Lower extremity skeletal muscle function in persons with incomplete spinal cord injury

Robotic locomotor training in a low-resource setting: a randomized pilot and feasibility trial

PURPOSE

Activity-based Training (ABT) represents the current standard of neurological rehabilitation. Robotic Locomotor Training (RLT), an innovative technique, aims to enhance rehabilitation outcomes. This study aimed to conduct a randomized pilot and feasibility trial of a locomotor training program within South Africa.

MATERIALS AND METHODS

Individuals with chronic traumatic motor incomplete tetraplegia (n = 16). Each intervention involved 60-minute sessions, 3x per week, for 24-weeks. Outcomes included feasibility measures and functional capacity.

RESULTS

17 out of 110 individuals initiated the program (recruitment rate = 15.4%) and 16 completed the program (drop-out rate = 5.8%) and attended sessions (attendance rate = 93.9%). Both groups showed a significant increase in upper extremity motor score (MS) and abdominal strength post intervention. Only the RLT group showed a significant change in lower extremity MS, with a mean increase of 3.00 [0.00; 16.5] points over time. Distance walked in the Functional Ambulatory Inventory (SCI-FAI) increased significantly (p = 0.02) over time only for the RLT group.

CONCLUSIONS

Feasibility rates of the intervention and functional outcomes justify a subsequent powered RCT comparing RLT to ABT as an effective rehabilitation tool for potentially improving functional strength and walking capacity in people with incomplete SCI.

The relationship between balance control and thigh muscle strength and muscle activity in persons with incomplete spinal cord injury

STUDY DESIGN

Cross-sectional study.

OBJECTIVES

A spinal cord injury (SCI) can compromise the ability to maintain sufficient balance control during activities in an upraised position. The objective of the study was to explore the relationship between balance control and muscle strength and muscle activation in the lower extremities in persons with incomplete SCI (iSCI).

SETTING

Sunnaas Rehabilitation Hospital, Norway.

METHODS

Thirteen men and two women with iSCI and 15 healthy, matched controls were included. Performance of the Berg Balance Scale (BBS) short version (7 items) was used to indicate balance control. Maximal voluntary contraction (MVC) was performed to measure isometric muscle strength in thigh muscles (knee extension/flexion), while surface electromyography (EMG) was measured from M. Vastus Lateralis and M. Biceps Femoris. The relative activation of each muscle during each of the BBS tasks was reported as the percentage of the maximal activation during the MVC (%EMGmax).

RESULTS

The iSCI participants had a significantly lower BBS sum score and up to 40% lower muscle strength in knee- flexion and extension compared to the matched healthy controls. They also exhibited a significantly higher %EMGmax, i.e. a higher muscle activation, during most of the balance tests. Univariate regression analysis revealed a significant association between balance control and mean values of %EMGmax in Biceps Femoris, averaged over the seven BBS tests.

CONCLUSIONS

The participants with iSCI had poorer balance control, reduced thigh muscle strength and a higher relative muscle activation in their thigh muscles, during balance-demanding activities.

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 ¼ 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%).

Corticospinal control of a challenging ankle task in incomplete spinal cord injury

After incomplete spinal cord injury (iSCI), the control of lower extremity movements may be affected by impairments in descending corticospinal tract function. Previous iSCI studies demonstrated relatively well-preserved movement control during simple alternating dorsi- and plantarflexions albeit with severely reduced motor strength and range of motion. However, this task required comparably limited fine motor control, impeding the sensitivity to assess the modulatory capacity of corticospinal control. Therefore, we introduced a more challenging ankle motor task requiring complex and dynamic feedback-based movement adjustments to modulate corticospinal drive. Nineteen individuals with iSCI and 22 control subjects performed two different ankle movement tasks: i) a regular, auditory-guided ankle movement task at a constant frequency as baseline assessment, and ii) an irregular, visually-guided ankle movement task following a predefined trajectory as a more challenging motor task. Both tasks were performed separately and in a randomised order. Electromyography (EMG) and kinematic data were recorded. EMG frequency characteristics were investigated using wavelet transformations. Control participants exhibited a shift of relative EMG intensity from higher (>100Hz) to lower frequencies (20-60Hz) comparing the regular with the irregular movement task. There is evidence that EMG activity within these lower frequencies comprise information on corticospinal drive. The EMG frequency shift was less pronounced for the less impaired leg and absent for the more impaired leg of individuals with iSCI. The precision error during the irregular task was significantly higher for individuals with iSCI (more impaired leg: 12.34±11.14%; less impaired leg: 6.93±2.74%) compared to control participants (4.10±0.84%). These results, along with the walking performance, correlated well with the delta frequency shift between the regular and irregular movement task in the 38Hz band (corticospinal drive frequency) in the iSCI group, suggesting that task performance is related to the capacity to modulate corticospinal control. The irregular movement task holds promise as a tool for revealing further insights into corticospinal control of single-joint movements. It may serve as a surrogate marker for the assessment of modulatory capacity and the integrity of corticospinal control in individuals with iSCI early after injury and throughout rehabilitation.

