How I Lost 70 Pounds and Ran My Fastest 5K — With a Fractured Pelvis

Post written by Susan Lacke.

Maybe I can’t be an astronaut, but at least I can run like one.

When Alter-G asked me to give their anti-gravity treadmill a whirl, here’s how they described it:

Alter-G Anti-Gravity Treadmills use patented NASA technology that allows for precise partial weight-bearing running, unweighing up to 80% of the your body weight. Simply put — it’s like running on the moon.

An invitation to run on the moon — how could I turn that down?

One Small Step for NASA, One Giant Leap for Runners

Matt Kraemer, director of Endurance Rehab in Phoenix, Arizona, served as my very knowledgable guide for this test. His group was one of the first in the region to have an Alter-G Treadmill, though he admits the technology itself has been around for more than 10 years, mostly used by professional athletes.  (NASA actually developed the technology as a way to keep astronauts weighted down in zero-gravity situations.)

An anti-gravity treadmill can eliminate 20 to 80 percent of the runner’s body weight, allowing for faster leg turnover and added endurance, without taxing the runner’s joints, muscles, and cardiovascular system. Professional football players began using the Alter-G to increase their speed and recover from injury, and elite marathoners starting using it to increase their miles without added recovery time.

It wasn’t long until anti-gravity was recognized as a rehabilitation tool, and began popping up in Physical Therapy offices to help runners maintain fitness while recovering from common injuries: stress fractures, ITB issues, shredded cartilage, sprained ankles, plantar fasciatis, and chondromalacia, to name a few.

Today, the Alter-G is available to the average runner at a growing number of exercise facilities (Endurance Rehabilitation charges $10 per 30-minute session; prices vary at other locations between $5-$30 per 30 minutes), and can be used at the runner’s discretion for performance, injury issues, or both.

(Moon) Bouncing Back from Injury

Though all I could think about was the sheer novelty of the experience, I wanted to truly test the effectiveness of the treadmill. I needed someone with an injury. Everyone I knew was healthy, so I did what any hard-hitting investigative journalist would do:

I got into a bike crash and fractured my pelvis.

Sigh. The things I do in the name of research.

Okay, that’s not entirely true. The bike crash and the contact for this test just happened to occur near each other. But you won’t hear me complaining. After a month off of running due to a fractured pelvis, I finally got clearance from my doctor, packed my astronaut boots, and headed to Endurance Rehabilitation to run on the moon.


The Alter-G experience starts in neoprene shorts, which zip into a vinyl skirt, which attach to the base of a treadmill. Not quite the astronaut suit I was envisioning, but I was assured I’d get the astronaut experience anyway. Once the machine calibrated itself to my weight, the engine roared to life, the vinyl skirt inflated with air, and then it happened:

I was running on the moon!

It’s hard to describe reduced gravity in the Alter-G. You’re still very much in control of your body, but it’s effortless. On the Alter-G, gravity seems like a babysitter who left the room for a moment — you know she’s still the boss, she’s still there, and she can come back at any time, but you still want to see what kind of trouble you can get away with in her absence.

Turns out, you can get away with a lot.

When Matt Kraemer described the treadmill’s capabilities to me before the test, he claimed he could go from his normal 5:30 mile pace to a four-minute mile. I was skeptical. A minute and a half off your time, just from a machine? It sounded a bit like snake oil to me.

While running with only 40 percent of my body weight (a 70-pound weight lifted – literally), I started at my normal marathon pace: 9:30 per mile. Without the gravity, the pace was a very easy jog — almost a walk. I increased my speed gradually until I was at a pace where I felt comfortable and sustainable for a three-mile run. It made me laugh with disbelief when I realized I was running 6-minute miles, two minutes  faster than my 5K PR pace!

Though reduced-gravity running is easier than running on your standard treadmill, it isn’t entirely without effort. The treadmill almost forces you to use good form while running — without it, you bounce around uncomfortably in the vinyl skirt (kind of like…well, the astronauts on the moon. Duh.). Though it’s almost impossible to fall over in the Alter-G (so that’s why I had to wear the shorts that zippered in to the skirt!), you still need to engage your core muscles to keep from tilting over within the skirt, especially as you pick up speed.

Back to Earth

As the run came to an end, gravity was gradually added back in to the equation, and it took a few minutes to adjust. In the end, I felt like I had run a 5K PR, but it didn’t feel nearly as exhausting as it would have been in a “normal” treadmill time trial.  I was a good kind of tired, a perfect welcome back to the world of running.

I was also HOT. That’s probably the biggest downside of the Alter-G: When I stepped out of the vinyl skirt and neoprene shorts, my running shorts beneath were soaked with sweat. Even though there’s a fan circulating air in the skirt, it still gets pretty warm down there, and after a while it’s uncomfortable.

