Current State, Needs, and Opportunities for Wearable Robots in Military Medical Rehabilitation and Force Protection.

Despite advances in wearable robots across various fields, there is no consensus definition or design framework for the application of this technology in rehabilitation or musculoskeletal (MSK) injury prevention. This paper aims to define wearable robots and explore their applications and challenges for military rehabilitation and force protection for MSK injury prevention. We conducted a modified Delphi method, including a steering group and 14 panelists with 10+ years of expertise in wearable robots. Panelists presented current wearable robots currently in use or in development for rehabilitation or assistance use in the military workforce and healthcare. The steering group and panelists met to obtain a consensus on the wearable robot definition applicable for rehabilitation or primary injury prevention. Panelists unanimously agreed that wearable robots can be grouped into three main applications, as follows: (1) primary and secondary MSK injury prevention, (2) enhancement of military activities and tasks, and (3) rehabilitation and reintegration. Each application was presented within the context of its target population and state-of-the-art technology currently in use or under development. Capturing expert opinions, this study defines wearable robots for military rehabilitation and MSK injury prevention, identifies health outcomes and assessment tools, and outlines design requirements for future advancements.

Design and Development of a Powered Myoelectric Elbow Orthosis for Neuromuscular Injuries.

INTRODUCTION: Recovering from neuromuscular injuries or conditions can be a challenging journey that involves complex surgeries and extensive physical rehabilitation. During this process, individuals often rely on orthotic devices to support and enable movement of the affected limb. However, users have criticized current commercially available powered orthotic devices for their bulky and heavy design. To address these limitations, we developed a novel powered myoelectric elbow orthosis. MATERIALS AND METHODS: The orthosis incorporates 3 mechanisms: a solenoid brake, a Bowden cable-powered constant torque elbow mechanism, and an extension limiter. The device controller and battery are in a backpack to reduce the weight on the affected arm. We performed extensive calculations and testing to ensure that the orthosis could withstand at least 15 Nm of elbow torque. We developed a custom software effectively control the orthosis, enhancing its usability and functionality. A certified orthotist fitted a subject who had undergone a gracilis free functioning muscle transfer surgery with the device. We studied the subject under Mayo clinic IRB no. 20-006849 and obtained objective measurements to assess the orthosis's impact on upper extremity functionality during daily activities. RESULTS: The results are promising since the orthosis significantly improved elbow flexion range of motion by 40° and reduced compensatory movements at the shoulder (humerothoracic joint) by 50°. Additionally, the subject was able to perform tasks which were not possible before, such as carrying a basket with weights, highlighting the enhanced functionality provided by the orthosis. CONCLUSION: In brief, by addressing the limitations of existing devices, this novel powered myoelectric elbow orthosis offers individuals with neuromuscular injuries/conditions improved quality of life. Further research will expand the patient population and control mechanisms.

Reduced trunk movement control during motor dual-tasking in older adults.

Older adults have a decreased trunk movement control which is linked to their higher fall risk. While motor/cognitive dual-tasking deteriorates balance and walking in older adults, there is limited understanding on how trunk kinematics and kinetics are affected by dual-tasking in scenarios where falls can occur. Therefore, the purpose of the study was to determine the impacts of a challenging motor dual-task, specifically obstacle avoidance during walking, on trunk and lower-body kinematics and kinetics of older adults compared to young adults. The study captured three-dimensional kinematic and kinetic data from 12 young adults and 10 older adults as they walked on a treadmill and stepped over an obstacle with both legs. The study analyzed trunk, hip, knee, and ankle angles and torques. Trunk torque was further broken down to trunk muscle torque, gravitational torque, and inertia torque. A linear mixed effects model was used to investigate the difference in each variable between the two groups. Older adults exhibited significantly increased trunk flexion angle and trunk extension muscle torque compared to young adults, with the trunk being the only segment/joint showing differences in both kinematics and kinetics. Trunk torque breakdown analysis revealed that larger trunk flexion led to a larger gravitational torque, which contributed to an increased compensatory trunk muscle torque. Moreover, older adults' less controlled trunk flexion during weight shifting from trail leg to the lead leg, necessitated a compensatory trunk deceleration during trail leg obstacle avoidance which was achieved by generating additional increase in trunk muscle torque. The study demonstrated that motor dual-tasking has the most negative effects on trunk control in older adults compared to young adults. This exposes older adults to a higher fall risk. Therefore, future work should focus on supporting trunk control during daily multi-tasking conditions where falls can occur.