Neuromuscular electrical stimulation for motor recovery in pediatric neurological conditions: a scoping review

AIM

To explore the breadth of pediatric neurological conditions for which neuromuscular electrical stimulation (NMES) has been studied.

METHOD

Databases (PubMed, Google Scholar, Scopus, and Embase) were searched from 2000 to 2020, using the search terms 'neuromuscular electrical stimulation' OR 'functional electrical stimulation' with at least one of the words 'pediatric OR child OR children OR adolescent', and without the words 'dysphagia OR implanted OR enuresis OR constipation'. Articles focused on adults or individuals with cerebral palsy (CP) were excluded.

RESULTS

Thirty-five studies met the inclusion criteria, with a total of 353 pediatric participants (293 unique participants; mean age 7y 4mo, range 1wk-38y). NMES was applied in a range of pediatric conditions other than CP, including stroke, spinal cord injury, myelomeningocele, scoliosis, congenital clubfoot, obstetric brachial plexus injury, genetic neuromuscular diseases, and other neuromuscular conditions causing weakness.

INTERPRETATION

All 35 studies concluded that NMES was well-tolerated and most studies suggested that NMES could augment traditional therapy methods to improve strength. Outcome measurements were heterogeneous. Further research on NMES with larger, randomized studies will help clarify its potential to improve physiology and mobility in pediatric patients with neuromuscular conditions. What this paper adds Neuromuscular electrical stimulation (NMES) appears to be tolerated by pediatric patients. NMES shows potential for augmenting recovery in pediatric patients with a range of rehabilitation needs.

Co-contraction of ankle muscle activity during quiet standing in individuals with incomplete spinal cord injury is associated with postural instability

Previous findings indicate that co-contractions of plantarflexors and dorsiflexors during quiet standing increase the ankle mechanical joint stiffness, resulting in increased postural sway. Balance impairments in individuals with incomplete spinal cord injury (iSCI) may be due to co-contractions like in other individuals with reduced balance ability. Here we investigated the effect of co-contraction between plantar- and dorsiflexors on postural balance in individuals with iSCI (iSCI-group) and able-bodied individuals (AB-group). Thirteen able-bodied individuals and 13 individuals with iSCI were asked to perform quiet standing with their eyes open (EO) and eyes closed (EC). Kinetics and electromyograms from the tibialis anterior (TA), soleus and medial gastrocnemius were collected bilaterally. The iSCI-group exhibited more co-contractions than the AB-group (EO: 0.208% vs. 75.163%, p = 0.004; EC: 1.767% vs. 92.373%, p = 0.016). Furthermore, postural sway was larger during co-contractions than during no co-contraction in the iSCI-group (EO: 1.405 cm/s² vs. 0.867 cm/s², p = 0.023; EC: 1.831 cm/s² vs. 1.179 cm/s², p = 0.030), but no differences were found for the AB-group (EO: 0.393 cm/s² vs. 0.499 cm/s², p = 1.00; EC: 0.686 cm/s² vs. 0.654 cm/s², p = 1.00). To investigate the mechanism, we performed a computational simulation study using an inverted pendulum model and linear controllers. An increase of mechanical stiffness in the simulated iSCI-group resulted in increased postural sway (EO: 2.520 cm/s² vs. 1.174 cm/s², p < 0.001; EC: 4.226 cm/s² vs. 1.836 cm/s², p < 0.001), but not for the simulated AB-group (EO: 0.658 cm/s² vs. 0.658 cm/s², p = 1.00; EC: 0.943 cm/s² vs. 0.926 cm/s², p = 0.190). Thus, we demonstrated that co-contractions may be a compensatory strategy for individuals with iSCI to accommodate for decreased motor function, but co-contractions may result in increased ankle mechanical joint stiffness and consequently postural sway.

