Exoskeleton could one day boost walking speed of older adults

A new ankle exoskeleton allowed users to walk, on average, 42% faster than when they wore normal shoes and no exoskeleton, researchers report.

Being unable to walk quickly can be frustrating and problematic, but it is a common issue, especially as people age. Noting the pervasiveness of slower-than-desired walking, engineers tested how well a prototype exoskeleton system—which attaches around the shin and into a running shoe and is externally powered by motors and controlled by an algorithm—increased the self-selected walking speed of people in an experimental setting.

“We were hoping that we could increase walking speed with exoskeleton assistance, but we were really surprised to find such a large improvement,” says study senior author Steve Collins, associate professor of mechanical engineering at Stanford University. “Forty percent is huge.”

For this initial set of experiments, the participants were young, healthy adults. Given their impressive results, the researchers plan to run future tests with older adults and to look at other ways they can improve the exoskeleton design. They also hope to eventually create an exoskeleton that can work outside the lab, though that goal is still a ways off.

“My research mission is to understand the science of biomechanics and motor control behind human locomotion and apply that to enhance the physical performance of humans in daily life,” says Seungmoon Song, a postdoctoral fellow in mechanical engineering and lead author of the paper in IEEE Transactions on Neural Systems and Rehabilitation Engineering.

“I think exoskeletons are very promising tools that could achieve that enhancement in physical quality of life.”

The exoskeleton also reduces energy use

The ankle exoskeleton system tested in this research is an experimental emulator that serves as a testbed for trying out different designs. It has a frame that fastens around the upper shin and into an integrated running shoe that the participant wears. It is attached to large motors that sit beside the walking surface and pull a tether that runs up the length of the back of the exoskeleton. Controlled by an algorithm, the tether tugs the wearer’s heel upward, helping them point their toe down as they push off the ground.

For this study, the researchers had 10 participants walk with five different modes of operation. They walked in normal shoes without the exoskeleton, with the exoskeleton turned off, and with the exoskeleton turned on with three different modes: optimized for speed, optimized for energy use, and a placebo mode adjusted to make them walk more slowly. In all of the tests, participants walked on a treadmill that adapts to their speed.

Researchers created the mode that was optimized for speed—which resulted in the 42% increase in walking pace—through a human-in-the-loop process. An algorithm repeatedly adjusted the exoskeleton settings while the user walked, with the goal of improving the user’s speed with each adjustment. Finding the speed-optimized mode of operation took about 150 rounds of adjustment and two hours per person.

In addition to greatly increasing walking speed, the speed-optimized mode also reduced energy use, by about 2% per meter traveled. However, that result varied widely from person to person, which is somewhat expected, given that it was not an intentional feature of that exoskeleton mode.

“The study was designed to specifically answer the scientific question about increasing walking speed,” Song says. “We didn’t care too much about the other performance measures, like comfort or energy. However, seven out of 10 participants not only walked faster but consumed less energy, which really shows how much potential exoskeletons have for helping people in an efficient way.”

The researchers borrowed the settings optimized specifically for energy use from a previous experiment. In the current study, this mode decreased energy use more than the speed-optimized settings but did not increase speed as much. As intended, the placebo mode both slowed down participants and boosted their energy use.

Better, faster, stronger

Now that the researchers have attained such significant speed assistance, they plan to focus future versions of the ankle exoskeleton emulator on reducing energy use consistently across users, while also being more comfortable.

In considering older adults specifically, Collins and his lab wonder whether future designs could reduce pain caused by weight on joints or improve balance. They plan to conduct similar walking tests with older adults and hope those provide encouraging results as well.

“A 40% increase in speed is more than the difference between younger adults and older adults,” says Collins. “So, it’s possible that devices like this could not only restore but enhance self-selected walking speed for older individuals and that’s something that we’re excited to test next.”

The National Science Foundation and the National Institutes of Health funded the work.

Source: Stanford University

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