Multivariable passive ankle impedance in stroke patients: A preliminary study

Multivariable ankle mechanical impedance was estimated in four stroke survivors, in coupled dorsi- plantarflexion and inversion-eversion. We applied external torque perturbation with an ankle robot and used multi-input, multi-output stochastic system identification methods to estimate impedance, in both paretic and nonparetic limbs. Subjects were instructed to remain at rest throughout the four trials performed on each leg. Impedance projected onto the directions of maximum and minimum stiffness was fit to a 2nd order linear model, including inertia, viscosity and stiffness. For most trials, stiffness and damping in dorsi-plantarflexion are increased on the paretic side. However, for two subjects, overall impedance is not increased in the absence of sustained involuntary tonic contraction, registering values comparable to the non-paretic side. Thus, we speculate that the intrinsic properties of the paretic ankle remained unaffected at the evaluated pose. Spasticity (hyperflexive stretch reflex) would have systematically increased stiffness and damping, even in the absence of involuntary contraction. Hence, we speculate that these two subjects did not exhibit spasticity, while the remaining two subjects did, since impedance was increased, with no involuntary tonic muscle contraction. Regarding inversion-eversion, impedance in this direction remained unaffected by stroke. We evaluated two volunteers before and after the application of botulinum toxin. Surprisingly, ankle stiffness was not reduced, but anisotropy was normalized.

Inter-limb Asymmetry of Equilibrium Regulation in the Legs of 10-11-Year-Old Boys during Overground Sprinting

Short-distance running at top speed is important in field sports. Previous studies have analyzed kinematic and kinetic properties of sprinting in adults, but equivalent knowledge in children is underexplored. Quantifying relevant aspects of children's sprinting is useful for classifying their running skills and providing effective coaching based on motor control theory. This study aimed to clarify differences in equilibrium regulation in more- and less-skilled boy sprinters. Five 10-11-year-old boys regularly participating in lessons at the Mizuno running school performed 30-meter and 50-meter field track sprints, and the kinematic and electromyography findings were recorded. Equilibrium-point-based synergy analysis was then applied to estimate their respective virtual trajectories. The virtual trajectory is an equilibrium time sequence that indicates how the central nervous system controls a skeletal system with multiple muscles. The results suggested that: (1) the equilibrium of the right and left legs was regulated differently, although together the legs showed similar kinematics; (2) in the first type of virtual trajectory (type-I) in one leg, the equilibria after foot-strike were regulated intermittently during the early swing phase; (3) in the second type of virtual trajectory (type-II) in the other leg, the equilibria after foot-strike were continuously regulated during the early swing phase; and (4) the less-skilled child runners showed a slow equilibrium action response in both types of virtual trajectory during the early swing phase. These findings provide insights for "tailor-made" coaching based on the type of leg control during sprinting.Clinical relevance-Information on gait asymmetry would be beneficial not only for coaching to improve sprint training but also from clinical and injury perspectives.

Sleep deprivation affects gait control

Different levels of sleep restriction affect human performance in multiple aspects. However, it is unclear how sleep deprivation affects gait control. We applied a paced gait paradigm that included subliminal rhythm changes to analyze the effects of different sleep restriction levels (acute, chronic and control) on performance. Acute sleep deprivation (one night) group exhibited impaired performance in the sensorimotor synchronization gait protocol, such as a decrease in the Period Error between the footfalls and the auditory stimulus as well as missing more frequently the auditory cues. The group with chronic sleep restriction also underperformed when compared to the control group with a tendency to a late footfall with respect to the RAC sound. Our results suggest that partial or total sleep deprivation leads to a decrease in the performance in the sensorimotor control of gait. The superior performance of the chronic sleep group when compared to the acute group suggests that there is a compensatory mechanism that helps to improve motor performance.

Economic evaluation of robot-assisted training versus an enhanced upper limb therapy programme or usual care for patients with moderate or severe upper limb functional limitation due to stroke: results from the RATULS randomised controlled trial

OBJECTIVE

To determine whether robot-assisted training is cost-effective compared with an enhanced upper limb therapy (EULT) programme or usual care.

DESIGN

Economic evaluation within a randomised controlled trial.

SETTING

Four National Health Service (NHS) centres in the UK: Queen's Hospital, Barking, Havering and Redbridge University Hospitals NHS Trust; Northwick Park Hospital, London Northwest Healthcare NHS Trust; Queen Elizabeth University Hospital, NHS Greater Glasgow and Clyde; and North Tyneside General Hospital, Northumbria Healthcare NHS Foundation Trust.

PARTICIPANTS

770 participants aged 18 years or older with moderate or severe upper limb functional limitation from first-ever stroke.

INTERVENTIONS

Participants randomised to one of three programmes provided over a 12-week period: robot-assisted training plus usual care; the EULT programme plus usual care or usual care.

MAIN ECONOMIC OUTCOME MEASURES

Mean healthcare resource use; costs to the NHS and personal social services in 2018 pounds; utility scores based on EQ-5D-5L responses and quality-adjusted life years (QALYs). Cost-effectiveness reported as incremental cost per QALY and cost-effectiveness acceptability curves.

RESULTS

At 6 months, on average usual care was the least costly option (£3785) followed by EULT (£4451) with robot-assisted training being the most costly (£5387). The mean difference in total costs between the usual care and robot-assisted training groups (£1601) was statistically significant (p<0.001). Mean QALYs were highest for the EULT group (0.23) but no evidence of a difference (p=0.995) was observed between the robot-assisted training (0.21) and usual care groups (0.21). The incremental cost per QALY at 6 months for participants randomised to EULT compared with usual care was £74 100. Cost-effectiveness acceptability curves showed that robot-assisted training was unlikely to be cost-effective and that EULT had a 19% chance of being cost-effective at the £20 000 willingness to pay (WTP) threshold. Usual care was most likely to be cost-effective at all the WTP values considered in the analysis.

CONCLUSIONS

The cost-effectiveness analysis suggested that neither robot-assisted training nor EULT, as delivered in this trial, were likely to be cost-effective at any of the cost per QALY thresholds considered.

TRIAL REGISTRATION NUMBER

ISRCTN69371850.

Effects of Robotic Therapy Associated With Noninvasive Brain Stimulation on Upper-Limb Rehabilitation After Stroke: Systematic Review and Meta-analysis of Randomized Clinical Trials

BACKGROUND

Robot-assisted therapy and noninvasive brain stimulation (NIBS) are promising strategies for stroke rehabilitation.