An Adaptive Assistance Controller to Optimize the Exoskeleton Contribution in Rehabilitation

In this paper, we present a novel adaptation rule to optimize the exoskeleton assistance in rehabilitation tasks. The proposed method adapts the exoskeleton contribution to user impairment severity without any prior knowledge about the user motor capacity. The proposed controller is a combination of an adaptive feedforward controller and a low gain adaptive PD controller. The PD controller guarantees the stability of the human-exoskeleton system during feedforward torque adaptation by utilizing only the human-exoskeleton joint positions as the sensory feedback for assistive torque optimization. In addition to providing a convergence proof, in order to study the performance of our method we applied it to a simplified 2-DOF model of human-arm and a generic 9-DOF model of lower limb to perform walking. In each simulated task, we implemented the impaired human torque to be insufficient for the task completion. Moreover, the scenarios that violate our convergence proof assumptions are considered. The simulation results show a converging behavior for the proposed controller; the maximum convergence time of 20 s is observed. In addition, a stable control performance that optimally supplements the remaining user motor contribution is observed; the joint angle tracking error in steady condition and its improvement compared to the start of adaptation are as follows: shoulder 0.96±2.53° (76%); elbow −0.35±0.81° (33%); hip 0.10±0.86° (38%); knee −0.19±0.67° (25%); and ankle −0.05±0.20° (60%). The presented simulation results verify the robustness of proposed adaptive method in cases that differ from our mathematical assumptions and indicate its potentials to be used in practice.

Triboelectric Nanogenerators for Therapeutic Electrical Stimulation

Current solutions developed for the purpose of in and on body (IOB) electrical stimulation (ES) lack autonomous qualities necessary for comfortable, practical, and self-dependent use. Consequently, recent focus has been placed on developing self-powered IOB therapeutic devices capable of generating therapeutic ES for human use. With the recent invention of the triboelectric nanogenerator (TENG), harnessing passive human biomechanical energy to develop self-powered systems has allowed for the introduction of novel therapeutic ES solutions. TENGs are especially effective at providing ES for IOB therapeutic systems given their bioconformability, low cost, simple manufacturability, and self-powering capabilities. Due to the key role of naturally induced electrical signals in many physiological functions, TENG-induced ES holds promise to provide a novel paradigm in therapeutic interventions. The aim here is to detail research on IOB TENG devices applied for ES-based therapy in the fields of regenerative medicine, neurology, rehabilitation, and pharmaceutical engineering. Furthermore, considering TENG-produced ES can be measured for sensing applications, this technology is paving the way to provide a fully autonomous personalized healthcare system, capable of IOB energy generation, sensing, and therapeutic intervention. Considering these grounds, it seems highly relevant to review TENG-ES research and applications, as they could constitute the foundation and future of personalized healthcare.

Characterizing inter-limb synchronization after incomplete spinal cord injury: A cross-sectional study

BACKGROUND

Individuals with incomplete spinal cord injury (iSCI) demonstrate greater postural sway and increased dependency on vision to maintain balance compared to able-bodied individuals. Research on standing balance after iSCI has focused on the joint contribution of the lower limbs; however, inter-limb synchrony in quiet standing is a sensitive measure of individual limb contributions to standing balance control in other neurological populations. It is unknown if and how reduced inter-limb synchrony contributes to the poor standing balance of individuals with iSCI.

RESEARCH QUESTION

How does an iSCI affect inter-limb synchrony and weight-bearing symmetry in standing?

METHODS

Eighteen individuals with non-progressive motor iSCI and 15 age- and sex-matched able-bodied individuals (M-AB) were included in the study. Participants stood in a standardized position on two adjacent force plates in eyes open and closed conditions for 70 s per condition. Net centre-of-pressure (COP) root mean square (RMS), net COP velocity, COP inter-limb synchrony (i.e. cross-correlation between left and right COP), and weight-bearing asymmetry (i.e. vertical force from each limb over total vertical force) were calculated. Muscle strength of the lower limbs was assessed with manual muscle testing.

RESULTS

Individuals with iSCI demonstrated reduced inter-limb synchrony when standing with eyes open and eyes closed, but did not differ to M-AB with respect to weight-bearing asymmetry. They also produced greater net COP RMS and velocity when compared to M-AB. Muscle strength of the two lower limbs demonstrated an overall asymmetry in individuals with iSCI.

SIGNIFICANCE

Individuals with iSCI demonstrated impaired balance control as evidenced by reduced inter-limb synchrony and greater COP RMS and velocity compared to M-AB individuals. This increased understanding of how balance control is impaired following iSCI may inform balance assessment and intervention for this population. Future work examining the association between inter-limb synchrony and the occurrence of falls in iSCI is warranted.

The Torque Referenced to a Perceived Exertion Level Is Affected by the Type of Movement in Men With Spinal Cord Injury

Objectives

To compare a standardized submaximal intensity (based on the rate of perceived exertion [RPE]) with the percentage of the average and peak torque during a familiarization session in individuals with different spinal cord injury (SCI) levels in gravity-resisted and gravity-assisted movements.

