Non-gait-specific intervention for the rehabilitation of walking after SCI: role of the arms

The effects of improvement in upper extremity function on gait and balance in children with upper extremity affected

BACKGROUND

This study aimed to investigate the effects of functional improvement in the upper extremity on gait and balance in children with upper extremity affected.

RESEARCH QUESTION

What are the effects of functional improvement in the upper extremity on gait and balance in children with upper extremity affected?

METHODS

Eighteen children with a diagnosis of rheumatologic diseases and 15 healthy children were evaluated with Shriners Hospital Upper Extremity Assessment, Jebsen-Taylor Hand Function Test, Abilhand Rheumatoid Arthritis Scale, 10-meter walk test and Childhood Health Assessment Questionnaire. For static balance assessment, the Biodex Balance was used. Ground reaction forces (peak forces (heel strike and push-off) and minimum force (loading response), single-limb support duration, Center-of-Force displacement and walking speed were evaluated with the Sensor Medica. Arm swing was evaluated with the Kinovea 2D motion analysis.

RESULTS

Before treatment, single-limb support duration and push-off force was higher and center-of-force displacement was lower on affected side compared to unaffected side in rheumatologic group. After the 6-week rehabilitation program, upper extremity function, quality of life and functional gait score improved. Single-limb support duration decreased on affected side and increased on unaffected side. On affected side, push-off force decreased. The arm swing parameters were similar before and after treatment.

SIGNIFICANCE

Improving upper extremity function can help with gait balance by decreasing the difference in walking and balance parameters between the affected and unaffected sides and providing for more symmetrical weight transfer.

A New Compound-Limbs Paradigm: Integrating Upper-Limb Swing Improves Lower-Limb Stepping Intention Decoding From EEG

Brain-computer interface (BCI) systems based on spontaneous electroencephalography (EEG) hold the promise to implement human voluntary control of lower-extremity powered exoskeletons. However, current EEG-BCI paradigms do not consider the cooperation of upper and lower limbs during walking, which is inconsistent with natural human stepping patterns. To deal with this problem, this study proposed a stepping-matched human EEG-BCI paradigm that involved actions of both unilateral lower and contralateral upper limbs (also referred to as compound-limbs movement). Experiments were conducted in motor execution (ME) and motor imagery (MI) conditions to validate the feasibility. Common spatial pattern (CSP) proposed subject-specific CSP (SSCSP), and filter-bank CSP (FBCSP) methods were applied for feature extraction, respectively. The best average classification results based on SSCSP indicated that the accuracies of compound-limbs paradigms in ME and MI conditions achieved 89.02% ± 12.84% and 73.70% ± 12.47%, respectively. Although they were 2.03% and 5.68% lower than those of the single-upper-limb mode that does not match human stepping patterns, they were 24.30% and 11.02% higher than those of the single-lower-limb mode. These findings indicated that the proposed compound-limbs EEG-BCI paradigm is feasible for decoding human stepping intention and thus provides a potential way for natural human control of walking assistance devices.

Disinhibition of short-latency but not long-latency afferent inhibition of the lower limb during upper-limb muscle contraction

Research has demonstrated that motor and sensory functions of the lower limbs can be modulated by upper-limb muscle contractions. However, whether sensorimotor integration of the lower limb can be modulated by upper-limb muscle contractions is still unknown. [AQ: NR Original articles do not require structured abstracts. Hence, abstract subsections have been deleted. Please check.]Human sensorimotor integration has been studied using short- or long-latency afferent inhibition (SAI or LAI, respectively), which refers to inhibition of motor-evoked potentials (MEPs) elicited via transcranial magnetic stimulation by preceding peripheral sensory stimulation. In the present study, we aimed to investigate whether upper-limb muscle contractions could modulate the sensorimotor integration of the lower limbs by examining SAI and LAI. Soleus muscle MEPs following electrical tibial nerve stimulation (TSTN) during rest or voluntary wrist flexion were recorded at inter-stimulus intervals (ISIs) of 30 (i.e. SAI), 100, and 200 ms (i.e. LAI). The soleus Hoffman reflex following TSTN was also measured to identify whether MEP modulation occurred at the cortical or the spinal level. Results showed that lower-limb SAI, but not LAI, was disinhibited during voluntary wrist flexion. Furthermore, the soleus Hoffman reflex following TSTN during voluntary wrist flexion was unchanged when compared with that during the resting state at any ISI. Our findings suggest that upper-limb muscle contractions modulate sensorimotor integration of the lower limbs and that disinhibition of lower-limb SAI during upper-limb muscle contractions is cortically based.

