Running on the moon

I recently had the chance to try running on an Alter-G anti gravity treadmill. It was something of an experience, but I must admit I initially resisted the invitation. I even stated that I’m not a technology kind of guy nor was predisposed to using an Alter-G to supplement training.

In the end we reached an accommodation that I’d be open-minded and see what the hype was about, but there would be no guarantee that I’d fall in love with it. Many thanks to Nicole and Seamus from Gravity Free Rehab for the learning opportunity.

These treadmills have got a kick-along amongst runners due to their use by well known coach and self confessed technology nut Alberto Salazar. He has star pupils Galen Rupp and Mo Farah do a little extra on the Alter-G each week to supplement their already high mileage.

My gut reaction

It’s hard to pick holes in an approach that delivered double gold for Farah and a one-two Farah, Rupp finish in the 10,000m. However, not for the first time I find myself swimming against the tide on this one.

There’s probably a lot of runners out there who would like the idea of doing more running on the Alter-G as a means to increase their performance levels. But there are many things we can work on other than volume to improve our running ability.

Alter-G Treadmill Review

Gravity isn’t bad for you

Runners and coaches are often fearful of gravity, their weight and the oft reenforced statistic that running puts three times your body weight in stress through your musculoskeletal system.

This kind of thinking leads runners and coaches to instil loss of weight as a training goal rather than a natural outcome of training. It’s an area I’m quite passionate about as the prevalence of disordered eating amongst runners has much to do with this type of thinking.

If you accept the notion that our bodies have evolved to cope with moving about under gravity you also have to accept that running in these conditions isn’t inherently dangerous – we’re designed to be able to cope with these forces. Moreover, we don’t need to weigh as much as a pretzel to run injury free or perform well.

Of course we have to train smart and give the body a better than even chance of adapting to our running goals and training. I’d wager that if the prevailing attitude was about increasing functional strength for running rather than loss of weight the injury rate for runners would be much lower than it is today.

Gravity Free Treadmill

How how does the Alter-G work?

You step into some quite snug fitting bike short style briefs that are made out of a wet-suit type of material. You locate yourself in the middle of what looks like an oxygen tent and the shorts are attached via a zipper to form an airtight environment from the hips down.

Manipulation of the air pressure in this hermetically sealed environment simulates reduced gravity. I’m not sure of the exact technical terminology, but the goal is to reduce your effective body weight by varying percentage points depending on your reason for using the machine.

What did it feel like?

Weird is the honest answer, once someone reduces your effective body weight by 20% running feels a lot different. I think this feeling of weirdness is exacerbated by the design of the machine, which feels like it holds you up at the hips.

I may be wrong in this, but I suspect running on an Alter-G would feel quite different than being outdoors and suddenly the earth losing 20% of its gravitational pull. To test the machine the gravity effect was reduced to ridiculously low levels, to the point where I could have used any movement pattern to continue running. At this point I’d argue that I’d ceased running in any true sense of the word.

The feeling of being held up at the hips didn’t seem to do great things for keeping my glutes working. I also wasn’t excited by the loss of feel during foot-contact and through the weight-bearing phase of running to toe-off. Having said that I made a mistake by wearing my Saucony Virrata (a well cushioned zero-drop trainer) on the treadmill and in hindsight I’d have gone barefoot to hang onto that bit of extra feel for longer.

The real indication of what’s happening comes when the gravity assistance is turned off and you find yourself hitting the treadmill much harder than normal. The body only uses what it needs to.

Caution on faster running

I did have tighter than normal calves after running on the Alter-G machine. I think the combination of loss of feel at the feet combined with lack of pressure down does mean you can let you calves over-stretch and/or do more of the work than they otherwise would under normal conditions.

This likely wouldn’t have happened if I stayed at a slower jogging speed, but I was there to test out what the experience was like so I ran up to about 16kph, or a bit quicker than 4 minute kilometer pace. I also ran easy with the Alter-G providing a very high level of assistance – no doubt this didn’t help with the tightness I felt the next day.

