The ground whizzes by, 5,000 feet below the rumbling plane. Buildings look like specks of dirt and the air is dizzyingly thin. It is a situation that would seem terrifying to most people, but retired Army Capt. Daniel Glanz simply takes a deep breath and leaps from the safety of the plane. And he does it all despite having a prosthetic arm, according to a U.Va. Magazine feature. Prosthetics have evolved from the stereotypical pirate's wooden peg leg to human-like appendages. As a result, recent innovations have allowed amputees to perform many of the functions that once required limbs. They can, for example, use fine motor skills to play the piano. With microprocessor knees, some amputees also can climb mountains and play golf. Prostheses even enable individuals to compete athletically, although some critics claim they have an unfair advantage because of the bionic appendages. "I think that if there's something that they really want to do, as long as it within reason, there is no reason they can't do it with a prosthetic," said J.D. Morris, a certified prosthetist and orthotist at Old Dominion Prosthetics & Orthotics. "A really good example is a guy who came the other day, and when we started talking, he asked if he could play the piano with [the prosthetic], but by the end of the session, he started laughing and said, 'I don't even know how to play the piano.' If the need and the skill are there, anything is possible." Prostheses are designed specifically for the individual's physical and functional needs. Currently, prostheses are made of carbon fibers instead of the fiberglass used 10 years ago. "We are always striving for lightweight, stronger materials; carbon fibers give us the strength we need but are also lightweight," Morris said. Nevertheless, function is still priority in the prostheses' construction. "The design is completely different ... [for] a situation where a person is working and they need to pivot or have to lift a certain amount of weight for their job," Morris said. "A guy yesterday was a cook and a below-the-knee amputee and he has to turn a lot from the grill to the service counter, so he will benefit from a device that allows the foot to remain stationary but the top part to pivot independently." According to the Defense Advanced Research Projects Agency's Bio-Revolution pamphlet, the majority of amputees are missing part, or all, of a lower extremity, often because of peripheral vascular disease. This condition affects 8 to 12 million Americans and can be caused by heart disease, diabetes and smoking, among other factors. If untreated, PAD can cause gangrene and ultimately may require amputation. One of the biggest challenges facing those lower-extremity amputees, Morris said, is fitting residual limbs. "This past September, I was in Seattle for our national convention, and there were some new products out that change the way we treat patients, especially transfemoral amputees," Morris said. "A new sub-atmospheric vacuum system literally holds the prosthetic to the body with a vacuum, something not typically used with above knee amputations because it was more difficult to stay on. This will be one of the biggest advances in the next five years as it continues to develop." A more recent innovation to prosthetic knee joints has been the addition of microprocessors. This technology allows a larger range of motion and physical activity. The 'C-leg' designed by Otto Bock allows the user to change the prosthetic's function with the tap of a toe or a wireless remote control. The prosthetic is also weatherproof and slip-proof to allow the user to kneel. "I just fit a C-leg on Wednesday and I can set it for bicycling, golfing, running, standing, anything depending on the type of mode people would use other than standard walking," Morris said. "I can fine-tune it for specific applications." Developments have been made in foot design, as well. The University of Michigan has created a power-harvesting device integrated into the foot that fuels a computerized prosthetic with kinetic energy from motion, according to Popular Science. This innovation reduces the energy demand from batteries to less than 1 watt of electricity. "We now have a foot with a microprocessor that allows foot to move depending on the part of gate cycle," Morris added. Upper-extremity prostheses, however, require a different design, said Col. Geoff Ling, a doctor and researcher in DARPA's Defense Sciences Office. "We use our hands and arms for thousands of different tasks, so that replacing an arm is a very complex problem," he said. "What we need is a smart, modular prosthetic arm and hand, one that will have human-like capabilities, look like the native limb, and be controlled directly by the wearer's brain." DARPA is heavily involved in the development of upper-extremity prostheses. Through the Human-Assisted Neural Device program, the agency is working to develop technology that would decode the electrical signals from the central nervous system, relaying them to an individual's prosthetics. Several prototypes exist so far, and one has been tested successfully with primates at Duke University and the University of Pittsburgh. Some of the prototypes even enable users to move prosthetic fingers independently and pick up M&M's from a table. The current prototypes, however, lack the sensory input component researchers hope to include in the envisioned prosthetic because they are linked to the nerves located in the muscle tissue near the amputation. DARPA officials hope their research efforts to improve prostheses will pay off, especially in light of the large number of military amputees. According to Popular Science, more than 130 Iraq War veterans are adapting to life with an amputated upper extremity. Glanz is no stranger to that lifestyle. The former University ROTC cadet was in Afghanistan on his second deployment, planning to return to the University to complete his second undergraduate degree, when a blast from a suicide bomber gave him seven fractures, 100 stitches worth of damage on his face, shrapnel wounds and nerve damage in his legs. With surgery, Glanz regained sense and function in his legs, but his right arm was amputated below the elbow. Regardless, there were bright spots in the recovery, Glanz said. "I can't say enough about the physical therapy and the occupational therapy," he said in the interview with U.Va. Magazine. "They work you hard, but they put me back together really fast." Today, he is president of Skydive Orange in his hometown, Orange, Va. With more than 1,500 jumps under his belt, Glanz is also a licensed United States Parachute Association coach. His ability to take part in these activities is thanks, in part, to the prosthetic limb he uses. With such successful recoveries in mind, prosthetists and researchers may have plenty of motivation to continue their work. "Every single person who walks through that door is different," Morris said. "Our job is to return them to as normal a life as possible and to allow them to go back into the workforce in some cases"