OBJECTIVE

This systematic review and meta-analysis aims to evaluate the evidence of NIBS as an add-on intervention to robotic therapy in order to improve outcomes of upper-limb motor impairment or activity in individuals with stroke.

METHODS

This study was performed according to the PRISMA Protocol and was previously registered on the PROSPERO Platform (CRD42017054563). Seven databases and gray literature were systematically searched by 2 reviewers, and 1176 registers were accessed. Eight randomized clinical trials with upper-limb body structure/function or activity limitation outcome measures were included. Subgroup analyses were performed according to phase poststroke, device characteristics (ie, arm support, joints involved, unimanual or bimanual training), NIBS paradigm, timing of stimulation, and number of sessions. The Grade-Pro Software was used to assess quality of the evidence.

RESULTS

A nonsignificant homogeneous summary effect size was found both for body structure function domain (mean difference [MD] = 0.15; 95% CI = -3.10 to 3.40; P = 0.93; I² = 0%) and activity limitation domain (standard MD = 0.03; 95% CI = -0.28 to 0.33; P = 0.87; I² = 0%).

CONCLUSIONS

According to this systematic review and meta-analysis, at the moment, there are not enough data about the benefits of NIBS as an add-on intervention to robot-assisted therapy on upper-limb motor function or activity in individuals with stroke.

Effects of innovative hip-knee-ankle interlimb coordinated robot training on ambulation, cardiopulmonary function, depression, and fall confidence in acute hemiplegia

BACKGROUND

While Walkbot-assisted locomotor training (WLT) provided ample evidence on balance and gait improvements, the therapeutic effects on cardiopulmonary and psychological elements as well as fall confidence are unknown in stroke survivors.

OBJECTIVE

The present study aimed to compare the effects of Walkbot locomotor training (WLT) with conventional locomotor training (CLT) on balance and gait, cardiopulmonary and psychological functions and fall confidence in acute hemiparetic stroke.

METHODS

Fourteen patients with acute hemiparetic stroke were randomized into either the WLT (60 min physical therapy + 30 min Walkbot-assisted gait training) or CLT (60 min physical therapy + 30 min gait training) groups, 7 days/week over 2 weeks. Clinical outcomes included the Berg Balance Scale (BBS), Functional Ambulation Category (FAC), heart rate (HR), Borg Rating of Perceived Exertion (BRPE), Beck Depression Inventory-II (BDI-II), and the activities-specific balance confidence (ABC) scale. The analysis of covariance (ANCOVA) was conducted at P < 0.05.

RESULTS

ANCOVA showed that WLT showed superior effects, compared to CLT, on FAC, HR, BRPE, BDI-II, and ABC scale (P < 0.05), but not on BBS (P = 0.061).

CONCLUSIONS

Our results provide novel, promising clinical evidence that WLT improved balance and gait function as well as cardiopulmonary and psychological functions, and fall confidence in acute stroke survivors who were unable to ambulate independently.

Effects of supraspinal feedback on human gait: rhythmic auditory distortion

BACKGROUND

Different types of sound cues have been used to adapt the human gait rhythm. We investigated whether young healthy volunteers followed subliminal metronome rhythm changes during gait.

METHODS

Twenty-two healthy adults walked at constant speed on a treadmill following a metronome sound cue (period 566 msec). The metronome rhythm was then either increased or decreased, without informing the subjects, at 1 msec increments or decrements to reach, respectively, a low (596 msec) or a high frequency (536 msec) plateaus. After 30 steps at one of these isochronous conditions, the rhythm returned to the original period with decrements or increments of 1 msec. Motion data were recorded with an optical measurement system to determine footfall. The relative phase between sound cue (stimulus) and foot contact (response) were compared.

RESULTS

Gait was entrained to the rhythmic auditory stimulus and subjects subconsciously adapted the step time and length to maintain treadmill speed, while following the rhythm changes. In most cases there was a lead error: the foot contact occurred before the sound cue. The mean error or the absolute mean relative phase increased during the isochronous high (536 msec) or low frequencies (596 msec).

CONCLUSION

These results showed that the gait period is strongly "entrained" with the first metronome rhythm while subjects still followed metronome changes with larger error. This suggests two processes: one slow-adapting, supraspinal oscillator with persistence that predicts the foot contact to occur ahead of the stimulus, and a second fast process linked to sensory inputs that adapts to the mismatch between peripheral sensory input (foot contact) and supraspinal sensory input (auditory rhythm).

Exploiting the Invariant Structure for Controlling Multiple Muscles in Anthropomorphic Legs: III. Reproducing Hemiparetic Walking from Equilibrium Point- Based Synergies

In the development of a robotic therapy system, tests must be first run to guarantee safety and performance of the system before actual human trials. Lower-limb robotic therapy system has an inherit injury risk and a human-like stunt robot is desirable. This study proposes such an alternative: anthropomorphic legs with a bio-inspired control method affording a human-like test bench for the robotic therapy system. Electromyography (EMG) of a mildly hemiparetic stroke patient was measured during body-weight-supported treadmill walking. The motor strategy of the hemiparetic gait was extracted from the EMG data and applied to the control of the anthropomorphic legs. We employed the concept of equilibrium point (EP) to extract motor synergies and strategy. The EP- based synergies expressed by the composites of muscle mechanical impedance clarified motor strategy including aspects related to the impedance and virtual trajectory. Results show that the EP-based synergies were able to characterize neuromuscular patterns of pathological gait. The anthropomorphic legs were able to reproduce patient's gait by mimicking the EP-based synergies.

Robot-Assisted Therapy in Upper Extremity Hemiparesis: Overview of an Evidence-Based Approach

Robot-mediated therapy is an innovative form of rehabilitation that enables highly repetitive, intensive, adaptive, and quantifiable physical training. It has been increasingly used to restore loss of motor function, mainly in stroke survivors suffering from an upper limb paresis. Multiple studies collated in a growing number of review articles showed the positive effects on motor impairment, less clearly on functional limitations. After describing the current status of robotic therapy after upper limb paresis due to stroke, this overview addresses basic principles related to robotic therapy applied to upper limb paresis. We demonstrate how this innovation is an evidence-based approach in that it meets both the improved clinical and more fundamental knowledge-base about regaining effective motor function after stroke and the need of more objective, flexible and controlled therapeutic paradigms.

