Bungee cord backpack lightens the load

NEW YORK (Reuters Health) - Using elastic cords to suspend a backpack from a rigid frame reduces the energy needed to carry the load, easing the stress on shoulders and joints, its developer reports in the journal Nature this week.

A conventional backpack is attached tightly to the wearer's body, and therefore moves up and down with the walker's footsteps. Dr. Lawrence C. Rome of the University of Pennsylvania, Philadelphia, designed a backpack that's suspended on a frame by bungee cords. This allows the backpack to remain in a fairly constant position instead of moving up and down while the wearer walks or runs.

The damped vertical movement of the load reduces the forces exerted on the body by up to 86 percent, Rome and his UPenn colleagues found. It also reduces the energy needed to walk or run with the backpack.

They calculate that a 27-kilogram (59.4 pounds) backpack can be carried using the same energy required to carry a conventional backpack weighing just 21.7 kilograms (47.7 pounds).

This same principle has been exploited by traditional Asian merchants who carry their wares using flexible bamboo poles, Rome and colleagues note.

Overloaded backpacks carried by schoolchildren are an "internationally recognized" public health problem, they point out. The bungee-cord backpack could help prevent injuries to children who carry backpacks, or in another application, it could allow emergency personnel to run more easily while carrying heavy equipment.

Rome has formed a company called Lightning Packs LLC to further develop and bring to market his Suspended-Load Ergonomic Backpack.

SOURCE: Nature, December 21, 2006.