Multi-tasking deteriorates trunk movement control during and after obstacle avoidance.

Dynamic and cognitive multi-tasking might affect balance and walking negatively and increase risk of falling. Trunk movement control is critical for balance maintenance and fall-prevention. The impact of multi-tasking on trunk movement control has not been thoroughly studied. In a challenging dynamic multi-tasking condition such as walking and obstacle avoidance, presence of a cognitive task not only increases risk of tripping but also may increase risk of falling by deteriorating trunk control. Our objective was to investigate the impacts of a challenging dynamic and cognitive multi-tasking condition (walking + obstacle avoidance + cognitive task) on trunk kinematics and kinetics and compare those with other joints/segments. Trunk, pelvis, hip, knee, and ankle kinematics and kinetics of 12 young adults were compared between joints/segments and conditions. During walking and obstacle avoidance (dynamic multi-tasking), the trunk had the largest normalized increase in peak flexion angle and extension torque compared to walking, among the other joints/segments. The presence of a cognitive task during walking and obstacle avoidance (dynamic and cognitive multi-tasking) did not impact any of the joints/segments biomechanics except the trunk peak extension torque that was increased. Furthermore, trunk kinematics showed the largest residual differences (post-effects) in 3 cycles after obstacle avoidance compared to walking. The presence of a cognitive task (dynamic and cognitive multi-tasking) did not impact the post-effects of obstacle avoidance on any joints/segments except the trunk with its residual difference from normal walking further increased. These results suggest that a cognitive task deteriorates trunk control and interferes with the ability to regain normal trunk biomechanics after obstacle avoidance. In summary, the trunk requires the largest biomechanical adjustments in a challenging dynamic and cognitive multi-tasking condition where there is a risk of falling. Our study provides baseline results suggesting that trunk control demands more attention and is more negatively affected by dynamic and cognitive multi-tasking. Our results raise a concern for elderly population as their trunk control is already impaired and common daily multi-tasking could further deteriorate their trunk control and increase fall risk.

Development and testing of the aerial porter exoskeleton.

Back pain is one of the largest drivers of workplace injury and lost productivity in industries around the world. Back injuries were one of the leading reasons in resulting in days away from work at 38.5% across all occupations, increasing for manual laborers to 43%. While the cause of the back pain can vary across occupations, for materiel movers it is often caused from repetitive poor lifting. To reduce the issues, the Aerial Porter Exoskeleton (APEx) was created. The APEx uses a hip-mounted, powered exoskeleton attached to an adjustable vest. An onboard computer calculates the configuration of the user to determine when to activate. Lift form is assisted by using a novel lumbar brace mounted on the sides of the hips. Properly worn, the APEx holds the user upright while providing additional hip torque through a lift. This was tested by having participants complete a lifting test with the exoskeleton worn in the "on" configuration compared with the exoskeleton not worn. The APEx has been shown to deliver 30 Nm of torque in lab testing. The activity recognition algorithm has also been shown to be accurate in 95% of tested conditions. When worn by subjects, testing has shown average peak reductions of 14.9% BPM, 8% in VO2 consumption, and an 8% change in perceived effort favoring the APEx.

Anticipatory muscle responses in transitions from rigid to compliant surfaces: towards smart ankle-foot prostheses.

Locomotion is paramount in enabling human beings to effectively respond in space and time to meet different needs. There are 2 million Americans living with an amputation and the majority of those amputations are of the lower limbs. Although current powered prostheses can accommodate walking, and in some cases running, basic functions like hiking or walking on various non-rigid or dynamic terrains are requirements that have yet to be met. This paper focuses on the mechanisms involved during human locomotion, while transitioning from rigid to compliant surfaces such as from pavement to sand, grass or granular media. Utilizing a unique tool, the Variable Stiffness Treadmill (VST), as the platform for human locomotion, rigid to compliant surface transitions are simulated. The analysis of muscular activation during the transition from rigid to compliant surfaces reveals specific anticipatory muscle activation that precedes stepping on the compliant surface. These results are novel and important since the evoked activation changes can be used for altering the powered prosthesis control parameters to adapt to the new surface, and therefore result in significantly increased robustness for smart powered lower limb prostheses.

Design, Development, and Control of a Fabric-Based Soft Ankle Module to Mimic Human Ankle Stiffness.

