A backpack with a suspension system

A new backpack design that uses elastic cords to minimize the pack’s vertical motion could lessen bodily strain on wearers and reduce the effort required to carry a load. It could be useful to schoolchildren encumbered with books or to emergency personnel and soldiers who sometimes need to sprint while carrying heavy loads, says the pack’s inventor, locomotion researcher Lawrence Rome of the University of Pennsylvania in Philadelphia.

BUNGEE BACK. An external-frame backpack with an elastic bungee cord (red) that suspends the load may be easier to carry than a conventional external-frame pack. Rome et al./Nature

Walking and especially running with a conventional backpack put strain on joints and muscles because, with each footfall, the wearer must reverse the downward momentum of both body and load. “When you run with a normal pack, it bounces up and down,” and the wearer repeatedly gets “squeezed in the vise between the load and the ground,” Rome says.

In the new pack, a bungee cord suspends the load from an external frame. While the frame straps firmly to the wearer’s back, the load rises and falls little with each step. In walking trials, the peak vertical force exerted by a 27-kilogram, suspended-load backpack was just one-sixth that exerted by a conventional, fixed backpack.

The new pack also saves the wearer effort: Carrying a 27-kg suspended load required no more metabolic power than carrying a 21.7-kg conventional load, the experiments showed. Rome and his colleagues describe their contraption in the Dec. 21/28, 2006 Nature.

Rome had previously designed a backpack that converts energy from the wearer’s steps into electricity (SN: 10/1/05, p. 221: Getting a charge out of backpacking), and he has created a company to commercialize both products.

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