A Scoping Review of the Characteristics of Activity-based Therapy Interventions Across the Continuum of Care for People Living With Spinal Cord Injury or Disease

Objective

To identify the characteristics of activity-based therapy (ABT) that individuals with spinal cord injury and disease (SCI/D) participate in across the continuum of care.

Data Sources

A search of 8 databases was conducted from inception to 4 March 2020: Medline, CINAHL, Embase, Emcare, PEDro, APA PsycINFO, Cochrane Database of Systematic Reviews, and the CENTRAL. The search strategy used terms identifying the population (SCI/D) and concept (ABT).

Study Selection

Original studies involving individuals with SCI/D ≥16 years of age participating in ABT interventions for >1 session were included in the review. The Joanna Briggs Institute guidelines for scoping reviews were followed. The initial search produced 2306 records. Title, abstract, and full-text screening by 2 independent reviewers yielded 140 articles.

Data Extraction

Data extraction was conducted by 3 independent reviewers and charted according to key themes. Data fields included participant demographics, ABT interventions, exercises, parameters, technology, and setting. Data synthesis included frequency counts and descriptive analysis of key themes.

Data Synthesis

Eighty percent of participants were male. Eighty-seven percent of studies included individuals with tetraplegia (26% exclusive). Fifty-six percent of studies occurred in a research lab. Fifty-four percent of studies were single modality interventions encompassing the whole body (71%). Sixteen main types of ABT exercises were identified. The most common were treadmill training (59%), muscle strengthening (36%), and overground walking (33%). Electrical stimulation (50%) and virtual reality (6%) were used in combination with an ABT exercise. Eighty-four types of parameters were identified. Six were general intervention parameters and 78 were specific to the type of ABT exercise. Sixteen main categories of technology were reported. The most common were motorized treadmills (47%) and transcutaneous electrical stimulation (44%).

Conclusions

The characteristics of ABT are diverse in scope. The results will inform the content to include in tools that track ABT participation and performance.

Step-to-step variability indicates disruption to balance control when linking the arms and legs during treadmill walking

We recently discovered that a rope-pulley system that mechanically coupling the arms, legs and treadmill during walking can assist with forward propulsion in healthy subjects, leading to significant reductions in metabolic cost. However, walking balance may have been compromised, which could hinder the potential use of this device for gait rehabilitation. We performed a secondary analysis by quantifying average step width, step length, and step time, and used their variability to reflect simple metrics of walking balance (n = 8). We predicted an increased variability in at least one of these metrics when using the device, which would indicate disruptions to walking balance. When walking with the device, subjects increased their average step width (p < 0.05), but variability in step width and step length remained similar (p’s > 0.05). However, the effect size for step length variability when compared to that of mechanical perturbation experiments suggest a minimal to moderate disruption in balance (Rosenthal ES = 0.385). The most notable decrement in walking balance was an increase in step time variability (p < 0.05; Cohen’s d = 1.286). Its effect size reveals a moderate disruption when compared to the effect sizes observed in those with balance deficits (effect sizes ranged between 0.486 to 1.509). Overall, we conclude that healthy subjects experienced minimal to moderate disruptions in walking balance when using with this device. These data indicate that in future clinical experiments, it will be important to not only consider the mechanical and metabolic effects of using such a device but also its potential to disrupt walking balance, which may be exacerbated in patients with poor balance control.

Overground gait kinematics and muscle activation patterns in the Yucatan mini pig

