What is an exoskeleton?
The field of exoskeleton systems is continuously evolving and reinventing itself, making it still difficult to create a singular definition. In general:
- Exoskeletons are wearable devices that work in tandem with the user. The opposite of an exoskeleton device would be an autonomous robot that works instead of the operator.
- Exoskeletons are placed (worn) on the user’s body between one or more body joints.
- They apply a physical force to the body that augments able-bodied individuals, assists those who may have a movement impairment, or, in some cases, applies a resistive force to prevent the body from moving. The opposite would be a mechanical prosthetic, such as a robotic arm or leg that replaces the original body part. In between are powered orthotics, which can be described as an exoskeleton or not, depending on the designer/manufacturer.
- Exoskeletons can be made out of rigid materials, such as metal or carbon fiber, or they can be entirely composed of soft and elastic parts, or a combination of both.
- Exoskeletons can be powered and equipped with sensors and actuators, or they can be entirely passive, relying on elastic elements for their functionality. Furthermore, they can be a combination of both (hybrid), or use powered motorized components only to apply a stopping force (quasi-passive).
- Exoskeletons can be mobile or fixed in place (fixed frame), such as mounted on a wall or in a stationary metal frame (the latter is almost exclusively for rehabilitation or teleoperation purposes).
- Exoskeletons can cover the entire body, just the upper or lower extremities, or a specific body segment, such as the ankle or hip.
In summary, robotics & automation tend to replace people (with one notable exception being the emerging field of cobots), while wearable robotics or exoskeletons are applications of robotics and biomechatronics that augment or assist humans in performing tasks or moving better.
Wearable exoskeletons have been given many names over the years, and can also be referred to as robotic suits, powered armor, exo-frame, exosuits, wearable machines, power jackets, powered clothing, ergoskeletons, dermoskeletons, etc.
Recent Historical Background:
Deriving a simple definition of what an “exoskeleton” is has proven to be elusive over the decades. Around 2010, there were only a handful of publicly known wearable exoskeleton devices. For the nonfictional ones, there were the HULC, HAL, XOS, and ReWalk; for the fictional ones, there were the Power Loader from Aliens and Iron Man. At the time, all fictional and nonfictional wearable robotic devices shared the same architecture: large, rigid metal frames that extended to the ground and featured sizable actuators.
Different names were proposed for this new family of fictional and real devices. For example, a “biomechatronics” device, which combines biology, mechanics, and electronics, gained significant popularity for a while but ultimately failed to gain traction. (Fun fact: the first version of the Exoskeleton Report was called Biomechatronics.net.) Instead, the term “Powered Exoskeletons” gained popularity. The addition of “powered” differentiated the term from insect exoskeletons, and “exoskeleton” was appropriate for the large and bulky devices, serving as a play on “endoskeleton” from the Terminator movie franchise.
Fast forward a few years, however, and developers began to build passive exoskeletons —wearable devices that had no motors or controllers, still performing useful physical work by primarily utilizing elastic elements. Just like that, PoweredExoskeletons.com (another early version of the Exoskeleton Report) became obsolete! So did the term “Powered Exoskeletons,” as now not all exoskeletons provide active force or torque. Thus, “Powered Exoskeleton” became shortened to “Exoskeleton,” which generated confusion between insect and wearable exoskeletons, but it was still a good term to describe the devices. As of 2025, the ExR catalog of devices is divided 135 to 105 in favor of powered solutions (link).
Then, along came projects like the Wyss Institute (and others) exosuit, which showed that wearable exoskeletons do not have to be rigid or extend all the way to the ground. This was a big departure from previous power suits, and while they were not the first, the research at the Wyss Institute really popularized this approach. However, this exciting development presented a conundrum: an “exoskeleton” is typically something hard and rigid, the very opposite of a soft exosuit.
At the time, the solution seemed easy, just rename all “exoskeletons” to “exosuits” since an exosuit can be soft or rigid. However, this solution was a nonstarter from the outset, creating a split that remains unresolved. That is why you may see ‘exoskeletons’ or ‘exosuits’ used interchangeably, or an exosuit specifically referring to a wearable device that doesn’t have a rigid frame (refer to Introduction to the Commercial Exoskeletons Catalog). Fast forward to 2025, and we are now getting closer and closer to 4D materials: a material that can change from soft and pliable to stiff in milliseconds, which can further complicate what is an exoskeleton or what is an exosuit (sometimes you will see Exoskeleton Report or others just write “exo” but that term contrinues to be dominated on the internet by a Kpop band).
The best solution for now appears to categorize soft exosuits with exoskeletons as a separate subcategory. Thus, “exoskeletons” can be the parent container, and then further differentiated by actuation methodology, structure, body area, or main envisioned application.
