Modulations in neural pathways excitability post transcutaneous spinal cord stimulation among individuals with spinal cord injury: a systematic review.

Introduction: Transcutaneous spinal cord stimulation (TSCS), a non-invasive form of spinal cord stimulation, has been shown to improve motor function in individuals living with spinal cord injury (SCI). However, the effects of different types of TSCS currents including direct current (DC-TSCS), alternating current (AC-TSCS), and spinal paired stimulation on the excitability of neural pathways have not been systematically investigated. The objective of this systematic review was to determine the effects of TSCS on the excitability of neural pathways in adults with non-progressive SCI at any level. Methods: The following databases were searched from their inception until June 2022: MEDLINE ALL, Embase, Web of Science, Cochrane Library, and clinical trials. A total of 4,431 abstracts were screened, and 23 articles were included. Results: Nineteen studies used TSCS at the thoracolumbar enlargement for lower limb rehabilitation (gait & balance) and four studies used cervical TSCS for upper limb rehabilitation. Sixteen studies measured spinal excitability by reporting different outcomes including Hoffmann reflex (H-reflex), flexion reflex excitability, spinal motor evoked potentials (SMEPs), cervicomedullay evoked potentials (CMEPs), and cutaneous-input-evoked muscle response. Seven studies measured corticospinal excitability using motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS), and one study measured somatosensory evoked potentials (SSEPs) following TSCS. Our findings indicated a decrease in the amplitude of H-reflex and long latency flexion reflex following AC-TSCS, alongside an increase in the amplitudes of SMEPs and CMEPs. Moreover, the application of the TSCS-TMS paired associative technique resulted in spinal reflex inhibition, manifested by reduced amplitudes in both the H-reflex and flexion reflex arc. In terms of corticospinal excitability, findings from 5 studies demonstrated an increase in the amplitude of MEPs linked to lower limb muscles following DC-TSCS, in addition to paired associative stimulation involving repetitive TMS on the brain and DC-TSCS on the spine. There was an observed improvement in the latency of SSEPs in a single study. Notably, the overall quality of evidence, assessed by the modified Downs and Black Quality assessment, was deemed poor. Discussion: This review unveils the systematic evidence supporting the potential of TSCS in reshaping both spinal and supraspinal neuronal circuitries post-SCI. Yet, it underscores the critical necessity for more rigorous, high-quality investigations.

Comparison of sensitivity among dynamic balance measures during walking with different tasks.

Although various measures have been proposed to evaluate dynamic balance during walking, it is currently unclear which measures are most sensitive to dynamic balance. We aimed to investigate which dynamic balance measure is most sensitive to detecting differences in dynamic balance during walking across various gait parameters, including short- and long-term Lyapunov exponents (λs and λl), margin of stability (MOS), distance between the desired and measured centre of pressure (dCOP-mCOP) and whole-body angular momentum (WBAM). A total of 10 healthy young adults were asked to walk on a treadmill under three different conditions (normal walking, dual-task walking with a Stroop task as an unstable walking condition, and arm-restricted walking with arms restricted in front of the chest as another unstable walking condition) that were expected to have different dynamic balance properties. Overall, we found that λs of the centre of mass velocity, λs of the trunk velocity, λs of the hip joint angle, and the magnitude of the mediolateral dCOP-mCOP at heel contact can identify differences between tasks with a high sensitivity. Our findings provide new insights into the selection of sensitive dynamic balance measures during human walking.

Feasibility of using a depth camera or pressure mat for visual feedback balance training with functional electrical stimulation.

Individuals with incomplete spinal-cord injury/disease are at an increased risk of falling due to their impaired ability to maintain balance. Our research group has developed a closed-loop visual-feedback balance training (VFBT) system coupled with functional electrical stimulation (FES) for rehabilitation of standing balance (FES + VFBT system); however, clinical usage of this system is limited by the use of force plates, which are expensive and not easily accessible. This study aimed to investigate the feasibility of a more affordable and accessible sensor such as a depth camera or pressure mat in place of the force plate. Ten able-bodied participants (7 males, 3 females) performed three sets of four different standing balance exercises using the FES + VFBT system with the force plate. A depth camera and pressure mat collected centre of mass and centre of pressure data passively, respectively. The depth camera showed higher Pearson's correlation (r > 98) and lower root mean squared error (RMSE < 10 mm) than the pressure mat (r > 0.82; RMSE < 4.5 mm) when compared with the force plate overall. Stimulation based on the depth camera showed lower RMSE than that based on the pressure mat relative to the FES + VFBT system. The depth camera shows potential as a replacement sensor to the force plate for providing feedback to the FES + VFBT system.