Objective The objectives of this study were to assess gait biomechanics and the effect of overground walking speed on gait parameters, kinematics, and electromyographic (EMG) activity in the hindlimb muscles of Yucatan Minipigs (YMPs). Approach Nine neurologically-intact, adult YMPs were trained to walk overground in a straight line. Whole-body kinematics and EMG activity of hindlimb muscles were recorded and analyzed at 6 different speed ranges (0.4-0.59, 0.6-0.79, 0.8-0.99, 1.0-1.19, 1.2-1.39, and 1.4-1.6 m/s). A MATLAB program was developed to detect strides and gait events automatically from motion-captured data. The kinematics and EMG activity were analyzed for each stride based on the detected events. Main results Significant decreases in stride duration, stance and swing times and an increase in stride length were observed with increasing speed. A transition in gait pattern occurred at the 1.0m/s walking speed. Significant increases in the range of motion of the knee and ankle joints were observed at higher speeds. Also, the points of minimum and maximum joint angles occurred earlier in the gait cycle as the walking speed increased. The onset of EMG activity in the biceps femoris muscle occurred significantly earlier in the gait cycle with increasing speed. Significance YMPs are becoming frequently used as large animal models for preclinical testing and translation of novel interventions to humans. A comprehensive characterization of overground walking in neurologically-intact YMPs is provided in this study. These normative measures set the basis against which the effects of future interventions on locomotor capacity in YMPs can be compared.

Neural Substrates of Transcutaneous Spinal Cord Stimulation: Neuromodulation across Multiple Segments of the Spinal Cord

Transcutaneous spinal cord stimulation (tSCS) has the potential to promote improved sensorimotor rehabilitation by modulating the circuitry of the spinal cord non-invasively. Little is currently known about how cervical or lumbar tSCS influences the excitability of spinal and corticospinal networks, or whether the synergistic effects of multi-segmental tSCS occur between remote segments of the spinal cord. The aim of this review is to describe the emergence and development of tSCS as a novel method to modulate the spinal cord, while highlighting the effectiveness of tSCS in improving sensorimotor recovery after spinal cord injury. This review underscores the ability of single-site tSCS to alter excitability across multiple segments of the spinal cord, while multiple sites of tSCS converge to facilitate spinal reflex and corticospinal networks. Finally, the potential and current limitations for engaging cervical and lumbar spinal cord networks through tSCS to enhance the effectiveness of rehabilitation interventions are discussed. Further mechanistic work is needed in order to optimize targeted rehabilitation strategies and improve clinical outcomes.

Motor improvements enabled by spinal cord stimulation combined with physical training after spinal cord injury: review of experimental evidence in animals and humans

Electrical spinal cord stimulation (SCS) has been gaining momentum as a potential therapy for motor paralysis in consequence of spinal cord injury (SCI). Specifically, recent studies combining SCS with activity-based training have reported unprecedented improvements in motor function in people with chronic SCI that persist even without stimulation. In this work, we first provide an overview of the critical scientific advancements that have led to the current uses of SCS in neurorehabilitation: e.g. the understanding that SCS activates dormant spinal circuits below the lesion by recruiting large-to-medium diameter sensory afferents within the posterior roots. We discuss how this led to the standardization of implant position which resulted in consistent observations by independent clinical studies that SCS in combination with physical training promotes improvements in motor performance and neurorecovery. While all reported participants were able to move previously paralyzed limbs from day 1, recovery of more complex motor functions was gradual, and the timeframe for first observations was proportional to the task complexity. Interestingly, individuals with SCI classified as AIS B and C regained motor function in paralyzed joints even without stimulation, but not individuals with motor and sensory complete SCI (AIS A). Experiments in animal models of SCI investigating the potential mechanisms underpinning this neurorecovery suggest a synaptic reorganization of cortico-reticulo-spinal circuits that correlate with improvements in voluntary motor control. Future experiments in humans and animal models of paralysis will be critical to understand the potential and limits for functional improvements in people with different types, levels, timeframes, and severities of SCI.

Using a simple rope-pulley system that mechanically couples the arms, legs, and treadmill reduces the metabolic cost of walking

BACKGROUND

Emphasizing the active use of the arms and coordinating them with the stepping motion of the legs may promote walking recovery in patients with impaired lower limb function. Yet, most approaches use seated devices to allow coupled arm and leg movements. To provide an option during treadmill walking, we designed a rope-pulley system that physically links the arms and legs. This arm-leg pulley system was grounded to the floor and made of commercially available slotted square tubing, solid strut channels, and low-friction pulleys that allowed us to use a rope to connect the subject's wrist to the ipsilateral foot. This set-up was based on our idea that during walking the arm could generate an assistive force during arm swing retraction and, therefore, aid in leg swing.

METHODS

To test this idea, we compared the mechanical, muscular, and metabolic effects between normal walking and walking with the arm-leg pulley system. We measured rope and ground reaction forces, electromyographic signals of key arm and leg muscles, and rates of metabolic energy consumption while healthy, young subjects walked at 1.25 m/s on a dual-belt instrumented treadmill (n = 8).

