What Are Exoskeletons?

Exoskeletons are wearable mechanical or electromechanical structures that are worn on the outside of the body to augment, assist, or restore human movement. In engineering terms, they are human-machine systems that transmit forces and torques between an external frame and the wearer's musculoskeletal structure, either to amplify the forces the user can produce or to guide and support movement when neuromuscular function is impaired. The field draws on robotics, biomechanics, control engineering, and materials science, with clinical applications in rehabilitation medicine and industrial applications in load-bearing and fatigue reduction.

Exoskeletons are distinguished from prosthetic devices by the fact that they are worn alongside an intact, though possibly impaired, limb rather than replacing a missing one. This distinction affects both the mechanical design, which must accommodate the residual anatomy, and the control strategy, which can incorporate voluntary effort from the user.

Structural Design

Exoskeleton frames fall into two broad categories: rigid and soft. Rigid exoskeletons use articulated metal or carbon fiber links aligned with the body's skeletal joints, driven by electric motors, hydraulic actuators, or pneumatic systems. They can deliver high joint torques suitable for patients with severe paralysis or for industrial strength amplification, but their mass and rigidity require careful joint alignment with the wearer's anatomy to avoid discomfort and injury.

Soft exoskeletons, sometimes called exosuits, use textile structures, cables, and compliant actuators to transmit assistive forces without a rigid frame. They are lighter and more comfortable but are limited in the peak torque they can provide, making them better suited to individuals with mild-to-moderate deficits or to fatigue-reduction applications rather than full weight-bearing support. A 2025 review of wearable technologies for assisted mobility surveys both approaches across lower-limb, upper-limb, and full-body configurations and discusses how device selection depends on the target user population and functional goals.

Control Systems and Intent Detection

The control architecture of an exoskeleton must interpret the user's intended motion and respond with appropriate assistive forces in real time. Control strategies range from simple position-based trajectory following, where the device imposes a pre-programmed gait pattern, to impedance control and admittance control schemes that respond to forces the user applies to the exoskeleton frame.

Biosignal-based control uses electromyography (EMG) signals from residual muscles or electroencephalography (EEG) signals from the motor cortex to infer the user's intent before mechanical motion begins, enabling more natural interaction. Research on AI-based upper limb exoskeletons published in PMC demonstrates that artificial neural networks and adaptive algorithms are the most commonly employed AI approaches for intent detection, with neural networks appearing in approximately 40 percent of reviewed systems. Deep learning models have achieved upper-limb joint motion prediction accuracies exceeding 96 percent in research settings, though clinical robustness and real-world validation remain active challenges.

Clinical and Rehabilitation Applications

In rehabilitation, exoskeletons enable intensive, task-specific training that would otherwise require substantial therapist effort. For stroke and spinal cord injury patients, repetitive gait training with an exoskeleton exploits neuroplasticity to promote motor recovery. Devices such as the Lokomat, EksoGT, and Indego support hip and knee motion during overground walking, providing programmable levels of assistance that decrease as patient capacity improves. Upper-limb systems address arm and hand rehabilitation after stroke, traumatic brain injury, or orthopedic surgery.

In industrial settings, passive and powered back-support exoskeletons reduce compressive spinal loading during heavy lifting and sustained forward-leaning postures, targeting the reduction of work-related musculoskeletal injury. The MSKTC fact sheet on robotic exoskeletons for spinal cord injury summarizes clinical evidence on overground walking outcomes and the practical considerations for device selection in rehabilitation practice.

Applications

Exoskeletons have applications in a range of fields, including:

• Neurological rehabilitation for stroke, spinal cord injury, and multiple sclerosis
• Overground walking assistance for mobility-impaired individuals
• Industrial ergonomic support and fatigue reduction
• Military load-carrying and endurance augmentation
• Physical therapy and motor learning research