Robotic Arm Rehabilitation in Chronic Stroke Patients With Aphasia May Promote Speech and Language Recovery (but Effect Is Not Enhanced by Supplementary tDCS)

Objective: This study aimed to determine the extent to which robotic arm rehabilitation for chronic stroke may promote recovery of speech and language function in individuals with aphasia.

Methods: We prospectively enrolled 17 individuals from a hemiparesis rehabilitation study pairing intensive robot assisted therapy with sham or active tDCS and evaluated their speech (N = 17) and language (N = 9) performance before and after a 12-week (36 session) treatment regimen. Performance changes were evaluated with paired t-tests comparing pre- and post-test measures. There was no speech therapy included in the treatment protocol.

Results: Overall, the individuals significantly improved on measures of motor speech production from pre-test to post-test. Of the subset who performed language testing (N = 9), overall aphasia severity on a standardized aphasia battery improved from pre-test baseline to post-test. Active tDCS was not associated with greater gains than sham tDCS.

Conclusions: This work indicates the importance of considering approaches to stroke rehabilitation across different domains of impairment, and warrants additional exploration of the possibility that robotic arm motor treatment may enhance rehabilitation for speech and language outcomes. Further investigation into the role of tDCS in the relationship of limb and speech/language rehabilitation is required, as active tDCS did not increase improvements over sham tDCS.

Passive Wrist Stiffness: The Influence of Handedness

OBJECTIVE

This paper reports on the quantification of passive wrist joint stiffness and investigates the potential influence of handedness and gender on stiffness estimates.

METHODS

We evaluated the torque-angle relationship during passive wrist movements in 2 degrees of freedom (into flexion-extension and radial-ulnar deviation) in 13 healthy subjects using a wrist robot. Experimental results determined intrasubject differences between dominant and nondominant wrist and intersubject differences between male and female participants.

RESULTS

We found differences in the magnitude of passive stiffness of left- and right-hand dominant males and right-hand dominant females suggesting that the dominant hand tends to be stiffer than the nondominant hand. Left-hand stiffness magnitude was found to be 37% higher than the right-hand stiffness magnitude in the left-handed male group and the right-hand stiffness magnitude was 11% and 40% higher in the right-handed male and female groups, respectively. Other joint stiffness features such as the orientation and the anisotropy of wrist stiffness followed the expected pattern from previous studies.

CONCLUSION

The observed difference in wrist stiffness between the dominant and nondominant limb is likely due to biomechanical adaptations to repetitive asymmetric activities (such as squash, tennis, basketball, or activities of daily living such as writing, teeth brushing, etc.).

SIGNIFICANCE

Understanding and quantifying handedness influence on stiffness may have critical implication for the optimization of surgical and rehabilitative interventions.

Improved grasp function with transcranial direct current stimulation in chronic spinal cord injury

BACKGROUND

Recovering hand function has important implications for improving independence of patients with tetraplegia after traumatic spinal cord injury (SCI). Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation technique that has potential to improve motor function.

OBJECTIVE

To investigate the effects of one session of 1 mA, 2 mA, and sham anodal tDCS (a-tDCS) in the upper extremity (hand) motor performance (grasp and lease) in patients with chronic cervical SCI.

METHODS

Eleven participants with incomplete SCI were randomized to receive 20 minutes of 1 mA, 2 mA, or sham stimulation over the targeted motor cortex over three separated sessions. Hand motor performance was measured by a hand robotic evaluation (kinematics) and the Box and Blocks (BB) test before and after the stimulation period.

RESULTS

A significant improvement on the grasp mean to peak speed ratio (GMP) was observed in the 2 mA group (pre: 0.38±0.02; post: 0.43±0.03; mean±SEM; p = 0.031). There was no statistically significant difference in BB test results, however the 2 mA intervention showed a positive trend for improvement.

CONCLUSIONS

A single session of 2 mA of a-tDCS showed gains in hand motor function in patients with chronic SCI that were not observed in functional clinical scales. The use of robotic kinematics showed promising results in assessing small changes in motor performance. Further studies are necessary to determine whether tDCS can be an effective long-term rehabilitation strategy for individuals with SCI.

MIT-Skywalker: considerations on the Design of a Body Weight Support System

BACKGROUND

To provide body weight support during walking and balance training, one can employ two distinct embodiments: support through a harness hanging from an overhead system or support through a saddle/seat type. This paper presents a comparison of these two approaches. Ultimately, this comparison determined our selection of the body weight support system employed in the MIT-Skywalker, a robotic device developed for the rehabilitation/habilitation of gait and balance after a neurological injury.

METHOD

Here we will summarize our results with eight healthy subjects walking on the treadmill without any support, with 30% unloading supported by a harness hanging from an overhead system, and with a saddle/seat-like support system. We compared the center of mass as well as vertical and mediolateral trunk displacements across different walking speeds and support.

RESULTS

The bicycle/saddle system had the highest values for the mediolateral inclination, while the overhead harness body weight support showed the lowest values at all speeds. The differences were statistically significant.

CONCLUSION

We selected the bicycle/saddle system for the MIT-Skywalker. It allows faster don-and-doff, better centers the patient to the split treadmill, and allows all forms of training. The overhead harness body weight support might be adequate for rhythmic walking training but limits any potential for balance training.

Effects of partial body-weight support and functional electrical stimulation on gait characteristics during treadmill locomotion: Pros and cons of saddle-seat-type body-weight support

Robotic therapy for rehabilitation of the lower extremity is currently in its early stage of development. Aiming at exploring an efficacious intervention for gait rehabilitation, we investigate the characteristics of an end-effector gait-training device that combines saddle-seat-type body-weight-supported treadmill training with functional electrical stimulation (FES). This is a task-oriented approach to restoring voluntary control of locomotion in patients with neuromuscular diseases. We evaluate the differences between walking with saddle-seat-type support and with harness-type support, in terms of personal preference, the preferred walking speed, profiles of kinematics and ground reaction force, and the effectiveness of FES. The results indicate that the proposed gait-training device maintains subjects in a natural posture and supports important gait functions such as hip extension and ankle push-off effectively, in particular, at slow walking speed.

Robot Assisted Training for the Upper Limb after Stroke (RATULS): study protocol for a randomised controlled trial

BACKGROUND

Loss of arm function is a common and distressing consequence of stroke. We describe the protocol for a pragmatic, multicentre randomised controlled trial to determine whether robot-assisted training improves upper limb function following stroke.

