Engineers Test Stumble Responses To Improve Prostheses

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 in the Journal of Neuro-Engineering and Rehabilitation.

While being observed with motion capturing sensors, seven healthy subjects walked on a force-instrumented treadmill at 1.1 m/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 protect 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 cancelling headphones as well as goggles that blocked their field of vision.

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 stumble, 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 doctoral 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.”

Sources: Vanderbilt University, The O&P Edge