Biomechanics: rubber bands reduce the cost of carrying loads.

Vertical movement of the hip during locomotion causes a loaded backpack to be accelerated with each step, which imposes large peak forces on the wearer. Here we show that using bungee cords to suspend the load from a backpack frame reduces not only its vertical movement, and hence its vertical force on the carrier, but also the energetic cost of walking with the pack. This permits larger loads to be carried while moving rapidly, and at the same time reduces the risk of orthopaedic and muscular injury.