METHODS/DESIGN

Study design: a pragmatic, three-arm, multicentre randomised controlled trial, economic analysis and process evaluation.

SETTING

NHS stroke services.

PARTICIPANTS

adults with acute or chronic first-ever stroke (1 week to 5 years post stroke) causing moderate to severe upper limb functional limitation. Randomisation groups: 1. Robot-assisted training using the InMotion robotic gym system for 45 min, three times/week for 12 weeks 2. Enhanced upper limb therapy for 45 min, three times/week for 12 weeks 3. Usual NHS care in accordance with local clinical practice Randomisation: individual participant randomisation stratified by centre, time since stroke, and severity of upper limb impairment.

PRIMARY OUTCOME

upper limb function measured by the Action Research Arm Test (ARAT) at 3 months post randomisation.

SECONDARY OUTCOMES

upper limb impairment (Fugl-Meyer Test), activities of daily living (Barthel ADL Index), quality of life (Stroke Impact Scale, EQ-5D-5L), resource use, cost per quality-adjusted life year and adverse events, at 3 and 6 months. Blinding: outcomes are undertaken by blinded assessors. Economic analysis: micro-costing and economic evaluation of interventions compared to usual NHS care. A within-trial analysis, with an economic model will be used to extrapolate longer-term costs and outcomes. Process evaluation: semi-structured interviews with participants and professionals to seek their views and experiences of the rehabilitation that they have received or provided, and factors affecting the implementation of the trial.

SAMPLE SIZE

allowing for 10% attrition, 720 participants provide 80% power to detect a 15% difference in successful outcome between each of the treatment pairs. Successful outcome definition: baseline ARAT 0-7 must improve by 3 or more points; baseline ARAT 8-13 improve by 4 or more points; baseline ARAT 14-19 improve by 5 or more points; baseline ARAT 20-39 improve by 6 or more points.

DISCUSSION

The results from this trial will determine whether robot-assisted training improves upper limb function post stroke.

TRIAL REGISTRATION

ISRCTN, identifier: ISRCTN69371850 . Registered 4 October 2013.

Pediatric robotic rehabilitation: Current knowledge and future trends in treating children with sensorimotor impairments

BACKGROUND

Robot-aided sensorimotor therapy imposes highly repetitive tasks that can translate to substantial improvement when patients remain cognitively engaged into the clinical procedure, a goal that most children find hard to pursue. Knowing that the child's brain is much more plastic than an adult's, it is reasonable to expect that the clinical gains observed in the adult population during the last two decades would be followed up by even greater gains in children. Nonetheless, and despite the multitude of adult studies, in children we are just getting started: There is scarcity of pediatric robotic rehabilitation devices that are currently available and the number of clinical studies that employ them is also very limited.

PURPOSE

We have recently developed the MIT's pedi-Anklebot, an adaptive habilitation robotic device that continuously motivates physically impaired children to do their best by tracking the child's performance and modifying their therapy accordingly. The robot's design is based on a multitude of studies we conducted focusing on the ankle sensorimotor control. In this paper, we briefly describe the device and the adaptive environment we built around the impaired children, present the initial clinical results and discuss how they could steer future trends in pediatric robotic therapy.

CONCLUSIONS

The results support the potential for future interventions to account for the differences in the sensorimotor control of the targeted limbs and their functional use (rhythmic vs. discrete movements and mechanical impedance training) and explore how the new technological advancements such as the augmented reality would employ new knowledge from neuroscience.

Summary of Human Ankle Mechanical Impedance During Walking

The human ankle joint plays a critical role during walking and understanding the biomechanical factors that govern ankle behavior and provides fundamental insight into normal and pathologically altered gait. Previous researchers have comprehensively studied ankle joint kinetics and kinematics during many biomechanical tasks, including locomotion; however, only recently have researchers been able to quantify how the mechanical impedance of the ankle varies during walking. The mechanical impedance describes the dynamic relationship between the joint position and the joint torque during perturbation, and is often represented in terms of stiffness, damping, and inertia. The purpose of this short communication is to unify the results of the first two studies measuring ankle mechanical impedance in the sagittal plane during walking, where each study investigated differing regions of the gait cycle. Rouse et al. measured ankle impedance from late loading response to terminal stance, where Lee et al. quantified ankle impedance from pre-swing to early loading response. While stiffness component of impedance increases significantly as the stance phase of walking progressed, the change in damping during the gait cycle is much less than the changes observed in stiffness. In addition, both stiffness and damping remained low during the swing phase of walking. Future work will focus on quantifying impedance during the “push off” region of stance phase, as well as measurement of these properties in the coronal plane.

MIT-Skywalker: A Novel Gait Neurorehabilitation Robot for Stroke and Cerebral Palsy

The MIT-Skywalker is a novel robotic device developed for the rehabilitation or habilitation of gait and balance after a neurological injury. It represents an embodiment of the concept exhibited by passive walkers for rehabilitation training. Its novelty extends beyond the passive walker quintessence to the unparalleled versatility among lower extremity devices. For example, it affords the potential to implement a novel training approach built upon our working model of movement primitives based on submovements, oscillations, and mechanical impedances. This translates into three distinct training modes: discrete, rhythmic, and balance. The system offers freedom of motion that forces self-directed movement for each of the three modes. This paper will present the technical details of the robotic system as well as a feasibility study done with one adult with stroke and two adults with cerebral palsy. Results of the one-month feasibility study demonstrated that the device is safe and suggested the potential advantages of the three modular training modes that can be added or subtracted to tailor therapy to a particular patient's need. Each participant demonstrated improvement in common clinical and kinematic measurements that must be confirmed in larger randomized control clinical trials.