Is It A Wearable Exoskeleton?
REX by Rex Bionics
The REX exoskeleton is clearly an exoskeleton. The REX is a rigid frame wearable device with motors and sensors. The REX is so powerful that it can move a person entirely on its own.
Verdict:
Exoskeleton
Subcategories: Powered, Medical, For Physical Rehabilitation
Foot Drop Splint
How about a food drop orthotics? Would that be an exoskeleton? This is another freebie. It is clearly not an exoskeleton. While it is a wearable and rigid, a splint falls within the well-established field of braces. It has no motors, sensors, or spring elements.
Verdict:
Not an exoskeleton.
Passive Ankle Exoskeleton
The Passive Ankle Exoskeleton is structurally similar to the foot drop brace (above), but it has a hinge at the ankle, a spring, and a clutch. All moving components are optimized and synchronized to decrease the metabolic cost while walking. For more, see Greg Sawicki on Successfully Reducing Walking Metabolic Cost.
Verdict:
Exoskeleton – Passive, Ankle
SaeboStep by Saebo
The SaeboStep is designed to be a replacement for the classic foot drop splint. Rather than having a rigid orthotic that enters inside the shoe, the foot is supported by a thin cable. The cable length is adjustable, similar to a ski boot.
Is this an exoskeleton? The core Exoskeleton Report team presented this for an internal discussion at the end of 2016 and decided that it is not an exoskeleton. However, the Wearable Robotics Association does list this family of wearables as exoskeletons (see WearRA slides).
Verdict:
Maybe?
Exoskeleton Report: No, this is not an exoskeleton.
WearRA: Yes, this is an exoskeleton.
L300 Foot Drop System by Bioness
Now let’s add another level of complication. Is the L300 an exoskeleton? The L300 is a foot drop prevention system that uses the client’s own muscles as actuators. A foot sensor below the heel and at the ankle monitors the position of the leg and the phase of the gait cycle. A leg brace below the knee utilizes functional electrical stimulation (FES) to activate the muscle groups responsible for raising the foot. A controller (off picture) handles the wireless communication between the components. In addition, the L300 can be expanded to include other joints in the leg.
So is this an exoskeleton!? There is no hard frame, no wires running up and down, and no springs, motors, hydraulics, or inflatables other than the already existing muscle groups to generate movement. Can a dormant muscle already existing in the body that is activated externally be considered as the “actuator” for an “exoskeleton” device? What if the controller and sensors were implanted below the skin?
Verdict: not an exoskeleton, but can be integrated with an exoskeleton
As of 2025, FES devices fall outside of the scope of exos, but more groups are investigating pairing the two technologies
At this point, in 2025, the parent term “exoskeleton” is not beloved by many, but it has simplified communication in the field. It is easier than ever to search for this technology by using just this one parent term. There is presently a significant overlap between powered braces and exoskeletons, but ultimately, the question is what this technology can do for you. After all, even “robot” doesn’t have a universally accepted definition, but that hasn’t stopped it from being useful.
In 2017, the concept of an “exoskeleton” was not entirely clear. It is not the fault of the term. As you saw above, originally, an exoskeleton device stood for more than 90% of all devices being developed. With more research being conducted in the field, however, the new solutions to old problems become increasingly distant from the original motorized, rigid metal wearables. Keeping everything under the same umbrella term is becoming more challenging.
Enter Hollywood
Perhaps attempting to change the term exoskeleton to something more inclusive is too late. Popular culture has always had an impact on what people expect from technology (think original Star Trek and cell phones). Hollywood has taken a liking to wearable robotics and the term exoskeleton. Movies such as Elysium, Avatar, Edge of Tomorrow, GI Joe, and Prometheus have begun to solidify the term “exoskeleton” into popular culture.
Why does it matter?
Having a single term that encompasses what the industry is about is critical for communication. Take David Cohen’s patent research: An Overview of the Exoskeleton Patent Landscape. There are patents for all manner of exoskeleton devices, which use various names and designations, sometimes as nondescript as simply “robot.” Therefore, creating a comprehensive analysis of the patent landscape for the exoskeleton industry will require dozens of search terms to achieve the same goal. This is very inefficient. The same challenge is encountered by insurance companies, investors, students, hobbyists, and medical and industrial professionals when they search for information on wearables. The same type of device can have completely different names based on the manufacturer’s preference. This hinders information gathering and needlessly complicates communications.
Similar Guides:
- Exoskeletons by application
- Common terminology with wearable robotics and exoskeletons
- Myths and misconceptions around exoskeletons
Revision History:
This article was originally published in 2017 (link to PDF). You can view the original version in PDF format (and evaluate how things have changed over time).
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