How it Works: The Anti-Gravity Treadmill

Astronaut tech comes down to Earth to rehab broken triathletes.

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Astronaut tech comes down to Earth to rehab broken triathletes

The treadmill that’ll make you float started off as something that did exactly the opposite. NASA engineers were trying to figure out how to prevent bone loss and muscle deterioration caused by the lack of gravity in space. So they came up with a loading harness that strapped over astronauts’ shoulders to hold them down while they ran on the space-station treadmill. But it was uncomfortable and kept the astronauts from maintaining form and intensity.

Enter Ames Research Center scientist Robert Whalen, who decided to use differential air pressure to mimic Earth’s gravity. Whalen patented the tech in 1992 and licensed that patent to Menlo Park, Calif.-based AlterG in 2005—a company that saw the contraption’s potential for athletes rehabbing from injury if, instead of putting the pressure on, they took it off.

How it Works

The AlterG applies air pressure to your lower body to unload your weight—like you’re standing in an inflatable raft with your legs plugging up the holes while someone blows it up. In more scientific terms, the system uses a difference in air pressure between the upper body (atmospheric pressure) and the lower body (higher pressure) to offset your weight.

It doesn’t take a ton of pressure to do that—about 2 pounds per square inch, no matter how much you weigh. An average person blowing up a stiff balloon can produce about 2–3 psi, so theoretically, you could lift yourself with the pressure of your  own breath.

Because it doesn’t take much to lighten you up, you won’t feel the pressure and can run with normal biomechanics without the impact. Athletes can add extra miles on the AlterG, work on improving their gait or rehab from injuries. It’s not uncommon to see pros Jesse Thomas, Gwen Jorgensen and Eric Lagerstrom on the AlterG at Red Bull HQ in Santa Monica. Lukas Verzbicas has been using one over the past few years as he heals from injuries suffered during a training ride crash in 2014 that required back surgery.

Other highlights:

  • Monitors can show you more info than the typical treadmill, from cadence and strike force to stance time and stride-length symmetry.
  • Neoprene shorts zip at the waist to an airtight bag.
  • The bag surrounds the runner’s lower body and the running belt and attaches to the treadmill.
  • Choose a running speed (up to 18 mph for the Pro 200 model), incline angle (up to 15 percent), and decide what percent of your weight you want to remove (from 20 up to 100 percent, in 1-percent increments).
  • Once you’re sealed in, the system calibrates to adjust to your size and weight.

Want to try it? Enter your ZIP code at to find locations where you can purchase sessions for about a buck a minute, depending on the provider. 

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