New research from Stanford University has found that wearing a powered exoskeleton rig can reduce the energy cost of running, making it 15% easier than running without an exoskeleton.

Researchers found that wearing a powered-off exoskeleton increases the energy cost of running, making it about 13% harder than running without the exoskeleton. However, when powered by a motor, an exoskeleton reduced the energy cost of running by as much as 15%. Using a powered exoskeleton also made running 25% easier than running with an exoskeleton that was switched off.

"When people run, their legs behave a lot like a spring, so we were very surprised that spring-like assistance was not effective," said Steve Collins, associate professor of mechanical engineering at Stanford. "We all have an intuition about how we run or walk but even leading scientists are still discovering how the human body allows us to move efficiently. That's why experiments like these are so important."

The frame of the ankle exoskeleton emulator used by researchers straps around the user’s shin and attaches to the shoe with a rope looped under the heel with a carbon fiber bar inserted into the sole near the toe. Meanwhile, attached motors produce 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 the energy as the toes push off. When powered, the motors tug a cable that runs through the back of the exoskeleton from the heel to the calf.

"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," said Delaney Miller, a graduate student at Stanford who is working on these exoskeletons and helping test the devices. "Speaking from experience, that feels really good. When the device is providing that assistance, you feel like you could run forever."

Researchers tested the exoskeleton on 11 volunteers running on a treadmill. They tested the runners as they wore the exoskeleton and again without any of the assistance mechanisms turned on. The researchers measured runners' energetic output using a mask that tracked how much oxygen they were breathing in and how much carbon dioxide they were breathing out.

The energy savings observed revealed that using a powered exoskeleton could boost speeds by as much as 10% and it could be even higher if runners have additional time for training and optimization.

In addition to providing physical support, confidence and increased speed, the exoskeleton could also be used to cover walking distances quicker or to help those who have trouble walking improve how they walk.

"You can almost think of it as a mode of transportation," said Guan Rong Tan, a graduate student in mechanical engineering who, like Miller, is continuing this research. "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."