RESULTS

With our arm-leg pulley system, we found that an assistive force could be generated, reaching peak values of 7% body weight on average. Contrary to our expectation, the force mainly coincided with the propulsive phase of walking and not leg swing. Our findings suggest that subjects actively used their arms to harness the energy from the moving treadmill belt, which helped to propel the whole body via the arm-leg rope linkage. This effectively decreased the muscular and mechanical demands placed on the legs, reducing the propulsive impulse by 43% (p < 0.001), which led to a 17% net reduction in the metabolic power required for walking (p = 0.001).

CONCLUSIONS

These findings provide the biomechanical and energetic basis for how we might reimagine the use of the arms in gait rehabilitation, opening the opportunity to explore if such a method could help patients regain their walking ability.

TRIAL REGISTRATION

 Study registered on 09/29/2018 in ClinicalTrials.gov (ID-NCT03689647).

Simultaneous Cervical and Lumbar Spinal Cord Stimulation Induces Facilitation of Both Spinal and Corticospinal Circuitry in Humans

Coupling between cervical and lumbar spinal networks (cervico-lumbar coupling) is vital during human locomotion. Impaired cervico-lumbar coupling after neural injuries or diseases can be reengaged via simultaneous arm and leg cycling training. Sensorimotor circuitry including cervico-lumbar coupling may further be enhanced by non-invasive modulation of spinal circuity using transcutaneous spinal cord stimulation (tSCS). This project aimed to determine the effect of cervical, lumbar, or combined tSCS on spinal reflex (Hoffmann [H-]) and corticospinal (motor evoked potential [MEP]) excitability during a static or cycling cervico-lumbar coupling task. Fourteen neurologically intact study participants were seated in a recumbent leg cycling system. H-reflex and MEP amplitudes were assessed in the left flexor carpi radialis (FCR) muscle during two tasks (Static and Cycling) and four conditions: (1) No tSCS, (2) tSCS applied to the cervical enlargement (Cervical); (3) tSCS applied to the lumbar enlargement (Lumbar); (4) simultaneous cervical and lumbar tSCS (Combined). While cervical tSCS did not alter FCR H-reflex amplitude relative to No tSCS, lumbar tSCS significantly facilitated H-reflex amplitude by 11.1%, and combined cervical and lumbar tSCS significantly enhanced the facilitation to 19.6%. Neither cervical nor lumbar tSCS altered MEP amplitude alone (+4.9 and 1.8% relative to legs static, No tSCS); however, combined tSCS significantly increased MEP amplitude by 19.7% compared to No tSCS. Leg cycling alone significantly suppressed the FCR H-reflex relative to static, No tSCS by 13.6%, while facilitating MEP amplitude by 18.6%. When combined with leg cycling, tSCS was unable to alter excitability for any condition. This indicates that in neurologically intact individuals where interlimb coordination and corticospinal tract are intact, the effect of leg cycling on cervico-lumbar coupling and corticospinal drive was not impacted significantly with the tSCS intensity used. This study demonstrates, for the first time, that tonic activation of spinal cord networks through multiple sites of tSCS provides a facilitation of both spinal reflex and corticospinal pathways. It remains vital to determine if combined tSCS can influence interlimb coupling after neural injury or disease when cervico-lumbar connectivity is impaired.

