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Research and Innovation

Springing Ahead of Nature: Device Increases Walking Efficiency

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Graduate student Audrey Westbrook looks on as Dr. Bruce Wiggin uses exoskeleton devices to walk on a treadmill. The devices increase walking efficiency by 7 percent in able-bodied adults. Photo courtesy of Marc Hall, NC State University.

For Immediate Release

Dr. Greg Sawicki

It’s taken millions of years for humans to perfect the art of walking. But research results published today in the journal Nature show that humans can get better “gas mileage” using an unpowered exoskeleton to modify the structure of their ankles. The device puts an extra spring in each human step, reducing metabolic energy consumption by 7 percent below walking in normal athletic shoes.

The finding may benefit both able-bodied people who are frequently on their feet – think of the military infantry or athletic baby-boomers, for example – as well as those who have been victims of stroke or other gait impairments.

To gain an advantage over nature, North Carolina State University and Carnegie Mellon University researchers tested the efficacy of a lightweight lower-leg device that uses a spring and clutch system working in tandem with calf muscles and the Achilles’ tendon while people walk. The streamlined, carbon-fiber device weighs about as much as a normal loafer – around 500 grams, or a bit more than a pound – and is not motorized, so it requires no energy from batteries or other external fuel sources.

“The unpowered exoskeleton is like a catapult. It has a spring that mimics the action of your Achilles’ tendon, and works in parallel with your calf muscles to reduce the load placed upon them,” said Dr. Gregory Sawicki, a biomedical engineer and locomotion physiologist in the joint NC State/University of North Carolina-Chapel Hill Department of Biomedical Engineering who co-authored the paper. “The clutch is essential to engage the spring only while the foot is on the ground, allowing it to store and then release elastic energy. Later it automatically disengages to allow free motion while the foot is in the air.”

Graduate student Audrey Westbrook looks on as Dr. Bruce Wiggin uses exoskeleton devices to walk on a treadmill. The devices increase walking efficiency by 7 percent in able-bodied adults. Photo courtesy of Marc Hall, NC State University.
Graduate student Audrey Westbrook looks on as Dr. Bruce Wiggin uses exoskeleton devices to walk on a treadmill. The devices increase walking efficiency by 7 percent in able-bodied adults. Photo courtesy of Marc Hall, NC State University.

The study participants – nine able-bodied adults – strapped the exoskeleton devices on both legs and walked at a normal speed on a treadmill after completing some practice training. The same subjects also walked without exoskeletons for a baseline comparison.

The researchers tested exoskeletons with springs that varied in stiffness. Like Baby Bear’s porridge in the Goldilocks story, the spring that provided the most benefit was moderately stiff. Walking with exoskeletons with springs that were too stiff or too compliant resulted in normal or higher-than-normal energy costs for participants.

“A 7 percent reduction in energy cost is like taking off a 10-pound backpack, which is significant,” Sawicki said. “Though it’s surprising that we were able to achieve this advantage over a system strongly shaped by evolution, this study shows that there’s still a lot to learn about human biomechanics and a seemingly simple behavior like walking.”

“Someday soon we may have simple, lightweight and relatively inexpensive exoskeletons to help us get around, especially if we’ve been slowed down by injury or aging,” said paper co-author Dr. Steven Collins, a mechanical engineer and roboticist from Carnegie Mellon University.

Dr. Bruce Wiggin, a former NC State graduate student, co-authored the paper. Funding was provided by grants to Sawicki from the NC State Faculty Research and Professional Development Fund; the NC State Chancellors Innovation Fund; Grant No. 2011152 from the U.S.-Israel Binational Science Foundation; and Award Number R01NR014756 from the National Institute of Nursing Research of the National Institutes of Health. It was also supported by the National Science Foundation under Grant No. IIS-1355716 to Collins.

