An unpowered exoskeleton increases walking efficiency for humans, according to an article published in Nature.

Carnegie Mellon University’s Steve Collins and his collaborator Gregory Sawicki at North Carolina State University have created a wearable boot-like apparatus that, when attached to the foot and ankle, reduces the energy expended in walking by around 7%.

That improvement is roughly equivalent to removing a 10-pound backpack. And, given this device’s simplicity, researchers say it would be low-cost to produce.

The lightweight carbon-based device uses a spring that acts like the Achilles' tendon and a clutch that mimics the calf muscles. Source: NatureThe lightweight carbon-based device uses a spring that acts like the Achilles’ tendon and a clutch that mimics the calf muscles.It reduces the load placed on the calf muscles and the spring stores and releases elastic energy. The clutch engages the spring while the foot is on the ground, disengaging it while the foot is in the air.

“The unpowered exoskeleton works in parallel with your muscles, thereby decreasing muscle force and the metabolic energy needed for contractions,” says Sawicki.

While muscles use energy in producing force, this device does so passively.