This paper investigates the design of a robotic fabric-based, soft ankle module capable of generating 50% of the human ankle stiffness, in plantarflexion and dorsiflexion for walking. Kinematics, dynamics, and anatomy of the human ankle joint are studied to set the functional requirements of the module. The design of the compliant and lightweight soft ankle module uses fabric-based inflatable actuator arrays for actuation. Models for the human ankle stiffness, as well as a data-driven model of soft ankle module is presented. A high-level stiffness controller utilizing the human ankle and soft ankle model with a low-level pressure controller is implemented. We demonstrate the ability to closely follow the ankle stiffness trajectory using soft ankle module.

A powered prosthetic ankle joint for walking and running.

BACKGROUND: Current prosthetic ankle joints are designed either for walking or for running. In order to mimic the capabilities of an able-bodied, a powered prosthetic ankle for walking and running was designed. A powered system has the potential to reduce the limitations in range of motion and positive work output of passive walking and running feet. METHODS: To perform the experiments a controller capable of transitions between standing, walking, and running with speed adaptations was developed. In the first case study the system was mounted on an ankle bypass in parallel with the foot of a non-amputee subject. By this method the functionality of hardware and controller was proven. RESULTS: The Walk-Run ankle was capable of mimicking desired torque and angle trajectories in walking and running up to 2.6 m/s. At 4 m/s running, ankle angle could be matched while ankle torque could not. Limited ankle output power resulting from a suboptimal spring stiffness value was identified as a main reason. CONCLUSIONS: Further studies have to show to what extent the findings can be transferred to amputees.

Optical angular constancy is maintained as a navigational control strategy when pursuing robots moving along complex pathways.

The optical navigational control strategy used to intercept moving targets was explored using a real-world object that travels along complex, evasive pathways. Fielders ran across a gymnasium attempting to catch a moving robot that varied in speed and direction, while ongoing position was measured using an infrared motion-capture system. Fielder running paths were compared with the predictions of three lateral control models, each based on maintaining a particular optical angle relative to the robotic target: (a) constant alignment angle (CAA), (b) constant eccentricity angle (CEA), and (c) linear optical trajectory (LOT). Findings reveal that running pathways were most consistent with maintenance of LOT and least consistent with CEA. This supports that fielders use the same optical control strategy of maintaining angular constancy using a LOT when navigating toward targets moving along complex pathways as when intercepting simple ballistic trajectories. In those cases in which a target dramatically deviates from its optical path, fielders appear to simply reset LOT parameters using a new constant angle value. Maintenance of such optical angular constancy has now been shown to work well with ballistic, complex, and evasive moving targets, confirming the LOT strategy as a robust, general-purpose optical control mechanism for navigating to intercept catchable targets, both airborne and ground based.

Navigational strategy used to intercept fly balls under real-world conditions with moving visual background fields.

This study explored the navigational strategy used to intercept fly balls in a real-world environment under conditions with moving visual background fields. Fielders ran across a gymnasium attempting to catch fly balls that varied in distance and direction. During each trial, the launched balls traveled in front of a moving background texture that was projected onto an entire wall of a gymnasium. The background texture consisted of a field of random dots that moved together, at a constant speed and direction that varied between trials. The fielder route deviation was defined as the signed area swept out between the actual running path and a straight-line path to the destination, and these route deviation values were compared as a function of the background motion conditions. The findings confirmed that the moving visual background fields systematically altered the fielder running paths, which curved more forward and then to the side when the background gradient moved laterally with the ball, and curved more to the side and then forward when the background gradient moved opposite the ball. Fielder running paths deviated systematically, in a manner consistent with the use of a geometric optical control strategy that helps guide real-world perception-action tasks of interception, such as catching balls.

Gaze anticipation during human locomotion.

During locomotion, a top-down organization has been previously demonstrated with the head as a stabilized platform and gaze anticipating the horizontal direction of the trajectory. However, the quantitative assessment of the anticipatory sequence from gaze to trajectory and body segments has not been documented. The present paper provides a detailed investigation into the spatial and temporal anticipatory relationships among the direction of gaze and body segments during locomotion. Participants had to walk along several mentally simulated complex trajectories, without any visual cues indicating the trajectory to follow. The trajectory shapes were presented to the participants on a sheet of paper. Our study includes an analysis of the relationships between horizontal gaze anticipatory behavior direction and the upcoming changes in the trajectory. Our findings confirm the following: 1) The hierarchical ordered organization of gaze and body segment orientations during complex trajectories and free locomotion. Gaze direction anticipates the head orientation, and head orientation anticipates reorientation of the other body segments. 2) The influence of the curvature of the trajectory and constraints of the tasks on the temporal and spatial relationships between gaze and the body segments: Increased curvature resulted in increased time and spatial anticipation. 3) A different sequence of gaze movements at inflection points where gaze plans a much later segment of the trajectory.