Alter-G Treadmill Gait Retraining

Supplemental training for runners?

Personally I wouldn’t be keen on runners using the Alter-G to supplement their normal training because of the potential to pick up or maintain bad habits. Most of the running coaching clients we see struggle with hip strength and stability, and running with the hips supported isn’t likely to do much to help the situation. However, I have to acknowledge that there are quite a few anecdotes emerging from runners that have found using the Alter-G beneficial. The only way to know if it’s for you will be to try it.

If I had to speculate I’d say that talented runners, whose mechanics are well bedded down, could do proportionally more Alter-G training without upsetting their mechanics for overground running. Sensibly, the practitioners where I ran on the Alter-G do enforce a limit to the amount of sessions runners can do on the machine each week.

One scenario where there use of the Alter-G makes more sense to me is where a runner has completed the majority of their preparation before a very important race, but suffers a minor injury in the last few weeks or days. Using the Alter-G may prove useful to keep things ticking over and provide mental relief to an athlete with undue fear of losing condition after a few days of reduced training. Alberto Salazar makes the case in the video below for increased volume.

Rehabilitation following injury?

This is an area that seems well suited to the Alter-G and perhaps even more so for non-runners than runners. There are many injuries and medical conditions that make even walking difficult and anything that promotes movement is likely to beneficial and encouraged.

I really don’t have the experience to comment much more on how runners have used the Alter-G in rehabilitation. If you are a runner that has used the Alter-G for this purpose, please drop a comment below to share your experience. I’d also be keen to hear from medical professionals and physical therapists working with injured runners and the results achieved.

Gait retraining?

The addition of cameras that track your foot and lower leg does afford the opportunity for runners to practice different movement patterns while having the advantage of seeing the instant result displayed on a screen in front of you.

More work is needed on whether this would be effective, but I can see the potential. Perhaps the most obvious use would be for runners wanting to go barefoot and work on foot-contact posture.

Conclusion and thoughts on usage of the Alter-G

While I’m not that excited about the Alter-G this does not mean use of the technology won’t be helpful to many runners to either supplement their training or to rehabilitate injuries. If I were using the machine or supervising an athlete who wanted to try it, I’d have these considerations front of mind:

  • If you are injured consult your doctor or referring physical therapist for guidance on your specific situation.
  • Reduce the gravity effect by minimum amount possible or needed.
  • Wear modestly cushioned flexible shoes – or go barefoot if you’re used to it.
  • Set the treadmill to a modest incline rather than running on the flat.
  • Do some body weight exercises before and after use to fire up and then wake-up your running muscles.
  • Walk through the key running drill the A-March before and after sessions.
  • Combine some over-ground running as quickly as possible in your rehabilitation program.
  • Don’t run too fast i.e. not faster than your marathon pace.
  • Don’t run too slow – run slightly quicker than your normal easy pace.
  • Do some strength work targeting the hips to make-up for the reduced gravity effect.
  • If supplementing training, don’t do more than 10 – 20% of your total milaege on the Alter-G.

Words and images by


6 Responses to Running on the moon

  1. Gerard Bourke July 2, 2013 at 3:39 pm #

    Dear Brian,

    My name is Gerard Bourke and I am a part owner of the Alter G treadmill at Gravity Free Rehab as well as an Orthopaedic Surgeon specialising in knee, foot, ankle and lower limb biomechanics.

    I appreciate your review of the Alter G and I just thought I would offer some thoughts of my own. The Alter G is predominately a rehabilitation treadmill and has been an exciting and successful adjunct in the recovery from not only surgery but running injuries. We have found that almost all types of running injuries are benefitted in particular stress fractures, tendon injuries and even muscle injuries. We have had several runners return to their pre injured state in a more controlled and rapid programme as a result of the Alter G. Although we do have our fair share of athletes who use it for extra training, I like you, would advise its use with some caution as any extra stress through the body can result in an overuse injury. It is however extremely useful to increase cardiovascular and aerobic fitness without endangering musculoskeletal structures through increased training.

