Scientists have developed an unpowered exoskeleton that increases human walking efficiency by helping individuals walk using less energy.
New research shows humans can get better "gas mileage" using the exoskeleton to modify the structure of their ankles.
The device puts an extra spring in each human step, reducing metabolic energy consumption by 7 per cent below walking in normal athletic shoes.
The finding may benefit both able-bodied people who are frequently on their feet - think of the military infantry or athletic baby-boomers, for example - as well as those who have been victims of stroke or other gait impairments.
To gain an advantage over nature, researchers tested the efficacy of a lightweight lower-leg device that uses a spring and clutch system working in tandem with calf muscles and the Achilles' tendon while people walk.
The streamlined, carbon-fibre device weighs about as much as a normal loafer - around 500 grams, or a bit more than a pound - and is not motorised, so it requires no energy from batteries or other external fuel sources.
"The unpowered exoskeleton is like a catapult. It has a spring that mimics the action of your Achilles' tendon, and works in parallel with your calf muscles to reduce the load placed upon them," said Dr Gregory Sawicki, a biomedical engineer and locomotion physiologist at the North Carolina State University, who co-authored the paper.
"The clutch is essential to engage the spring only while the foot is on the ground, allowing it to store and then release elastic energy. Later it automatically disengages to allow free motion while the foot is in the air," said Sawicki.
The study participants - nine able-bodied adults - strapped the exoskeleton devices on both legs and walked at a normal speed on a treadmill after completing some practice training. The same subjects also walked without exoskeletons for a baseline comparison.
The researchers tested exoskeletons with springs that varied in stiffness. The spring that provided the most benefit was moderately stiff.
Walking with exoskeletons with springs that were too stiff or too compliant resulted in normal or higher-than-normal energy costs for participants.
"A 7 per cent reduction in energy cost is like taking off a 10-pound backpack, which is significant," Sawicki said.
"Someday soon we may have simple, lightweight and relatively inexpensive exoskeletons to help us get around, especially if we've been slowed down by injury or ageing," said paper co-author Dr Steven Collins, a mechanical engineer and roboticist from Carnegie Mellon University.
The research was published in the journal Nature.