Stroke Survivors' Gait Adaptations to a Powered Ankle Foot Orthosis.

BACKGROUND AND PURPOSE: Stroke is the leading cause of long term disability in the United States, and for many it causes loss of gait function. The purpose of this research is to examine stroke survivors' gait adaptations to training on the Powered Ankle Foot Orthosis (PAFO). Of particular interest is the stroke survivors' ability to learn how to store and release energy properly while using the device. The PAFO utilizes robotic tendon technology and supports motion with a single degree of freedom, ankle rotation in the sagittal plane. This actuator comprises a motor and series spring. The user interacts with the output side of the spring while the robot controls the input side of the spring such that typical able body ankle moments would be generated, assuming able body ankle kinematics are seen at the output side of the spring. METHODS: Three individuals post-stroke participated in a three week training protocol. Outcome measures (temporal, kinematic, and kinetic) were derived from robot sensors and recorded for every step. These data are used to evaluate each stroke survivor's adaptations to robotic gait assistance. The robot was worn only on the paretic ankle. For validation of the kinematic results, motion capture data were collected on the third subject. RESULTS: All subjects showed increased cadence, ankle range of motion, and power generation capabilities. Additionally, all subjects were able to achieve a larger power output than power input from the robot. Motion capture data collected from subject three validated the robot sensor kinematic data on the affected side, but also demonstrated an unexpected gait adaptation on the unaffected ankle. CONCLUSIONS: Sensors on the gait assisting robot provide large volumes of valuable information on how gait parameters change over time. We have developed key gait evaluation metrics based on the available robot sensor information that may be useful to future researchers. All subjects adapted their gait to the robotic assistance, and many of their key metrics moved closer to typical able body values. This suggests that each subject learned to utilize the assistive moments generated by the robot, despite having no predefined ankle trajectory input from the robot. The security of being harnessed on the treadmill led to more dramatic and favorable results.

Evidence for axis-aligned motion bias: football axis-trajectory misalignment causes systematic error in projected final destinations of thrown American footballs.

The axis-aligned motion (AAM) bias is the tendency of observers to assume that symmetric moving objects maintain axis-trajectory alignment and to bias their judgments of trajectory toward the axis when they are misaligned. We tested whether humans exhibit an AAM bias in a realistic, cue-rich, 3-D setting by examining the impact of axis-trajectory misalignment on estimates of final destinations of thrown American footballs. In experiments 1 and 2 we show that observers are significantly worse in judging destinations of footballs than those of volleyballs and basketballs. This difference in performance is due to the deviation of the football's axis from trajectory in flight, as shown by the correspondence of participants' lateral judgment error and the football's lateral axial deviation from trajectory, which was predicted by passer handedness. Nearly all animals exhibit bilateral symmetry and maintain axis-trajectory alignment during locomotion, and we argue that the AAM bias is complementary mental attunement to the natural regularity of this axis-aligned motion. Furthermore, this bias is also a prototypical example of a perceptual regularity that is a mixed blessing-advantageous in perceptual judgment tasks of axis trajectory-aligned moving entities like most living creatures, and disadvantageous in tasks demanding judgments of axis-trajectory-misaligned moving objects which are typically artifacts.

Evidence for a generic interceptive strategy.

In the present work, we first clarify a more precise definition of instantaneous optical angles in control tasks such as interception. We then test how well two interceptive strategies that have been proposed for catching fly balls account for human Frisbee-catching behavior. The first strategy is to maintain the ball's image along a linear optical trajectory (LOT). The second is to keep vertical optical ball velocity decreasing while maintaining constant lateral optical velocity. We found that an LOT accounted for an average of over 96% of the variance in optical Frisbee movement, while maintenance of vertical and lateral optical velocities was random. This work confirms a common interception strategy used across interceptive tasks, extending to complex target trajectories.

Design and control of RUPERT: a device for robotic upper extremity repetitive therapy.

