Erica Garbarini

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.

Training Response to Longitudinal Powered Exoskeleton Training for SCI

The goal of this research is to assess how powered exoskeleton-training for 5 h per week over 20 weeks can change gait parameters to increase walking speed for chronic SCI. Gait parameters include Center of Mass (CoM) excursions, walking velocity, initial double stance time (IDS), single stance time (SS), terminal double stance time (TDS), swing time (SW), and spatial parameters such as step length, step width and stride length. Exoskeleton training had a significant effect on walking velocity due to specific temporal spatial gait parameters (IDS, TDS, Step and Stride Length) and increased stability (CoM).

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.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.

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.

Exoskeleton Controller and Design Considerations: Effect on Training Response for Persons with SCI

The objective of this research is to identify the demographic, physiological, kinematic and biomechanical determinants of exoskeleton assisted gait speed for individuals with a spinal cord injury (SCI). High number (300) of gait cycles across multiple time-points were analyzed to identify the parameter estimates from mixed model for dependent variable walk speed. Step length, step width, single stance time did not contribute to walk speed whereas trunk lean mass, stride length, step frequency were the most significant contributors. These variables were more significant than any of the spatial temporal parameters that are associated with human gait. Future research should determine the relative contributions of each independent variable to walk speed for different devices. Understanding the effects of exoskeleton/human interface for different devices is crucial for developing effective/efficient training protocols for community ambulation, rehabilitation and recovery post SCI.

Center of Mass and Postural Adaptations During Robotic Exoskeleton-Assisted Walking for Individuals with Spinal Cord Injury

The goal of this study is to understand the postural adaptations characterized by the whole body center of mass (COM) for individuals with SCI while walking with powered robotic exoskeletons, EksoGTTM and ReWalkTM. COM excursions showed a greater medial-lateral weight shift approach while walking in the EksoGTTM compared to a more forward-lean approach in the ReWalk™, however, postural trunk lean was significantly (p < 0.05) higher in the ReWalkTM. Understanding the effects of exoskeleton designs on posture and sway is crucial towards developing effective and efficient training protocols for rehabilitation and recovery post 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.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.