On the Origin of Muscle Synergies: Invariant Balance in the Co-activation of Agonist and Antagonist Muscle Pairs

Investigation of neural representation of movement planning has attracted the attention of neuroscientists, as it may reveal the sensorimotor transformation essential to motor control. The analysis of muscle synergies based on the activity of agonist–antagonist (AA) muscle pairs may provide insight into such transformations, especially for a reference frame in the muscle space. In this study, we examined the AA concept using the following explanatory variables: the AA ratio, which is related to the equilibrium-joint angle, and the AA sum, which is associated with joint stiffness. We formulated muscle synergies as a function of AA sums, positing that muscle synergies are composite units of mechanical impedance. The AA concept can be regarded as another form of the equilibrium-point (EP) hypothesis, and it can be extended to the concept of EP-based synergies. We introduce, here, a novel tool for analyzing the neurological and motor functions underlying human movements and review some initial insights from our results about the relationships between muscle synergies, endpoint stiffness, and virtual trajectories (time series of EP). Our results suggest that (1) muscle synergies reflect an invariant balance in the co-activation of AA muscle pairs; (2) each synergy represents the basis for the radial, tangential, and null movements of the virtual trajectory in the polar coordinates centered on the specific joint at the base of the body; and (3) the alteration of muscle synergies (for example, due to spasticity or rigidity following neurological injury) results in significant distortion of endpoint stiffness and concomitant virtual trajectories. These results indicate that muscle synergies (i.e., the balance of muscle mechanical impedance) are essential for motor control.

Interlimb coordination in body-weight supported locomotion: A pilot study

Locomotion involves complex neural networks responsible for automatic and volitional actions. During locomotion, motor strategies can rapidly compensate for any obstruction or perturbation that could interfere with forward progression. In this pilot study, we examined the contribution of interlimb pathways for evoking muscle activation patterns in the contralateral limb when a unilateral perturbation was applied and in the case where body weight was externally supported. In particular, the latency of neuromuscular responses was measured, while the stimulus to afferent feedback was limited. The pilot experiment was conducted with six healthy young subjects. It employed the MIT-Skywalker (beta-prototype), a novel device intended for gait therapy. Subjects were asked to walk on the split-belt treadmill, while a fast unilateral perturbation was applied mid-stance by unexpectedly lowering one side of the split-treadmill walking surfaces. Subject's weight was externally supported via the body-weight support system consisting of an underneath bicycle seat and the torso was stabilized via a loosely fitted chest harness. Both the weight support and the chest harness limited the afferent feedback. The unilateral perturbations evoked changes in the electromyographic activity of the non-perturbed contralateral leg. The latency of all muscle responses exceeded 100ms, which precludes the conjecture that spinal cord alone is responsible for the perturbation response. It suggests the role of supraspinal or midbrain level pathways at the inter-leg coordination during gait.

Multivariable dynamic ankle mechanical impedance with active muscles

Multivariable dynamic ankle mechanical impedance in two coupled degrees-of-freedom (DOFs) was quantified when muscles were active. Measurements were performed at five different target activation levels of tibialis anterior and soleus, from 10% to 30% of maximum voluntary contraction (MVC) with increments of 5% MVC. Interestingly, several ankle behaviors characterized in our previous study of the relaxed ankle were observed with muscles active: ankle mechanical impedance in joint coordinates showed responses largely consistent with a second-order system consisting of inertia, viscosity, and stiffness; stiffness was greater in the sagittal plane than in the frontal plane at all activation conditions for all subjects; and the coupling between dorsiflexion-plantarflexion and inversion-eversion was small-the two DOF measurements were well explained by a strictly diagonal impedance matrix. In general, ankle stiffness increased linearly with muscle activation in all directions in the 2-D space formed by the sagittal and frontal planes, but more in the sagittal than in the frontal plane, resulting in an accentuated "peanut shape." This characterization of young healthy subjects' ankle mechanical impedance with active muscles will serve as a baseline to investigate pathophysiological ankle behaviors of biomechanically and/or neurologically impaired patients.

Robot-Aided Neurorehabilitation: A Pediatric Robot for Ankle Rehabilitation

This paper presents the pediAnklebot, an impedance-controlled low-friction, backdriveable robotic device developed at the Massachusetts Institute of Technology that trains the ankle of neurologically impaired children of ages 6-10 years old. The design attempts to overcome the known limitations of the lower extremity robotics and the unknown difficulties of what constitutes an appropriate therapeutic interaction with children. The robot's pilot clinical evaluation is on-going and it incorporates our recent findings on the ankle sensorimotor control in neurologically intact subjects, namely the speed-accuracy tradeoff, the deviation from an ideally smooth ankle trajectory, and the reaction time. We used these concepts to develop the kinematic and kinetic performance metrics that guided the ankle therapy in a similar fashion that we have done for our upper extremity devices. Here we report on the use of the device in at least nine training sessions for three neurologically impaired children. Results demonstrated a statistically significant improvement in the performance metrics assessing explicit and implicit motor learning. Based on these initial results, we are confident that the device will become an effective tool that harnesses plasticity to guide habilitation during childhood.

A Comparative Analysis of Speed Profile Models for Ankle Pointing Movements: Evidence that Lower and Upper Extremity Discrete Movements are Controlled by a Single Invariant Strategy

Little is known about whether our knowledge of how the central nervous system controls the upper extremities (UE), can generalize, and to what extent to the lower limbs. Our continuous efforts to design the ideal adaptive robotic therapy for the lower limbs of stroke patients and children with cerebral palsy highlighted the importance of analyzing and modeling the kinematics of the lower limbs, in general, and those of the ankle joints, in particular. We recruited 15 young healthy adults that performed in total 1,386 visually evoked, visually guided, and target-directed discrete pointing movements with their ankle in dorsal-plantar and inversion-eversion directions. Using a non-linear, least-squares error-minimization procedure, we estimated the parameters for 19 models, which were initially designed to capture the dynamics of upper limb movements of various complexity. We validated our models based on their ability to reconstruct the experimental data. Our results suggest a remarkable similarity between the top-performing models that described the speed profiles of ankle pointing movements and the ones previously found for the UE both during arm reaching and wrist pointing movements. Among the top performers were the support-bounded lognormal and the beta models that have a neurophysiological basis and have been successfully used in upper extremity studies with normal subjects and patients. Our findings suggest that the same model can be applied to different "human" hardware, perhaps revealing a key invariant in human motor control. These findings have a great potential to enhance our rehabilitation efforts in any population with lower extremity deficits by, for example, assessing the level of motor impairment and improvement as well as informing the design of control algorithms for therapeutic ankle robots.

