In treadmill tests, the researchers report in Nature, the exoskeleton reduced the amount of energy expended on walking by 4.6 to 9.8%, or an average of about 7%. The improvement takes into account the extra energy used in carrying the weight of the exoskeleton, which comes in at about 0.5kg for each leg.
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“When you first put it on it feels a bit odd, but once you’ve walked with it for a while, it starts to feel quite comfortable,” Collins said. “But it’s when you take it off that you really feel a big difference. Your leg feels heavy and weak.”
The prototype has some wrinkles that need to be ironed out. The tranquility of a countryside walk might broken by the regular metallic twang that follows the wearer around. Stairs pose another problem. “There’s a lever that sticks out at the back of the heel about 10cm. That makes going downstairs an invitation to disaster. So there are lots of little things that would need to be improved before it was a real product,” said Collins.
Collins says he was motivated in part by sheer scientific curiosity, to see if he could improve the efficiency of human walking. But he hopes that a future version of the device could alleviate the effort of walking for disabled people. People who have had strokes, for example, can use much more energy walking around, because their coordination may be worse, and in time, their muscles weaken.
“A more sophisticated version could be used by recreational hikers, casual runners to keep up with their more fit companions, or first responders, such as nurses,” he said. “For a lot of people who walk a lot in their jobs, for hours and hours on end, fatigue can be a limiting factor.”
The exoskeleton raises another question that comes up whenever Collins gives a talk on the device. Even though it could help disabled and elderly people, walking is the only exercise some individuals get. Might his device, perversely, put people even more at risk of being overweigh or obese? “It’s a good suspiscion,” he said. “But it’s not clear whether reducing the energy of each step would reduce people’s exercise from walking over, say, a week. It could be that if each step is easier, people take more of them.”
Robert McNeill Alexander, a specialist in human movement at Leeds University, had reservations about the device. “I’m 80 years old and because of my back, walking is very hard work. But a 7% saving isn’t very much. You’d be better off on a bicycle.”
He went on to explain that when running, a human expends 280 joules of energy per metre covered. The energy used for cycling varies with speed, but at 6 metres per second, a person uses only 40 joules per metre on a bike, he said.
“You might not be able to cycle around a shopping centre, but as it is, you’d look pretty peculiar with all this stuff attached to your leg. People would be roaring with laughter”.
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