31 year-old Zac Vawter made history on Sunday when he became the first person to scale the 103 flights of stairs in Chicago’s Willis Tower with a mind-controlled robotic leg, reports the Associated Press. The artificial limb takes advantage of targeted muscle reinnervation (TMR), a technique that connects nerves severed in an amputation to other, viable muscles. In Vawter’s case, the nerves that would ordinarily control his missing lower leg have been rerouted to his hamstring, whose electrical impulses are converted into control signals that move his prosthesis.

The first of these kinds of "bionic" limbs, called myoelectric prostheses, was introduced in 2005 by a team lead by the Rehabilitation Institute of Chicago (RIC) Center for Bionic Medicine. Former high-power electrical lineman Jesse Sullivan was outfitted with a "Bionic Arm" he could control with his thoughts, a procedure that has since been performed on 50 people around the world. The RIC is also leading the research effort for Vawter’s bionic leg, in conjunction with the University of New Brunswick, Vanderbilt University, MIT, and URI. Funding was provided by the Department of Defense’s Army Telemedicine and Advanced Technology Research Center.

"I take stairs like I used to, and can even take two at a time."

Vawter’s $8 million, 10-pound robotic leg has two motors that power the knee and ankle separately. As the RIC explains on its website, when Vawter pushes on the device to stand up, the leg pushes back, propelling him upward — a huge boon over a conventional prosthesis. As Vawter himself explains, ordinarily, "I have to take every step with my good foot first and sort of lift or drag the prosthetic leg up. With the bionic leg, it’s simple, I take stairs like I used to, and can even take two at a time."

By all accounts, Sunday’s event was a success, with Vawker completing the climb in 53 minutes and 9 seconds. "The prosthetic leg did its part, and I did my part," he told reporters.