Still heavily medicated at the time, he slowly came to terms with his new reality. "It was hard for me when I first realized I was missing something," he says. "I didn't know what to do or how my life was going to look like in the future. ... The doctors said I was really lucky that I survived and nothing was damaged inside, no heart issues, that I 'just' lost my leg."

Lukas Kalemba outside Ossur HQ in Reykjavik, Iceland.

Now, 12 years later, Kalemba is a regular prosthesis user who is competing in the Cybathlon, an international competition for people with disabilities who are using technologies to enhance their daily lives. He will wear and pilot a prototype from Össur, one of the largest manufacturers of noninvasive orthopedic equipment and lower-limb prostheses, where he now works as a prosthetic technician.

The company, headquartered in Reykjavik, Iceland, is one of the global leaders for prosthetic legs. And with the recent acquisition of Touch Bionics, a Scottish company that manufacturers bionic arms, Össur now houses some of the most innovative prosthetic technologies for both lower and upper limbs. The company also has a long history of supporting and sponsoring Paralympians. Now for the Cybathlon in Zurich next month, it's sending four pilots, including Kalemba, to compete in the powered-leg-prosthesis race that will see competitors stand up from a couch without support and walk on an inclined ramp before climbing a flight of steps at the end.

One of the most popular products from the Icelandic company is the Power Knee, which has an internal motor to re-create the movements of the missing joint in the leg. The machine responds to a user's movements and provides the right force needed to complete a task. Every time Kalemba wants to stand up wearing the Power Knee, he moves forward to shift some of his body load onto the joint. The motor backs the shifting weight with its own force to push him up.

"I almost don't need my energy to lift me up," says Kalemba, dressed in a pale blue shirt and jeans at his home in Reykjavik. "The leg does it for me."

That kind of automated movement replicates the actions of a natural knee and reduces the effort required to walk on a passive prosthetic leg, but it takes practice to avoid triggering unintended movements. "Sometimes the knee extends accidentally," says Kalemba. "If you want to go closer to the dinner table, it's almost the same movement as wanting to get up. So it pushes you up."

"Going out and meeting friends again was the hardest thing at the beginning. ... You fall more often, you feel insecure and uncomfortable." - Lukas Kalemba

Kalemba is an experienced prosthesis user who spends hours testing both new and old prosthetic legs on a treadmill, a wooden ramp or the stairs around the Ossur campus. But the powered leg that he will use in the obstacle course at the Cybathlon has never been tested. The prototype that the team at Ossur -- led by David Langlois, who oversees the Power Knee operations -- has been built especially for the competition and is not expected the become a commercial product for at least a few years.

The experimental powered leg combines the company's popular motorized knee with an ankle that has its own internal motor. "It has ground contact sensors so it recognizes immediately where you're putting load with your toe or heel," says Kalemba. "Then the knee recognizes it and works with it. Both together give [me] the active power that I don't have anymore because I don't have my muscles anymore."

Having lost a limb at an early age, it was hard for Kalemba to consider the use of a mechanical leg at first. He remembers being introduced to a sticklike alternative when he met the certified prosthetist orthotists (CPOs) at the hospital 12 years ago. He did not want to use it. But he eventually gave in and started using a basic mechanical leg with free-swinging motion that enabled him to move again.

"Going out and meeting friends again was the hardest thing at the beginning," he says. "I wasn't feeling safe on the knee when I had the mechanical leg. You fall more often, you feel insecure and uncomfortable. Maybe you want to go out but you don't want to because you don't want to fall in front of some kind of audience."

Ossur HQ in Reykjavik, Iceland. Photo credit: Arnaldur Halldorsson/Bloomberg/Getty Images.

But as Kalemba spent more time on a prosthetic leg, he learned to accept it as a part of his life. He did not become a football player as he had once planned, but he went on to become a CPO and moved to Iceland three years ago to test and give feedback on the prosthetic legs at Ossur.

"I can't play football like I would if I had two sound legs," he says. "[But] I try to make things better [as a CPO] not just for me but other people who are in the same situation as me."

Even as he continues to contribute to the improvement of the technology at work, he doesn't think the field of prosthetics is advanced enough. "It makes my life easier again but it's not a benefit compared to my real leg yet," he says. "Maybe [...] if I could have a leg like the Terminator movies, that would be a huge benefit. But it's still a minus point right now."

The challenges that he points out validate the need for an event like the Cybathlon. The competitive platform has created a space that's conducive to innovation within rehabilitative robotics like powered prostheses. "We would not be where we are right now with the powered leg [if it were not for the event]," he says. "It's very hard to imitate the knee joint with technology. But we are really close and we are getting closer with every generation as we are evolving."

***

Claudia Breidbach smiled as she looked around at the group of skydivers huddled on the floor of a small, seatless plane. A couple of minutes into her flight, as the aircraft swiftly gained altitude over the Sky High dropzone in Eschbach, Germany, she glanced at the altimeter wrapped around the prosthetic on her left arm.

