Treadmill-Based Locomotor Training With Robotic Pelvic Assist and Visual Feedback: A Feasibility Study.

BACKGROUND AND PURPOSE: Gait asymmetries are common after stroke, and often persist despite conventional rehabilitation. Robots provide training at a greater practice frequency than conventional approaches. However, prior studies of have found the transfer of learned skills outside of the device to be inadequate. The tethered pelvic assist device (TPAD) promotes weight shifting, yet allows users to independently navigate spatiotemporal aspects of gait. The purpose of this study was to evaluate feasibility and preliminary efficacy of a 5-day intervention combining TPAD training with visual feedback and task-specific overground training to promote improved force and stance symmetry in individuals after stroke. METHODS: After baseline assessments, 11 participants chronically after stroke received 1 hour of practice for 5 consecutive days. Training sessions included visual feedback during TPAD treadmill training followed by overground gait training. Safety, perceived exertion, and adherence were recorded as measures of feasibility. Load and stance symmetry were reassessed after the intervention (posttraining) and again 1 week later. RESULTS: No adverse events were reported. Mean (SD) perceived exertion (3.61 (0.23)) was low and did not significantly change throughout the intervention. Overall adherence was 96.4%. Load asymmetry was not significantly reduced on the treadmill from baseline to posttraining (P = 0.075). Overground stance symmetry significantly improved on posttraining (F = 8.498, P = 0.002), but was not sustained at follow-up. (See the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A311, which summarizes the study background, methods, and results.) DISCUSSION AND CONCLUSIONS:: Results demonstrate this combined interventional approach was feasible and improved stance symmetry overground, yet further work should consider increasing training intensity and/or duration to induce gains lasting through follow-up.

The effect of transcutaneous spinal cord stimulation on the balance and neurophysiological characteristics of young healthy adults.

Transcutaneous spinal cord stimulation (TSCS) is gaining popularity as a noninvasive alternative to epidural stimulation. However, there is still much to learn about its effects and utility in assisting recovery of motor control. In this study, we applied TSCS to healthy subjects concurrently performing a functional training task to study its effects during a training intervention. We first carried out neurophysiological tests to characterize the H-reflex, H-reflex recovery, and posterior root muscle reflex thresholds, and then conducted balance tests, first without TSCS and then with TSCS. Balance tests included trunk perturbations in forward, backward, left, and right directions, and subjects' balance was characterized by their response to force perturbations. A balance training task involved the subjects playing a catch-and-throw game in virtual reality (VR) while receiving trunk perturbations and TSCS. Balance tests with and without TSCS were conducted after the VR training to measure subjects' post-training balance characteristics and then neurophysiological tests were carried out again. Statistical comparisons using t-tests between the balance and neurophysiological data collected before and after the VR training intervention found that the immediate effect of TSCS was to increase muscle activity during forward perturbations and to reduce balance performance in that direction. Muscle activity decreased after training and even more once TSCS was turned off. We thus observed an interaction of effects where TSCS increased muscle activity while the physical training decreased it.

Robotic Postural Training With Epidural Stimulation for the Recovery of Upright Postural Control in Individuals With Motor Complete Spinal Cord Injury: A Pilot Study.

Activity-based training and lumbosacral spinal cord epidural stimulation (scES) have the potential to restore standing and walking with self-balance assistance after motor complete spinal cord injury (SCI). However, improvements in upright postural control have not previously been addressed in this population. Here, we implemented a novel robotic postural training with scES, performed with free hands, to restore upright postural control in individuals with chronic, cervical (n = 5) or high-thoracic (n = 1) motor complete SCI, who had previously undergone stand training with scES using a walker or a standing frame for self-balance assistance. Robotic postural training re-enabled and/or largely improved the participants' ability to control steady standing, self-initiated trunk movements and upper limb reaching movements while standing with free hands, receiving only external assistance for pelvic control. These improvements were associated with neuromuscular activation pattern adaptations above and below the lesion. These findings suggest that the human spinal cord below the level of injury can generate meaningful postural responses when its excitability is modulated by scES, and can learn to improve these responses. Upright postural control improvements can enhance functional motor recovery promoted by scES after severe SCI.

