bungee-powered backpack

press release from biologists at the University of Pennsylvania

In this week's edition of the journal Nature, Penn researchers have announced details for a suspended-load ergonomic backpack that reduces the force of a backpacks load on the wearer by 86%, allowing wearers to run far more comfortably with heavy loads.

... the backpack was created with soldiers and emergency workers in mind and could prevent the sort of muscle and joint injuries associated with running while carrying heavy items. The Penn researchers also point out that the backpack will also benefit schoolchildren, since heavy book bags have been linked to muscle and orthopedic injury.

"For the same energetic cost, you can either carry 48 pounds in a normal backpack or 60 pounds in a suspended-load ergonomic backpack," Larry Rome, a professor in Penn's Department of Biology, said. "It is like carrying an extra 12 pounds for 'free.'"

The backpack is based on a rigid frame pack, much like the type familiar to hikers everywhere; however, rather than being rigidly attached to the frame, the sack carrying the load is suspended from the frame by bungee cords...

"The ergonomic backpack reduces the force of the load on the wearer by reducing the effect of the load as it shifts up and down," Rome said. "What is striking is that you can feel the 86% reduction in force with every step."

With a normal backpack, the peak force exerted by the load on the body during walking is twice as high as the static force, and during running its three times as large, exerting extreme forces on the joints.

The backpack shifts the timing of how force is applied as the wearer takes a step.

Essentially, the bungee cords permit the load to stay at nearly constant height from the ground while the wearer walks or runs around it, Rome said. The pack actually reduces the metabolic cost of walking from one point to another by about 40 watts, or the equivalent of carrying 12 extra pounds.