New York, Dec. 21 (Reuters): 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.

Lawrence C. Rome of the University of Pennsylvania, Philadelphia, designed a backpack that is 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 bungee-cord backpack could help prevent injuries to children carrying overloaded schoolbags.

The damped vertical movement of the load reduces the forces exerted on the body by up to 86 per cent. It also reduces the energy needed to move with the backpack.

They calculate that a 27-kg backpack can be carried using the same energy required to carry a conventional backpack weighing just 21.7 kg.