– kulikowski –

“Reducing the energy cost of human walking using an unpowered exoskelton”

Authors: Steven Collins, Carnegie Mellon University; M.B. Wiggin and Gregory S. Sawicki, North Carolina State University

Published: April 1, 2015, in Nature

DOI: 10.1038/nature14288

Abstract: With efficiencies derived from evolution, growth and learning, humans are very well-tuned for locomotion. Metabolic energy used during walking can be partially replaced by power input from an exoskeleton, but is it possible to reduce metabolic rate without providing an additional energy source? This would require an improvement in the efficiency of the human-machine system as a whole, and would be remarkable given the apparent optimality of human gait. Here we show that the metabolic rate of human walking can be reduced by an unpowered ankle exoskeleton. We built a lightweight elastic device that acts in parallel with the user’s calf muscles, off-loading muscle force and thereby reducing the metabolic energy consumed in contractions. The device uses a mechanical clutch to hold a spring as it is stretched and relaxed by ankle movements when the foot is on the ground, helping to fulfill one function of the calf muscles and Achilles tendon. Unlike muscles, however, the clutch sustains force passively. The exoskeleton consumes no chemical or electrical energy and delivers no net positive mechanical work, yet reduces the metabolic cost of walking by 7.2 ± 2.6% for healthy human users under natural conditions, comparable to savings with powered devices. Improving upon walking economy in this way is analogous to altering the structure of the body such that it is more energy-effective at walking. While strong natural pressures have already shaped human locomotion, improvements in efficiency are still possible. Much remains to be learned about this seemingly simple behavior.

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  1. I have a brain timer that I had for thirty years. They gave me six months to live. I have a pontine glyoma. It causes a drop foot only on my left foot. I also had to have a knee replacement I believe because I have been walking for years. I would love to walk again.

  2. I have Fibromyalgia, and can only walk a few minutes at a time. Would love to see it these would help me.

  3. I damaged my Achilles’ tendon on both my feet and wonder if I may be helped by this spring device. Can you please send information on where to buy it? Thank you.

  4. When these become available to the public, I would love to be notified. Please email of further developments in this sysytem. Thanks

  5. I have no serious physical limitations, but I am 81+ years old and have back problems that cause siatic (?) type pain in my legs and limit my ability to walk distances. I still play golf twice a week and occasional shoot my age, but your aid sounds as if it would help me. Are they available?

  6. Are there any clues as to future development and marketability is it being pursued as a therapeutic device available by Rx only or as a sports device. As someone with bilateral partial thickness Achilles’ tendon ruptures I would be interested in the application of kickstarters for this product

  7. The Exoskeleton is a leap when it comes to new material, biomechanics and application. The main challenge remains in the cost/efficiency and ROI. Most of the existing Exoskeletons are either expensive, heavy and/or have limited functionalities. The moment this concept becomes available i will be interested in seeing the Industrial version.

  8. Ridiculous. All these comments – all these people you’ve given hope to, and no one can reply with further information?

  9. my wife broke her neck at 19 years old . However she taught herself the walk with a bad gate. Now she is now 58 years old and her walking has become extremely difficult for her. She seems to drag her toes when working. Would something like this be good for her.

  10. I would was wondering what would result if you were to replace that spring with a pneumatic piston, putting pressure in the opposite direction? I have a good friend who has lost so much due to a condition where he no longer can lift his feet up when he walks, they just go limp, so he has to take big awkward steps to set his foot on the ground right to keep from tripping. I do wonder is something like this could help him.

  11. Dear Sirs,
    My wife has Myotonic Dystrophy which has affected her calf muscles. It would be interesting to see how this could improve her gait.

    Thank you , and keep up to the great work.
    Nino Arzon
    Plano, Texas

  12. This sounds really great. I have lost my achilles tendon three years ago as a consequence of a severe infection. I would love to try out the exosceleton to see if I would be able to run a marathon again with it.

  13. I had GBS when I was a kid which caused me to have drop foot all my life. Also had a stroke 9 years ago, that added to the challenge. I would love to try these devices.

