Spinal Cord Transcutaneous Stimulation Enables Volitional Knee Extension in Motor-complete SCI.

Non-invasive spinal cord transcutaneous stimulation (scTS) is often applied to one or multiple spinal segments and may improve motor control after spinal cord injury (SCI). The purpose of this pilot study was to apply tonic scTS to an individual with motor-complete spinal cord injury (SCI) in order to initiate and maintain volitional control during a specific lower-extremity motor task. The participant's legs were placed in a gravity-neutral position, and he was asked to extend his knee, with and without the presence of tonic scTS. Our results show intentional voluntary control of knee extension with scTS (with no assistance). Our preliminary findings highlight how scTS neuromodulation of the spinal circuitry has the potential to restore motor function for people with motor-complete SCI. Clinical Relevance- This investigation is critical to better understand the neuromodulatory effects of tonic scTS for augmentation of voluntary-induced muscle activations in individuals with motor-complete SCI.

Corticomuscular Connectivity during Walking in Able Bodied and Individuals with Incomplete Spinal Cord Injury.

This exploratory study used EEG as mobile imaging method to study cortico-muscular connectivity (CMC) during walking in able-bodied individuals (AB) and individuals with spinal cord injury (iSCI), while walking with and without exoskeleton walking robot (EWR) assistance. We also explored change in CMC after intensive training using EWR assistance in iSCI. Results showed no different in CMC within the AB group during walking with and without robot assistance. However, before training the iSCI subjects showed lower CMC during walking with robot assistance. The intensive 40 hours of walking training with EWR improved the walking function in iSCI participants allowing them to walk with robot assistance set to lower assistance level. This decrease in assistance level and improvement in walking function correlated with increase in CMC, reducing the difference in CMC during walking with and without EWR assistance. The findings suggest that high level of robot assistance and low walking function in iSCI correlates with weaker connectivity between primary motor cortices and lower extremity muscles. Further research is needed to better understand the importance of intention and cortical involvement in training of walking function using EWRs. Clinical Relevance - This study provides innovative data on CMC during walking and how it changes with EWR assistance and with training. This research is important to the clinical field to provide recommendations of how training of walking function can be delivered to maximize cortical engagement and improve rehabilitation outcomes.

Effects of Multi-Muscle Electrical Stimulation and Stand Training on Stepping for an Individual With SCI.

The objective of this study was to evaluate the biomechanical, neural, and functional outcomes during a 10-min treadmill stepping trial before and after two independent interventions with neuromuscular electrical stimulation (ES) in an individual with spinal cord injury (SCI). In this longitudinal study, a 34-year-old male with sensory- and motor-complete SCI (C5/C6) underwent two consecutive interventions: 61 h of supine lower limb ES (ES-alone) followed by 51 h of ES combined with stand training (ST) using an overhead body-weight support (BWS) system (ST + ES). In post ES-alone (unloaded), compared to baseline, the majority (∼60%) of lower extremity muscles decreased their peak surface electromyography (sEMG) amplitude, while in post ST + ES (loaded), compared to post ES-alone, there was a restoration in muscle activation that endured the continuous 10-min stepping. Temporal α-motor neuron activity patterns were observed for the SCI participant. In post ST + ES, there were increases in spinal activity patterns during mid-stance at spinal levels L5-S2 for the right and left limbs. Moreover, in post ES-alone, trunk stability increased with excursions from the midline of the base-of-support (50%) to the left (44.2%; Baseline: 54.2%) and right (66.4%; baseline: 77.5%). The least amount of trunk excursion observed post ST + ES, from midline to left (43%; AB: 22%) and right (64%; AB: 64%). Overall, in post ES-alone, there were gains in trunk independence with a decrease in lower limb muscle activation, whereas in post ST + ES, there were gains in trunk independence and increased muscle activation in both bilateral trunk muscles as well as lower limb muscles during the treadmill stepping paradigm. The results of the study illustrate the importance of loading during the stimulation for neural and mechanical gains.

Use of Surface EMG in Clinical Rehabilitation of Individuals With SCI: Barriers and Future Considerations.

Surface electromyography (sEMG) is a widely used technology in rehabilitation research and provides quantifiable information on the myoelectric output of a muscle. In this perspective, we discuss the barriers which have restricted the wide-spread use of sEMG in clinical rehabilitation of individuals with spinal cord injury (SCI). One of the major obstacles is integrating the time-consuming aspects of sEMG in the already demanding schedule of physical therapists, occupational therapists, and other clinicians. From the clinicians' perspective, the lack of confidence to use sEMG technology is also apparent due to their limited exposure to the sEMG technology and possibly limited mathematical foundation through educational and professional curricula. Several technical challenges include the limited technology-transfer of ever-evolving knowledge from sEMG research into the off-the-shelf EMG systems, lack of demand from the clinicians for systems with advanced features, lack of user-friendly intuitive interfaces, and the need for a multidisciplinary approach for accurate handling and interpretation of data. We also discuss the challenges in the application and interpretation of sEMG that are specific to SCI, which are characterized by non-standardized approaches in recording and interpretation of EMGs due to the physiological and structural state of the spinal cord. Addressing the current barriers will require a collaborative, interdisciplinary, and unified approach. The most relevant steps could include enhancing user-experience for students pursuing clinical education through revised curricula through sEMG-based case studies/projects, hands-on involvement in the research, and formation of a common platform for clinicians and technicians for self-education and knowledge share.

