Exoskeleton (human)

An exoskeleton is a wearable device that augments, enables, assists, or enhances motion, posture, or physical activity through mechanical interaction with and force applied to the user's body.
Other common names for a wearable exoskeleton include exo, exo technology, assistive exoskeleton, and human augmentation exoskeleton. The term exosuit is sometimes used, but typically this refers specifically to a subset of exoskeletons composed largely of soft materials. The term wearable robot is also sometimes used to refer to an exoskeleton, and this does encompass a subset of exoskeletons; however, not all exoskeletons are robotic in nature. Similarly, some but not all exoskeletons can be categorized as bionic devices.
Exoskeletons are also related to orthoses. Orthoses are devices such as braces and splints that provide physical support to an injured body part, such as a hand, arm, leg, or foot. The definition of exoskeleton and definition of orthosis are partially overlapping, but there is no formal consensus and there is a bit of a gray area in terms of classifying different devices. Some orthoses, such as motorized orthoses, are generally considered to also be exoskeletons. However, simple orthoses such as back braces or splints are generally not considered to be exoskeletons. For some orthoses, experts in the field have differing opinions on whether they are exoskeletons or not.
Exoskeletons are related to, but distinct from, prostheses. Prostheses are devices that replace missing biological body parts, such as an arm or a leg. In contrast, exoskeletons assist or enhance existing biological body parts.
Wearable devices or apparel that provide small or negligible amounts of force to the user's body are not considered to be exoskeletons. For instance, clothing and compression garments would not qualify as exoskeletons, nor would wristwatches or wearable devices that vibrate. Well-established, pre-existing categories of such as shoes or footwear are generally not considered to be exoskeletons; however, gray areas exist, and new devices may be developed that span multiple categories or are difficult to classify.

Purposes

Exoskeletons can serve various purposes related to medical, occupational, or recreational uses and are frequently categorized by their general field of use.

Medical

Medical exoskeletons typically serve one or more purposes, such as:

To assist movement or posture for a person with a physical disability or neuromotor impairment
To rehabilitate a person after an injury or disorder

Medical exoskeletons have been designed to support people with certain types of physical disabilities or neurological impairments including stroke, spinal cord injury, cerebral palsy, or limb loss. These exoskeletons can target various specific purposes such as to help balance, ambulation, reaching, grasping, coordination, or other functional movements. For rehabilitation, an exoskeleton may only be used temporarily during a limited period of recovery, after which they may no longer require the device. A rehabilitation exoskeleton can be designed to assist a person with movement impairment, for instance, to help stabilize movement or suppress tremors. Alternatively, an exoskeleton can be designed to resist movement to enhance physical training or to help restore strength. In this case, the exoskeleton is resisting the user in the near-term in order to assist them in recovering strength or capabilities in the longer-term. In either case, exoskeletons can be used to enhance the rehabilitation process by increasing the therapeutic dose, constraining exercises to specific movements, reducing the required number of clinicians or clinician effort to provide therapy, or providing assessment of performance through on-board sensing. For assistance, an exoskeleton may be used chronically, intermittently, or only temporarily. Exoskeleton assistance can also be paired with other technologies or modalities, such as functional electrical stimulation or epidural electrical stimulation.

Occupational

Occupational exoskeletons have primarily been developed and deployed for the purpose of reducing injuries and fatigue in the workplace. However, occupational exoskeletons may serve various purposes related to improving workplace safety or operations. The most common purposes are:

To reduce injury risk, such as musculoskeletal disorders due to overexertion or prolonged postures
To increase worker performance or operational efficiency
To reduce worker turnover or enhance recruitment of new workers by improving worker well-being

Military exoskeletons are often viewed as a sub-category of occupational exoskeletons. The term military exoskeleton refers to exoskeletons that are used to support military service members in performing their job duties. Some military jobs are similar or identical to the equivalent civilian jobs. For example, a military mechanic or logistics worker may experience similar physical demands as a civilian mechanic or logistics worker. However, other jobs are unique to military service, for instance, for tank or artillery crewmembers. Physical demands associated with body armor and load carriage are also often elevated and unique for military relative to civilian jobs. For these reasons, some military exoskeletons have been developed to address military-specific jobs, environments, and challenges.

