Carrying heavy loads could become easier thanks to a new ergonomic backpack that uses bungee cords to take the strain off the joints, scientists reported this week in the journal Nature.
The cords suspend the load in the pack so it stays at the same height while the wearer is running or walking and reduces the risks of muscle and joint problems.
Its designers said it will allow users to carry an extra 12 pounds while expending the same amount of energy as when carrying a normal backpack.
"For the same energetic cost, you can either carry 48 pounds in a normal backpack or 60 pounds in a suspended ergonomic backpack," said Lawrence Rome, a biology professor at the University of Pennsylvania.
"It is like carrying an extra 12 pounds for free," he added.
The backpack, designed for soldiers and emergency workers, could also be useful for children and hikers.
"Being able to move at relatively high speeds is crucial for many professions as well as in some athletic competitions and recreation," said Rome, who collaborated with researchers at the Marine Biological Laboratory in Woods Hole, Mass.
In traditional backpacks, the load is attached to the frame, which is strapped to the body. As a person walks it moves in line with the hip. The new pack reduces the vertical displacement of the load.
The scientists have formed a company to produce the backpacks and plan a lighter version.