The Center for Rehabilitation Engineering and Assistive Technology at Vanderbilt University conducted tests as a first step toward learning to prevent stumbles and falls for users of prosthetic devices. The open-access results were published this month in the Journal of NeuroEngineering and Rehabilitation.
Schematic of the stumble perturbation system. The subject walks on the instrumented treadmill. Ground reaction forces and moments are collected and used to calculate the center of pressure under the foot, which is then used to detect gait events.
Image courtesy of the study authors and Creative Commons.
While being observed with motion-capturing sensors, seven healthy subjects walked on a force-instrumented treadmill at 1.1m/s. The handrails were removed so they could not be used as a recovery aid; however, a full-body harness with slackened safety rope was worn to prevent a true fall. To prevent subjects from hearing or seeing the obstacle being deployed, each subject listened to white noise via earbuds and wore noise-canceling headphones and goggles that blocked the visual field. Subjects watched on-screen visual feedback to ensure a centered position on the treadmill and avoid crossing over to the contralateral force plate. As a distraction technique, subjects were instructed to count backwards aloud from an arbitrary number by intervals of seven. They were given several minutes to walk on the treadmill prior to testing in order to acclimate to the setup.
As the first step toward improving the stumble response of lower-limb prostheses, the tests were intended to understand the way people with two legs catch themselves when they stumbled, which required tripping each subject 190 times. In addition to protecting test subjects, the harness included a scale. If a subject put 50 percent or more of his or her weight on it during a stumble, that counted as a fall.
“Not only did our treadmill device have to trip them, it had to trip them at specific points in their gait,” said Shane King, a PhD student and lead author on the paper. “People stumble differently depending on when their foot hits a barrier. The device also had to overcome their fear of falling, so they couldn’t see or feel when the block was coming.”
“So now we understand what the stumble reflex should look like,” said Michael Goldfarb, PhD, a professor of mechanical engineering at Vanderbilt and the principal investigator on the study. “The next phase is to take that information and program it into computer-controlled prosthetic legs. After that, we will safely stumble amputees wearing both commercially available prosthetics and the ones we’ve designed with these reflexes and learn whether ours can prevent more falls.”
To watch a video of the testing, visit Vanderbilt News.
Editor’s note: This story was adapted from materials provided by Vanderbilt University.
