Air hockey-like treadmill lifts athletes, speeds recoveries

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Air hockey-like treadmill lifts athletes, speeds recoveries

By cushioning joints, gravity-altering device promotes post-injury healing
Jake Siegel

With a little help from NASA, injured runners can defy both gravity and the typical recovery timetable. 

Meet the AlterG “anti-gravity” treadmill. It uses air pressure to lift a runner, reducing body weight by as much as 80 percent and lightening the load on limbs. A NASA engineer developed the technology two decades ago as an exercise tool for astronauts; its benefit to hobbled athletes on Earth was recognized in 2008, when the FDA cleared it for use as a rehab device. 

Returning an injured runner to the road and track is part art, part science – and the science has lagged, said Dr. Mark Harrast, a UW Medicine specialist in sports medicine and rehabilitation medicine. 

Clare McLean
Runners wear shorts that zip in to the trainer to take advantage of its cushion of air.
Runners wear shorts that zip in to the trainer to take advantage of a cushion of air.

“There’s lots of literature on how to treat a stress fracture but then what?” he said. “How do we return these injured athletes to running?”

Harrast is medical director of the Sports Medicine Center at Husky Stadium, one of a handful of Seattle-area clinics with an AlterG. With the treadmill, he can precisely calibrate a patient’s weight, speed and incline during every workout, and increase the load to the injured structure gradually. 

Patient Moira O’Connor Lenth suffered a stress fracture in her lower back during her senior year of high school. Just days after winning a 3200-meter race (and setting a new personal record for the distance), O’Connor Lenth went for a run and felt a sharp pain in her back. She was despondent; she’d never been injured before, was coming off an amazing season, and was set to run in college that fall. 

Harrast treated her stress fracture and said it would take her eight weeks to heal fully. She could, however, start running on the AlterG in five weeks, he said, leading her to wonder what an “anti-gravity” machine might look like.

“I imagined running in the air,” said O’Connor Lenth, now a junior at Seattle University.

Clare McLean
Dr. Mark Harrast, a UW Medicine sports-medicine and rehab specialist, talks with patient Moira O'Connor Lenth.
picture of Dr. Mark Harrast, UW Medicine sports-medicine specialist, talking with patient Moira O'Connor Lenth.

Reality is not quite so cinematic. Users step into a special outfit that is part Spandex shorts and part kayak skirt, and then get zipped into an air chamber. The chamber inflates and the runner’s lower body starts to float slightly – akin to an air-hockey puck. 

After adjusting to the odd sensation, O’Connor Lenth was immediately hooked. “I remember the first time I ran I couldn’t believe I wasn’t in pain,” she said. “The next day my calves were sore, so I knew I got a great workout. It really helped me come back for my first cross-country season in college.”

The Sports Medicine Center’s AlterG is also available to the public and costs $15 per half hour. Most patients use it as part of their physical therapy, but Harrast says the machine also can boost performance. For example, competitive distance runners could add miles but not lots of wear and tear on the body. 

Little research has been done on the AlterG, Harrast acknowledged, although he co-authored a paper on its rehabilitation merits. One of his co-authors was Hallie Truswell, a running and triathlon coach and former Ironman triathlete. 

She sends injured patients as well as high-mileage runners to the center. The machine’s greatest value is rehabilitative, Truswell said. 

“When you’re injured, you’re also in some mental pain. You think, ‘my racing career is over.’ Being able to run again brings peace of mind.”