Methods

This was a cross-sectional study at a rehabilitation hospital. Thirty-six individuals stratified in tetraplegia (TP), high paraplegia (HP), and low paraplegia (LP) groups and 12 matched control participants (CG) were enrolled in the study. Participants performed a maximum strength test using isokinetic dynamometry. The familiarization consisted of 10 submaximal repetitions with a level 2 (i.e., 20% of the maximum score) in the Resistance Exercise Scale (OMNI-RES). Fisher's exact test compared the percentages of the average torque (%AT_Fam) and peak torque (%PT_Fam) of the familiarization (based on the peak torque during the maximum strength tests) to the %AT_Fam and %PT_Fam attained with 20% of RPE. The coefficient of variation (CV) was calculated to assess the torque dispersion during each familiarization set.

Results

The %AT_Fam was lower for gravity-assisted compared to gravity-resisted movements for HP, LP, and CG (p ≤ .05). The CV was significantly lower in gravity-resisted movements during familiarization for TP, LP, and CG.

Conclusion

Different RPE levels should be adopted for gravity-resisted or gravity-assisted upper limb exercises to maintain the same relative intensity during a familiarization session.

Immediate Effects of Transcutaneous Spinal Cord Stimulation on Motor Function in Chronic, Sensorimotor Incomplete Spinal Cord Injury

Deficient ankle control after incomplete spinal cord injury (iSCI) often accentuates walking impairments. Transcutaneous electrical spinal cord stimulation (tSCS) has been shown to augment locomotor activity after iSCI, presumably due to modulation of spinal excitability. However, the effects of possible excitability modulations induced by tSCS on ankle control have not yet been assessed. This study investigated the immediate (i.e., without training) effects during single-sessions of tonic tSCS on ankle control, spinal excitability, and locomotion in ten individuals with chronic, sensorimotor iSCI (American Spinal Injury Association Impairment Scale D). Participants performed rhythmic ankle movements (dorsi- and plantar flexion) at a given rate, and irregular ankle movements following a predetermined trajectory with and without tonic tSCS at 15 Hz, 30 Hz, and 50 Hz. In a subgroup of eight participants, the effects of tSCS on assisted over-ground walking were studied. Furthermore, the activity of a polysynaptic spinal reflex, associated with spinal locomotor networks, was investigated to study the effect of the stimulation on the dedicated spinal circuitry associated with locomotor function. Tonic tSCS at 30 Hz immediately improved maximum dorsiflexion by +4.6° ± 0.9° in the more affected lower limb during the rhythmic ankle movement task, resulting in an increase of +2.9° ± 0.9° in active range of motion. Coordination of ankle movements, assessed by the ability to perform rhythmic ankle movements at a given target rate and to perform irregular movements according to a trajectory, was unchanged during stimulation. tSCS at 30 Hz modulated spinal reflex activity, reflected by a significant suppression of pathological activity specific to SCI in the assessed polysynaptic spinal reflex. During walking, there was no statistical group effect of tSCS. In the subgroup of eight assessed participants, the three with the lowest as well as the one with the highest walking function scores showed positive stimulation effects, including increased maximum walking speed, or more continuous and faster stepping at a self-selected speed. Future studies need to investigate if multiple applications and individual optimization of the stimulation parameters can increase the effects of tSCS, and if the technique can improve the outcome of locomotor rehabilitation after iSCI.

Does prolonged walking cause greater muscle fatigability in individuals with incomplete spinal cord injury compared with matched-controls?

BACKGROUND

Individuals with incomplete spinal cord injury (iSCI) might show muscle fatigability during walking, primarily over long distances. The cause can be related to the motor impairment and walking compensations identified in this population. However, evidence on the occurrence of muscle fatigability after prolonged walking in individuals with iSCI is conflicting.

RESEARCH QUESTION

Does prolonged walking cause higher muscle fatigability in individuals with iSCI compared with matched-controls?

METHODS

We adopted a repeated measures design, in which maximal voluntary isometric contractions were performed before and after a walking test to induce the fatigability, in 24 individuals with iSCI and 24 matched-controls. Body weight-normalized peak torque (PT/BW), rate of force development (RFD), root mean square (RMS) and neuromuscular efficiency were used to assess the muscle fatigability. A mixed model ANOVA (2 × 2) was used for between-group and within-group comparisons. The significance was set in 5%.

RESULTS

Individuals with iSCI showed a greater decline in the PT/BW and RMS after the walking test. However, the RFD presented a greater decrease in the control group.

SIGNIFICANCE

Our results showed that prolonged walking caused higher muscle fatigability in individuals with iSCI compared to healthy individuals. Therefore, muscle fatigability should be considered during the rehabilitation planning and in activities of daily living of individuals with iSCI. Moreover, the identification of muscle fatigability in individuals with iSCI might be useful to prevent high levels of physical exertion and, possibly, the risk of fall.

