A battery-powered hip exoskeleton has helped above-the-knee amputees walk with less effort.
The device gives the user just enough extra power for walking, much like an electric bike with a motor that gives the rider assistance in pedalling the bike uphill.
It wraps around the wearer’s waist and leg, uses battery-powered electric motors and embedded computer chips enabling an amputee to walk with much less effort.
Because standard prosthetic legs for amputees cannot fully replicate the biomechanical functions of a human leg, above-knee amputees work harder while walking.
They overexert their residual-limb and intact-limb muscles to compensate for the lack of energy from the prosthesis.
While autonomously-powered hip exoskeletons have been shown to reduce the energy demands associated with walking in young people who have not undergone amputation, their use by people with above-knee amputation had not yet been tested.
Tommaso Lenzi, from the University of Utah, America, and colleagues tested the efficacy of a powered hip exoskeleton for six people (four male, two female).
They had an average age of 33.8 years and had above-knee amputations.
Researchers tested the devices as they walked on a treadmill at a speed of one metre per second and also as they walked on a 12-metre walkway.
They found that compared with the energy used with a standard prosthesis, the use of the hip exoskeleton reduced the metabolic cost of walking by 15.6%.
According to the study, this improvement is equivalent to removing a 12kg backpack from a person who has not undergone amputation.
All participants were additionally able to walk with the exoskeleton without a negative effect on their gait.
Prof Lenzi said: “We’re very close to what an average person would expend at the same speed.
“The metabolic consumption is almost indistinguishable from that of an able-bodied person, depending on the fitness level.”
Stan Schaar, who lost his left leg in an accident while helping a neighbour, never thought he would again feel the sensation of effortlessly walking with two healthy legs.
After trying the exoskeleton, the 74-year-old said: “It just felt like a big wind was behind me, pushing me down the road.”
Engineering assistant professor Lenzi, said: “The consequence of this, even though you have the ability to move your hip, is your abilities in walking are quite impaired.
“There is a lack of strength and range of motion.”
The device is lightweight, with the frame made of a carbon-fibre material, while other parts are constructed of plastic composites and aluminium.
In total it only weighs 2.44 kilograms.
Mr Schaar said: “The first time I used it, it was like my muscles were totally fused with this exoskeleton, and it was helping them move faster.
“It helped my leg to relax and just move forward and walk. I could probably walk for miles with this thing on because it was helping my muscles move.”
He added: “This device makes up for a lot of what they had to take away.
“There’s nothing that will ever replace a flesh-and-bone leg, but this comes pretty close. I hope they get this thing on the market soon.”
Researchers say further clinical studies are needed to optimise the device and to assess its efficacy for people with different types of amputation and with varying potential for rehabilitation.
They hope the exoskeleton could become available in as early as a couple of years.
The research is published in Nature Medicine.