When Zac Vawter put his mind to climbing the 103 floors of Chicago's iconic Willis Tower, his legs did the rest.
Even the one that isn't human.
The Seattle resident scaled the skyscraper's stairway heights on Sunday thanks to what the Rehabilitation Institute of Chicago calls the "world's first neural-controlled bionic leg."
In other words, when Vawter thinks about going somewhere, it sends a signal to his prosthetic right leg that spurs it to move. This kind of technology has been implemented before in arms and fingers, but never before in a leg.
While Vawter, 31, has been part of the Illinois rehab center's trial for about a year, this weekend's fourth annual SkyRise Chicago fundraiser was the first public test of the technology. There was no guarantee he'd successfully climb the entire skyscraper formerly known as the Sears Tower, but he'd certainly give it a shot.
Yet there he was -- 53 minutes, 9 seconds after he set off -- in the tower's SkyDeck Chicago, and seemingly on top of the world.
"It was a good goal for the team to shoot for, and we hit it," he said immediately afterward.
This perch was a far cry from where Vawter found himself three years earlier, in a hospital room after his leg was amputated following a motorcycle accident.
He'd long been a runner, competing for St. Martin's University in Lacey, Washington, in races like the 800, 3,000 and 5,000 meters as well as in cross-country events.
And now, all of a sudden, he was a patient with just one leg.
But Vawter took a positive turn when he teamed up with the Rehabilitation Institute of Chicago, which U.S. News and World Report ranks as the nation's top rehab hospital.
He became a willing human guinea pig for researchers testing the one-of-a-kind prosthetic. In an interview with CNN affiliate WLS prior to Sunday's climb, Vawter called the new leg "a dramatic improvement over my normal prosthetic."
"It's something exciting and fun, and I hope that we push the boundaries of what the research and the leg is capable of," he said.
Levi Hargrove, from the Chicago rehab center, told WLS that "really advanced hardware" makes the device work.
"We record all of the data on the computer, and then teach this small microcomputer what it looks like" as the leg moves, Hargrove adds.
Vawter was met with cheers as he entered the skyscraper's front door on Sunday morning, then again after he trekked up the final steps. He had plenty of company and fellow inspiration as he went skyward, as one of about 3,000 people making the climb and raising roughly $1 million for the rehab center.
Among them was U.S. Sen. Mark Kirk, who has worked tirelessly with the Rehabilitation Institute since suffering a stroke last January. In his first public appearance since then, he climbed 37 flights in about an hour.
"However bad it looks, if you or a loved one has suffered a debilitating stroke, you could be climbing the tower one day with us," Kirk said afterward, in comments provided by RIC. "Don't give up!"
That is Vawter's mindset as well. He's happy to help the cause, and to move forward in his own life with his new prosthetic's help.
"It feels awesome," he said of the leg.