Effects of Boundary-Based Assist-as-Needed Force Field on Lower Limb Muscle Synergies During Standing Posture Training.

The boundary-based assist-as-needed (BAAN) force field is widely used in robotic rehabilitation and has shown promising results in improving trunk control and postural stability. However, the fundamental understanding of how the BAAN force field affects the neuromuscular control remains unclear. In this study, we investigate how the BAAN force field impacts muscle synergy in the lower limbs during standing posture training. We integrated virtual reality (VR) into a cable-driven Robotic Upright Stand Trainer (RobUST) to define a complex standing task that requires both reactive and voluntary dynamic postural control. Ten healthy subjects were randomly assigned to two groups. Each subject performed 100 trials of the standing task with or without assistance from the BAAN force field provided by RobUST. The BAAN force field significantly improved balance control and motor task performance. Our results also indicate that the BAAN force field reduced the total number of lower limb muscle synergies while concurrently increasing the synergy density (i.e., number of muscles recruited in each synergy) during both reactive and voluntary dynamic posture training. This pilot study provides fundamental insights into understanding the neuromuscular basis of the BAAN robotic rehabilitation strategy and its potential for clinical applications. In addition, we expanded the repertoire of training with RobUST that integrates both perturbation training and goal-oriented functional motor training within a single task. This approach can be extended to other rehabilitation robots and training approaches with them.

Training Postural Balance Control with Pelvic Force Field at the Boundary of Stability.

This study characterizes the effects of a postural training program on balance and muscle control strategies in a virtual reality (VR) environment. The Robotic Upright Stand Trainer (RobUST), which applies perturbative forces on the trunk and assistive forces on the pelvis, was used to deliver perturbation-based balance training (PBT) in a sample of 10 healthy participants. The VR task consisted of catching, aiming, and throwing a ball at a target. All participants received trunk perturbations during the VR task with forces tailored to the participant's maximum tolerance. A subgroup of these participants additionally received assistive forces at the pelvis during training. Postural kinematics were calculated before and after RobUST training, including (i) maximum perturbation force tolerated, (ii) center of pressure (COP) and pelvic excursions, (iii) postural muscle activations (EMG), and (iv) postural control strategies (the ankle and hip strategies). We observed an improvement in the maximum perturbation force and postural stability area in both groups and decreases in muscle activity. The behavior of the two groups differed for perturbations in the posterior direction where the unassisted group moved towards greater use of the hip strategy. In addition, the assisted group changed towards a lower margin of stability and higher pelvic excursion. We show that training with force assistance leads to a reactive balance strategy that permits pelvic excursion but that is efficient at restoring balance from displaced positions while training without assistance leads to reactive balance strategies that restrain pelvic excursion. Patient populations can benefit from a platform that encourages greater use of their range of motion.

Robotic upright stand trainer (RobUST) and postural control in individuals with spinal cord injury.

CONTEXT/OBJECTIVE: Assessed feasibility and potential effectiveness of using a novel robotic upright stand trainer (RobUST) to deliver postural perturbations or provide assistance-as-needed at the trunk while individuals with spinal cord injury (SCI) performed stable standing and self-initiated trunk movements. These tasks were assessed with research participants' hands on handlebars for self-balance assistance (hands on) and with hands off (free hands). DESIGN: Proof of concept study. PARTICIPANTS: Four individuals with motor complete (n = 3) or incomplete (n = 1) SCI who were not able to achieve independent standing and presented a neurological lesion level ranging from cervical 4 to thoracic 2. OUTCOME MEASURES: Ground reaction forces, trunk displacement, and electromyography activity of trunk and lower limb muscles. RESULTS: Research participants received continuous pelvic assistance via RobUST, and manual trainer assistance at the knees to maintain standing. Participants were able to attempt all tasks. Free hands trunk perturbations resulted in greater load bearing-related sensory information (73% ipsilateral vertical loading), trunk displacement (57%), and muscle activation compared to hands on. Similarly, free hands stable standing with RobUST assistance-as-needed resulted in 8.5% larger bodyweight bearing, 112% larger trunk movement velocity, and higher trunk muscles activation compared to standing with hands on. Self-initiated trunk movements controlled by hands on showed 116% greater trunk displacement, 10% greater vertical ground reaction force, and greater ankle muscle activation compared to free hands. CONCLUSION: RobUST established a safe and challenging standing environment for individuals with SCI and has the potential to improve training paradigms and assessments of standing postural control.