Effects of gravity and kinematic constraints on muscle synergies in arm cycling

Arm cycling is a bimanual motor task used in medical rehabilitation and in sports training. Understanding how muscle coordination changes across different biomechanical constraints in arm cycling is a step toward improved rehabilitation approaches. This exploratory study aims to get new insights on motor control during arm cycling. To achieve our main goal, we used the muscle synergies analysis to test three hypotheses: 1) body position with respect to gravity (sitting and supine) has an effect on muscle synergies; 2) the movement size (crank length) has an effect on the synergistic behavior; 3) the bimanual cranking mode (asynchronous and synchronous) requires different synergistic control. Thirteen able-bodied volunteers performed arm cranking on a custom-made device with unconnected cranks, which allowed testing three different conditions: body position (sitting vs. supine), crank length (10 cm vs. 15 cm), and cranking mode (synchronous vs. asynchronous). For each of the eight possible combinations, subjects cycled for 30 s while electromyography of eight muscles (four from each arm) were recorded: biceps brachii, triceps brachii, anterior deltoid, and posterior deltoid. Muscle synergies in this eight-dimensional muscle space were extracted by nonnegative matrix factorization. Four synergies accounted for over 90% of muscle activation variances in all conditions. Results showed that synergies were affected by body position and cranking mode but practically unaffected by movement size. These results suggest that the central nervous system may employ different motor control strategies in response to external constraints such as cranking mode and body position during arm cycling.NEW & NOTEWORTHY Recent studies analyzed muscle synergies in lower limb cycling. Here, we examine upper limb cycling and specifically the effect of body position with respect to gravity, movement size, and cranking mode on muscle coordination during arm cranking tasks. We show that altered body position and cranking mode affects modular organization of muscle activities. To our knowledge, this is the first study assessing motor control through muscle synergies framework during upper limb cycling with different constraints.

The Effect of Crank Resistance on Arm Configuration and Muscle Activation Variances in Arm Cycling Movements

Arm cycling on an ergometer is common in sports training and rehabilitation protocols. The hand movement is constrained along a circular path, and the user is working against a resistance, maintaining a cadence. Even if the desired hand trajectory is given, there is the flexibility to choose patterns of joint coordination and muscle activation, given the kinematic redundancy of the upper limb. With changing external load, motor noise and changing joint stiffness may affect the pose of the arm even though the endpoint trajectory is unchanged. The objective of this study was to examine how the crank resistance influences the variances of joint configuration and muscle activation. Fifteen healthy participants performed arm cranking on an arm-cycle ergometer both unimanually and bimanually with a cadence of 60 rpm against three crank resistances. Joint configuration was represented in a 3-dimensional joint space defined by inter-segmental joint angles, while muscle activation in a 4-dimensional "muscle activation space" defined by EMGs of 4 arm muscles. Joint configuration variance in the course of arm cranking was not affected by crank resistance, whereas muscle activation variance was proportional to the square of muscle activation. The shape of the variance time profiles for both joint configuration and muscle activation was not affected by crank resistance. Contrary to the prevailing assumption that an increased motor noise would affect the variance of auxiliary movements, the influence of noise doesn't appear at the joint configuration level even when the system is redundant. Our results suggest the separation of kinematic- and force-control, via mechanisms that are compensating for dynamic nonlinearities. Arm cranking may be suitable when the aim is to perform training under different load conditions, preserving stable and secure control of joint movements and muscle activations.

Mediolateral damping of an overhead body weight support system assists stability during treadmill walking

BACKGROUND

Body weight support systems with three or more degrees of freedom (3-DoF) are permissive and safe environments that provide unloading and allow unrestricted movement in any direction. This enables training of walking and balance control at an early stage in rehabilitation. Transparent systems generate a support force vector that is near vertical at all positions in the workspace to only minimally interfere with natural movement patterns. Patients with impaired balance, however, may benefit from additional mediolateral support that can be adjusted according to their capacity. An elegant solution for providing balance support might be by rendering viscous damping along the mediolateral axis via the software controller. Before use with patients, we evaluated if control-rendered mediolateral damping evokes the desired stability enhancement in able-bodied individuals.

METHODS

A transparent, cable-driven robotic body weight support system (FLOAT) was used to provide transparent body weight support with and without mediolateral damping to 21 able-bodied volunteers while walking at preferred gait velocity on a treadmill. Stability metrics reflecting resistance to small and large perturbations were derived from walking kinematics and compared between conditions and to free walking.

RESULTS

Compared to free walking, the application of body weight support per-se resulted in gait alterations typically associated with body weight support, namely increased step length and swing phase. Frontal plane dynamic stability, measured by kinematic variability and nonlinear dynamics of the center of mass, was increased under body weight support, indicating reduced balance requirements in both damped and undamped support conditions. Adding damping to the body weight support resulted in a greater increase of frontal plane stability.

CONCLUSION

Adding mediolateral damping to 3-DoF body weight support systems is an effective method of increasing frontal plane stability during walking in able-bodied participants. Building on these results, adjustable mediolateral damping could enable therapists to select combinations of unloading and stability specifically for each patient and to adapt this in a task specific manner. This could extend the impact of transparent 3-DoF body weight support systems, enabling training of gait and active balance from an early time point onwards in the rehabilitation process for a wide range of mobility activities of daily life.

