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This mechanical exoskeleton makes walking more efficient

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'Walking... can be improved by manmade technology'

Stephen Thrift

For the first time, researchers can improve the way humans walk without using an external power source, according to a study published in Nature today. A boot-like exoskeleton that fits into a regular running shoe reduces the energetic costs of walking by about 7 percent. In short, it makes walking less tiring without resorting to a battery pack or a motor — something that could really come in handy for people who have trouble walking, or military personnel in remote areas.

They improved human walking — without a power source

"Our study shows that walking, a highly evolved human task, can be improved by manmade technology and engineering," says Gregory Sawicki, a co-author of the study and a physiologist at North Carolina State University. "That’s what’s so exciting for us."

A 7 percent reduction in the energy cost of walking isn’t entirely new: researchers have achieved similar gains in the past. In 2013, a group of researchers achieved a 6 percent reduction in energy costs thanks to an air compression system. Others have worked on exoskeletons that are powered by motors and battery packs. But the device that Sawicki and his team came up with doesn’t need any of that; it's unpowered. It makes walking less tiring by rerouting the energy that normally goes through your calf muscles and tendons into carbon fibre, metal — and a very basic spring.

"It’s sort of been a grand challenge in the field," Sawicki says. "All the way back to graduate school, we had our eyes on this — and whether or not this was even possible."

"It’s sort of been a grand challenge in the field."

Unlike most muscles, the calf muscle doesn’t "turn on" by shortening itself and contracting. Instead, is provides a rigid link upon which the Achilles tendon can stretch and recoil. This is what the exoskeleton is replicating thanks to a system of springs and clutches. When the heel strikes the ground — a time when the Achilles tendon would normally hold onto the calf muscle with a high force — the clutch holds on to the spring of the exoskeleton. "From that point on, the forward momentum of your body is exchanged with the stretch of the spring; the spring kind of catches your forward movements," Sawicki says. This means that when the spring stretches, some of the energy of the human body is transferred into it.

Collins, et al (2015)

The device is also super light weight. That means that the there’s no significant mass penalty that needs to be factored into the energy gains you get from wearing the exoskeleton on both legs. "The device weighs between 300 and 500 grams, which is a little heavier than your really lightweight running shoes," Sawicki says. "It’s about the weight of a normal dress loafer."

"The reported savings are impressive," says Heike Vallery, a biomechanical engineer at the Delft University of Technology in the Netherlands who didn't take part in the study. Art Kuo, a University of Michigan biomechanical engineer, also thinks that the findings are sound, but cautions that this is only a first step — medical applications are still far away, he says.

Others wonder how the device will fair with everyday use. "It isn't clear how the device would respond to non-rhythmical cyclic tasks," says Daniel Ferris, a biomedical engineer, also at the University of Michigan. Energy savings might not occur during tasks like standing, turning maneuvers, sit-to-stand and stand-to-sit motions. Still, Ferris thinks that the exoskeleton could prove useful for people who have reduced ankle strength — people with incomplete spinal cord injuries, the elderly, and people who suffer from multiple sclerosis, for instance.

Using the boot isn’t very hard, Sawicki says. "After 20 minutes or so, most people aren’t conscious of it; it gets integrated into their being." The only time users notice it is when they take it off. "There’s this heavy leg feeling after, that lasts for up to five minutes for some people," he says. "You feel like your leg is collapsing under you."

When you take it off, "you feel like your leg is collapsing under you."

This hints at something that researchers will undoubtedly have to investigate: what are the effects of wearing the exoskeleton for long periods of time, on a regular basis? Given what happens when people spend a lot of time in wheelchairs, it’s possible that a user's leg muscles would become weak with extended use. "My instinct is to say that if you wore it all the time, the body would recognize the parallel pathway, and the morphology of your leg would change," Sawicki says. But "we just don’t know yet."

It took over five years to come up with this design. And the fact that they were able to do this at all has a lot to do with advancements in medical imaging techniques. "That whole 'clutch-holding and Achilles-stretching' thing — we didn’t know about that until the late 2000s, when people were started using ultrasound imaging to look at what muscles were doing," Sawicki says. Thanks to these techniques, researchers were able to see that the calf muscle and the Achilles tendon were acting like the clutch and spring in the exoskeleton. "It changed the way we look at exoskeletons."

There’s a lot that the exoskeleton can’t do right now; it really only works at certain speeds. "The device in the paper will break during running," Sawicki says. The researchers still have to find a way to make a sturdier (and bulkier) device that can withstand harder impacts. Different materials, like electroactive polymers, might help them do that. "We need to build a device that can do it all."

Still, if all you want to do is go for a walk, the exoskeleton can help. People who like to go hiking might want to wear it, Sawicki says. The exoskeleton might also prove useful for military personnel. But what the team is really interested in are the medical applications. "It could be a mobility aid for people who have had a stroke," Sawicki says. Given the regulations surrounding medical devices, the exoskeleton might end up making it to market as a recreational device first, however. Sawicki thinks that the final product would cost a little under $1,000.

"Even if we could build Ironman, how practical would it be for regular use?"

But before the researchers can think of marketing the exoskeleton to hikers, Sawicki and his team will have to come up with a name. They’re open to suggestions, he told The Verge. You might want to stay away from superhero references, however. "I love science fiction and stuff — I think it has provided a lot of motivation for our field — but it’s so far removed from where we are in the field in terms of capability," Sawicki says. Moreover, making a superhero suit doesn't align very well with what the researchers are trying to achieve. "Even if we could build Ironman, how practical would it be for regular use? People wouldn’t be able to afford it. We want to make things that are simple and accessible to a large amount of people."