  14. I am Physiotherapist, practising here in Coimbatore. I have many patients with problems walking independently. Even with optimal length and strength developed, the muscles require additional strength. Which I demanded my orthotist…but this seems to be effective, hopefully..!

  15. I have nerve damage to the S1 andL 5 from a bad back operation 5 years ago. I cannot stand on my toes so cannot push off and my gait is terrible. I do not have foot drop . I’ m just lacking the spring to the step, and my balance is probably 50% less than it should be. I use bilateral canes to push off. I think this device would improve my gait. When will it be available to the general public?

  16. Sir,I am student of mechanical engineering and I want to make similar kind of project for supporting others. Can I get some more information for making this type of device.
    I shall be thankful for your favour…

  17. I would love to be a candidate for your study. Please let me know what I can do to get these devices in Texas.thanks for share……

  18. I have severe damage to both feet and can hardly walk. The bones is left foot are totally gone and I am walking on my ankle. My right foot is not much better. I am almost totally handicapped from walking, limited to about 100 paces a day. Would love to have one of these devices when they are available. How can I find out more.

  19. How do I receive more information on this? Is it available? Do you need subjects to study? Had a stroke 11 years ago and have hemiparesis on the right side. Am able to still continue my sculpting career ( but would love to be able to walk easier.

  20. My mom is in her early 70. She can’t walk and go with us to many places due to her weak ankles. This is something that would definitely help her walk and going places again. If this product is available, I would love to get one for her. Please let me know if you are accepting test subject. We would pay for any travel expenses just to get her one of these.

  21. I had an arachnoid cyst removed from my spinal cord in 2007. After they removed it I had nerve damage. I have a foot drop on the left side. I was also diagnosed with neurosarcoidosis and see a specialist at Cleveland Clinic. I would be interested in this if someone could email some more information! Thanks so much for your time!

  22. Hi I have a spinal cord injury and I would love to be a candidate for your study. Please let me know what I can do to get these devices in Texas.

  23. I am interested learning more about your exoskeleton.

    I have a rare genetic neurological condition, HSP (Hereditary Spastic Paraparesis) a degenerative upper motor neuron disease Impairment of nerve signaling in the motor neurons of the corticospinal tract causes a combination of spasticity and weakness in the lower limbs. It is estimated that about 20,000 people in the US have HSP, and around half a million worldwide.

    Reading about your technology led me to wonder if the device might be effective for treating HSP symptoms. I may be a good candidate as I have the most common, pure form of HSP (SPG4), I have a significant, but not totally debilitating level of symptoms, walking with the aid of a cane, and I take no prescription drugs.

    I am happy to travel to participate in trials at my own expense, and also happy to answer any questions or provide further information.

    Thank you
    Karen Johnson

  24. I had a major compression injury of L1 in 1989 and had a laminectomy at the level of T10 – L3, 2 plates and 8 screws remain in my spine. This injury left me with very little plantar flexion, therefore I have a severe limp and I have to wear AVO braces and use a cane on a daily basis. If possible I would love to be a part of this study. I am licensed Chiropractic Physician and Acupuncturist and would love to know more about your study and products that may can help me and many of my patients.

  25. What an amazingly simple and effective invention. And I am also amazed at the response from disabled people around the world itching to try it. I too am ambulant disabled and would love to use it as I am slowing down (age 45) and don’t want o slow down! If the opportunity ever arises please let me know. And I hope you will keep all these people updated as to progress and getting beyond prototypes. Very best of luck with the project.
    Best wishes
    (London Uk)

  26. Hello
    I went online to find a walker w/seat (stroke) and found you. Are these braces available to the public now?
    Ready to try.

  27. I have CMT and would be honored if I could be involved with further testing of this exoskeleton. I currently wear a carbon fiber AFO that helps, but would like something the doesn’t restrict range of motion in the ankles.

