One of the more interesting parts of this job is the endless stream of product pitches I receive from the multibillion-dollar fitness industry. Much of it is junk or snake oil, easily ignored. Some of it is revealing: Based solely on my e-mail inbox, we are a nation obsessed with foot odor.

But every once in a while, a true game-changer comes along, an offer so intriguing or different that I have to give it a try. I had been reading about “anti-gravity treadmills” in running magazines for a couple of years, wondering occasionally how such a thing could work, when I received an offer from Gainesville chiropractor Kevin Maggs to try one.

At his office, Maggs helped me slip on a specially designed pair of shorts before I stepped onto the treadmill he bought a few weeks ago from the AlterG company of Fremont, Calif. He raised a plastic bubble that enclosed the device up to my waist, and I zipped the shorts to it, creating an airtight seal.

Like any other treadmill, this one had speed and incline controls, and I started walking, just as I have during countless other warm-ups. But then I began to take weight off my feet in 1 percentage-point increments by pumping air into the clear bubble. Slowly the air pressure began to support me.

At 80 percent of my body weight, I felt as if I could fly. I told Maggs to go home; I’d be here running all day. At 20 percent of my body weight, the least the machine allows, my toes were barely touching the treadmill.

Medical benefits

“You feel invincible,” said Lachlan Leach, who was walking slowly on the treadmill when I arrived, the first steps of her rehabilitation for a stress fracture in her foot. “You feel like you can just take off running.”

She can't; that wouldn’t be good therapy. But placing a small load on the stress fracture while it heals, and staying in shape rather than eliminating all cardiovascular activity, will speed her recovery, Maggs said. Some health insurance may cover the therapy, he said.

“It’s very hard to tell a runner not to run,” said Maggs, who estimates that about 80 percent of his patients are runners and triathletes. We are an obsessive lot, prone to persisting through injuries no matter how much long-term damage we’re doing.

Joe Kehoe swears the treadmill saved his half-marathon in March. The 35-year-old Haymarket resident had been training diligently for the race when he strained a calf muscle trying to alter his gait.

“I would have had to completely stop running,” Kehoe told me. Instead, Maggs treated him, then put him on the device at a slower speed than normal and at about 60 percent of his body weight. As his injury healed, Kehoe gradually increased both. He said he ran a personal best in the 13.1-mile race.

And at Walter Reed Army Medical Center, wounded veterans, most of whom suffered limb damage from roadside bombs, are using the treadmill.

“It lets them run with confidence,” said physical therapist Bo Bergeron. “They’re not going to fall. And if they stumble, they’re not going to hit the treadmill.”

The treadmill isn’t perfect. The model for athletes sells for $75,000; the one designed for medical use costs $30,000. Therapists can’t get at a patient’s legs to help while he’s walking. It gets really warm in that bubble, the shorts and air pressure are somewhat uncomfortable and when you remove the air you feel the toll in your quads. So far, there are only a handful in this area, according to the company’s Web site.

Invention and success

The idea of supported running is nothing new. Rehab facilities feature treadmills with harnesses that hold up patients as they recover from leg injuries and strokes. Coaches and physicians have been sending injured athletes to work out in the pool for years. These are much cheaper and, in most cases, more accessible alternatives. But they also are much less precise, and water will not support as much weight.

The treadmill’s purpose isn’t only therapeutic. Athletes, especially elite runners, have figured out that they can train at faster paces while saving wear on their legs. There’s even a formula, worked out by the company: For every 10 percent decrease in body weight on the treadmill, cardiovascular fitness can be maintained by increasing speed 0.6 miles per hour.

The development of the anti-gravity treadmill is a story in itself. NASA scientist Robert Whelan spent years working on technology that would help keep weightless astronauts in space on their treadmills. For a graduate school engineering project, his son, Sean, decided to reverse the concept and build a treadmill that takes weight off runners’ legs.

He later formed a company and in 2006 demonstrated the first one for Alberto Salazar, the legendary former marathoner who coaches elite U.S. distance runners at the Nike Oregon Project, according to Kate Yanov, director of marketing for AlterG. Salazar bought five, she said.

From there, the treadmill spread to more than 80 professional and collegiate football, basketball and soccer teams, including the Washington Redskins, the New York Knicks and AC Milan, according to the company’s Web site. The U.S. military has bought them to help rehabilitate troops with leg wounds and traumatic brain injuries, Yanov said. Top women marathoners have trained on them during their pregnancies.

The company has sold more than 400 to date, Yanov said, about 65 percent to medical facilities and the rest to athletic teams or sports facilities.

Where to try it

Active Spine and Sport. 7400 Heritage Village Plaza, No. 101, Gainesville. 703-753-5599. $30 for 30 minutes by appointment.

Harborview Sports Medicine and Physical Therapy. 2900 S. Hanover St., Suite 102, Baltimore. 410-350-8372. $25 for 30 minutes with a doctor’s prescription.

Metro Orthopedics and Sports Therapy. 8401 Colesville Road, Metro Level, Suite 50, Silver Spring. 301-588-7888 ext. 219. Doctor’s prescription not required.

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Where to try it

3 Active Spine and Sport. 7400 Heritage Village Plaza, No. 101, Gainesville. 703-753-5599. $30 for
30 minutes by appointment.

3 Harborview Sports Medicine and Physical Therapy. 2900 S. Hanover St.,
Suite 102, Baltimore. 410-350-8372. $25 for 30 minutes with a doctor’s prescription.