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Step Lightly: A Space-Age Treadmill That Reproduces Microgravity on Earth [Slide Show]

Rehabbing soldiers, seniors and surgery patients alike find comfort in a gravity-negating treadmill inspired by efforts to keep astronauts healthy and strong during extended orbital missions
army,physical therapy,space, gravity



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.

Altering rehab
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.

Out-of-this-world origin
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.

Whalen built a prototype treadmill that pressurized the upper body by placing it in an airtight fabric bubble made from very thin sail cloth coated with urethane. The astronaut would be inside the inflated bubble from the waist up with the bubble tethered by straps to the treadmill while the air pressure inside the bubble pushed the body down onto the treadmill. "The upper body system also has complete freedom of motion at the waist given the lateral degrees of freedom afforded by the tethering straps, which makes this method a very good simulator of gravitational loading during gait," Whalen says.

Brought down to Earth
Once Whalen had created the downward pressure device, it was not a great leap to create a device that could do the opposite. "Lessening the load evolved from the original idea pretty quickly," Whalen says. "If you could push someone down, you could also push them up."

Whalen's gravity differential technology, which he patented in 1992, eventually was mothballed due to a lack of interest from NASA in the loading treadmill model. Whalen had begun working with the U.S. Department of Veterans Affairs (VA) to give rehabbing soldiers access to the unloading model, but "unresolved differences between NASA's and the VA's human subjects regulations" prevented him from continuing that work, he says.

The technology remained fallow until Sean Whalen, Robert's son, took a special interest in the prototype treadmill stored in the family garage. Sean, himself a Stanford engineering student, was in search of a project idea for his Department of Management Science and Engineering class on technology venture formation, and decided to take the idea of a treadmill capable of simulating a reduced gravity environment and run with it.

The project was a success, and Sean licensed his father's patent in 2005 so he could start a company that would help rehabilitate patients needing support as they learned (or re-learned) to stand, walk and run. This attracted the attention of legendary marathon runner Alberto Salazar, who e-mailed Sean that year to inquire about the treadmill. Salazar had recently been hired by Nike as part of its Oregon Project to train elite athletes, who of course were expected to win while wearing the company's attire. Nike ended up buying six unloading treadmills. "It was really just full speed ahead from there," AlterG's Barfod says. Nike has used his company's technology as part of the training regimen for a number of athletes, including two-time U.S. Olympic marathoner Dathan Ritzenhein, who placed eighth in last weekend's ING New York City Marathon.

Moving forward
Most of AlterG's research and development today involves improving the treadmill's software, according to Barfod. The company is also taking a close look at the neoprene shorts. Barfod says they work well at keeping people on the treadmill stable and creating an airtight seal, but he admits (and Sgt. Warren agrees) that the formfitting outfit could be easier to get into and out of, particularly for those suffering from leg and hip injuries.

The company is also considering a feature that would enable doctors and physical therapists to reach into the treadmill's lower chamber and manipulate a patient's legs without losing air pressure. A prototype of this feature, which Barfod expects to be available by early next year, has a neoprene sleeve that extends toward the patient's legs. When not in use, the sleeve would be sealed by an airtight cap. When a doctor needs to use the sleeve, however, he would remove the cap and extend an arm into the sleeve. The air pressure around the doctor's arm in the bag would form a seal around the sleeve so that no air escaped while the doctor worked. AlterG is also working on a lift system to help patients with more severe disabilities get on and off the treadmill.

Robert Whalen continues to work for Ames, most recently on projects that plan for the need to send medical devices with astronauts on long-term missions. Whalen believes that long-duration deep-space exploration is in humanity's future, even if it is two or three decades away. Such missions, he adds, would require that astronauts equip their ship with a medical clinic of sorts.

When Whalen thinks about the company his son co-founded with the help of technology he developed decades ago, "I just shake my head in amazement," he says. "I don't pinch myself—well, maybe I do. I told my kids just to have fun with whatever they do and learn from those experiences."

View a slide show of the Anti-Gravity Treadmill's development

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