Postural Control Strategies in Standing With Handrail Support and Active Assistance From Robotic Upright Stand Trainer (RobUST).

In people with severe neuromotor deficits of trunk and lower extremities, regaining balance in standing is often performed in rehabilitation with manual assistance, rigid body supports or by the use of handrails. To investigate and further expand postural control training in standing, we developed a Robotic Upright Stand Trainer (RobUST). In this study, we used RobUST to deliver trunk perturbations while simultaneously providing postural assistive forces on the pelvis in 10 able-bodied adults. Posture control responses with 'pelvic support' was then compared to 'no support' and 'hand supported' standing, with and without assistance from RobUST. We characterize postural imbalance with kinematic displacements and center of pressure (COP) outcomes, such as amplitude and root mean square of the excursions of COP. Surface electromyography (sEMG) was also applied to investigate muscle control. We additionally investigated ground reaction and handrail forces during standing to analyze how postural strategies and muscle mechanisms with 'pelvic support' via RobUST would differ from standing with 'no support' and with the 'handrail support'. Our results show that during perturbations, pelvic assistive support decreased kinematic and COP excursions compared to standing with no support. The pelvic assistance from RobUST showed similar level of COP changes as the use of handrail support but without reducing muscle activity or ground reaction forces. As expected, the maximum level of postural stability was observed when participants used the handrail and received pelvic assistive forces. In conclusion, RobUST demonstrates potential as a training device since it enhances postural balance without significantly removing muscular control mechanisms that are of interest in re-training postural control strategies in standing.

Stand Trainer With Applied Forces at the Pelvis and Trunk: Response to Perturbations and Assist-As-Needed Support.

Functional rehabilitation of patients with spinal cord injury remains a current challenge. Training these patients to successfully stand is the first step towards restoring advanced skills such as walking. To address this need, we have developed a novel robotic stand trainer that can apply controlled forces on the trunk and the pelvis of a user, while controlling the knee angle. The stand trainer utilizes cables to apply assistive, resistive, or perturbation forces at the trunk, pelvis, and the knees, simultaneously. We have conducted a human study to validate the system. In this study, we applied multi-direction perturbation forces either at the pelvis or the trunk while assist-as-needed forces were applied to the other segment to keep balance. This study characterizes the human kinematics and measures of balance under the perturbations and assistive forces on the human body. Results shows that the level of force-field assistance (trunk or pelvis) directly affects the motion of the trunk, pelvis, and center of pressure. This provides a quantitative framework to restore balance in patients while providing assistance only when needed. This stand trainer can potentially free up therapists to attend to higher level rehabilitation goals and objectively assist patients to engage in interventions that challenge both their musculoskeletal and sensorimotor impairments.

Capture, learning, and classification of upper extremity movement primitives in healthy controls and stroke patients.

There currently exist no practical tools to identify functional movements in the upper extremities (UEs). This absence has limited the precise therapeutic dosing of patients recovering from stroke. In this proof-of-principle study, we aimed to develop an accurate approach for classifying UE functional movement primitives, which comprise functional movements. Data were generated from inertial measurement units (IMUs) placed on upper body segments of older healthy individuals and chronic stroke patients. Subjects performed activities commonly trained during rehabilitation after stroke. Data processing involved the use of a sliding window to obtain statistical descriptors, and resulting features were processed by a Hidden Markov Model (HMM). The likelihoods of the states, resulting from the HMM, were segmented by a second sliding window and their averages were calculated. The final predictions were mapped to human functional movement primitives using a Logistic Regression algorithm. Algorithm performance was assessed with a leave-one-out analysis, which determined its sensitivity, specificity, and positive and negative predictive values for all classified primitives. In healthy control and stroke participants, our approach identified functional movement primitives embedded in training activities with, on average, 80% precision. This approach may support functional movement dosing in stroke rehabilitation.