Recreational

Recreational exoskeletons serve the purpose of helping people to do or enjoy recreational activities, such as walking, hiking, skiing, or sports. In this context, an exoskeleton may help a person to do a recreational activity for longer, to do it better, to do it with less strain, pain, or fatigue, or to do a recreational activity that they would otherwise be unable to do without the assistance and support of the exoskeleton. A common goal for recreational exoskeletons is related to healthy aging, in other words, to empower people as they age and undergo natural physical decline to remain physically active and to engage in activities they enjoy. In some cases, recreational exoskeletons may be designed to resist movement to increase muscle strength training by making the movement more challenging. Recreational exoskeletons are sometimes also referred to as sports exoskeletons or consumer exoskeletons. However, some occupational and medical exoskeletons can have uses in non-professional, consumer settings so these categories can blur and some devices can fit into multiple exoskeleton categories. Recreational exoskeletons are a more nascent category and their purpose and scope may continue to evolve over time.

Other

Exoskeletons have also been designed for other purposes. There are some exoskeletons designed primarily for research or educational purposes, and these are termed research exoskeletons and educational exoskeletons, respectively. Exoskeletons for assistance or muscle training purposes in space may be termed space exoskeletons. While these are somewhat similar to certain medical or occupational exoskeletons, they may not overlap completely. In some cases, a given exoskeleton may fit within multiple categories. As an emerging technology, exoskeleton categories are not rigidly defined. New categories or sub-categories of exoskeletons are gradually being added and refined over time.

Categories

Beyond categorizing based on their general purpose or field of use, there are various other ways to categorize or sub-categorize exoskeletons. Exoskeletons exist that support different body parts and tasks, and these vary widely in terms of their size, design, control, complexity, cost, structure, function, and transportability.

By body parts or tasks

Exoskeletons have been developed to assist a wide variety of body parts and tasks, and are often categorized by these. However, unlike many Hollywood movies, real exoskeletons are not designed to do every task or to support every part of the body. In general, exoskeletons are more akin to wearable tools that are each designed to serve a specific purpose, such as to assist a subset of body parts during a subset of tasks. Thus, there are a wide variety of exoskeletons to support different types of tasks and body parts for different types of users, use cases, and environments.
There are exoskeletons that assist one or more of the following body parts: neck, shoulders, elbows, wrists, hands, fingers, back, hips, knees, ankles, and feet. Sometimes, rather than specify body parts, broader terms are used such as upper-body, lower-body, or full-body to describe an exoskeleton. There are exoskeletons designed to assist tasks or activities such as walking, running, jumping, standing, transitioning from sit-to-stand, ascending/descending stairs, bending, lifting, kneeling, holding tools, handling objects, maintaining posture, working overhead, carrying, gripping, balancing, throwing, and skiing. This list is not comprehensive, and new exoskeletons are continuously being developed to support new applications.

By structure

Structure refers to whether the overall construction of an exoskeleton is more rigid or softer. Exoskeletons with hard frames or composed primarily of rigid structures are generally referred to as rigid exoskeletons or traditional exoskeletons. Exoskeletons made primarily of soft structures are generally referred to as soft exoskeletons, also called exosuits, exo-suits, or soft-shell exoskeletons. Soft exosuits emerged as one way to try to overcome some practical challenges associated with rigid exoskeletons being cumbersome, causing discomfort, or interfering with freedom of movement. The term hybrid is occasionally used for devices that contain substantial sections composed primarily of rigid structures and separate substantial sections made primarily of soft structures. However, the term hybrid is typically used sparingly because, in reality, all exoskeletons comprise both rigid and soft components. However, for simplicity and conversational purposes, it is common to group exoskeletons into these structural categories of rigid or soft. These are colloquial categories, not formally defined.