Changing coupling between the arms and legs with slow walking speeds alters regulation of somatosensory feedback

Arm swing movement is coordinated with movement of the legs during walking, where the frequency of coordination depends on walking speed. At typical speeds, arm and leg movements, respectively, are frequency locked in a 1:1 ratio but at slow speeds this changes to a 2:1 ratio. It is unknown if the changes in interlimb ratio that accompany slow walking speeds alters regulation of somatosensory feedback. To probe the neural interactions between the arms and legs, somatosensory linkages in the form of interlimb cutaneous reflexes were examined. It was hypothesized that different interlimb frequencies and walking speeds would result in changes in the modulation of cutaneous reflexes between the arms and legs. To test this hypothesis, participants walked in four combinations of walking speed (typical, slow) and interlimb coordination (1:1, and 2:1), while cutaneous reflexes and background muscle activity were evaluated with stimulation applied to the superficial peroneal nerve at the ankle and superficial radial nerve at the wrist. Results show main effects of interlimb coordination and walking speed on cutaneous reflex modulation, effects are largest in the swing phase, and a directional coupling was observed, where changes in the frequency of arm movements had a greater effect on muscle activity in the legs compared to the reverse. Task-dependent modulation was also revealed from stimulation at local and remote sources. Understanding the underlying neural mechanisms for the organization of rhythmic arm movement, and its coordination with the legs in healthy participants, can give insight into pathological walking, and will facilitate the development of effective strategies for the rehabilitation of walking.

Transcutaneous spinal cord stimulation of the cervical cord modulates lumbar networks

It has been established that coordinated arm and leg (A&L) cycling facilitates corticospinal drive and modulation of cervico-lumbar connectivity and ultimately improves overground walking in people with incomplete spinal cord injury or stroke. This study examined the effect of noninvasive transcutaneous spinal cord stimulation (tSCS) on the modulation of cervico-lumbar connectivity. Thirteen neurologically intact adults participated in the study. The excitability of the Hoffmann (H) reflex elicited in the soleus muscle was examined under multiple conditions involving either the arms held in a static position or rhythmic arm cycling while tSCS was applied to either the cervical or lumbar cord. As expected, soleus H-reflex amplitude was significantly suppressed by 19.2% during arm cycling (without tSCS) relative to arms static (without tSCS). Interestingly, tSCS of the cervical cord with arms static significantly suppressed the soleus H-reflex (−22.9%), whereas tSCS over the lumbar cord did not suppress the soleus H-reflex (−3.8%). The combination of arm cycling with cervical or lumbar tSCS did not yield additional suppression of the soleus H-reflex beyond that obtained with arm cycling alone or cervical tSCS alone. The results demonstrate that activation of the cervical spinal cord through both rhythmic arm cycling and tonic tSCS significantly modulates the activity of lumbar networks. This highlights the potential for engaging cervical spinal cord networks through tSCS during rehabilitation interventions to enhance cervico-lumbar connectivity. This connectivity is influential in facilitating improvements in walking function after neurological impairment.

NEW & NOTEWORTHY This is the first study to investigate the modulatory effects of transcutaneous spinal cord stimulation (tSCS) on cervico-lumbar connectivity. We report that both rhythmic activation of the cervical spinal cord through arm cycling and tonic activation of the cervical cord through tSCS significantly modulate the activity of lumbar networks. This suggests that engaging cervical spinal cord networks through tSCS during locomotor retraining interventions may not only enhance cervico-lumbar connectivity but also further improve walking capacity.

Robot controlled, continuous passive movement of the ankle reduces spinal cord excitability in participants with spasticity: a pilot study

