Key Roles in Dynamic Exoskeletons for O&P Practitioners

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In this edition of Stepping Out, The O&P EDGE makes a departure from the usual focus on pedorthics, as Steven King, DPM, CPed, and Steven A. Gard, PhD, examine how pedorthists and other O&P practitioners can play a key role in the rapidly changing exoskeleton market.

Exoskeletons are machines that consist primarily of an outer framework a person wears that is powered by a system of motors, hydraulics, or pneumatics that deliver at least part of the energy for limb movement and task completion.

girl in Passive Dynamic Bipedal Walking Machine

Vereshchagin Dmitry /

In 2014, the exoskeleton robot market was $16.5 million and is expected to grow to $2.1 billion by 2021, reports Wintergreen Research.1

Market growth is expected to come as a result of the effectiveness of these robotic treatments for human movement challenges. As the ability of exoskeletons to perform more sophisticated combinations of tasks increases, their usefulness in a variety of areas, including O&P and rehabilitation as well as military and industrial applications, is also growing.1 The availability of affordable devices that improve mobility and function is not likely to go unnoticed by workers’ compensation agencies and the U.S. Department of Veterans Affairs as they try to fully rehabilitate and support injured workers and soldiers. Further, as members of the baby boomer generation seek to maintain an active lifestyle, there may be demand for exoskeletons that can assist with tasks in the home, at work, and at play. As professionals well versed in gait challenges and biomechanics, O&P professionals have a key role to play in the burgeoning field.

The leaps in technology are significant, with some systems capable of a great variety of movements with more fluid, coordinated motions and enhanced by increasingly sophisticated software. An apt description of much of modern exoskeleton technology is “mechatronics,” a term that encompasses the principles of mechanics, electronics, and computing to generate a simpler, more economical and reliable system. As more rehabilitation and occupational therapy practices adopt the use of “intelligent mechatronics,” more patients will find use for them at home and at work to achieve tasks that could otherwise be harmful, painful, or unattainable. The focus on mechatronic exoskeletons has been increasing and multiple conferences are covering the subject area, such as the upcoming 2016 Wearable Robotics Association inaugural meeting cosponsored by the IEEE (Institute of Electrical and Electronics Engineers) Robotics & Automation Society and the Dynamic Walking Conference. Never before has there been such cooperation between professional specialties to help improve gait and overall user functions. Synergies can often be found when goals are made common.

As the number of articles in popular and scientific literature increases, and conferences devoted in whole or part to exoskeleton technology attests, interest in the field is growing. That growth may become exponential should exoskeleton technology developed and tested to increase stamina in soldiers through the Defense Advanced Research Projects Agency (DARPA)2 reach the civilian market in the next five to ten years and give able-bodied people the ability to perform better than ever physically with the assistance of their exoskeleton mechanical systems—a potential that multiple articles have suggested. However, with the excitement comes concerns. Among these concerns is that as the technology becomes more powerful, the systems might encounter problems with robotic shakes similar to those that plagued General Electric’s early exoskeleton prototype, Hardiman—a device whose control system made it jerk so violently that it was never tested with a person wearing it.3 Additionally, what type of joint forces and balance issues, as well as other safety issues, will need to be solved before allowing people to strap on a machine that will help them run over 25 miles per hour? Where should the airbags be placed? We must remember there is a possibility of a “frog swimming in a blender” scenario, where everything is fine until someone pushes the on switch.

These advanced mechanical gait systems can be helpful yet possibly dangerous if not properly prescribed, fitted, and tuned for the user. When the force of the mechanical system is not in sync with the user, friction and torsion points can arise, which can cause blisters or musculoskeletal injuries to the deeper tissues. For instance, when the force of the mechanical system significantly overpowers the user, it can also lead to muscle and joint strains. These are the types of problems that can be solved by including O&P practitioners in the dispensing and use of exoskeletons, as they already address similar issues in the normal course of their work when fitting, fabricating, and dispensing orthoses and prostheses.

Passive Dynamic Bipedal Walking Machines Maximize Exoskeleton Development and O&P Care

To appreciate the role O&P practitioners can play in fitting, training, and tuning exoskeleton technology, it’s helpful to look at the work in bipedal walking machines that helped to maximize their development, and how that work may have added to the understanding of bipedal biomechanics.

Tad McGeer, PhD, built and demonstrated one of the first passive dynamic bipedal walking machines; it was constructed with rocker-bottom feet and needed a downhill slope to self-propel without tethers or an energy source other than gravity. McGeer’s design recognizes that bipedal human gait is mechanically designed to maximize energy efficiency and reduce center of mass oscillations by “riding” on an inverted pendulum that allows fluid movement—like an upside down grandfather clock or piano metronome, the hips ride on legs connected by ball-and-socket hip joints. (Editor’s note: To see the principle in action, visit

Dynamic Walking

Passive dynamic walker

Passive dynamic walker utilizing a convex rocker-type foot structure to assist with the fluid motion of the stance phase of gait. Image courtesy of Seoul National University.