The structural design, control system, and integrated biofeedback for a wearable exoskeletal robot for upper extremity stroke rehabilitation are presented. Assisted with clinical evaluation, designers, engineers, and scientists have built a device for robotic assisted upper extremity repetitive therapy (RUPERT). Intense, repetitive physical rehabilitation has been shown to be beneficial overcoming upper extremity deficits, but the therapy is labor intensive and expensive and difficult to evaluate quantitatively and objectively. The RUPERT is developed to provide a low cost, safe and easy-to-use, robotic-device to assist the patient and therapist to achieve more systematic therapy at home or in the clinic. The RUPERT has four actuated degrees-of-freedom driven by compliant and safe pneumatic muscles (PMs) on the shoulder, elbow, and wrist. They are programmed to actuate the device to extend the arm and move the arm in 3-D space. It is very important to note that gravity is not compensated and the daily tasks are practiced in a natural setting. Because the device is wearable and lightweight to increase portability, it can be worn standing or sitting providing therapy tasks that better mimic activities of daily living. The sensors feed back position and force information for quantitative evaluation of task performance. The device can also provide real-time, objective assessment of functional improvement. We have tested the device on stroke survivors performing two critical activities of daily living (ADL): reaching out and self feeding. The future improvement of the device involves increased degrees-of-freedom and interactive control to adapt to a user's physical conditions.

An efficient robotic tendon for gait assistance.

A robotic tendon is a spring based, linear actuator in which the stiffness of the spring is crucial for its successful use in a lightweight, energy efficient, powered ankle orthosis. Like its human analog, the robotic tendon uses its inherent elastic nature to reduce both peak power and energy requirements for its motor. In the ideal example, peak power required of the motor for ankle gait is reduced from 250 W to just 77 W. In addition, ideal energy requirements are reduced from nearly 36 J to just 21 J. Using this approach, an initial prototype has provided 100% of the power and energy necessary for ankle gait in a compact 0.95 kg package, seven times less than an equivalent motor/gearbox system.

A unified fielder theory for interception of moving objects either above or below the horizon.

A unified fielder theory is presented that explains how humans navigate to intercept targets that approach from either above or below the horizon. Despite vastly different physical forces affecting airborne and ground-based moving targets, a common set of invariant perception-action principles appears to guide pursuers. When intercepting airborne projectiles, fielders keep the target image rising at a constant optical speed in a vertical image plane and moving in a constantoptical direction in an image plane that remains perpendicular to gaze direction. We confirm that fielders use the same strategies to intercept grounders. Fielders maintained a cotangent of gaze angle that decreases linearly with time (accounting for 98.7% of variance in ball speed) and a linear optical trajectory along an image plane that remains perpendicular to gaze direction (accounting for 98.2% of variance in ball position). The universality of maintaining optical speed and direction for both airborne and ground-based targets supports the theory that these mechanisms are domain independent.

The Galileo bias: a naive conceptual belief that influences people's perceptions and performance in a ball-dropping task.

This research introduces a new naive physics belief, the Galileo bias, whereby people ignore air resistance and falsely believe that all objects fall at the same rate. Survey results revealed that this bias is held by many and is surprisingly strongest for those with formal physics instruction. In 2 experiments, 98 participants dropped ball pairs varying in volume and/or mass from a height of 10 m, with the goal of both balls hitting the ground simultaneously. The majority of participants in both experiments adopted a single strategy consistent with the Galileo bias, showing no improvement across trials. Yet, for participants reporting intentions of dropping both balls at the same time, the differences between release points were significantly greater than 0 ms. These findings support separate but interacting cognition and perception-action systems.

Design of a robotic gait trainer using spring over muscle actuators for ankle stroke rehabilitation.

Repetitive task training is an effective form of rehabilitation for people suffering from debilitating injuries of stroke. We present the design and working concept of a robotic gait trainer (RGT), an ankle rehabilitation device for assisting stroke patients during gait. Structurally based on a tripod mechanism, the device is a parallel robot that incorporates two pneumatically powered, double-acting, compliant, spring over muscle actuators as actuation links which move the ankle in dorsiflex ion/plantarflexion and inversion/eversion. A unique feature in the tripod design is that the human anatomy is part of the robot, the first fixed link being the patient's leg. The kinematics and workspace of the tripod device have been analyzed determining its range of motion. Experimental gait data from an able-bodied person wearing the working RGT prototype are presented.

Spring over muscle (SOM) actuator for rehabilitation devices.

For people affected by stroke, frequent physical therapy has been shown to be an effective form of rehabilitation. To this goal, several home therapy devices have been developed. Many of these devices may benefit from the use of a bidirectional pneumatic muscle actuator. This work presents the concept and design of the double-acting, compliant, spring over muscle (SOM) actuator. The principle design uses a spring in parallel with a pneumatic muscle actuator. This concept is economical, and easily scalable. Additionally, a design proposal for an ankle rehabilitation device, which incorporates the SOM actuator, is discussed.