Spasticity of the ankle reduces quality of life by impeding walking and other activities of daily living. Robot-driven continuous passive movement (CPM) is a strategy for lower limb spasticity management but effects on spasticity, walking ability and spinal cord excitability (SCE) are unknown. The objectives of this experiment were to evaluate (1) acute changes in SCE induced by 30 min of CPM at the ankle joint, in individuals without neurological impairment and those with lower limb spasticity; and, (2) the effects of 6 weeks of CPM training on SCE, spasticity and walking ability in those with lower limb spasticity. SCE was assessed using soleus Hoffmann (H-) reflexes, collected prior to and immediately after CPM for acute assessments, whereas a multiple baseline repeated measures design assessed changes following 18 CPM sessions. Spasticity and walking ability were assessed using the Modified Ashworth Scale, the 10 m Walk test, and the Timed Up and Go test. Twenty-one neurologically intact and nine participants with spasticity (various neurological conditions) were recruited. In the neurologically intact group, CPM caused bi-directional modulation of H-reflexes creating 'facilitation' and 'suppression' groups. In contrast, amongst participants with spasticity, acute CPM facilitated H-reflexes. After CPM training, H-reflex excitability on both the more-affected and less-affected sides was reduced; on the more affected side H@Thres, H@50 and H@100 all significantly decreased following CPM training by 96.5 ± 7.7%, 90.9 ± 9.2%, and 62.9 ± 21.1%, respectively. After training there were modest improvements in walking and clinical measures of spasticity for some participants. We conclude that CPM of the ankle can significantly alter SCE. The use of CPM in those with spasticity can provide a temporary period of improved walking, but efficacy of treatment remains unknown.

Effects of neuromuscular electrical stimulation and voluntary commands on the spinal reflex excitability of remote limb muscles

It is well known that contracting the upper limbs can affect spinal reflexes of the lower limb muscle, via intraneuronal networks within the central nervous system. However, it remains unknown whether neuromuscular electrical stimulation (NMES), which can generate muscle contractions without central commands from the cortex, can also play a role in such inter-limb facilitation. Therefore, the objective of this study was to compare the effects of unilateral upper limb contractions using NMES and voluntary unilateral upper limb contractions on the inter-limb spinal reflex facilitation in the lower limb muscles. Spinal reflex excitability was assessed using transcutaneous spinal cord stimulation (tSCS) to elicit responses bilaterally in multiple lower limb muscles, including ankle and thigh muscles. Five interventions were applied on the right wrist flexors for 70 s: (1) sensory-level NMES; (2) motor-level NMES; (3) voluntary contraction; (4) voluntary contraction and sensory-level NMES; (5) voluntary contraction and motor-level NMES. Results showed that spinal reflex excitability of ankle muscles was facilitated bilaterally during voluntary contraction of the upper limb unilaterally and that voluntary contraction with motor-level NMES had similar effects as just contracting voluntarily. Meanwhile, motor-level NMES facilitated contralateral thigh muscles, and sensory-level NMES had no effect. Overall, our results suggest that inter-limb facilitation effect of spinal reflex excitability in lower limb muscles depends, to a larger extent, on the presence of the central commands from the cortex during voluntary contractions. However, peripheral input generated by muscle contractions using NMES might have effects on the spinal reflex excitability of inter-limb muscles via spinal intraneuronal networks.

Exploiting cervicolumbar connections enhances short-term spinal cord plasticity induced by rhythmic movement

Arm cycling causes suppression of soleus (SOL) Hoffmann (H-) reflex that outlasts the activity period. Arm cycling presumably activates propriospinal networks that modulate Ia presynaptic inhibition. Interlimb pathways are thought to relate to the control of quadrupedal locomotion, allowing for smooth, coordinated movement of the arms and legs. We examined whether the number of active limb pairs affects the amount and duration of activity-dependent plasticity of the SOL H-reflex. On separate days, 14 participants completed 4 randomly ordered 30 min experimental sessions: (1) quiet sitting (CTRL); (2) arm cycling (ARM); (3) leg cycling (LEG); and (4) arm and leg cycling (A&L) on an ergometer. SOL H-reflex and M-wave were evoked via electrical stimulation of the tibial nerve. M-wave and H-reflex recruitment curves were recorded, while the participants sat quietly prior to, 10 and 20 min into, immediately after, and at 2.5, 5, 7.5, 10, 15, 20, 25, and 30 min after each experimental session. Normalized maximal H-reflexes were unchanged in CTRL, but were suppressed by > 30% during the ARM, LEG, and A&L. H-reflex suppression outlasted activity duration for ARM (≤ 2.5 mins), LEG (≤ 5 mins), and A&L (≤ 30 mins). The duration of reflex suppression after A&L was greater than the algebraic summation of ARM and LEG. This non-linear summation suggests that using the arms and legs simultaneously-as in typical locomotor synergies-amplifies networks responsible for the short-term plasticity of lumbar spinal cord excitability. Enhanced activity of spinal networks may have important implications for the implementation of locomotor training for targeted rehabilitation.