And, to answer the injury question: I didn’t have any pain. Though I wouldn’t have attempted my 5K pace on land (and still have yet to do so), I could do speedwork on the Alter-G. Since the test, I’ve begun running shorter (albeit slower) distances on my regular treadmill and run routes, but I still can’t do speedwork in a normal setting – the impact is too much. The Alter-G serves as a nice stand-in when I need to increase my speed without worrying about the impact jarring my injury.

Would I use the Alter-G even if I weren’t injured?

I’m not sure.

Mentally, using the Alter-G is a huge boost. Seeing 6:00 per mile makes me drunk with excitement. It’s a huge motivating factor, and if I could continue to train with the Alter-G, I could continue to increase the amount of gravity on my system while maintaining high speed and good running form…but without the risk of injury. Plus, there’s the novelty factor: If someone’s looking to shake up their running routine, this is a good way to do it.

But as someone who barely has enough money to buy new running shoes, much less extraneous training experiences, I can’t say it’s worth spending 10 dollars (or, in some places, more) to run for 30 minutes. It’s fun, yes, and if someone has a lot at stake (say, qualifying for the Olympics), along with the cash to afford it, then this is certainly something to consider. But I’d be cautious of encouraging the average runner to use this for reasons other than injury – especially if someone is looking to use this method as a substitute for good old-fashioned hard work.

Though I won’t be training for a marathon on the moon anytime soon, I’m still tickled by the experience, and grateful there’s an option out there for injured runners. Thanks to Alter-G, Outside PR, and the awesome staff at Endurance Rehabilitation (especially Matt Kraemer) for letting this alien creature hang out in zero gravity for a while.

What do you think? Have you tried the Alter-G for performance training  or to maintain fitness through injury? Would you consider it?

Susan Lacke, No Meat Athlete’s Resident Triathlete, balances training for Ironman Arizona with a healthy dose of cupcakes, naps, and whining. You can read her monthly column in Competitor Magazine and her weekly blog on and follow her on Twitter: @SusanLacke.



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  1. The Alter-G is some really cool tech. In fact, I wrote about the Alter-G way back in January while I was using it to get over a bad case of plantar fasciitis.

    Don’t get me wrong, it’s still a treadmill. However, I haven’t encountered anything more perfectly suited to an active recovery. Cool that you were able to try it out (and sorry you had the fractured hip to require it).

  2. WOW, that sounds pretty cool. I would love to give it a go!

  3. Does anyone know how this compares to running in water?

    • In my experience, you don’t have the added resistance of water. That could be either good or bad, depending on what you’re looking for. I always feel like I’m really slogging if I’m running in a pool, but YMMV.

      The other major difference is that, with water, you can’t adjust buoyancy. H20’s one-size fits all. However, the Alter-G allows you to adjust the “buoyancy” to remove as much as 80% of your total body weight, or as little as 1% depending on your needs.

      Those are the major differences I can think of off-hand. Does that help?

    • I did some aquajogging as I was recovering from my injury, too, and wasn’t much of a fan. The Alter-G has virtually zero resistance, whereas aquajogging was uncomfortable. Also, I find that I don’t use good running form while aquajogging…some people have mastered this, but I don’t seem to be one. 🙂

  4. Michael says:

    I’ve found the AlterG to be a great tool even when not injured. True, it’s expensive but it seems like it’s becoming more accessible. If you have the means, using it once a week even for an overspeed workout or just an easy recovery run can get you an extra boost of cardio and speed without risking getting hurt. I run pretty much every day and have had a fair share of overuse injuries and using the AlterG even just a once a week has helped a ton.

  5. Kaitlin says:

    Omg!! I can’t believe this was the post today, just the motivation and hope I needed. I’ve been recovering very slowly from a pelvic stress fracture since JANUARY 2011, and still cannot run without pain. Very VERY frustrating! Cycling and swimming and everything else are fine, but running hurts like hell. I’m gonna have to find me one of these treadmills to feed my hunger to run! Thanks, Susan!

  6. Jon Weisblatt says:

    What may be more affordbale to those who are injured is to find a rehab facility that does body weight supported treamill training. Most insurances should cover physical therapy. There’s a lot of great research out there on this activity, mostly with adults who have suffered strokes and children with develomental delays, or Cerebral Palsy, Down’s Syndrome, etc. Just a thought.

  7. I wonder if this wouldn’t be a great tool for the very obese… The main reason obese people fail to get an exercise regime off the ground is that their weight makes movement very painful and difficult. Yes, it does get better with time, but initially it’s excruciating.

  8. Super cool – I would really love to try one of these – sorry a fractured hip was your reason for doing it but still cool!

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