As workout studios close their doors amid a global pandemic, people are left with one of the cheapest and easiest ways to break a sweat: running.

But just because you know you could be running, doesn't mean you'll actually go out and jog. That's where a new Nike-funded research team comes in. They want to help people struggling to go the distance — and invented a wearable ankle "exoskeleton" that makes running 14 percent easier and energy-efficient compared to normal running shoes.

"People report that it feels effortless — like you are soaring and flying," co-author Steve Collins, a mechanical engineer at Stanford University, tells Inverse. His team revealed its winning "exoskeleton" in a study published Wednesday in the journal Science Robotics.

"You get to go a bit faster for the same energy and that makes it more appealing."

The wearable wasn't invented so people can beat speed records or cut corners in a race. The goal is that it can make running a bit more fun, exciting, and easy to take up, Collins says. The working theory is that if people run farther and faster, they'll lace up more often.

Personally, Collins just wants to keep up with his younger brother, a marathoner: "I think it'd be pretty fun to be able to get out there and not be holding him back so much."

The goal? Get people to love running

Collins and his team typically work on technology that can help people who have suffered strokes or amputations walk better. But in this case, they wanted to "hack" running .

In 2018, only one in four Americans between the ages of 18 to 29 reported going for a run or jog at least once in the past year. That number drops to one in five as people approach mid-life. Collins and his team argue that these low rates of activity contribute to rising obesity rates.

The team hypothesized that why people don't pick up running stems from not feeling athletic — and the simple fact that running can feel hard.

"We thought that maybe our exoskeletons could make it easier and more fun to run so that people would do it more, and have more enjoyable longer lives," Collins says.

Participants trying different wearable robots compared to regular running shoes in the lab. Witte et al.

To test their designs, the researchers recruited 11 competitive runners between the ages of 18 to 40. While the runners did their thing (run) they wore different types of ankle exoskeletons. Meanwhile, the team harnessed data and made real-time design adjustments using artificial intelligence technology. The exoskeletons tested were:

"Optimized power": An applied force design intended to enhance the ankle's ankle’s natural movement, effectively boosting people’s stride.

"Optimized spring-like": An exoskeleton that exoskeleton mechanically applied a spring-like push onto the ankle but didn't include extra power to their stride.

"Zero torque mode": This was the control condition. Runners wore exoskeleton hardware without turning it on. The goal here was to estimate how much extra energy people have to generate to carry the extra weight from the device.

The final control element was the Nike Zoom Pegasus 32 — a neutral running shoe the runners used on a treadmill, with no ankle exoskeleton attached.

When they weren't wearing the Zoom Pegasus 32, the wore their own running shoes. Each trial involved running on a treadmill with an average pace of 2.7 meters per second, which culminates at about a ten-minute mile.

Researchers documented the runner's metabolic rates , breath by breath, based on how much oxygen they took in and CO2 they exhaled. They also captured participants' metabolic rate at rest, when they were standing still. The metabolic rate is how much energy a human is using second by second, and shows how hard people are working to run.

"It can do things your muscles can't do."

The researchers also charted how much mechanical work the exoskeleton was performing and how much extra power the device provided.

The design of the Nike-backed running robot. Witte et al., Sci. Robot. 5, eaay9108 (2020)

The "optimized power" design proved to be the most helpful of the running robots. This wearable helped participants save 24 percent more energy compared with wearing an unpowered exoskeleton that didn't offer any extra force on the ankle.

Crucially, the runners saved about 14 percent more energy with this powered exoskeleton compared to running wearable-less with the Nike shoes.

"We think that the key to the benefits from the powered device is that it can do things your muscles can't do," Collins explains.

The powered exoskeleton provided a surge of "torque," or a twisting force, very late people's stride as the foot was still in contact with the ground. Normally, at this moment, the amount of force muscles can produce drops off as the muscles quickly contract. The running robot artificially fills in this drop, allowing the combined human-robot system to "outperform" the biological system alone, Collins says.

The "optimized spring-like" feature only reduced energy expenditure by 2 percent. It also, surprisingly, increased metabolic rate by roughly 11 percent compared to running shoes — meaning it made running more, not less difficult.

A few weeks ago, Collins helped a new user try the powered exoskeleton in the lab.

"'Wow, I feel weightless,'" Collins recalls the user exclaiming. "'Can I please take it home?'"

And when people take it off? They report stark differences, Collins says.

"When it's removed, everybody says, 'My legs feel so heavy and my calf muscles feel super weak."

For now, the "optimized power" ankle robot is still in the testing phase. But the team does hope to build an untethered, lightweight version that could go on the market in the next few years.

The devices' energy gains may attract the same consumers who rushed stores for the "fastest running shoe in the world": Nike's Vaporfly marathon shoes. Vaporflys claim to make running about 4 percent easier. This new running robot, could triple that number.

If they're successful in creating a sleek, effective exoskeleton, we could see a future where everyone slips into their "running robot" before lapping the block. Down the line, the device could help people with disabilities, the elderly, and running-avoiders zoom around the neighborhood. The team can also see a future where it can be a boon to first responders.

"You could imagine first responders being able to cover more ground while getting less tired and in some cases, that could help people to save lives," Collins says.

And even if just a few more people get off the couch for a jog, Collins and his team will be pleased.

Abstract: Exoskeletons that reduce energetic cost could make recreational running more enjoyable and improve running performance. Although there are many ways to assist runners, the best approaches remain unclear. In our study, we used a tethered ankle exoskeleton emulator to optimize both powered and spring-like exoskeleton characteristics while participants ran on a treadmill. We expected powered conditions to provide large improvements in energy economy and for spring-like patterns to provide smaller benefits achievable with simpler devices. We used human-in-the-loop optimization to attempt to identify the best exoskeleton characteristics for each device type and individual user, allowing for a well-controlled comparison. We found that optimized powered assistance improved energy economy by 24.7 ± 6.9% compared with zero torque and 14.6 ± 7.7% compared with running in normal shoes. Optimized powered torque patterns for individuals varied substantially, but all resulted in relatively high mechanical work input (0.36 ± 0.09 joule kilogram−1 per step) and late timing of peak torque (75.7 ± 5.0% stance). Unexpectedly, spring-like assistance was ineffective, improving energy economy by only 2.1 ± 2.4% compared with zero torque and increasing metabolic rate by 11.1 ± 2.8% compared with control shoes. The energy savings we observed imply that running velocity could be increased by as much as 10% with no added effort for the user and could influence the design of future products.