night vision goggles. But those all need batteries, and if your batteries run down in the hills of Afghanistan, there's no place to charge them. The result: about 20 extra pounds of batteries, including the necessary backups.

If the movement of the soldier could be tapped to produce electricity, that 20 pounds could be replaced by a rechargeable battery of about 1 pound. So the Navy asked Rome if he could figure out how to do that.

"I almost laughed," he recalls. "I have never really invented anything. It's like why is this guy asking me?"

But with Sept. 11 weighing heavily on the national consciousness, and on his as well, he wanted to do something. So he said he would give it a shot.

And he pulled it off.

Rome teamed with a couple of engineers at the University of Pennsylvania, and they created a backpack that uses rack-and-pinion technology to power a tiny generator. With a normal backpack, the load moves up and down about 2 inches with each step.

It's the upward movement that is the killer. A 50-pound backpack that is accelerated upward just 2 inches feels like an 85 pound backpack, if the wearer is simply walking. If the wearer is running, it feels like a 150-pound load.

"That's extraordinarily painful," Rome says. "It's bad news for people who hurt their knees and shoulders and other stuff."

Rome's backpack allows the load to slide up and down on the rack of the backpack, in effect remaining stationary relative to the distance from the ground as the wearer walks or runs. That energy produced by the movement of the load, relative to the backpack, is what drives the generator.

The result is a backpack that produces 7.4 watts of electricity, more than enough to run a host of electronic gizmos.

Rome and his colleagues have since focused their attention on reducing the workload for the wearer, and that has led to the ergonomic backpack. The load floats along the rack, remaining the same distance from the ground. That eliminates those costly peaks in energy, so a 50-pound backpack remains 50 pounds, even if the wearer is running, because it doesn't accelerate up with each step.

"In effect, the load stays in one place while the person runs around it," Rome says.

After he had already built a prototype, Rome ran across a description of Asian merchants who run down the street with a bamboo pole. Each end of the pole has a heavy load that remains about a foot off the ground because the pole flexes as the merchant runs. That eliminates the energy required to accelerate the load upward with each step.

"That's the same effect that we see," Rome says. Except he managed to stuff that long pole into a backpack.