Identification of Myofascial Trigger Point Using the Combination of Texture Analysis in B-Mode Ultrasound with Machine Learning Classifiers.

Myofascial pain syndrome is a chronic pain disorder characterized by myofascial trigger points (MTrPs). Quantitative ultrasound (US) techniques can be used to discriminate MTrPs from healthy muscle. In this study, 90 B-mode US images of upper trapezius muscles were collected from 63 participants (left and/or right side(s)). Four texture feature approaches (individually and a combination of them) were employed that focused on identifying spots, and edges were used to explore the discrimination between the three groups: active MTrPs (n = 30), latent MTrPs (n = 30), and healthy muscle (n = 30). Machine learning (ML) and one-way analysis of variance were used to investigate the discrimination ability of the different approaches. Statistically significant results were seen in almost all examined features for each texture feature approach, but, in contrast, ML techniques struggled to produce robust discrimination. The ML techniques showed that two texture features (i.e., correlation and mean) within the combination of texture features were most important in classifying the three groups. This discrepancy between traditional statistical analysis and ML techniques prompts the need for further investigation of texture-based approaches in US for the discrimination of MTrPs.

Identifying priorities for balance interventions through a participatory co-design approach with end-users.

BACKGROUND: Most individuals living with spinal cord injuries/diseases (SCI/D) or stroke experience at least one fall each year; hence, the development of interventions and technologies that target balance control is needed. The purpose of this study was to identify and explore the priorities for balance-focused interventions and technologies from the perspectives of end-users to assist with the design of an intervention that combines functional electrical stimulation (FES) with visual feedback training for standing balance. METHODS: Two individuals with SCI/D, one individual with stroke, two physical therapists (PT) and one hospital administrator were recruited. Participants attended three focus group meetings that followed a participatory co-design approach. A semi-structured interview guide, developed from the FAME (Feasibility, Appropriateness, Meaningfulness, Effectiveness, Economic Evidence) framework, was used to lead the discussion, querying participants' experiences with balance deficits and interventions, and FES. Meetings were audio-recorded and transcribed verbatim. An iterative and reflexive inductive thematic analysis was applied to the transcripts by three researchers. RESULTS: Four themes were identified: (1) Balance is meaningful for daily life and rehabilitation. Participants acknowledged various factors influencing balance control and how balance deficits interfered with participation in activities. End-users stressed the importance of continuing to work on one's balance after discharge from hospital-based rehabilitation. (2) Desired characteristics of balance interventions. Participants explained that balance interventions should be tailored to an individual's unique needs and goals, relevant to their lives, balance their safety and risk, and be engaging. (3) Prior experiences with FES to inform future therapeutic use. Participants with stroke or SCI/D described initial apprehension with FES, but experienced numerous benefits that motivated them to continue with FES. Challenges with FES were mentioned, including wires, cost, and time of set up. (4) Potential role of FES in balance interventions. Participants felt that FES would complement balance interventions; however, they had not experienced this combination of therapies previously. CONCLUSIONS: End-users described how their experiences with balance deficits, rehabilitation, and FES informed their priorities for balance interventions. The findings inform the design and implementation of future balance interventions for individuals with SCI/D or stroke, including an intervention involving FES and visual feedback training.

Spatial characteristics of reactive stepping among people living with chronic incomplete spinal cord injury.