At about 13,000 feet, when the sweeping farmscapes on the ground had started to look like a green mosaic in the distance, Breidbach made her way to the door. Seconds later, she lunged out of the plane with her teammate, Michael Sigl. The two, dressed in bright-orange jumpsuits, quickly found each other's hands to make formations as they fell through the sky. They both spun around midair, held hands for a split second, then spun away from each other again. They repeated the free-fall pattern until it was time to release their parachutes and steer themselves back to the ground.

Breidbach is a competitive skydiver from Koblenz, Germany, who was born without a left forearm. When she decided to be a skydiver in 2008 after her first tandem jump, she quickly learned that she would have to fight for her spot in the world of parachuting. "When I [first] asked to be a competition skydiver, they said: 'Claudia, you need two hands,'" she recalls, standing outside a hangar on the ground. "I said: 'Hey, you need two hands, not me. Give me a chance.'"

The i-limb quantum powered arm from Touch Bionics.

Skydiving is a strenuous sport. It requires muscle strength, especially in the arms, to cut through the wind and create acrobatic formations in the sky. It can take years of training and hundreds of jumps to perfect. Over the last eight years, Breidbach has completed 680 jumps and participated in skydiving competitions across Europe. She's now popularly known as the "one-handed skydiver" among her peers.

A training manager at Touch Bionics, Breidbach will soon represent the upper-limb prosthetics company at the Cybathlon in Zurich next month. As a pilot in the arm-prostheses race, she will use the i-limb quantum, a multidirectional prosthetic that she wears daily, to complete an obstacle course of otherwise routine tasks. Competitors will be asked to open jars, slice bread, spread jam, complete a puzzle and screw a lightbulb into a table lamp.

The event might not have the adrenaline-pumping appeal of jumping out of planes, but it is another opportunity for Breidbach, who is the only female pilot in the powered-arm discipline, to indulge her competitive spirit. "I heard there was no woman in the [race] and I was like: 'Hey, this won't work. I'm here and I'd like to take part in the competition,'" she says. "I want to win but the biggest thing is to take part to show how we can do different tasks in our situation."

Claudia Breidbach at the Sky High dropzone in Eschbach, Germany.

Movements required in the race range from forceful to reflexive. For most people, picking up a knife or rotating a bulb is not a complex undertaking. But for anyone wearing a prosthetic arm, every movement requires a conscious thought. "You need to work with the power in your body and the muscles in your arm," says Breidbach. "You carry the weight of the object and the weight of the prostheses. You need more force. When you open a can, it's a combination of the force from the body and also the force in the hand."

But for Breidbach, who has been using the i-limb for the past five years, the experience makes all of her tasks much more effortless and even enjoyable. For most of her life, she tried variations of prosthetic arms that left her wanting more. A static silicone version had aesthetic value but no flexibility. An early iteration of a motorized arm allowed some movement but would not let her type or hold her phone with her left hand. It wasn't until she tried the Touch Bionics arm at a medical exhibition that she felt the impact of using both hands.

"It moves like a natural hand," she says. "In the morning when I put on my hand, I think it's my hand. I feel it rotating in my stump. I feel the movement of each finger. If something is hot or cold I don't feel it but when I grab something I feel it and it's amazing."

With electrodes placed on her upper left arm muscles and the stump, the powered arm picks up the natural signals to initiate one of 24 grips. When she flexes her muscle on the outside of her arm, for instance, the prosthetic hand opens. A flex on the inside closes it again. "If I think about a rotation of the thumb, the hand rotates," says Breidbach, as the semitransparent gray hand spins with a whirring sound. "It's changed my life."

Unlike other powered arms, the i-limb has a wide range of multi-articulating movements that can be done simultaneously. The hand creates gestures even when it's spinning around. In addition to pre-programmed functions, a user can program 12 extra grips using an accompanying mobile app. Breidbach created her own for holding chopsticks. Now she can connect her arm to the app via Bluetooth or tap her Apple watch when she wants to eat sushi.

"For me this is not a prosthesis, it's my hand." - Claudia Breidbach

As someone who was missing a limb at birth, every time Breidbach programs the technology to form a new grip or encounters a new task, she learns how to move her left hand for the first time. "You need to think about all the smallest movements when you're learning how to use it," she says. "Not just to learn how to work with it but to do all the things in a different movement with two hands. At the Cybathlon, if someone lost an arm, they [already] know how to work with two hands. Sometimes I do many things with my shoulders, I don't move with the arm because that's how I always did it without the left arm and prostheses."

As she continues to train for the Cybathlon, she's learning to rely on her powered hand every day. Sitting outside her camper at the Sky High dropzone one morning, she poured hot water from a kettle into her pour-over coffee maker before slicing through an English muffin with a knife. She held a jar of strawberry jam in her prosthetic hand and used the knife to spread the bright pink preservative.

"For me, this is not a prosthesis, it's my hand," she said as she held her gray left hand with her right. "When I close my eyes at night and relax, the feeling doesn't stop at my stump. I feel it all the way through my left arm. The first time I felt that, I had tears in my eyes."