  28. I suffered a ischemic stroke in 2009, left side. I wear an orthotic but my walking has been limited and difficult.
    I have participated in Robot Therapy at Feinstein for my ankle and left leg with some improvement in strength, however it was a six week program. It gave me some improved strength. I would love to try the exoskeleton.
    I live in NYC area. I am 75 years of age and healthy. I have limited use of my left hand and of course the weakness of my left leg and ankle.

  29. My husband had 2 strokes within a week span in 2000. He was 55. It left him partially paralyzed on the right side. Getting botox injections in arm for spastisity and uses the bioness system for his drop foot. He is interested in your device. If you need patients for trials to go further with your design keep him in mind. Can the device be purchased now?

  30. My 81 year old father is suffering from muscle atrophy and having difficulty walking. I would like more information on this to help him walk again. Can I make a donation or purchase?

  31. To everyone on here interested in this check into the IDEO device Intrepid Dynamic Exoskeleton Device. I have one and can assure you it works and is a life changer. Some insurance companies do cover it. I got mine from Walter Reed National Military Medical Center. It was invented at San Antonio Military Medical Center by Ryan Blanck he has left his job there and work at Hanger Labs clinic in Gig Harbor Washington and it is now offered on the civilian side he can tell you if you are a candidate and send you a referral letter for insurance. It is made of carbon fiber and the foot plate is built rocker bottom shape with 2 struts that run up the back and attach to the cuff the struts work like springs and return the energy. The brace stabilizes the ankle and does not depend on ankle ROM.

  32. I’ve had four spinal surgeries due to a Spinal Cord Injury due to spinal stenosis caused by Achondroplasia Dwarfism. I’m trying to recondition/strengthen my legs to get back up and walking. Who would I need to talk to in order to be a case study and have the opportunity to try these out?!?!?

    Thank you,

    Cindy Charrier

  33. I had a hemilaminectomy and after walking a lot, sometimes my back just gets all tight. I think this would help. Let me know if you need a beta tester! Best Wishes,

  34. I have a limp and a metal plate in my ankle as a result of it being crushed in a car wreck. The pain level ranges from a minor annoyance to excruciating, to the point where I don’t even want to walk. I would love to try out this device and see if it helps me any.

  35. I have MS and have difficulty walking. When I read about your exoskeleton I became hopeful. I pray this will become available soon. I would love more information.

  36. I have drop foot (left) due to spinal cord injury. Ive tried several devices with no help or that are painful to use.
    I would be willing to test something like this. Im a very athletic individual but cannot run and have pain walking for an extended time.

  37. I had an AVM similar to a stroke I was left with a peralisis of the left side of my body I am really interested in this exoskeleton to improve my walking. At the moment I use an AFO which is similar but I really want an exoskeleton to improve my lifestyle( I can see the exoskeleton from a different point of view coming from using an AFO to using a exoskeleton). Please contact me via email to know if I can purchase an exoskeleton.

  38. I am very excited to see these types of advancements in technology.
    I was born with severely clubbed feet as well as other ankle issues which limit my mobility. I can walk almost normally but I begin to hit my limit after 45 minutes of walking and even less time if I’m not wearing heavy boots for support. I would love to hear more information on your program and if you are taking volunteers for future trials involving individuals with disabilities.

  39. My fiance suffers from CMT, Charcot-Marie-Tooth disease. Would this be something that could help him? He’s had multiple surgeries on his feet, and even now has a hard time walking/being on his feet for more than 2 hours on a good day. 1 normally. Would love to get some more information on this.

  40. Due to a motorcycle accident, I have suffered nerve damage in my left knee that is causing foot drop in my left foot. I would like to gain for info about this device if it will be able to assist me with my injuries.