Objective: Compare the spatial characteristics of reactive stepping between individuals with chronic motor incomplete spinal cord injuries (iSCI) and able-bodied (AB) individuals.Design: Cross sectional.Setting: Lyndhurst Centre.Participants: Twelve individuals with iSCI (3 males, 53.6 ± 15.2 years old) and 11 age- and sex-matched AB individuals (3 males, 54.8 ± 14.0 years old).Interventions: The Lean-and-Release test was used to elicit reactive stepping. A horizontal cable, attached at waist height, was released when 8-12% body weight was supported in a forward lean position. Participants underwent up to 10 Lean-and-Release trials in a session. Kinematic and kinetic data were recorded.Outcome measures: The length, width and height of the first reactive step of each trial were calculated. Standard deviation between trials was calculated to represent the variability in step length, width and height within a participant. Among participants with iSCI, correlation coefficients were used to explore the relationship between step length and width variability and (1) Lean-and-Release test behavioral responses, (2) 3-month fall history, and (3) lower extremity strength.Results: Step length (P = 0.94), width (P = 0.52) and height (P = 0.97), normalized for participant height, did not differ between groups. Participants with iSCI showed greater variability in step length (P = 0.02) and width (P = 0.01), but not height (P = 0.32). No correlation was found between step length or width variability and behavioral responses, 3-month fall history, or lower extremity strength.Conclusions: Individuals with iSCI showed increased variability in length and width of reactive stepping compared to AB individuals, which may contribute to their impaired ability to execute single-step reactive responses.Trial registration: ClinicalTrials.gov identifier: NCT02960178.

Stepping responses for reactive balance for individuals with incomplete spinal cord injury.

Incomplete spinal cord injury (iSCI) causes impairment of reactive balance control, leading to higher fall risk. In our previous work, we found that individuals with iSCI were more likely to exhibit multiple-step response during the lean-and-release (LR) test, where the participant leaned forward while a tether supported 8-12% of the body weight and received a sudden release, inducing reactive steps. Here we investigated the foot placement of people with iSCI during the LR test using margin-of-stability (MOS). Twenty-one individuals with iSCI (age: 56.1 ± 16.1 years old; mass: 72.5 ± 19.0 kg; height: 166 ± 12 cm), and fifteen age- and sex-matched able-bodied (AB) individuals (age: 56.1 ± 12.9 years old; mass: 57.4 ± 10.9 kg; height: 164 ± 8 cm) participated in the study. The participants performed ten trials of the LR test and also completed clinical assessment of balance and strengths, including the Mini-Balance Evaluations Systems Test, the Community Balance and Mobility Scale, gait speed, and lower extremity manual muscle testing. MOS was significantly smaller during multiple-step responses than during single-step responses for both individuals with iSCI and AB counterparts. Using binary logistic regression and receiver operating characteristic analyses, we demonstrated that MOS can distinguish single- and multiple-step responses. In addition, individuals with iSCI demonstrated significantly larger intra-subject variability of MOS compared to AB individuals at first foot contact. Further, we found that MOS correlated with clinical measures of balance including one for reactive balance. We conclude that individuals with iSCI were less likely to demonstrate foot placement with sufficiently large MOS, which may increase the tendency to exhibit multiple-step responses.

Paired associative stimulation on the soleus H-Reflex using motor point and peripheral nerve stimulation.

Paired associative stimulation (PAS) has been shown to modulate the corticospinal excitability via spike timing dependent plasticity (STDP). In this study, we aimed to suppress the spinal H-Reflex using PAS. We paired two stimulation modalities, i.e., peripheral nerve stimulation (PNS) and motor point stimulation (MPS). We used PNS to dominantly activate the Ia sensory axon, and we used MPS to dominantly activate the α-motoneuron cell body antidromically. Thus, we applied both PNS and MPS such that the α-motoneuron cell body was activated 5 ms before the activation of the Ia sensory axon ending at the Ia-α motoneuron synapse. If the spinal reflexes can be modulated by STDP, and a combination of MPS and PNS is timed appropriately, then the H-Reflex amplitude will decrease while no change in H-Reflex amplitude is expected for MPS or PNS only. To test this hypothesis, six young healthy participants (5M/1F: 26.8 ± 4.1 yrs) received one of the three following conditions on days separated by at least 24 hr: 1) PAS, 2) MPS only or 3) PNS only. The H-Reflex and M-wave recruitment curves of the soleus were measured immediately prior to, immediately after, 30 min and 60 min after the intervention. The normalized H-Reflex amplitudes were then compared across conditions and times using a two-way ANOVA (3 conditions × 4 times). No main effects of condition or time, or interaction effect were found. These results suggest that relying solely on STDP may be insufficient to inhibit the soleus H-Reflex.

