Walking easier in high-tech 'boot'
A boot-like exoskeleton has been developed that takes 7% of the effort out of walking.
The lightweight device has no motor and works in conjunction with the user's calf muscles.
A clutch mechanism and spring allows muscle force to be off-loaded to reduce energy consumption.
Tests on volunteers showed that it cuts the amount of energy expended in walking by 7.2%, the equivalent of removing a four kilogram backpack.
Lead scientist Dr Steven Collins, from Carnegie Mellon University in Pittsburgh, said: "Having worn these exoskeletons myself I can tell you that when you take them off your legs feel really heavy and weak."
Future versions of the device could help people who find walking difficult, such as stroke patients or amputees.
But Dr Collins said they might also be routinely used to help prevent tiredness when walking.
"I think it's just a matter of time," he said. "These kind of devices may become as commonplace as reading glasses."
The research, published in the journal Nature, builds on earlier work Dr Collins did trying to improve the walking efficiency of experimental robots.
The challenge was to develop a system that increased walking efficiency without requiring an electrical power source.
"It's sort of like changing the structure of the body to make it more efficient," said Dr Collins, speaking in a recorded interview with Nature. "In theory, these kind of structural changes could have been discovered through evolution. What we wanted to try to do is leap-frog evolution if you like."
The clutch-spring mechanism proved a simple solution.
Dr Collins added: "The clutch engages the spring when the foot is on the ground and releases it when your foot is in the air. The clutch is in parallel with your calf muscles and the spring is in parallel with your Achilles' tendon, and their function is really similar when the foot's on the ground.
"But unlike the muscle, the clutch does this passively; it doesn't use any energy."