Dynamic Margins of Stability During Robot-Assisted Walking in Able-Bodied Individuals: A Preliminary Study.

Background: Gait analysis studies during robot-assisted walking have been predominantly focused on lower limb biomechanics. During robot-assisted walking, the users' interaction with the robot and their adaptations translate into altered gait mechanics. Hence, robust and objective metrics for quantifying walking performance during robot-assisted gait are especially relevant as it relates to dynamic stability. In this study, we assessed bi-planar dynamic stability margins for healthy adults during robot-assisted walking using EksoGT™, ReWalk™, and Indego® compared to independent overground walking at slow, self-selected, and fast speeds. Further, we examined the use of forearm crutches and its influence on dynamic gait stability margins. Methods: Kinematic data were collected at 60 Hz under several walking conditions with and without the robotic exoskeleton for six healthy controls. Outcome measures included (i) whole-body center of mass (CoM) and extrapolated CoM (XCoM), (ii) base of support (BoS), (iii) margin of stability (MoS) with respect to both feet and bilateral crutches. Results: Stability outcomes during exoskeleton-assisted walking at self-selected, comfortable walking speeds were significantly (p < 0.05) different compared to overground walking at self-selected speeds. Unlike overground walking, the control mechanisms for stability using these exoskeletons were not related to walking speed. MoSs were lower during the single support phase of gait, especially in the medial-lateral direction for all devices. MoSs relative to feet were significantly (p < 0.05) lower than those relative to crutches. The spatial location of crutches during exoskeleton-assisted walking pushed the whole-body CoM, during single support, beyond the lateral boundary of the lead foot, increasing the risk for falls if crutch slippage were to occur. Conclusion: Careful consideration of crutch placement is critical to ensuring that the margins of stability are always within the limits of the BoS to control stability and decrease fall risk.

Multi-muscle electrical stimulation and stand training: Effects on standing.

OBJECTIVE: To examine the biomechanical and neuromuscular effects of a longitudinal multi-muscle electrical stimulation (submaximal intensities) training of the lower limbs combined with/without activity-based stand training, on the recovery of stability and function for one individual with spinal cord injury (SCI). DESIGN: Single-subject, longitudinal study. SETTING: Neuroplasticity laboratory. PARTICIPANT: A 34-year-old male, with sensory- and motor-complete SCI (C5/C6). INTERVENTIONS: Two consecutive interventions: 61 hours of supine, lower-limb ES (ES-alone) and 51 hours of ES combined with stand training using an overhead body-weight support system (ST + ES). OUTCOME MEASURES: Clinical measures, trunk stability, and muscle activity were assessed and compared across time points. Trunk Stability Limit (TSL) determined improvements in trunk independence. RESULTS: Functional clinical values increased after both interventions, with further increases post ST + ES. Post ES-alone, trunk stability was maintained at 81% body-weight (BW) loading before failure; post ST + ES, BW loading increased to 95%. TSL values decreased post ST + ES (TSLA/P=54.0 kg.cm, TSLM/L=14.5 kg.cm), compared to ES-alone (TSLA/P=8.5 kg.cm, TSLM/L=3.9 kg.cm). Trunk muscle activity decreased post ST + ES training, compared to ES-alone. CONCLUSION: Neuromuscular and postural trunk control dramatically improved following the multi-muscle ES of the lower limbs with stand training. Multi-muscle ES training paradigm of the lower limb, using traditional parameters, may contribute to the functional recovery of the trunk.

Mechanisms for improving walking speed after longitudinal powered robotic exoskeleton training for individuals with spinal cord injury.

The goal of this study was to establish strideparameter gait models correlated to speed on individuals with chronic SCI and able-bodied controls walking with a powered robotic exoskeleton (EksoGT $^{\mathrm{ TM}}$). Longitudinal exoskeleton training $( >100$ hours) across eight individuals with SCI resulted in a 30% increase in walking speed. A simple linear regression between step length, stride length for given speed were very tightly correlated along a line of best fit $( \mathrm {p}<$.001). The temporal parameters of stride time, stance time and double support time depicted a non-linear exponentially decaying relationship for given walking speed. The research findings indicate that although longitudinal exoskeleton training reduces the temporal parameters, increases in spatial parameters are only marginal.

Neuromechanical adaptations during a robotic powered exoskeleton assisted walking session.