F-waves induced by motor point stimulation are facilitated during handgrip and motor imagery tasks.

The F-wave is a motor response elicited via the antidromic firings of motor nerves by the electrical stimulation of peripheral nerves, which reflects the motoneuron pool excitability. However, the F-wave generally has low robustness i.e., low persistence and small amplitude. We recently found that motor point stimulation (MPS), which provides the muscle belly with electrical stimulation, shows different neural responses compared to nerve stimulation, e.g., MPS elicits F-waves more robustly than nerve stimulation. Here, we investigated whether F-waves induced by MPS can identify changes in motoneuron pool excitability during handgrip and motor imagery. Twelve participants participated in the present study. We applied MPS on their soleus muscle and recorded F-waves during eyes-open (EO), eyes-closed (EC), handgrip (HG), and motor imagery (MI) conditions. In the EO and EC conditions, participants relaxed with their eyes open and closed, respectively. In the HG, participants matched the handgrip force level to 30% of the maximum voluntary force with visual feedback. In the MI, they performed kinesthetic MI of plantarflexion at the maximal strength with closed eyes. In the HG and MI, the amplitudes of the F-waves induced by MPS were increased compared with those in the EO and EC, respectively. These results indicate that the motoneuron pool excitability was facilitated during the HG and MI conditions, consistent with findings in previous studies. Our findings suggest that F-waves elicited by MPS can be a good tool in human neurophysiology to assess the motoneuron pool excitability during cognitive and motor tasks.

Neuromuscular recruitment pattern in motor point stimulation.

BACKGROUND: Transcutaneous electrical stimulation on the motor points over muscle belly, i.e., motor point stimulation (MPS), is widely used in clinical settings, however it is not fully understood how MPS recruits motor nerves. Here we investigated the recruitment pattern of the motor nerve and twitch force during MPS and compared to the recruitment during peripheral nerve stimulation (PNS). METHODS: Ten healthy individuals participated in this study. Using MPS on the soleus muscle and PNS on the tibial nerve, a single pulse stimulation was applied with various stimulation intensities from subthreshold to the maximum intensity. We measured the evoked potentials in the lower leg muscles and twitch force. Between MPS and PNS, we compared the recruitment curves of M-waves and the dynamics of twitch force such as duration from force onset to peak (time-to-peak). RESULTS: The maximum M-wave was not different between MPS and PNS in the soleus muscle, while it was much smaller in MPS than in PNS in the other lower leg muscles. This reflected the smaller twitch force of plantarflexion in MPS than PNS. In addition, the slope of the recruitment curve for the soleus M-wave was smaller in MPS than PNS. CONCLUSION: Therefore, unlike PNS, MPS can efficiently and selectively recruit motor nerves of the target muscle and gradually increase the recruitment of the motor nerve.

The Orthotic Effects of Different Functional Electrical Stimulation Protocols on Walking Performance in Individuals with Incomplete Spinal Cord Injury: A Case Series.