    As a recreational runner who has had periods of down time due to injury the Alter G offers an opportunity to maintain joint motion, muscle strength and all the psychological benefits of running even when injured. Obviously it is not a replacement for the joy achieved in running outside but it prevents many of the secondary issues that affect runners if they are prevented from training due to injury. In addition the Alter G has introduced the joy of running to many people who otherwise would have been precluded. These include older athletes as well as previous non athletes such as the chronically ill or obese.

    With respect to gait training it is useful as an adjunct to take many elements of fatigue and poor core strength out of the equation when trying to train a runner to improve their form. In addition the use of cameras projecting onto a screen in front of the runner and he or she is able to use visual feedback methods to improve their style.

    Overall the Alter G has been an excellent adjunct for rehabilitation and introduction to running to injured or previously incapable athletes however it can play a role in increasing endurance and speed to the non injured athlete. It is not meant to replace running outside and does carry all the differences that treadmill running carries compared to running outside but is certainly worth considering if you are recovering from injury or just want to gain that extra edge in competition.

    I would be pleased to communicate with anybody wishes to gather further information on the Alter G and can be contacted through Bayside Orthopaedics Victoria, email

    • Brian July 2, 2013 at 8:57 pm #

      Hi Gerard, Thanks for adding your thoughts to the article. I’m sure there will be a few practitioners who’d be keen to get in touch with you. The various conversations on Twitter seem to indicate it’s an evolving area that everyone it continuing to learn about. Cheers

  2. sportinjurymatt June 3, 2013 at 9:58 pm #

    Fascinating article Brian!
    Though I understand the theory of Alter-G allowing runners to notch up further volume without inviting injuries associated with vertical ground reaction force, I’m interested to hear exactly what benefits Salazar/other users believe/have shown subjects are getting. The reduction of vGRF seems to have involved so much change to sensory input and neuromuscular demand placed on the body that I would imagine the majority of gains you see come with “normal” running no longer apply (Principle of Specificity).
    With my current level of understanding, I find it easier to place use of the Alter-G in a rehab program for certain injuries (as Kevin pointed out above) but I wonder whether the time they spend at that stage before progressing to a “real” environment would warrant what I imagine is a somewhat expensive piece of equipment?
    I hope people who have used this kit for either performance enhancement or rehab leave some comments as it’s a very interesting area!

    • Brian June 3, 2013 at 10:20 pm #

      Thanks Matt. I agree it seems more suited to rehab as discussed. I wonder if Salazar’s athletes get more of a mental boost than actual physiological benefit? The expense is much less than I thought it would be – seem to be a few clinics around where buying time on the Alter-G isn’t going to break the bank.

  3. Kevin Maggs DC June 3, 2013 at 7:54 pm #

    Hey Brian,
    Nice post. Well thought out.
    I had an AlterG in my clinic for a year and felt pretty much the same way you do. I agree that it may start causing some altered mechanics if the runner uses it too much. It is however, a great way to augment some extra miles with less chance of injury due to the reduced vertical ground reaction force (vGRF) that may be associated with some injuries.
    With respect to using it for runners who are already injured and want to prevent a loss of fitness while recovering from injury, it is certainly helpful with some injuries. However, only in injuries associated with a high vGRF.
    For example, it would not be helpful for someone with a hamstring strain since the peak load in the hamstring occurs at terminal swing phase, which wouldn’t have a huge influence if they had less vGRF. Same would apply for a hip flexor strain etc.
    I found it good for injuries which were assoc. with high vGRF such as shin splints or recovery from any stress reactions.
    Best of luck and keep up the good work.

    • Brian June 3, 2013 at 8:17 pm #

      Thanks Kevin, I appreciate the feedback, and also the thoughtful suggestions for use in rehab – makes sense to me!