Effect of cervicolumbar coupling on spinal reflexes during cycling after incomplete spinal cord injury

Spinal networks in the cervical and lumbar cord are actively coupled during locomotion to coordinate arm and leg activity. The goals of this project were to investigate the intersegmental cervicolumbar connectivity during cycling after incomplete spinal cord injury (iSCI) and to assess the effect of rehabilitation training on improving reflex modulation mediated by cervicolumbar pathways. Two studies were conducted. In the first, 22 neurologically intact (NI) people and 10 people with chronic iSCI were recruited. The change in H-reflex amplitude in flexor carpi radialis (FCR) during leg cycling and H-reflex amplitude in soleus (SOL) during arm cycling were investigated. In the second study, two groups of participants with chronic iSCI underwent 12 wk of cycling training: one performed combined arm and leg cycling (A&L) and the other legs only cycling (Leg). The effect of training paradigm on the amplitude of the SOL H-reflex was assessed. Significant reduction in the amplitude of both FCR and SOL H-reflexes during dynamic cycling of the opposite limbs was found in NI participants but not in participants with iSCI. Nonetheless, there was a significant reduction in the SOL H-reflex during dynamic arm cycling in iSCI participants after training. Substantial improvements in SOL H-reflex properties were found in the A&L group after training. The results demonstrate that cervicolumbar modulation during rhythmic movements is disrupted in people with chronic iSCI; however, this modulation is restored after cycling training. Furthermore, involvement of the arms simultaneously with the legs during training may better regulate the leg spinal reflexes.

NEW & NOTEWORTHY This work systematically demonstrates the disruptive effect of incomplete spinal cord injury on cervicolumbar coupling during rhythmic locomotor movements. It also shows that the impaired cervicolumbar coupling could be significantly restored after cycling training. Actively engaging the arms in rehabilitation paradigms for the improvement of walking substantially regulates the excitability of the lumbar spinal networks. The resulting regulation may be better than that obtained by interventions that focus on training of the legs only.

Bone marrow stromal cells improved functional recovery in spinal cord injury rats partly via the Toll-like receptor-4/nuclear factor-κB signaling pathway

Spinal cord injury (SCI) results in inflammation, and TLR4, which is an inflammatory factor, has an important role in the pathological injury that occurs following SCI. Recently, bone marrow stromal cells (BMSCs) have been demonstrated to be a novel treatment in SCI. However, the underlying mechanism of neuroprotection in SCI by BMSCs remains unclear. The present study was designed to investigate the therapeutic mechanism of BMSCs in SCI by analysis of Toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) expression. The present results demonstrated that BMSC transplantation promoted functional recovery and tissue repair in SCI rats. Interestingly, it also reduced the expression of TLR4 and NF-κB after SCI. Furthermore, it was demonstrated that BMSCs downregulated the expression of apoptosis factor caspase-12 in the SCI rat model. The present results demonstrated that BMSCs may have incorporated into the spinal cord to improve locomotor function after SCI, partly via the TLR4/NF-κB signaling pathway. To the best of our knowledge, this is the first study to determine that BMSCs prevented secondary injury and enhanced functional recovery in SCI via inhibition of TLR4/NF-κB-mediated inflammation.

Sherlock Holmes and the curious case of the human locomotor central pattern generator

Evidence first described in reduced animal models over 100 years ago led to deductions about the control of locomotion through spinal locomotor central pattern-generating (CPG) networks. These discoveries in nature were contemporaneous with another form of deductive reasoning found in popular culture, that of Arthur Conan Doyle's detective, Sherlock Holmes. Because the invasive methods used in reduced nonhuman animal preparations are not amenable to study in humans, we are left instead with deducing from other measures and observations. Using the deductive reasoning approach of Sherlock Holmes as a metaphor for framing research into human CPGs, we speculate and weigh the evidence that should be observable in humans based on knowledge from other species. This review summarizes indirect inference to assess "observable evidence" of pattern-generating activity that leads to the logical deduction of CPG contributions to arm and leg activity during locomotion in humans. The question of where a CPG may be housed in the human nervous system remains incompletely resolved at this time. Ongoing understanding, elaboration, and application of functioning locomotor CPGs in humans is important for gait rehabilitation strategies in those with neurological injuries.