The effect of paired corticospinal-motoneuronal stimulation on maximal voluntary elbow flexion in cervical spinal cord injury: an experimental study

STUDY DESIGN

Randomised, controlled, crossover study.

OBJECTIVES

Paired corticospinal-motoneuronal stimulation (PCMS) involves repeatedly pairing stimuli to corticospinal neurones and motoneurones to induce changes in corticospinal transmission. Here, we examined whether PCMS could enhance maximal voluntary elbow flexion in people with cervical spinal cord injury.

SETTING

Neuroscience Research Australia, Sydney, Australia.

METHODS

PCMS comprised 100 pairs of transcranial magnetic and electrical peripheral nerve stimulation (0.1 Hz), timed so corticospinal potentials arrived at corticospinal-motoneuronal synapses 1.5 ms before antidromic motoneuronal potentials. On two separate days, sets of five maximal elbow flexions were performed by 11 individuals with weak elbow flexors post C4 or C5 spinal cord injury before and after PCMS or control (100 peripheral nerve stimuli) conditioning. During contractions, supramaximal biceps brachii stimulation elicited superimposed twitches, which were expressed as a proportion of resting twitches to give maximal voluntary activation. Maximal torque and electromyographic activity were also assessed.

RESULTS

Baseline median (range) maximal torque was 11 Nm (6-41 Nm) and voluntary activation was 92% (62-99%). Linear mixed modelling revealed no significant differences between PCMS and control protocols after conditioning (maximal torque: p = 0.87, superimposed twitch: p = 0.87, resting twitch: p = 0.44, voluntary activation: p = 0.36, biceps EMG: p = 0.25, brachioradialis EMG: 0.67).

CONCLUSIONS

Possible explanations for the lack of effect include a potential ceiling effect for voluntary activation, or that PCMS may be less effective for elbow flexors than distal muscles. Despite results, previous studies suggest that PCMS is worthy of further investigation.

Activity-Based Physical Rehabilitation with Adjuvant Testosterone to Promote Neuromuscular Recovery after Spinal Cord Injury

Neuromuscular impairment and reduced musculoskeletal integrity are hallmarks of spinal cord injury (SCI) that hinder locomotor recovery. These impairments are precipitated by the neurological insult and resulting disuse, which has stimulated interest in activity-based physical rehabilitation therapies (ABTs) that promote neuromuscular plasticity after SCI. However, ABT efficacy declines as SCI severity increases. Additionally, many men with SCI exhibit low testosterone, which may exacerbate neuromusculoskeletal impairment. Incorporating testosterone adjuvant to ABTs may improve musculoskeletal recovery and neuroplasticity because androgens attenuate muscle loss and the slow-to-fast muscle fiber-type transition after SCI, in a manner independent from mechanical strain, and promote motoneuron survival. These neuromusculoskeletal benefits are promising, although testosterone alone produces only limited functional improvement in rodent SCI models. In this review, we discuss the (1) molecular deficits underlying muscle loss after SCI; (2) independent influences of testosterone and locomotor training on neuromuscular function and musculoskeletal integrity post-SCI; (3) hormonal and molecular mechanisms underlying the therapeutic efficacy of these strategies; and (4) evidence supporting a multimodal strategy involving ABT with adjuvant testosterone, as a potential means to promote more comprehensive neuromusculoskeletal recovery than either strategy alone.

EVALUATION OF MUSCLE STRENGTH IN MEDULLAR INJURY: A LITERATURE REVIEW

ABSTRACT Objective: To identify the tools used to evaluate muscle strength in subjects with spinal cord injury in both clinical practice and scientific research. Methods: Initially, the literature review was carried out to identify the tools used in scientific research. The search was conducted in the following databases: Virtual Health Library (VHL), Pedro, and PubMed. Studies published between 1990 and 2016 were considered and selected, depicting an evaluation of muscle strength as an endpoint or for characterization of the sample. Next, a survey was carried out with physiotherapists to identify the instruments used for evaluation in clinical practice, and the degree of satisfaction of professionals with respect to them. Results: 495 studies were found; 93 were included for qualitative evaluation. In the studies, we verified the use of manual muscle test with different graduation systems, isokinetic dynamometer, hand-held dynamometer, and manual dynamometer. In clinical practice, the manual muscle test using the motor score recommended by the American Spinal Cord Injury Association was the most used method, despite the limitations highlighted by the physiotherapists interviewed. Conclusion: In scientific research, there is great variation in the methods and tools used to evaluate muscle strength in individuals with spinal cord injury, differently from clinical practice. The tools available and currently used have important limitations, which were highlighted by the professionals interviewed. No instrument depicts direct relationship of muscle strength and functionality of the subject. There is no consensus as to the best method for assessing muscle strength in spinal cord injury, and new instruments are needed that are specific for use in this population.

