Few individuals would consider tackling the 2,200-mile trek through the Appalachian Mountains—and even fewer would dream of doing so after becoming paralyzed from the waist down.

Try telling that to Stacey Kozel.

Kozel, of Madison, Ohio, is one of an estimated 1.5 million Americans suffering from lupus, which cost her the use of her legs in 2014. She also happens to be one of the thousands of individuals who will attempt to hike the Appalachian trail this year.

The trip is daunting for even the most experienced hikers, and would be impossible for Kozel without the aid of an amazing orthotic system called the C-Brace. With the support of the “custom electronic leg brace ,” manufactured by German prosthetics company Ottobock, Kozel is hiking an average of 20 miles a day on the Appalachian Trail (and writing about it on her Facebook page ).

With her inspiring story, Kozel joins the ranks of athletes who are accomplishing awesome feats with the help of prostheses and “bionic” braces. Mike Coots, a professional photographer in Hawaii, for example, is a pioneer in prosthetic surfing—using his Ossur “pro-flex” carbon fiber leg to surf just as he did before a shark attack took his limb nearly 20 years ago.

Coots recalls being afraid to enter the water wearing a prosthetic, much less surf with one on: “It’ll rust, or it’ll break. Springs are gonna pop out and fly everywhere, I thought,” he told The Daily Beast. One day back in college, Coots decided to take his chances. “I just went out on my longboard... and caught a wave,” he said. “Back then I just wanted to spend more time in the water… now I want to show myself surfing to show others it’s possible.”

It took Coots years to find out what worked and what didn’t—buying prosthetic feet off Ebay and “cutting toes off and modifying the feet,” or sometimes even “taking a saw and cutting off pieces of the rubber.” Then he received a carbon-fiber prosthetic from Ossur over two years ago. According to Coots, the difference between the carbon fiber prosthetic and the rubber ones he used just after the accident “is like night and day.” While the “rubber ball foot” he started with simply absorbed energy, the pro-flex limb allows him to control the surfboard similarly to how he would with his biological foot. It was “like getting that magic surfboard,” he says.

Tim Hurst, a 57-year-old who lost his foot in a motorcycle accident 35 years ago, told The Daily Beast about a similar struggle with his first prosthetic leg. “Back in those days it was mostly made of wood,” he remembers, “I struggled with the prosthetic I had because of the technology.” After spending almost a year in the hospital and re-learning to walk after being “paralyzed from the waist down,” Hurst knew he wanted return to the athletic lifestyle he enjoyed before the accident. Despite having only a walking prosthetic to run on, Hurst started running “at least a mile a day, six days a week,” as soon as he was able. After learning about the Ossur running blade from a prosthetics catalog nearly 10 years ago, his “entire life changed. On that first day I ran probably five miles. It was just great to finally be… equal and be on the same level.”

Now he runs marathons.

To date, Hurst has finished 53 marathons in 47 states and has plans to complete a 50 marathons in 50 states challenge . He was convinced to join the “50 states club” after meeting Larry Malcolm, the world record holder for most marathons. Hurst plans to complete the challenge in January 2017 at the Goofy Marathon at Disney World in Orlando, Florida . “It’s a really apt name,” he says, “because you have to be a little bit goofy to do this.” The challenge is immense—both logistically and physically. “It’s the hardest thing you’ll ever do in your whole life,” Hurst says of running marathons, “but I’m addicted.” When asked how he completes these arduous 26.2-mile runs, Hurst gives a great deal of the credit to what he calls his “space-age technology” prosthetic: “it would be impossible to run the marathons without it…. I feel like the bionic man.”

Indeed, some might argue that these bionic limbs and “orthotronic” braces are facilitating physical activity that is beyond a human being’s natural biological capacity. Hugh Herr, head biomechatronics researcher at the Massachusetts Institute of Technology Media Lab, himself a double-amputee and a designer of prosthetics and bionic legs, is one of those people.

Herr lost his legs to frostbite after a mountain climbing accident at the age of 17, but within weeks of receiving his first prostheses, he began augmenting them to enable him to climb again. Early on, Herr developed narrow blade devices, welded a rock-climbing crampon to a prosthesis, and crafted longer prosthetic legs, allowing him to wedge his prosthetic into small crevices, use it to climb frozen routes, and “reach holds able-bodied climbers couldn’t stretch to.” Since those early days, Herr has moved beyond simple augmentations and began working in the field of “biomechatronics,” which aims to integrate human physiology with electromechanics in order to, as he said in a 2014 TEDTalk , create “structures that could extend beyond biological capability.” Bionic integration—attaching or implanting electromechanics into the body—Herr believes, is “beginning to bridge the gap between disability and ability, between human limitation and human potential.”

The question of whether bionic limbs create super-ability was a hot-button issue leading up to the London Olympics in 2012 , when Oscar Pistorius was given the green-light to compete with able-bodied runners in the Games. An article published by Wired that summer asked point-blank: “Will Bionic Limbs Put the Olympics to Shame?” While Ossur, the company that produced the “Flex-Foot Cheetah” prosthetics Pistorius wore during the Games, claimed that the blades return less than one-third the amount of energy an able-bodied foot accumulates during each stride, researchers at Southern Methodist University found that the lightness of the limbs made Pistorius faster than he would have been otherwise.

While Coots doesn’t think his prosthetic gives him an advantage in the water while he’s surfing, he believes that in the future, it will. In fact, he’s currently working with Ossur to develop a four-prong carbon fiber foot specially designed for surfing and other water sports. “The idea is to have something that can bring up my surfing to a level it wouldn’t be normally,” he said, “I’d love to see the technology develop to have the prosthetic become an advantage.”