Multivariable dynamic ankle mechanical impedance with relaxed muscles

Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair locomotor function. This paper presents a quantitative characterization of multivariable ankle mechanical impedance of young healthy subjects when their muscles were relaxed, to serve as a baseline to compare with pathophysiological ankle properties of biomechanically and/or neurologically impaired patients. Measurements using a highly backdrivable wearable ankle robot combined with multi-input multi-output stochastic system identification methods enabled reliable characterization of ankle mechanical impedance in two degrees-of-freedom (DOFs) simultaneously, the sagittal and frontal planes. The characterization included important ankle properties unavailable from single DOF studies: coupling between DOFs and anisotropy as a function of frequency. Ankle impedance in joint coordinates showed responses largely consistent with a second-order system consisting of inertia, viscosity, and stiffness in both seated (knee flexed) and standing (knee straightened) postures. Stiffness in the sagittal plane was greater than in the frontal plane and furthermore, was greater when standing than when seated, most likely due to the stretch of bi-articular muscles (medial and lateral gastrocnemius). Very low off-diagonal partial coherences implied negligible coupling between dorsiflexion-plantarflexion and inversion-eversion. The directions of principal axes were tilted slightly counterclockwise from the original joint coordinates. The directional variation (anisotropy) of ankle impedance in the 2-D space formed by rotations in the sagittal and frontal planes exhibited a characteristic "peanut" shape, weak in inversion-eversion over a wide range of frequencies from the stiffness dominated region up to the inertia dominated region. Implications for the assessment of neurological and biomechanical impairments are discussed.

Reaction time in ankle movements: a diffusion model analysis

Reaction time (RT) is one of the most commonly used measures of neurological function and dysfunction. Despite the extensive studies on it, no study has ever examined the RT in the ankle. Twenty-two subjects were recruited to perform simple, 2- and 4-choice RT tasks by visually guiding a cursor inside a rectangular target with their ankle. RT did not change with spatial accuracy constraints imposed by different target widths in the direction of the movement. RT increased as a linear function of potential target stimuli, as would be predicted by Hick-Hyman law. Although the slopes of the regressions were similar, the intercept in dorsal-plantar (DP) direction was significantly smaller than the intercept in inversion-eversion (IE) direction. To explain this difference, we used a hierarchical Bayesian estimation of the Ratcliff's (Psychol Rev 85:59, 1978) diffusion model parameters and divided processing time into cognitive components. The model gave a good account of RTs, their distribution and accuracy values, and hence provided a testimony that the non-decision processing time (overlap of posterior distributions between DP and IE < 0.045), the boundary separation (overlap of the posterior distributions < 0.1) and the evidence accumulation rate (overlap of the posterior distributions < 0.01) components of the RT accounted for the intercept difference between DP and IE. The model also proposed that there was no systematic change in non-decision processing time or drift rate when spatial accuracy constraints were altered. The results were in agreement with the memory drum hypothesis and could be further justified neurophysiologically by the larger innervation of the muscles controlling DP movements. This study might contribute to assessing deficits in sensorimotor control of the ankle and enlighten a possible target for correction in the framework of our on-going effort to develop robotic therapeutic interventions to the ankle of children with cerebral palsy.

Improved motor performance in chronic spinal cord injury following upper-limb robotic training

BACKGROUND

Recovering upper-limb motor function has important implications for improving independence of patients with tetraplegia after traumatic spinal cord injury (SCI).

OBJECTIVE

To evaluate the feasibility, safety and effectiveness of robotic-assisted training of upper limb in a chronic SCI population.

METHODS

A total of 10 chronic tetraplegic SCI patients (C4 to C6 level of injury, American Spinal Injury Association Impairment Scale, A to D) participated in a 6-week wrist-robot training protocol (1 hour/day 3 times/week). The following outcome measures were recorded at baseline and after the robotic training: a) motor performance, assessed by robot-measured kinematics, b) corticospinal excitability measured by transcranial magnetic stimulation (TMS), and c) changes in clinical scales: motor strength (Upper extremity motor score), pain level (Visual Analog Scale) and spasticity (Modified Ashworth scale).

RESULTS

No adverse effects were observed during or after the robotic training. Statistically significant improvements were found in motor performance kinematics: aim (pre 1.17 ± 0.11 raduans, post 1.03 ± 0.08 raduans, p = 0.03) and smoothness of movement (pre 0.26 ± 0.03, post 0.31 ± 0.02, p = 0.03). These changes were not accompanied by changes in upper-extremity muscle strength or corticospinal excitability. No changes in pain or spasticity were found.

CONCLUSIONS

Robotic-assisted training of the upper limb over six weeks is a feasible and safe intervention that can enhance movement kinematics without negatively affecting pain or spasticity in chronic SCI. In addition, robot-assisted devices are an excellent tool to quantify motor performance (kinematics) and can be used to sensitively measure changes after a given rehabilitative intervention.

Clinical application of a modular ankle robot for stroke rehabilitation

BACKGROUND

Advances in our understanding of neuroplasticity and motor learning post-stroke are now being leveraged with the use of robotics technology to enhance physical rehabilitation strategies. Major advances have been made with upper extremity robotics, which have been tested for efficacy in multi-site trials across the subacute and chronic phases of stroke. In contrast, use of lower extremity robotics to promote locomotor re-learning has been more recent and presents unique challenges by virtue of the complex multi-segmental mechanics of gait.

OBJECTIVES

Here we review a programmatic effort to develop and apply the concept of joint-specific modular robotics to the paretic ankle as a means to improve underlying impairments in distal motor control that may have a significant impact on gait biomechanics and balance.

METHODS

An impedance controlled ankle robot module (anklebot) is described as a platform to test the idea that a modular approach can be used to modify training and measure the time profile of treatment response.

RESULTS

Pilot studies using seated visuomotor anklebot training with chronic patients are reviewed, along with results from initial efforts to evaluate the anklebot's utility as a clinical tool for assessing intrinsic ankle stiffness. The review includes a brief discussion of future directions for using the seated anklebot training in the earliest phases of sub-acute therapy, and to incorporate neurophysiological measures of cerebro-cortical activity as a means to reveal underlying mechanistic processes of motor learning and brain plasticity associated with robotic training.

CONCLUSIONS

Finally we conclude with an initial control systems strategy for utilizing the anklebot as a gait training tool that includes integrating an Internal Model-based adaptive controller to both accommodate individual deficit severities and adapt to changes in patient performance.

Transcranial direct current stimulation (tDCS) and robotic practice in chronic stroke: the dimension of timing

BACKGROUND

Combining tDCS with robotic therapy is a new and promising form of neurorehabilitation after stroke, however the effectiveness of this approach is likely to be influenced by the relative timing of the brain stimulation and the therapy.