    Looking forward to hear from you

  41. This is great! One of my life dreams from little girl was to see my mom walk like everyone else. I gave up on the dream and now you gave me hope once more. She lost the use of her left leg when I was 6 years old (I’m 27 now)and I had to take care of her though the years until I left at age 17. It would be nice to be able to take her out for lunch one day and not have to worry about a accident. Is there anyway I can get her signed up for this? This would be a dream come true for me and even her.

  42. I very interested in these I had a Stroke in 2010 and have left side drop foot Does Medicare pay for these if not how much are they?
    John S. Greenwald

    1. Does medicade pay for these,my husband had a stroke 2 years ago will these help him walk

  43. I personally think this walking ¨assistant¨will help me walk better, I suffered a slipped disc in 2002, and was told to never walk again… I am mobile but due to my handicap, I suffer from Droopy foot an my left foot. I have no upward movement on my left foot, causing me to stumble pretty often. after watching the video, I am hopeful that oneday I will be able to take walks without stumbling and falling.

  44. I’ve had a stroke in 2010, I’d like to try this. I do walk 2 miles a day but I lack ankle control & plantar & dorsiflexion. Walking on uneven surfaces can make my ankle roll. This might help. Traditional AFO are uncomfortable to use & bulky! Can I be a product tester?

  45. how can I get involved with this research as a test subject or any other capacity? I’d like to have one for myself.

  46. Exoskeleton is a great device , i hope it may be helpfull for my mom, as few year ago she had stroke/ left side paralysis attack, still she isnt recovered .
    Her left arm is stiff and unmovable / near useless, her left leg is weak , has walking difficulties and im-balance, and left leg is too much cooler than the normal body temperature which adds up futher problem. FROM WHERE I CAN BUY such devices , need more details
    Thank you,
    Milandeep Singh

  47. I love the idea but how could it help someone who walks on there toes such as my self, i have spoken to doctors about my toe walking and they have said that many other people with autism do the same thing and that it is one of the trates of autism.
    From the video i have seen of the man walking it looks like the spring is only effective if you are a heal to toe walker.

  48. Please do you can response
    My son needs your help.
    Ataxia espinocerebelosa esporadica. 18 years.
    Dificulty walk.

  49. Dear Dr.
    Struck with Polio durinf infancy,I use crutches with callipers for moving.
    Of late, I feeldifficulty in moving with heavy Callipers tied from waist to rt. lower limb.
    Can your organisation help me in proper light weight equipment for safe and easy movement.
    I shall wait for your response.
    Thanks and Regards,
    Prof. I K Chopra
    +919888225007 Chandigarh,India

  50. Hello sir, I realy need this badly,,,, for relax walk 48 years old ……u can help me to send this I will introduce to people who r unable 2 walk easily because of joint pain…uricacid,,, over weight

  51. Hello,

    This is amazing! I was wondering if this would help with someone who has nerve damage to their feet? Commonly known as drop foot. Any information would be greatly appreciated.

    Thank you,

    1. i too would be interested in this for the same reason. My Grandmother suffers from Charcott-Marie-Tooth, the major symptom being drop foot. She currently wears braces, but still has issues moving around. I wonder if this might help! Also, I wonder if it might help prolong the health of my own ankles and legs for the future to put off the need for braces longer, as I also have CMT and get to look forward to the same fate.

  52. Praise God for science and technology, I need these devices very badly. Where and how can I get one? I used to work as a government dentist in the Philippines. Since i had stroke 4 May 2013, I am unable to walk normally. I had an embolus in my right brain so my left upper and lower extremeties affected. Please help me get one Left Exoskeleton so that I could live a normal life. Praying fervently that God will use you mightily to help the world’s people with disabilities.

    1. I have bilateral drop foot from spinal injury. This device looks like it would enable me to walk without comperson braces.. please contact me via email. Thank you.

    1. Wow I want this I have MS and spend to much time inside this new year I want to get out more this will help I’m so excited how can I start the process of buying this great product.

  53. I have RA with particular problems in my ankles. I would also love to try these out. Need a volunteer?