An anti gravity treadmill does not switch off gravity. It lifts part of your weight off your legs with air pressure, so you can walk or run while your joints carry only a fraction of the usual load. You will find these machines in physical therapy clinics, sports medicine centers, and the training rooms of pro teams, almost never in a home gym. This guide covers how the machine works, who books time on one, and how to get value from a session if your doctor or physio sends you there.
The air chamber behind the “anti-gravity” name
The best-known version is the AlterG, and most clinics use some generation of it. The design looks odd the first time you see it: a normal treadmill deck sealed inside an inflatable bag that rises to waist height.
A session goes like this:
- You put on a pair of neoprene shorts with a zipper skirt around the waist.
- You step onto the deck and the skirt zips into an opening at the top of the bag, sealing you in from the waist down.
- The machine calibrates by reading your full body weight.
- Air pumps into the chamber. The higher pressure under you pushes up on your body, roughly like a gentle hand under the hips, and your feet press into the belt with less force.
- You choose a body-weight setting, then start walking or running as you would on any treadmill.
The amount of support is precise. Huntington Beach Physical Therapy Specialists describes selecting any weight between 20% and 100% of body weight in 1% increments. Put the other way, the machine can take up to 80% of body mass off your legs, according to a federal procurement listing for the equipment.
So a 75 kg runner set to 60% body weight runs as if they weighed 45 kg. Set to 20%, they move like a 15 kg child.
Why air instead of a harness
Older body-weight support systems hang you from an overhead harness. That works, but the straps pull at the groin and chest, and they tend to change how you move. Air pressure spreads the lift around your lower body, so your stride stays closer to normal. You still swing your arms freely, and your feet still land and push off the belt the way they do outdoors.
Who actually uses one
The category exists for one reason: to let people keep moving when full body weight is too much. That covers a wider group than you might expect.
- People recovering from lower-body surgery. Knee, hip, ankle and foot procedures are the classic cases. Walking at reduced weight lets a patient practice a normal gait before the joint is ready for full load.
- Injured runners. A runner with a stress injury or a sore Achilles can keep some aerobic fitness and running rhythm while the injured tissue gets a break. Clinics like the San Antonio Center for Physical Therapy describe the machine’s purpose as reducing stress and strain on the body during exercise.
- People with neurological conditions. After a stroke, or with conditions that affect balance and coordination, the support can make walking practice safer and longer.
- Heavier beginners. Someone starting exercise with a lot of weight to lose may find that ten minutes of walking hurts their knees. Taking some load off can make the first weeks bearable.
- Older adults working on mobility. Reduced weight plus the enclosed chamber gives a sense of stability that a normal treadmill does not.
- Elite athletes. Teams use the machine to return players to running sooner after injury, and some distance runners add volume at reduced weight to spare their legs.
What these groups share is a gap between what the heart and lungs can handle and what the joints, bones or tendons can handle right now. The machine closes that gap.
What a typical session looks like
Every protocol is set by the physio or doctor, so treat the numbers below as an illustration of how settings progress, not a plan to follow on your own.
A common pattern for a runner coming back from a lower-leg injury:
- Week 1: walking at 50-60% body weight, 4-5 km/h, 15-20 minutes.
- Week 2: walking at 70% body weight, then short jogging intervals at 60%, 7-8 km/h.
- Weeks 3-4: continuous easy running at 70-80% body weight, 9-10 km/h, 20-30 minutes.
- Later: running at 85-95% body weight, then a move back to a normal treadmill or the road.
The idea is to raise one variable at a time. If you add body weight, hold the speed steady. If you add speed, hold the body weight. Pain the next morning is a signal to step back to the last setting that felt fine.
It feels strange at first
Expect your first few minutes to feel off. At low settings your stride gets bouncy, and you may float a little longer between steps than you are used to. Most people settle in within one session. Arm swing and posture stay normal, which is part of why the machine is useful for gait retraining.
Your speed will also feel easier than the same pace on a regular belt. At 60% body weight, a 10 km/h run takes far less effort than it does at full weight. If you are used to steering your training by pace, our treadmill pace chart is a helpful reference once you are back on a normal treadmill, but expect those numbers to feel harder at first.
Cost, access and whether you can own one
An anti-gravity treadmill is a medical-grade machine, priced and sized like one. A new unit is priced like hospital equipment, far above any home treadmill, needs a dedicated power supply, and takes up far more floor space than a standard treadmill. It also needs servicing that most homeowners cannot arrange.
For almost everyone, the realistic options are:
- Physical therapy clinics. Sessions are part of a treatment plan, and some insurers cover them when the machine is prescribed as part of rehab.
- Sports medicine and performance centers. Many sell single sessions or packages to runners without a referral.
- University and pro-team facilities. Usually limited to their own athletes.
Call ahead and ask what the session includes. Some clinics charge for supervised time with a therapist, others rent the machine by the half hour.
We make Treadmill Pro, a phone app that works with regular treadmills. We don’t make or sell anti-gravity treadmills.
What to use at home instead
If your goal is low-impact cardio rather than formal rehab, a regular motorized treadmill can do more than you might think. Slow walking at a steep incline keeps the pace low while still raising your heart rate. Our guide to treadmills with incline explains how to set that up, and the guide to walking treadmills covers machines built for long, gentle sessions. Neither one reduces your body weight, so they are not a substitute when a clinician has prescribed unweighted training. They are a sensible next step once you are cleared for full weight.
How it compares with other specialist treadmills
Specialist treadmills each solve a narrow problem. A curved treadmill makes you drive the belt yourself and is built for sprint work. An anti-gravity treadmill reduces how much of you the belt has to carry. A VR treadmill is built for movement inside a virtual world rather than for fitness or rehab.
| Machine | Main job | Typical setting |
|---|---|---|
| Anti-gravity | Moving at reduced body weight | Clinic, rehab center |
| Curved, non-motorized | Self-powered speed work | Performance gym |
| VR | Walking inside games and simulations | Home, arcade, lab |
| Standard motorized | General cardio | Home, gym |
If you are shopping for a home machine, none of the specialist types is likely to be the right buy. A good standard treadmill with incline covers more needs per dollar.
Making the return to a normal treadmill
The handoff from unweighted training to full body weight is where many people stall or re-injure themselves. A few habits make it smoother:
- Start slower than your last anti-gravity session. Running at 90% body weight and 10 km/h does not mean you can run at 100% and 10 km/h. Drop your speed by 1-2 km/h for the first full-weight runs.
- Shorten the session. If you ran 30 minutes on the anti-gravity machine, run 15-20 at full weight and see how you feel the next day.
- Use walk breaks. Intervals such as 3 minutes running, 1 minute walking let you build time on feet without a continuous block of full load.
- Change one thing per week. Duration, speed or incline, never all three together.
- Keep a record. Write down speed, incline, duration and how the injured area felt that day and the next morning.
That last habit is the one people skip, and it is the one your physio will ask about. Treadmill Pro logs each session’s speed, incline and duration automatically, lets you adjust the belt from your phone on supported treadmills, and syncs workouts to Apple Health, so you can show your clinician the full history instead of trying to recall it.
Next steps
If you have been told to try an anti-gravity treadmill, ask your physio three questions before the first session: what body-weight percentage to start at, what speed to hold, and what symptoms should make you stop. Book a short first session so you can get used to the feel of the chamber. Once you are cleared for full weight, plan the move back to a normal treadmill in small steps, and keep logging every run so you and your clinician can see the trend.