OBJECTIVE

To measure the kinematic and neurophysiological effects of delivering tDCS before, during and after a single session of robotic motor practice (wrist extension).

METHODS

We used a within-subjects repeated-measurement design in 12 chronic (>6 months) stroke survivors. Twenty minutes of anodal tDCS was delivered to the affected hemisphere before, during, or after a 20-minute session of robotic practice. Sham tDCS was also applied during motor practice. Robotic motor performance and corticomotor excitability, assessed through transcranial magnetic stimulation (TMS), were evaluated pre- and post-intervention.

RESULTS

Movement speed was increased after motor training (sham tDCS) by ∼20%. Movement smoothness was improved when tDCS was delivered before motor practice (∼15%). TDCS delivered during practice did not offer any benefit, whereas it reduced speed when delivered after practice (∼10%). MEPs were present in ∼50% of patients at baseline; in these subjects motor practice increased corticomotor excitability to the trained muscle.

CONCLUSIONS

In a cohort of stroke survivors, motor performance kinematics improved when tDCS was delivered prior to robotic training, but not when delivered during or after training. The temporal relationship between non-invasive brain stimulation and neurorehabilitation is important in determining the efficacy and outcome of this combined therapy.

Modular ankle robotics training in early subacute stroke: a randomized controlled pilot study

BACKGROUND. Modular lower extremity robotics may offer a valuable avenue for restoring neuromotor control after hemiparetic stroke. Prior studies show that visually guided and visually evoked practice with an ankle robot (anklebot) improves paretic ankle motor control that translates into improved overground walking.

OBJECTIVE

To assess the feasibility and efficacy of daily anklebot training during early subacute hospitalization poststroke.

METHODS

Thirty-four inpatients from a stroke unit were randomly assigned to anklebot (n = 18) or passive manual stretching (n = 16) treatments. All suffered a first stroke with residual hemiparesis (ankle manual muscle test grade 1/5 to 4/5), and at least trace muscle activation in plantar- or dorsiflexion. Anklebot training employed an "assist-as-needed" approach during >200 volitional targeted paretic ankle movements, with difficulty adjusted to active range of motion and success rate. Stretching included >200 daily mobilizations in these same ranges. All sessions lasted 1 hour and assessments were not blinded.

RESULTS

Both groups walked faster at discharge; however, the robot group improved more in percentage change of temporal symmetry (P = .032) and also of step length symmetry (P = .038), with longer nonparetic step lengths in the robot (133%) versus stretching (31%) groups. Paretic ankle control improved in the robot group, with increased peak (P ≤ .001) and mean (P ≤ .01) angular speeds, and increased movement smoothness (P ≤ .01). There were no adverse events.

CONCLUSION

Though limited by small sample size and restricted entry criteria, our findings suggest that modular lower extremity robotics during early subacute hospitalization is well tolerated and improves ankle motor control and gait patterning.

Pointing with the ankle: the speed-accuracy trade-off

This study investigated the trade-off between speed and accuracy in pointing movements with the ankle during goal-directed movements in dorsal-plantar (DP) and inversion-eversion (IE). Nine subjects completed a series of discrete pointing movements with the ankle between spatial targets of varying difficulty. Six different target sets were presented, with a range of task difficulty between 2.2 and 3.8 bits of information. Our results demonstrated that for visually evoked, visually guided discrete DP and IE ankle pointing movements, performance can be described by a linear function, as predicted by Fitts' law. These results support our ongoing effort to develop an adaptive algorithm employing the speed-accuracy trade-off concept to control our pediatric anklebot while delivering therapy for children with cerebral palsy.

Feasibility study of a wearable exoskeleton for children: is the gait altered by adding masses on lower limbs?

We are designing a pediatric exoskeletal ankle robot (pediatric Anklebot) to promote gait habilitation in children with Cerebral Palsy (CP). Few studies have evaluated how much or whether the unilateral loading of a wearable exoskeleton may have the unwanted effect of altering significantly the gait. The purpose of this study was to evaluate whether adding masses up to 2.5 kg, the estimated overall added mass of the mentioned device, at the knee level alters the gait kinematics. Ten healthy children and eight children with CP, with light or mild gait impairment, walked wearing a knee brace with several masses. Gait parameters and lower-limb joint kinematics were analyzed with an optoelectronic system under six conditions: without brace (natural gait) and with masses placed at the knee level (0.5, 1.0, 1.5, 2.0, 2.5 kg). T-tests and repeated measures ANOVA tests were conducted in order to find noteworthy differences among the trial conditions and between loaded and unloaded legs. No statistically significant differences in gait parameters for both healthy children and children with CP were observed in the five "with added mass" conditions. We found significant differences among "natural gait" and "with added masses" conditions in knee flexion and hip extension angles for healthy children and in knee flexion angle for children with CP. This result can be interpreted as an effect of the mechanical constraint induced by the knee brace rather than the effect associated with load increase. The study demonstrates that the mechanical constraint induced by the brace has a measurable effect on the gait of healthy children and children with CP and that the added mass up to 2.5 kg does not alter the lower limb kinematics. This suggests that wearable devices weighing 25 N or less will not noticeably modify the gait patterns of the population examined here.

EMG-based pattern recognition approach in post stroke robot-aided rehabilitation: a feasibility study

Background

Several studies investigating the use of electromyographic (EMG) signals in robot-based stroke neuro-rehabilitation to enhance functional recovery. Here we explored whether a classical EMG-based patterns recognition approach could be employed to predict patients’ intentions while attempting to generate goal-directed movements in the horizontal plane.

Methods

Nine right-handed healthy subjects and seven right-handed stroke survivors performed reaching movements in the horizontal plane. EMG signals were recorded and used to identify the intended motion direction of the subjects. To this aim, a standard pattern recognition algorithm (i.e., Support Vector Machine, SVM) was used. Different tests were carried out to understand the role of the inter- and intra-subjects’ variability in affecting classifier accuracy. Abnormal muscular spatial patterns generating misclassification were evaluated by means of an assessment index calculated from the results achieved with the PCA, i.e., the so-called Coefficient of Expressiveness (CoE).