OBJECTIVE: To evaluate gait parameters and neuromuscular profiles of exoskeleton-assisted walking under Max Assist condition during a single-session for; (i) able bodied (AB) individuals walking assisted with (EXO) and without (non-EXO) a powered exoskeleton, (ii) non-ambulatory SCI individuals walking assisted with a powered exoskeleton. DESIGN: Single-session. SETTING: Motion analysis laboratory. PARTICIPANTS: Four AB individuals and four individuals with SCI. INTERVENTIONS: Powered lower extremity exoskeleton. OUTCOME MEASURES: Temporal-spatial parameters, kinematics, walking velocity and electromyography data. RESULTS: AB individuals in exoskeleton showed greater stance time and a significant reduction in walking velocity (P < 0.05) compared to non-EXO walking. Interestingly, when the AB individuals voluntarily assisted the exoskeleton movements, they walked with an increased velocity and lowered stance time to resemble that of slow walking. For SCI individuals, mean percent stance time was higher and walking velocity was lower compared to all AB walking conditions (P < 0.05). There was muscle activation in several lower limb muscles for SCI group. For AB individuals, there were similarities among EXO and non-EXO walking conditions however there were differences in several lower limb EMGs for phasing of muscle activation. CONCLUSION: The data suggests that our AB individuals experienced reduction in walking velocity and muscle activation amplitudes while walking in the exoskeleton and moreover with voluntary control there is a greater temporal-spatial response of the lower limbs. Also, there are neuromuscular phasic adaptions for both AB and SCI groups while walking in the exoskeleton that are inconsistent to non-EXO gait muscle activation.

Validation of empirical mode decomposition combined with notch filtering to extract electrical stimulation artifact from surface electromyograms during functional electrical stimulation.

This paper presents the validity of Empirical Mode Decomposition (EMD) combined with Notch filtering to remove the electrical stimulation (ES) artifact from surface electromyogram (EMG) data for interpretation of muscle responses during Functional Electrical Stimulation (FES) experiments. We hypothesized that the EMD algorithm provides a suitable platform for decomposing the EMG signal into physically meaningful intrinsic mode functions (IMFs) which can be further used to isolate electrical stimulation (ES) artifact. The basic EMD algorithm was used to decompose the ES induced EMG signals into IMFs. IMFs most contaminated by ES were identified based on the standard deviation (SD) criterion. An IMF with the maximum signal to noise ratio (SNR) was Notch filtered and added to IMFs containing pure EMG data to get the filtered EMG signal. The method was tested on 5 able bodied (AB) and 2 spinal cord injured (SCI) participants. The validity of the filtered signal was assessed by normalized root mean squared error (NRMSE) and signal to noise (SNR) ratio values obtained by comparing a clean EMG collected during maximum volitional contraction (MVC) and EMD-Notch filtered signal from the combination of a clean EMG with i) simulated ES and, ii) real ES with no activation generated at different ES amplitudes. The results showed that the EMD-Notch filtering approach was successful, reliable and repeatable in extracting pure muscle responses during ES showing improved values for NRMSE and SNR in both AB and SCI individuals.

Neuromotor response of the leg muscles following a supine, stand retraining with/without neuromuscular electrical stimulation training intervention for individuals with SCI: A case series.

The goal of this paper is to study the effects of supine and stand retraining (SRT) interventions with and without multi muscle neuromuscular electrical stimulation (NMES) on the neuromuscular EMG responses of the leg muscles for individuals with motor complete SCI during walking on a body-weight support (BWS) treadmill. The main outcome variables were EMG amplitude, integrated EMG and co-contraction indices (co-excitation and co-activation) collected during a 10-minute walking treadmill trial. Data was analyzed for the first, fifth and tenth minute of walking. Results showed that both Supine+NMES and SRT+NMES interventions increased spatial-temporal aspects of muscle activity (mean EMG amplitude and integrated EMG) of lower limb muscles. SRT+NMES (loading) showed greater gains in the proximal anterior leg compartments. On the contrary, SRT without NMES (SRT only) exhibited deterioration of activity within the same muscle groups. Co-contraction indices increased for both post-NMES interventions suggesting that task-specificity of training is important to achieve the fundamental reciprocal firing known to able-bodied gait. These results show that combination of NMES+loading during passive rhythmic gait will induce neuroplasticity in the lower limbs that ultimately provides a potential effective means to recover gait in individuals with SCI.

Effects of lower limb electrical stimulation on trunk stability in persons with SCI during walking: a case series.

The purpose of the present case series was to investigate whether three lower limb rehabilitation training approaches have any effects on trunk stability of persons with motor complete SCI during a 10-minute assisted walk. These trainings included electrical stimulation (ES), standing retraining (SRT), and a novel multi-modality approach that combined ES with SRT. We observed that multi-muscle ES directed at the lower limbs had a prominent, indirect effect on the upper and lower muscles of the trunk. More specifically, trunk muscle activations of the ES+SRT subject increased after training for the more distal muscles of the trunk. This study provides preliminary evidence that combining lower limb ES with SRT may provide beneficial effects in improving trunk control and stability.