Background: Functional electrical stimulation (FES) of paralyzed muscles can facilitate walking after spinal cord injury (SCI). Objectives: To test the orthotic effects of different FES walking protocols on lower joint kinematics and walking speed. Methods: Three adults with incomplete SCI participated in this study. Their lower extremity motor scores and 10-meter walk test results were as follows: subject A: 50, 1.05 m/s, subject B: 44, 0.29 m/s, and subject C: 32, 0.27 m/s. Participants completed four conditions of over-ground walking including no FES and three bilateral FES-walking protocols as follows: multi-muscle stimulation (stimulation of quadriceps and gastrocnemius in the stance phase, and hamstring and tibialis anterior in the swing phase), drop foot (tibialis anterior stimulation), and flexor withdrawal (common peroneal nerve stimulation). The FES system obtained gait phase information from foot switches located under the individuals' heels. Three-dimensional kinematic analysis was undertaken to measure minimum toe clearance (MTC); ankle, knee, and hip range of motion (ROM); stride length; and stride speed. Results: Compared to no-FES walking, MTC increased during drop foot (all subjects), flexor withdrawal (subjects A and B), and multi-muscle stimulation (subjects B and C) protocols. A significant decrease in ankle ROM was seen with drop foot (all subjects), flexor withdrawal (subjects A), and multi-muscle stimulation (subjects A and C) protocols. Hip ROM increased with drop foot (subjects B and C), flexor withdrawal (subject B), and multi-muscle stimulation (subject C) protocols. Conclusion: Three FES walking protocols induced positive kinematic changes as indicated by increased MTC, decreased ankle ROM, and increased hip ROM during walking in subjects with incomplete SCI.

Combining transcutaneous spinal stimulation and functional electrical stimulation increases force generated by lower limbs: When more is more.

Background: Transcutaneous Spinal Stimulation (TSS) has been shown to promote activation of the lower limb and trunk muscles and is being actively explored for improving the motor outcomes of people with neurological conditions. However, individual responses to TSS vary, and often the muscle responses are insufficient to produce enough force for self-supported standing. Functional electrical stimulation (FES) can activate individual muscles and assist in closing this functional gap, but it introduces questions regarding timing between modalities. Methods: To assess the effects of TSS and FES on force generation, ten neurologically intact participants underwent (1) TSS only, (2) FES only, and (3) TSS + FES. TSS was delivered using four electrodes placed at T10-T11 through the L1-L2 intervertebral spaces simultaneously, while FES was delivered to the skin over the right knee extensors and plantarflexors. For all conditions, TSS and FES were delivered using three 0.5 ms biphasic square-wave pulses at 15 Hz. During the TSS + FES condition, timing between the two modalities was adjusted in increments of » time between pulses (16.5 ms). Results: When TSS preceded FES, a larger force production was observed. We also determined several changes in muscle activation amplitude at different relative stimulus intervals, which help characterize our finding and indicate the facilitating and inhibitory effects of the modalities. Conclusions: Utilizing a delay ranging from 15 to 30 ms between stimuli resulted in higher mean force generation in both the knee and ankle joints, regardless of the selected FES location (Average; knee: 112.0%, ankle: 103.1%).

Effects of age on dynamic balance measures and their correlation during walking across the adult lifespan.

In this study, we aimed to discover (1) the effects of age on dynamic balance measures, including the margin of stability (MOS), whole-body angular momentum (H), and misalignment of the desired and measured centers of pressure (dCOP and mCOP, respectively) in the anteroposterior (AP) and mediolateral (ML) directions, (2) the relationship between gait parameters and these balance measures, and (3) the relationships between these balance measures. We used the kinetic and kinematic data of 151 participants aged 20-77 years from a publicly available database. Participants were divided into three groups: young, middle-aged, and old. The step width of the old group was higher than that of the young group. Age-related differences in dynamic measures were found in the ML direction and not in the AP direction: MOS, peak-to-peak range of H, and dCOP-mCOP in the old group were greater than in the young group. ML MOS positively correlated with the frontal peak-to-peak range of H. The ML peak-to-peak range of H positively correlated with ML dCOP-mCOP across the adult lifespan. Our findings provide new insights for understanding the effects of age on dynamic balance and the relationships between the metrics. Older adults walked with a larger step width, resulting in a large stability margin in the ML direction, although with increased moment and momentum around the center of mass in the frontal plane.

The experiences of people with incomplete spinal cord injury or disease during intensive balance training and the impact of the program: A qualitative study.

