Exoskeletons are a promising tool to support individuals with a decreased level of motor performance. Due to their built-in sensors, exoskeletons offer the possibility of continuously recording and assessing user data, for example, related to motor performance. The aim of this article is to provide an overview of studies that rely on using exoskeletons to measure motor performance. Therefore, we conducted a systematic literature review, following the PRISMA Statement guidelines. A total of 49 studies using lower limb exoskeletons for the assessment of human motor performance were included. Of these, 19 studies were validity studies, and six were reliability studies. We found 33 different exoskeletons; seven can be considered stationary, and 26 were mobile exoskeletons. The majority of the studies measured parameters such as range of motion, muscle strength, gait parameters, spasticity, and proprioception. We conclude that exoskeletons can be used to measure a wide range of motor performance parameters through built-in sensors, and seem to be more objective and specific than manual test procedures. However, since these parameters are usually estimated from built-in sensor data, the quality and specificity of an exoskeleton to assess certain motor performance parameters must be examined before an exoskeleton can be used, for example, in a research or clinical setting.

With increasing age, motor performance declines. This decline is associated with less favorable health outcomes such as impaired activities of daily living, reduced quality of life, or increased mortality. Through regular assessment of motor performance, changes over time can be monitored, and targeted therapeutic programs and interventions may be informed. This can ensure better individualization of any intervention approach (e.g. by considering the current motor performance status of a person) and thus potentially increase its effectiveness with regard to maintaining current performance status or delaying further decline. However, in older adults, motor performance assessment is time consuming and requires experienced examiners and specific equipment, amongst others. This is particularly not feasible in care facility/nursing home settings. Wearable robotic devices, such as exoskeletons, have the potential of being used to assess motor performance and provide assistance during physical activities and exercise training for older adults or individuals with mobility impairments, thereby potentially enhancing motor performance. In this manuscript, we aim to (1) provide a brief overview of age-related changes of motor performance, (2) summarize established clinical and laboratory test procedures for the assessment of motor performance, (3) discuss the possibilities of translating established test procedures into exoskeleton-based procedures, and (4) highlight the feasibility, technological requirements and prerequisites for the assessment of human motor performance using lower limb exoskeletons.

Exoskeleton devices may impose kinematic constraints on a user’s motion and affect their stability due to added mass and inertia, but also due to the simplified mechanical design. This study explores the impact of kinematic constraints imposed by exoskeletons on user gait, stability, and perceived discomfort. Specifically, it examines how the varying degrees of freedom (DoF) in an ankle exoskeleton influence these factors. The exoskeleton utilized in this study can be configured to allow one, two, or three DoF, thereby simulating different levels of mechanical complexity and kinematic compatibility. A pilot study was conducted with six participants walking on a straight path to evaluate these effects. The findings indicate that increasing DoF of the exoskeleton improves several criteria, including kinematics and stability. In particular, the transition from 1 DoF to 2 DoF yielded a larger improvement than the transition from 2 DoF to 3 DoF, although the 3 DoF configuration produced the best overall results. Higher DoF configurations also resulted in stability values that resemble more closely those of walking without the exoskeleton, despite the added weight. Subjective feedback from participants corroborated these results, indicating the lowest discomfort with the 3 DoF ankle exoskeleton.

Sensory-motor impairments due to age or neurological diseases can influence a person’s ability to maintain balance, and increase the risk of falls. Recently, wearable Control Moment Gyroscopes (CMGs) have proven to provide effective balance support. Here, we show a new design of a Series-Elastic Control Moment Gyroscope (SECMG) enhanced by an additional passive degree of freedom, namely a second, orthogonal gimbal that is supported by a (visco)elastic element. The design mainly aims to reject disturbances originating from human movement and render a low remaining impedance, as well as to provide more accurate torque sensing, based on angular deflection of the compliant element. Evaluation of the torque tracking performance with regards to a classic rigid Single-Gimbal Control Moment Gyroscope (SGCMG) showed that the device equally exceeds the bandwidth requirements for its application in human augmentation. However, characterization of our current compliant construction also revealed some backlash occluding the torque-deflection relation. In the future, the SECMG could be evaluated in experiments with humans, to validate its predicted low remaining impedance.

Ankle exoskeletons alter joint kinematics during walking, yet their effects on whole-body coordination remain unclear. This study investigated how ankle exoskeleton assistance influences the structure of motor variability and center-of-mass movement during steady-state walking. Twenty healthy adults walked on a treadmill at 1.1 m/s without the exoskeleton (noExo) and with active exoskeleton assistance (Exo). Whole-body kinematics were recorded. Variability was analyzed using the Uncontrolled Manifold (UCM) approach. Joint angle variability was decomposed into components that do not affect center-of-mass position (UCM_||) and components that do (UCM_⊥). Their ratio (UCM_ratio), reflecting the synergy stabilizing the center-of-mass, was calculated. Center-of-mass position was analyzed separately in three dimensions. Time-continuous differences across the gait cycle were evaluated using statistical parametric mapping. UCM_|| and UCM_ratio showed no significant differences between conditions. UCM_⊥ was higher with exoskeleton assistance over large portions of the gait cycle (0-80%, p = 0.001; 91-100%, p = 0.022). Center-of-mass movement in the mediolateral and anteroposterior directions did not differ between conditions, while small differences were observed in the vertical direction (higher in Exo at 23-31% and 75-84%, p = 0.037; lower at 48-54%, p = 0.042). Ankle exoskeleton assistance increased joint-level variability affecting center-of-mass movement, but overall center-of-mass control was preserved, with only small changes in vertical center-of-mass displacement. Healthy adults maintained whole-body coordination despite altered mechanical conditions introduced by the exoskeleton. These findings are relevant for clinical exoskeleton use, where assistive devices should support walking without compromising center-of-mass control and balance.

Background: Ankle exoskeletons alter joint kinematics during walking, yet their effects on the whole-body coordination remain unclear. This study investigated how ankle exoskeleton assistance influences the structure of motor variability and center of mass (COM) movement during steady-state walking.Methods: Twenty healthy adults walked on a treadmill at 1.1 m/s with (Exo) and without (noExo) ankle exoskeleton assistance. Whole-body kinematics were recorded, and variability was analyzed using the Uncontrolled Manifold (UCM) approach. Joint angle variability was decomposed into components that do not affect COM position (UCM||) and components that do (UCM⊥). Their ratio (UCMratio), reflecting the synergy stabilizing the COM, was then calculated. COM position was additionally analyzed separately in three dimensions. Time-continuous differences across the gait cycle were evaluated using statistical parametric mapping.Results: UCM|| and UCMratio showed no significant differences between conditions. In contrast, UCM⊥ was higher with exoskeleton assistance over large portions of the gait cycle (0–80%, p = 0.001; 91–100%, p = 0.022). COM movement in the mediolateral and anteroposterior directions did not differ between conditions, while small differences were observed in the vertical direction (higher in Exo at 23–31% and 75–84%, p = 0.037; lower at 48–54%, p = 0.042).Conclusion: These findings indicate that ankle exoskeleton assistance increases variability affecting COM movement without changing the synergy stabilizing the COM. Task-level motor coordination was preserved, suggesting that control of the COM is maintained despite altered mechanical conditions associated with ankle exoskeleton assistance.