Put Away Your Flags and Bumper Stickers....

...this is the stuff we need to be concentrating on, making it as easy as we can for our soldiers who get paid very little to do what most of us could never imagine.

A backpack that reduces the forces on your body when carrying heavy loads could help prevent injury, allow soldiers to carry more equipment and even speed up the response time of emergency services, its designer claims.

When people walk, they tend to raise and lower their bodies by between 5 centimetres and 7 cm with each step. If they are carrying a backpack, the extra load must also be raised by the same amount and this puts extra strain on the body.

Now Larry Rome, a muscle physiologist at the University of Pennsylvania in Philadelphia, US, has worked out a way to reduce these forces by fundamentally changing the design of the backpack.

His new design consists of a frame which a person wears like an ordinary backpack. However, the load is suspended from the frame by elasticated bungee cords which lengthen as the wearer takes a stride, thereby keeping the load at a constant height. A video (AVI format, 6mb) of the backpack is available here.

“By suspending the load, you knock out 86% of this extra force, making it comfortable to run with a heavy load,” says Rome, who has published his results in the journal Nature. The principle is similar to that used by traditional Asian merchants who carry their wares using flexible bamboo poles.
Pile on the pounds

Rome says being able to run comfortably while carrying a heavy load could make life easier for many groups of people. He points out that children often suffer bone and muscle injuries from carrying heavy schoolbooks and believes his backpack could help. And first responders in the emergency services also often have to carry heavy loads.

The backpack also reduces the total energy needed to carry heavy loads by around 40%. That may make it possible for people such as soldiers to carry heavier loads. “You can carry 60 lbs in our backpack for the same metabolic cost as 48 lbs in a normal backpack, hence you can carry 12 lbs for free,” he says.

The load can also be locked in place to function as a conventional backpack, which might be useful when the wearer is not walking in a rhythmic way, Rome suggests, such as when crossing a stream.
Military use

Rome was initially approached by the US Office of Naval Research to design a backpack that could generate power from the wearer’s body movements (see Backpack generates a powerful punch). The military had found that soldiers’ ever increasing reliance on electronic equipment such as GPS systems, night-vision sights and computers meant they were replacing food and medical equipment in their backpacks with batteries. The ONR was looking for a way for soldiers to generate their own power on the move.

“My knowledge of biomechanics made me realise that the way people were trying to do it – with heel strike devices – was not the best way,” says Rome. Instead he came up with an electricity-generating backpack in which a sliding action between the load and the backpack frame generates power.

He suspected that the mechanism also reduced the forces on the body and further development of the idea led to the new ergonomic backpack. Rome has set up a company called Lightning Packs to bring the backpack to market.

Others agree that the work will have a significant benefit. Rodger Kram, a specialist in body movement at the University of Colorado in Boulder, US, says: “The biggest advantage will be for people who need to run with heavy loads, such as marines and fire fighters. It can be much more comfortable and less injurious. I would buy one.”