If you think wearing an exoskeleton will turn you into a superhero, think again.
Researchers at Ohio State University tested a commercially available mechanical arm on a harness that is typically worn by workers to help them carry heavy objects. They found that the device relieved stress on the arms just as intended – but also increased stress on the back by more than 50 percent.
Exoskeletons inherently change the way we move, explains William Marras, a professor of integrated systems engineering and director of The Ohio State University Spine Research Institute. "The simplest way to describe it is like dancing with a really bad partner," he says. "Someone is tugging and pulling on you in directions you're not expecting, and your body has to compensate for that. And the way you compensate is by recruiting different muscles to perform the task."
As part of the study, a dozen volunteers tested out two pneumatic tools commonly used in industry — a torque wrench and an impact wrench — both with and without the aid of the exoskeleton. The mechanical arm was capable of transferring the weight of each tool to the vest-like harness, allowing the volunteers to easily grip and move the wrench to tighten bolts. But over the course of a few hours, the researchers found, compressive forces on the harness-wearers’ back and spine muscles increased up to nearly 53 percent. Stress on different muscles in the torso also increases anywhere from 56 to 120 percent.
"This exoskeleton is meant to offload weight from your arms, so for your arms it's great," adds Gregory Knapik, senior researcher at the institute. "The problem is, the weight of the tool, the weight of the mechanical arm and the weight of the vest you're wearing — that all goes to your back. At the end of the day, you're just trading one problem for a potentially even worse problem."
The volunteers didn’t seem to notice the extra back strain — but did report discomfort wearing the harness, which is lined with stiff metal rods that restrict movement. “Every single person said they would never wear this if they didn't have to," says Knapik.
The manufacturer of the exoskeleton, acknowledging the potential for back fatigue, recommends muscle conditioning to prevent injury while wearing it.
The tested device is considered a “passive” exoskeleton, as it depends on braces and springs to help support areas of the body. Active exoskeletons, like those seen in action films such as “Iron Man” or “Aliens,” are more a product of Hollywood magic — but they are beginning to become a reality. Marras refers to active exoskeletons as “power steering for the body.” He and Knapik will be testing the spinal loads on just such a device this fall.
The research may be found in the April 2018 edition of Applied Ergonomics.