STUDY DESIGN: Qualitative descriptive study. OBJECTIVES: To gain insight into if and how participation in intensive balance training impacted the daily lives and risk of falling of people living with incomplete spinal cord injury or disease (SCI/D), as well as to understand what motivated participation and what benefits and challenges, if any, they experienced while completing training. SETTING: Tertiary rehabilitation hospital. METHODS: Semi-structured interviews were conducted three to four months after 20 participants with incomplete SCI/D completed either Perturbation-based Balance Training or Conventional Intensive Balance Training as part of a randomized clinical trial. Interviews were transcribed verbatim and coded using conventional content analysis by two researchers. Codes were discussed for consensus, and subcategories and categories were created, which were confirmed by another two researchers. RESULTS: The following categories were identified: 1) goals of balance training, 2) valuable components of balance training, 3) physical gains from balance training, 4) psychosocial gains from participating in balance training, and 5) unique aspects of Perturbation-based Balance Training. Each category consisted of several subcategories. CONCLUSIONS: Collecting qualitative data facilitated the evaluation of the meaningfulness of the balance training programs to the participants. These findings demonstrate that balance training was perceived as beneficial and enjoyable for individuals with incomplete SCI/D, and that these programs provided challenge and educational opportunities for the participants while improving balance confidence and reducing perceived fall risk. These findings have implications to direct future research studies or implementation of balance training in rehabilitation.

Effect of Spatially Distributed Sequential Stimulation on Fatigue in Functional Electrical Stimulation Rowing.

OBJECTIVE: A critical limitation in clinical applications using functional electrical stimulation (FES) for rehabilitation exercises is the rapid onset of muscle fatigue. Spatially distributed sequential stimulation (SDSS) has been demonstrated to reduce muscle fatigue during FES compared to conventional single electrode stimulation (SES) in single joint movements. Here we investigated the fatigue reducing ability of SDSS in a clinical application, i.e., FES-rowing, in able-bodied (AB) participants. METHODS: FES was delivered to the quadriceps and hamstring of 15 AB participants (five female, ten male) for fatiguing FES-rowing trials using SES and SDSS, participants rowed with voluntary arm effort while endeavoring to keep their legs relaxed. Fatigue was characterized by the time elapsed until a percent decrease occurred in power output (TTF), as well as the trial length indicating the time elapsed until the complete stop of rowing. RESULT: Trial length was significantly longer in SDSS rowing than in SES (t-test, , d=0.71 ), with an average SDSS:SES trial length ratio of 1.31 ± 0.47. TTF SDSS was significantly longer than TTF SES with a median TTF SDSS :TTF SES ratio of 1.34 ranging from 1.03 to 5.41 (Wilcoxon Ranked Sum, , r=0.62 ). No rower experienced a decrease in TTF with SDSS. CONCLUSION: SDSS reduced fatigue during FES-rowing when compared to SES in AB individuals, resulting in a lengthened FES-rowing period by approximately 30%. Application of SDSS would increase the effectiveness of FES-rowing as rehabilitative exercise for individuals with paralyses.

Development of a Coaching System for Functional Electrical Stimulation Rowing: A Feasibility Study in Able-Bodied Individuals.

BACKGROUND: Functional electrical stimulation (FES) during rowing has substantial effects on cardiovascular health in individuals with spinal cord injuries. Currently, manual stimulation control where stimulation is operated by rowers is mostly utilized. However, it takes time to obtain the skill to initiate FES at the optimal timing. The purpose of this study was to develop a coaching system that helps rowers to initiate FES at the optimal timing. METHODS: The optimal range for FES application was identified based on the electromyography of the left quadriceps in 10 able-bodied individuals (AB). Then, the effects of the coaching system on the timing of button-pressing, power, and work were investigated in 7 AB. RESULTS: Vastus lateralis (VL) activation began consistently before the seat reached the anterior-most position. Therefore, seat position at the onset of VL was used as the variable to control the switch timing in the coaching system. The results revealed significantly higher power and work outputs in the coaching than the no-coaching condition (median power coaching: 19.10 W, power no-coaching: 16.48 W, p = 0.031; median work coaching: 109.74 J, work no-coaching: 65.25 J, p = 0.047). CONCLUSIONS: The coaching system can provide the optimal timing for FES, resulting in improved performance.

Motor point stimulation induces more robust F-waves than peripheral nerve stimulation.