Exploration of Hand Grasp Patterns Elicitable Through Non-Invasive Proximal Nerve Stimulation

Various neurological conditions, such as stroke or spinal cord injury, result in an impaired control of the hand. One method of restoring this impairment is through functional electrical stimulation (FES). However, traditional FES techniques often lead to quick fatigue and unnatural ballistic movements. In this study, we sought to explore the capabilities of a non-invasive proximal nerve stimulation technique in eliciting various hand grasp patterns. The ulnar and median nerves proximal to the elbow joint were activated transcutanously using a programmable stimulator, and the resultant finger flexion joint angles were recorded using a motion capture system. The individual finger motions averaged across the three joints were analyzed using a cluster analysis, in order to classify the different hand grasp patterns. With low current intensity (<5 mA and 100 µs pulse width) stimulation, our results show that all of our subjects demonstrated a variety of consistent hand grasp patterns including single finger movement and coordinated multi-finger movements. This study provides initial evidence on the feasibility of a proximal nerve stimulation technique in controlling a variety of finger movements and grasp patterns. Our approach could also be developed into a rehabilitative/assistive tool that can result in flexible movements of the fingers.

Strategies to augment volitional and reflex function may improve locomotor capacity following incomplete spinal cord injury

Many studies highlight the remarkable plasticity demonstrated by spinal circuits following an incomplete spinal cord injury (SCI). Such plasticity can contribute to improvements in volitional motor recovery, such as walking function, although similar mechanisms underlying this recovery may also contribute to the manifestation of exaggerated responses to afferent input, or spastic behaviors. Rehabilitation interventions directed toward augmenting spinal excitability have shown some initial success in improving locomotor function. However, the potential effects of these strategies on involuntary motor behaviors may be of concern. In this article, we provide a brief review of the mechanisms underlying recovery of volitional function and exaggerated reflexes, and the potential overlap between these changes. We then highlight findings from studies that explore changes in spinal excitability during volitional movement in controlled conditions, as well as altered kinematic and behavioral performance during functional tasks. The initial focus will be directed toward recovery of reflex and volitional behaviors following incomplete SCI, followed by recent work elucidating neurophysiological mechanisms underlying patterns of static and dynamic muscle activation following chronic incomplete SCI during primarily single-joint movements. We will then transition to studies of locomotor function and the role of altered spinal integration following incomplete SCI, including enhanced excitability of specific spinal circuits with physical and pharmacological interventions that can modulate locomotor output. The effects of previous and newly developed strategies will need to focus on changes in both volitional function and involuntary spastic reflexes for the successful translation of effective therapies to the clinical setting.

Constraints on Stance-Phase Force Production during Overground Walking in Persons with Chronic Incomplete Spinal Cord Injury

Persons with incomplete spinal cord injury (iSCI) face ongoing struggles with walking, including reduced speed and increased reliance on assistive devices (ADs). The forces underlying body weight support and gait, as measured by ground reaction forces (GRFs), are likely altered after iSCI because of weakness and AD dependence but have not been studied. The purpose of this study was to examine GRF production during overground walking after iSCI, because greater insight into GRF constraints is important for refining therapeutic interventions. Because of reduced and discoordinated motor output after iSCI, we hypothesized that persons with iSCI would exert smaller GRFs and altered GRF modifications to increased cadence compared with able-bodied (AB) persons, especially when using an AD. Fifteen persons with chronic iSCI, stratified into no AD (n = 7) and AD (n = 8) groups, walked across an instrumented walkway at self-selected and fast (115% self-selected) cadences. Fifteen age-matched AB controls walked at their own cadences and iSCI-matched conditions (cadence and AD). Results showed fore-aft GRFs are reduced in persons with iSCI compared with AB controls, with reductions greatest in persons dependent on an AD. When controlling for cadence and AD, propulsive forces were still lower in persons with iSCI. Compared with AB controls, persons with iSCI demonstrated altered GRF modifications to increased cadence. Persons with iSCI exhibit different stance-phase forces compared with AB controls, which are impacted further by AD use and slower walking speed. Minimizing AD use and/or providing propulsive biofeedback during walking could enhance GRF production after iSCI.

