Running on Air … Or Something Like That

Injuries are the pits. There are days when getting back to running seems almost impossible. Wouldn’t it be great if there were a bridge between nursing your injury and running freely on any surface your heart desires?

Good news – there is! It’s the Alter G Anti-Gravity Treadmill.

Anti-gravity treadmill? What sort of treadmill voodoo is this?

Maybe your favorite athlete used one to get back from an injury or used one while pregnant. Maybe you have seen that Lebron James owns two of them? Alter-G’s are normally found in physical therapy clinics, including mine. Several Salty Running contributors have utilized the Alter-G as part of their recovery from injury or to experience the feeling of “unweighting.”

I’m a huge fan of the Alter-G and use it often in my work. I wanted to give a little insight into how it works and who can benefit from it.

How it works

The Anti-Gravity Treadmill uses a NASA-patented technology called Differential Air Pressure that enables the “unweighting” feeling for therapy and training.

You start by putting on a very attractive pair of shorts; I tell my patients that they are “space tutus.” They are neoprene shorts that come in various sizes from 3XS to 4XL and have a zipper around them. You step into the opening of the plastic-enclosed treadmill chamber, lift it up the chamber, and lock it in place.

Hint: When you lift up the chamber, do not bring it up too high. When the chamber fills up with air, this can cause the chamber to expand higher up your torso than you might like. If it is up too high, it diminishes natural arm swing and can lead to a more extended position in the lumbar spine. You don’t want back pain, too, do you?

Then, using the zipper on your lovely shorts and the connecting zipper on the chamber opening, you zip yourself securely into the chamber, shutting your lower half away from the pressures and gravity of the outside world. This is where the magic begins.

The pressurized chamber fills up with air and calibrates to your weight. Once this is done, you can adjust weight from 100% to as low as 20%, meaning that the pressure in the chamber will adjust to make it seem as though you are up to 80% lighter. You will feel a lifting force as you decrease the percentage of your body weight.

What percentage of body weight should you go down to? It varies from person to person. You should go down to the percentage that allows you to walk or run pain-free. Aside from pain-reduced movement, the lifting force reduces impact and effort during activity. All of these things combined provide an environment where you can run or walk with full range of motion and your normal gait and natural movement. Then you just do your thing!

Who is the alter-g for?

The Anti-Gravity Treadmill is not just for runners! In the world of orthopedics, we use it for a variety of musculoskeletal issues. It allows us to begin weight-bearing exercise at appropriate bodyweight percentages sooner for post-operative patients, without risk to healing tissues. For patients with inappropriate gait strategies due to pain or weakness, it provides support for patients to work on more normalized walking or running mechanics. It can be a good way to work with deconditioned patients to improve endurance in a gravity-lessened environment.

For people with neurological conditions, the Alter G can provide a fall-safe (mostly – you can sort of fall in it if you really try) environment to support motor learning, motor, control, and balance. You can also perform standing balance activities, static or with dynamic movement.

The Alter G can reduce the exercise barrier for people who are deconditioned, overweight, or dealing with chronic conditions. It allows people to gradually progress their training programs, and seeing changes in distance, speed, and body weight percentage can motivate them to continue exercising. They are able to gradually increase the exercise volume while minimizing the stress of full body weight workload. This is also a good thing for the active aging population who want to stay active long-term.

In the world of sports performance, the Alter G has found a fan base because it limits downtime from sport. Athletes can train through injury and return to their sport in better condition than if they’d taken time off. For post-operative athletes, appropriate training can begin sooner (make sure you are following the surgical protocol, of course!) Runners with stress-related injuries can continue training at the same volume.

We often see local cross country runners during the season for this very reason. For healthy athletes, it allows the opportunity to increase training volume while minimizing the chances of stress-related injury. This is done by Nike Oregon Project coach Alberto Salazar, enabling him to add 15-25% more weekly mileage volume with less stress-related and overtraining injuries.

The Alter G Anti-Gravity treadmill is a great rehabilitation or training tool that can be used for a wide variety of people. As your friendly physical therapist, I must remind you that it is not the only thing needed for rehabilitation, but it perfectly supplements many aspects for our patient care.

There are few things more beautiful in life than a pain-free run! What are you waiting for?


A born and raised Hoosier running to stay sane. I've done 5Ks to marathons, but am currently running to enjoy running. I'm an orthopedic physical therapist, with clinical specialization in treating people with vestibular disorders. Other things I specialize in? Knowing the lyrics to every Backstreet Boys song and being an awesome cat mom! Living with Crohn's disease, but trying to show it who really is the boss.

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  1. I’ve used the Alt-G several times as I was recovering from hamstring injury and when I broke my arm and couldn’t yet engage upper body torso. One thing I noticed (but was afraid to ask): the pressure on my pelvis area made me feel like I had to pee (and to get in/out of the shorts is not the easiest to do). Is that normal? Otherwise good experience.

    1. I don’t know if it is normal for everybody, but it definitely would make me feel like I had to as well … on several occasions! I am between 2 different sizes for shorts, so I would notice if I would wear the smaller one, I felt more pressure! I’m guessing it’s not just the two of us!

  2. It was super interesting to hear about non-runners using the Alter-G. I’ve never tried one mainly because I don’t think my small town has any! But it was great to learn what they are all about, so thanks!

    1. Yes! I would say most of the people who use our Alter G aren’t necessarily runners … lots of post-operative patients or deconditioned patients! We have had runners come from over an hour away to utilize our treadmill, they tend to be in clusters!