This Battery-Powered Partial Exoskeleton Cuts the Energy Cost of Walking for Stroke Survivors

Engineers from the University of Utah have developed a lightweight exoskeleton system which, they say, can reduce the energy required for stroke survivors suffering from hemiparesis to walk by nearly 20 percent.

"Improving quality of life after a stroke is one of the biggest unmet challenges in healthcare today," claims senior author Tommaso Lenzi, associate professor in the University of Utah's Department of Mechanical Engineering, of the team's work. "We're now showing that robotics can make a measurable impact here."

"Portable ankle exoskeletons have failed to reduce the energy required for stroke patients to walk, so we proposed a different approach," explains lead author Kai Pruyn, a graduate student in Lenzi’s HGN Lab for Bionic Engineering. "Patients with ankle weakness often compensate with their hip joints, which requires extra energy. Our goal was to develop a powerful and fully portable hip exoskeleton. Hip exoskeletons can also be extremely lightweight because they are worn closer to the user's center of mass and have lower torque requirements compared to ankle exoskeletons. We found that the hip assistance effectively compensated for reduced ankle propulsion."

The team's exoskeleton specifically focuses on people with hemiparesis — a loss of strength on one side of the body that causes the muscles on the other side to overcompensate, which can increase the amount of energy expended to walk by up to 60 percent. Worn around the hips and strapped to the thighs, the exoskeleton includes battery-powered motors to assist with the user's natural walking gait — providing a boost that offloads almost 30 percent of the work carried out by the hip joints, resulting in an overall 18 percent decrease in energy expended.

"For a person with a healthy gait, this would be like taking off a 30-pound backpack," says co-author Bo Foreman, professor of Physical Therapy & Athletic Training at the University. "For someone with hemiparesis, that’s a life-changing difference."

The team's research is in press with the journal Nature Communications, with an unedited version available under open-access terms; the next step in the project will be expanding the device's capabilities to other activities beyond walking. "Our goal is to ensure that a stroke doesn’t define the limits of where a person can go or how they can live," Lenzi says.