MRI measures of fat infiltration in the lower extremities following motor incomplete spinal cord injury: reliability and potential implications for muscle activation

Muscle fat infiltration (MFI) is an expected consequence of incomplete spinal cord injury (iSCI). The MFI magnitude may have clinical value in determining functional recovery. However, there is a lack of understanding of how MFI relates to the volitional muscle activity in people with motor incomplete spinal cord injury (iSCI). Five iSCI and 5 uninjured age-matched control subjects participated in the study. In this preliminary study, we established the reliability of MFI quantification of select lower extremity muscles across different raters. Secondly, we assessed the magnitude and distribution of MFI in the lower legs of iSCI and uninjured control participants. Thirdly, we explored the relationship between MFI in the plantar flexor muscles and the ability to volitionally activate these muscles. High levels of inter-rater reliability were observed. The iSCI group had significantly elevated and a vastly different MFI distribution in the lower leg muscles compared to healthy controls. MFI was negatively correlated with volitional activation in iSCI. Our preliminary results sanction the importance of lower extremity MFI quantification as a potential measure in determining the functional outcomes in iSCI, and the subsequent pathological sequelae.

Does Neuromuscular Electrical Stimulation Therapy Increase Voluntary Muscle Strength After Spinal Cord Injury? A Systematic Review

Background: Physical therapists frequently use neuromuscular electrical stimulation (NMES) therapy in an effort to increase the voluntary strength of partially paralyzed muscles in people with spinal cord injury (SCI), but it is not clear whether this treatment is effective. Objective: To determine the effectiveness of NMES for increasing voluntary strength in the partially paralyzed muscles of people with SCI. Methods: A systematic review of scientific literature was conducted in MEDLINE, CINAHL, PEDro, ScienceDirect, and Embase. Inclusion criteria were randomized controlled trials and controlled trials that compared NMES aimed at increasing strength in partially paralyzed muscles versus placebo/nothing or versus a nonstrengthening intervention or versus any other type of strengthening intervention in adults with SCI. Results: Five studies were included. Two studies found an increase in strength measured by peak force and manual muscle force test after an NMES protocol. One study found a between-group difference in favor of the NMES associated with progressive resistance training, and the other study showed an increase in the number of muscles improved by at least 1 degree of strength after NMES in combination with a cycle ergometer. The other 3 studies made several comparisons and found no differences between groups that received NMES and the controls. Conclusions: There is some suggestion that NMES increases voluntary strength in partially paralyzed muscle following SCI. However, there is no strong evidence to affirm the superiority of NMES over other treatment strategies used to gain strength in partially paralyzed muscles after SCI. These findings need replicating in large high-quality randomized controlled trials.

Ambulatory function in motor incomplete spinal cord injury: a magnetic resonance imaging study of spinal cord edema and lower extremity muscle morphometry

Study Design

This research utilized a cross-sectional design.

Objectives

Spinal cord edema length has been measured with T2-weighted sagittal MRI to predict motor recovery following spinal cord injury. The purpose of our study was to establish the correlational value of axial spinal cord edema using T2-weighted MRI. We hypothesized a direct relationship between the size of damage on axial MRI and walking ability, motor function, and distal muscle changes seen in motor incomplete spinal cord injury (iSCI).

Setting

University based laboratory in Chicago, IL USA.

Methods

Fourteen participants with iSCI took part in the study. Spinal cord axial damage ratios were assessed using axial T2-weighted MRI. Walking ability was investigated using the 6-minute walk test and daily stride counts. Maximum plantarflexion torque was quantified using isometric dynomometry. Muscle fat infiltration (MFI) and relative muscle cross sectional area (rmCSA) were quantified using fat/water separation magnetic resonance imaging.

Results

Damage ratios were negatively correlated with distance walked in 6 minutes, average daily strides, and maximum plantarflexion torque, and a negative linear trend was found between damage ratios and lower leg rmCSA. While damage ratios were not significantly correlated with MFI, we found significantly higher MFI in the wheelchair user participant group compared to community walkers.

Conclusions

Damage ratios may be useful in prognosis of motor recovery in spinal cord injury. The results warrant a large multi-site research study to investigate the value of high-resolution axial T2-weighted imaging to predict walking recovery following motor incomplete spinal cord injury.

Lower extremity muscle structure in incomplete spinal cord injury: a comparison between ultrasonography and magnetic resonance imaging

INTRODUCTION

Ultrasound (US) measures of muscle thickness are used in the management and monitoring of muscle changes during rehabilitation, but it is unknown how this measure compares to magnetic resonance imaging (MRI) measures of muscle cross-sectional area (CSA) in patients with spinal cord injury (SCI).

CASE PRESENTATION

Six participants with incomplete SCI underwent US imaging and MRI of their gastrocnemius and tibialis anterior (TA) muscles.

DISCUSSION

Significant correlations were found between US muscle thickness and MRI CSA in the gastrocnemius (R=0.91, P<0.001), and TA muscles (R=0.58, P<0.05). US muscle thickness in the gastrocnemius and TA of patients with incomplete SCI may be used as a cheaper alternative measure of CSA as measured using MRI, and this measure may be clinically useful to track progress in muscle gains during rehabilitation.

