DEFYING GRAVITY: AlterG's Anti-Gravity Treadmill uses differential air pressure to reduce the force of gravity on the mass of a runner or walker's lower extremities. U.S. Army Sgt. Damon Warren has been working out on AlterG's treadmill for months as part of his rehabilitation for injuries sustained during combat in Iraq. Image: COURTESY OF DAMON WARREN
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While on his third deployment to Iraq in March, U.S. Army Sgt. Damon Warren's vehicle was hit by a roadside bomb that left him with fractured ribs, a torn rotator cuff, and a shattered left femur that required a rod be placed in his leg from his knee to his hip. Despite the severity of his injuries, Warren was back on his feet by July with the help of a NASA-inspired rehabilitation device allowing him to defy gravity while working out on a specialized treadmill.
Walking and, later, jogging on AlterG, Inc.'s Anti-Gravity Treadmill were a bit awkward at first for the 105-kilogram soldier. "I wasn't used to something else holding my weight while I walked," says Warren, 36, who is on leave but still on active duty in the Army. "It's a rush of air that pushes you up."
The Anti-Gravity Treadmill, which looks like a normal treadmill encased in a large, clear plastic bubble, uses differential air pressure to reduce the force of gravity on the mass of a runner or walker's lower extremities. Patients, athletes and others must first don a pair of formfitting neoprene shorts that zip into the opening at the top of the treadmill's shell and form an airtight seal. The treadmill then measures a user's weight with the help of load cells located in its base. The area from the waist (where the shorts zip) down is actually a pressure-controlled chamber that fills with air, gently lifting the user and relieving the lower body of some of the effects of gravity. "From there, it calculates how much air is needed to unload a specific amount of a person's weight," AlterG CEO Lars Barfod says. "You don't actually feel the air pressure at all because it's uniform and low, between one and two pounds per square inch. You basically feel the same that you would feel in water, except you're not wet."
Warren works out on AlterG's treadmill, which can alleviate up to 80 percent of his weight by lessening the gravitational pull on his mass, at Peak Physical Therapy and Sports Medicine in Plano, Tex., near his hometown of Carrollton. Initially, his rehabilitation involved walking on about 55 percent of his weight, but he is now able to reduce the treadmill's differential pressure and walk or run on 70 percent.
AlterG's technology has been available to rehabbing surgery patients such as Warren as well as professional athletes and senior citizens since it received U.S. Food and Drug Administration (FDA) clearance in January 2008. To use the treadmill, a person must be able to flex and extend his or her hips, knees and ankles to a certain degree and must have a doctor's approval to walk or run on at least 25 percent of their weight.
Soon after FDA approval studies at hospitals and universities began to assess the AlterG treadmill's effectiveness for patients with cardiovascular complications, lower-limb arthritis, ankle fractures and mobility issues associated with Parkinson's disease. AlterG is also considering the development of new devices for other patients, including children with cerebral palsy or other disorders that interfere with the ability to walk.
The P200, AlterG's $75,000 original model, is specifically designed for rehabilitating athletes—marathoners, football players and others—enabling them to run at speeds up to 29 kilometers per hour while reducing impact on their legs. The company introduced its second model, the $27,000 M300, in October 2009 for less-serious athletes, surgery patients and seniors, allowing them to move at up to 19 kilometers per hour. Barfod says the company has sold about 500 Anti-Gravity Treadmills in 21 countries to professional sports teams, the military and hospitals.
AlterG's goal is to create a rehab environment that relieves strain on the lower body, but the technology's inspiration was actually designed to do the opposite—help astronauts in microgravity environments exercise with gravitylike resistance to stave off bone and muscle loss.
As a Stanford University graduate-level engineering student in the mid- to late 1980s, Robert Whalen studied exercise devices that the U.S. and Soviet Union had developed for astronauts and cosmonauts. "The need for astronauts to exercise in space was well known in the late 1960s and early 70s, but a lot of people were confusing activity with loading," Whalen says. Cardiovascular exercise, including exercise bicycles, conditioned an astronaut metabolically but did not provide the loading forces that the body requires to maintain bone health and muscle strength. "Treadmills were used in space, but the loading harness was unnatural and uncomfortable, and the exercise provided only a fraction of the loading compared to normal daily activity on Earth—a problem that exists to this day," he adds.
Whalen's research earned him a National Research Council postdoctoral fellowship at NASA Ames Research Center, at Moffett Field, Calif., from 1988 through 1989 (he would later join NASA full-time), where he helped develop effective exercise regimens for astronauts. Whalen initially sketched out a gimbaled waist harness system for the space agency that strapped the astronaut down to the treadmill with a constant force to try to emulate body weight on Earth. Whalen then began to consider the use of air pressure as a way of applying a strong force—equal to body weight—to astronauts during treadmill exercise that would work better than the waist harness system.