Passive dynamic walking models effectively duplicate many of the biomechanical functions of able-bodied gait. One important function of able-bodied walking involves the principle of energy conservation. That is, able-bodied individuals walk in such a way that with each step, mechanical energy associated with the forward velocity of the body (kinetic energy) is transformed into energy associated with vertical displacement of the body (potential energy), and vice versa. This energy conservation principle is based on the inverted pendulum model of walking.4 By conserving mechanical energy during gait, the metabolic energy that is expended by the ambulator can be reduced.

person in full exoskeleton

A diminished ability to transform mechanical energy is one of the reasons why prosthesis and orthosis users typically walk slower than able-bodied individuals and have higher costs of transport and may have more lossy impedance during gait.

Traditional lossy gait impedance is made more so by using soft foams for cushioning friction points in the system or mechatronic energy harvesting. Reactive impedance allows for the addition of lossy energy harvesting with less energy loss and discomfort.

While this may be a new concept in application to O&P, lossy and reactive impedance are used regularly in the world of electronics and the concept fits well in the mechanical world. Soft foamy shoes (that may be used under these exoskeletons and thereby become part of the kinetic chain of the system) absorb energy at contact and at toe off—much like walking in soft snow or sand, which has a higher cost of transport and greater lossy impedance. This is where a pedorthist would make the decision about which shoe system should be incorporated.

In theory, O&P practitioners can improve the efficiency of the locomotor mechanism and enable prosthesis and orthosis users to walk faster by either addressing deficiences in the altered inverted pendulum mechanism or by providing prosthetic and orthotic devices that effectively store and release energy at appropriate times during the gait cycle. Thus, the O&P profession would benefit tremendously from an increased understanding of the mechanisms that are utilized by passive bipedal models and by facilitating the design of improved componentry to increase gait efficiency through practical implementations of the biomechanical functions associated with gait. A goal of every O&P practitioner should be to minimize the metabolic energy expenditure of their patients during walking through careful consideration for and effective implementation of biomechanical gait functions.

The Role of O&P Professionals in the Exoskeleton Market

O&P professionals may simply regard their provision of prostheses and orthoses as being beneficial and necessary for their clients to achieve bipedal walking, but this minimizes their contributions. Some practitioners may overlook or underestimate their roles in the restoration of normal gait functions such as upright balance and stability, shock absorption, forward progression, and energy conservation and efficiency, among others.5 To optimize and maximize the gait of individuals with lower-limb impairments, O&P practitioners need to be cognizant of these functions when designing, prescribing, and fitting prostheses and orthoses. Effectively restoring these functions will make the difference between merely providing a patient with an ability to walk versus enabling him or her to achieve superior performance through the provision of well-designed and carefully constructed assistive technologies.

Some of the obstacles to overcome with human bipedal gait will be the same ones faced by users of mechanical walking systems, such as improving their stability, energy efficiency, and safety, and some will be very different. The blending of the sciences will lead to more students, researchers, and practitioners experimenting with and working on advancing these systems and related science.

O&P professionals are charged with the responsibility for interfacing advanced technologies to the human body with the intent of improving performance of individuals who have physical impairments. Therefore, O&P practitioners need to regularly evaluate current and future educational needs to enable the field to be ready to meet anticipated challenges that will come with the fitting, training, and tuning of new technologies.

Steven King, DPM, is the co-principal investigator for research grant SBIR A11-109 for the U.S. Department of Defense and Army Medical Research and Materiel Command, testing U.S. Patent No. 8,353,968 (Spring Lever Orthotic Device), and is a voting member of American Society for Testing and Materials committees. King is the managing member of Kingetics, Rapid City, South Dakota. He can be reached at .

Steven A. Gard, PhD, is executive director at the Northwestern University Prosthetics-Orthotics Center; an associate professor in the Department of Physical Medicine & Rehabilitation, Feinberg School of Medicine; and director of the Jesse Brown VA Medical Center’s Motion Analysis Research Laboratory. He can be reached at .

Editor’s note: According to a press release from ReWalk Robotics, Yokneam Ilit, Israel, and Marlborough, Massachusetts, dated December 17, 2015, the U.S. Department of Veterans Affairs has issued a national policy for the evaluation, training, and procurement of the ReWalk personal exoskeleton systems for qualifying veterans who have suffered spinal cord injuries.


  1. Wintergreen Research. 2015. Medical Exoskeletons: Market Shares, Strategies, and Forecasts, Worldwide, 2015 to 2021.
  2. Harvard’s Wyss Institute awarded DARPA contract to advance exosuit. 2015. The O&P EDGE (13) 11:14,
  3. Nathan, S. 2015. Power dressing: Why it’s exoskeleton time. The Engineer,
  4. Kuo, A. D. 2007. The six determinants of gait and the inverted pendulum analogy: A dynamic walking perspective. Human Movement Science 26 (4):617-56.
  5. Gard, S.A., and S. Fatone. 2004. Biomechanics of lower limb function and gait. In Report of a Consensus Conference on the Orthotic Management of Stroke Patients. E. Condie, editor. (Ellecom, the Netherlands, September 21-26, 2003.) Copenhagen, Denmark: ISPO Publications 55-61.

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