The F-wave is a motor response induced by electrical stimulation of peripheral nerves via the antidromic firing of motor nerves, which reflects the motoneuron excitability. To induce F-waves, transcutaneous peripheral nerve stimulation (PNS) is used, which activates nerve branches via transcutaneous electrodes over the nerve branches. An alternative method to activate peripheral nerves, that is, motor point stimulation (MPS), which delivers electrical stimulation over the muscle belly, has not been used to induce F-waves. In our previous studies, we observed that MPS induced F-wave-like responses, that is, motor responses at the latency of F-waves at a supramaximal stimulation. Here, we further investigated the F-wave-like responses induced by MPS in comparison with PNS in the soleus muscle. Thirteen individuals participated in this study. We applied MPS and PNS on the participant's left soleus muscle. Using a monopolar double-pulse stimulation, the amplitude of the second H-reflex induced by PNS decreased, whereas the amplitude of the motor response at the F-wave latency induced by MPS did not decrease. These results suggest that the motor response at the F-wave latency induced by MPS was not an H-reflex but an F-wave. We also found that the F-wave induced by MPS had a greater amplitude and higher persistence and caused less pain when compared with the F-waves induced using PNS. We conclude that MPS evokes antidromic firing inducing F-waves more consistently compared with PNS.

The measurement properties of the Lean-and-Release test in people with incomplete spinal cord injury or disease.

OBJECTIVE: To evaluate test-retest reliability, agreement, and convergent validity of the Lean-and-Release test for the assessment of reactive stepping among individuals with incomplete spinal cord injury or disease (iSCI/D). DESIGN: Multi-center cross-sectional multiple test design. SETTING: SCI/D rehabilitation hospital and biomechanics laboratory. PARTICIPANTS: Individuals with motor incomplete SCI/D (iSCI/D). INTERVENTIONS: None. OUTCOME MEASURES: Twenty-six participants attended two sessions to complete the Lean-and-Release test and a battery of clinical tests. Behavioral (i.e. one-step, multi-step, loss of balance) and temporal (i.e. timing of foot off, foot contact, swing of reactive step) parameters were measured. Test-retest reliability was determined with intraclass correlation coefficients, and agreement was evaluated with Bland-Altman plots. Convergent validity was assessed through correlations with clinical tests. RESULTS: The behavioral responses were reliable for the Lean-and-Release test (ICC = 0.76), but foot contact was the only reliable temporal parameter using data from a single site (ICC = 0.79). All variables showed agreement according to the Bland-Altman plots. The behavioral responses correlated with scores of lower extremity strength (0.54, P<0.01) and balance confidence (0.55, P < 0.01). Swing time of reactive stepping correlated with step time (0.73, P < 0.01) and cadence (-0.73 P < 0.01) of over ground walking. CONCLUSIONS: The behavioral response of the Lean-and-Release test is a reliable and valid measure for people with iSCI/D. Our findings support the use of the behavioral responses to evaluate reactive stepping for research and clinical purposes. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02960178.

Computational Study on Spatially Distributed Sequential Stimulation for Fatigue Resistant Neuromuscular Electrical Stimulation.

Neuromuscular electrical stimulation (NMES) is used to artificially induce muscle contractions of paralyzed limbs in individuals with stroke or spinal cord injury, however, the therapeutic efficacy can be significantly limited by rapid fatiguing of the targeted muscle. A unique stimulation method, called spatially distributed sequential stimulation (SDSS), has been shown clinically to reduce fatiguing during FES, but further improvement is needed. The purpose of this study was to gain a better understanding of SDSS-induced neural activation in the human lower leg using a computational approach. We developed a realistic finite element model of the lower leg to investigate SDSS, by solving the electric field generated by SDSS and predicting neural activation. SDSS applied at 10 Hz was further compared with conventional transcutaneous stimulation that delivered electrical pulses at 40 Hz through a single electrode. We found that SDSS electrically activated multiple sub-populations of motor neurons within the TA muscle that fired at frequencies ranging between 10 Hz and 40 Hz. This complex nerve activation pattern depicts the mechanism of action of SDSS for reducing muscle fatigue during NMES.