Exoskeletons could turn us all into Olympic runners

Departments - Medical Innovations

Stanford researchers study devices that could let people run up to 24mph “without breaking a sweat.”

“You can almost think of it as a mode of transportation. You could get off a bus, slap on an exoskeleton, and cover the last one-to-two miles to work in five minutes without breaking a sweat.”
Graduate student Delaney Miller runs on a treadmill aided by the ankle exoskeleton emulator. Fellow graduate student Guan Rong Tan controls the emulator and monitors Miller’s gait and respiration.

Stanford engineers are studying devices to make running easier. In experiments with exoskeleton emulators, researchers investigated two different modes of running assistance: motor-powered assistance and spring-based assistance.

Wearing a switched off exoskeleton made running 13% harder than without the exoskeleton. When powered by a motor, the exoskeleton reduced the energy cost of running, making it 15% easier than running without the exoskeleton and 25% easier than running with the exoskeleton switched off.

In contrast, the study suggested if the exoskeleton was powered to mimic a spring it was 11% harder than running exoskeleton-free and only 2% easier than the non-powered exoskeleton.

“When people run, their legs behave a lot like a spring, so we were very surprised that spring-like assistance was not effective,” says Steve Collins, associate professor of mechanical engineering at Stanford and senior author of a paper covering the results published in Science Robotics.

Powering your step

The frame of the ankle exoskeleton emulator straps around the user’s shin, attaches to the shoe with a rope looped under the heel, and has a carbon fiber bar inserted into the sole, near the toe. Motors produce the two modes of assistance.

The spring-like mode mimics the influence of a spring running parallel to the calf, storing energy during the beginning of the step and unloading that energy as the toes push off. In powered mode, motors tug a cable that runs through the back of the exoskeleton from the heel to the calf. It pulls upward during toe-off to help extend the ankle at the end of a running step.

“Powered assistance took off a lot of the energy burden of the calf muscles. It was very springy and very bouncy compared to normal running,” says Delaney Miller, a graduate student at Stanford working on and run-testing the exoskeletons.

Eleven experienced runners tested the two assistance types on a treadmill, with and without any assistance mechanisms turned on. Researchers measured runners’ energetic output through a mask tracking how much oxygen they were inhaling and how much carbon dioxide they were exhaling. Tests lasted 6 minutes; researchers based findings on the last 3 minutes of each exercise.

The energy savings observed indicate a runner using a powered exoskeleton could boost speed up to 10%, even higher with additional time for training and optimization.

Researchers from Carnegie Mellon University, Ghent University, and Nike Inc. are co-authors of this paper. Collins is also a member of Stanford Bio-X. This research was funded by Nike and the National Science Foundation.

Stanford University