Results

Processing the EMG signals of the healthy subjects, in most of the cases we were able to build a static functional map of the EMG activation patterns for point-to-point reaching movements on the horizontal plane. On the contrary, when processing the EMG signals of the pathological subjects a good classification was not possible. In particular, patients’ aimed movement direction was not predictable with sufficient accuracy either when using the general map extracted from data of normal subjects and when tuning the classifier on the EMG signals recorded from each patient.

Conclusions

The experimental findings herein reported show that the use of EMG patterns recognition approach might not be practical to decode movement intention in subjects with neurological injury such as stroke. Rather than estimate motion from EMGs, future scenarios should encourage the utilization of these signals to detect and interpret the normal and abnormal muscle patterns and provide feedback on their correct recruitment.

A comparative analysis of speed profile models for wrist pointing movements

Following two decades of design and clinical research on robot-mediated therapy for the shoulder and elbow, therapeutic robotic devices for other joints are being proposed: several research groups including ours have designed robots for the wrist, either to be used as stand-alone devices or in conjunction with shoulder and elbow devices. However, in contrast with robots for the shoulder and elbow which were able to take advantage of descriptive kinematic models developed in neuroscience for the past 30 years, design of wrist robots controllers cannot rely on similar prior art: wrist movement kinematics has been largely unexplored. This study aimed at examining speed profiles of fast, visually evoked, visually guided, target-directed human wrist pointing movements. One thousand three-hundred ninety-eight (1398) trials were recorded from seven unimpaired subjects who performed center-out flexion/extension and abduction/adduction wrist movements and fitted with 19 models previously proposed for describing reaching speed profiles. A nonlinear, least squares optimization procedure extracted parameters' sets that minimized error between experimental and reconstructed data. Models' performances were compared based on their ability to reconstruct experimental data. Results suggest that the support-bounded lognormal is the best model for speed profiles of fast, wrist pointing movements. Applications include design of control algorithms for therapeutic wrist robots and quantitative metrics of motor recovery.

Robotic technology and physical medicine and rehabilitation

In this opinion piece, I will revisit the basis for our belief that robotic manipulation is a valid approach to promote speedier and better recovery following a stroke and discuss some of the clinical evidence that led to the September 2010 guidelines for stroke care of the American Heart Association as well as the December 2010 guidelines of the Veterans Administration endorsing the use of robotic technology for the upper extremity (UE) but not for the lower extremity (LE) post-stroke rehabilitation effort.

EEG correlates of submovements

Numerous studies on motor control in humans and primates have suggested that the Central Nervous System (CNS) generates and controls continuous movement via discrete, elementary units of movement or submovements. While most studies are based on analysis of kinematic data, investigations of neural correlates have been lacking. To fill this gap we recorded and analyzed kinematic and high-density electroencephalographic (64-channel EEG) data from three right-handed normal adults during a reaching task that required online movement corrections. Each kinematic submovement was accompanied by stereotyped scalp maps. Furthermore, the peaks of event-related potentials (ERP) recorded at electrode C1 (over contralateral motor cortex) were time-locked to kinematic submovement peaks. These results provide further evidence for the hypothesis that the CNS generates and controls continuous movement via discrete submovements. Applications include design of quantitative outcome metrics for motor disorders of neurological origin such as stroke and Parkinson's disease.

Static ankle impedance in stroke and multiple sclerosis: a feasibility study

Quantitative characterization of ankle mechanical impedance is critical for understanding lower extremity function in persons with neurological disorders. In this paper, we examine the feasibility of employing an ankle robot and multivariable analysis to determine static ankle impedance in 4 patients: 1 with multiple sclerosis and 3 with stroke. We employed a scalar based vector field approximation method which was successful in identifying young healthy subjects' ankle impedance. It enabled clear interpretation of spatial ankle impedance structure and intermuscular feedback at the ankle for both affected and unaffected legs. Measured impedance of two patients was comparable to healthy young subjects, while the other two patients had significantly different static ankle impedance properties.

Effects of implicit visual feedback distortion on human gait

Gait rehabilitation after stroke often utilizes treadmill training delivered by either therapists or robotic devices. However, clinical results have shown no benefit from this modality when compared to usual care. On the contrary, results were inferior; perhaps, because in its present form it is not interactive and at least for stroke, central pattern generators at the spinal level do not appear to be the key to promote recovery. To enable gait therapy to be more effective, therapy must be interactive and visual feedback appears to be an important option to engage patients' participation. In this study, we tested healthy subjects to see whether an implicit "visual feedback distortion" influences gait spatial pattern. Subjects were not aware of the visual distortion nor did they realize changes in their gait pattern. The visual feedback of step length symmetry was distorted so that subjects perceived their step length as being asymmetric during treadmill training. We found that a gradual distortion of visual feedback, without explicit knowledge of the manipulation, systematically modulated gait step length away from symmetry and that the visual distortion effect was robust even in the presence of cognitive load. This indicates that although the visual feedback display used in this study did not create a conscious and vivid sensation of self-motion (the properties of the optical flow), experimental modifications of visual information of subjects' movement were found to cause implicit gait modulation. Nevertheless, our results indicate that modulation with visual distortion may require cognitive resources because during the distraction task, the amount of gait modulation was reduced. Our results suggest that a therapeutic program involving visual feedback distortion, in the context of gait rehabilitation, may provide an effective way to help subjects correct gait patterns, thereby improving the outcome of rehabilitation.

Learning, not adaptation, characterizes stroke motor recovery: evidence from kinematic changes induced by robot-assisted therapy in trained and untrained task in the same workspace

Both the American Heart Association and the VA/DoD endorse upper-extremity robot-mediated rehabilitation therapy for stroke care. However, we do not know yet how to optimize therapy for a particular patient's needs. Here, we explore whether we must train patients for each functional task that they must perform during their activities of daily living or alternatively capacitate patients to perform a class of tasks and have therapists assist them later in translating the observed gains into activities of daily living. The former implies that motor adaptation is a better model for motor recovery. The latter implies that motor learning (which allows for generalization) is a better model for motor recovery. We quantified trained and untrained movements performed by 158 recovering stroke patients via 13 metrics, including movement smoothness and submovements. Improvements were observed both in trained and untrained movements suggesting that generalization occurred. Our findings suggest that, as motor recovery progresses, an internal representation of the task is rebuilt by the brain in a process that better resembles motor learning than motor adaptation. Our findings highlight possible improvements for therapeutic algorithms design, suggesting sparse-activity-set training should suffice over exhaustive sets of task specific training.