Remodeling the Dendritic Spines in the Hindlimb Representation of the Sensory Cortex after Spinal Cord Hemisection in Mice

Spinal cord injury (SCI) can induce remodeling of multiple levels of the cerebral cortex system especially in the sensory cortex. The aim of this study was to assess, in vivo and bilaterally, the remodeling of dendritic spines in the hindlimb representation of the sensory cortex after spinal cord hemisection. Thy1-YFP transgenic mice were randomly divided into the control group and the SCI group, and the spinal vertebral plates (T11–T12) of all mice were excised. Next, the left hemisphere of the spinal cord (T12) was hemisected in the SCI group. The hindlimb representations of the sensory cortex in both groups were imaged bilaterally on the day before (0d), and three days (3d), two weeks (2w), and one month (1m) after the SCI. The rates of stable, newly formed, and eliminated spines were calculated by comparing images of individual dendritic spine in the same areas at different time points. In comparison to the control group, the rate of newly formed spines in the contralateral sensory cortex of the SCI group increased at three days and two weeks after injury. The rates of eliminated spines in the bilateral sensory cortices increased and the rate of stable spines in the bilateral cortices declined at two weeks and one month. From three days to two weeks, the stable rates of bilaterally stable spines in the SCI group decreased. In comparison to the control group and contralateral cortex in the SCI group, the re-emerging rate of eliminated spines in ipsilateral cortex of the SCI group decreased significantly. The stable rates of newly formed spines in bilateral cortices of the SCI group decreased from two weeks to one month. We found that the remodeling in the hindlimb representation of the sensory cortex after spinal cord hemisection occurred bilaterally. This remodeling included eliminating spines and forming new spines, as well as changing the reorganized regions of the brain cortex after the SCI over time. Soon after the SCI, the cortex was remodeled by increasing spine formation in the contralateral cortex. Then it was remodeled prominently by eliminating spines of bilateral cortices. Spinal cord hemisection also caused traditional stable spines to become unstable and led the eliminated spines even more hard to recur especially in the ipsilateral cortex of the SCI group. In addition, it also made the new formed spines unstable.

Evaluation of central and peripheral fatigue in the quadriceps using fractal dimension and conduction velocity in young females

PURPOSE

Over the past decade, linear and non-linear surface electromyography descriptors for central and peripheral components of fatigue have been developed. In the current study, we tested fractal dimension (FD) and conduction velocity (CV) as myoelectric descriptors of central and peripheral fatigue, respectively. To this aim, we analyzed FD and CV slopes during sustained fatiguing contractions of the quadriceps femoris in healthy humans.

METHODS

A total of 29 recreationally active women (mean age±standard deviation: 24±4 years) and two female elite athletes (one power athlete, age 24 and one endurance athlete, age 30 years) performed two knee extensions: (1) at 20% maximal voluntary contraction (MVC) for 30 s, and (2) at 60% MVC held until exhaustion. Surface EMG signals were detected from the vastus lateralis and vastus medialis using bidimensional arrays.

RESULTS

Central and peripheral fatigue were described as decreases in FD and CV, respectively. A positive correlation between FD and CV (R=0.51, p<0.01) was found during the sustained 60% MVC, probably as a result of simultaneous motor unit synchronization and a decrease in muscle fiber CV during the fatiguing task.

CONCLUSIONS

Central and peripheral fatigue can be described as changes in FD and CV, at least in young, healthy women. The significant correlation between FD and CV observed at 60% MVC suggests that a mutual interaction between central and peripheral fatigue can arise during submaximal isometric contractions.

Lower Extremity Strength Is Correlated with Walking Function After Incomplete SCI

BACKGROUND

Lower extremity strength has been reported to relate to walking ability, however, the relationship between voluntary lower extremity muscle function as measured by isokinetic dynamometry and walking have not been thoroughly examined in individuals with incomplete spinal cord injury (iSCI).

OBJECTIVE

To determine the extent to which measures of maximal voluntary isometric contraction (MVIC) and rate of torque development (RTD) in the knee extensor (KE) and plantar flexor (PF) muscle groups correlate with self-selected overground walking speed and spatiotemporal characteristics of walking.

METHODS

Twenty-two subjects with chronic (>6 months) iSCI participated in a cross-sectional study. Values for MVIC and RTD in the KE and PF muscle groups were determined by isokinetic dynamometry. Walking speed and spatiotemporal characteristics of walking were measured during overground walking.

RESULTS

MVIC in the KE and PF muscle groups correlated significantly with walking speed. RTD was significantly correlated with walking speed in both muscle groups, the more-involved PF muscle group showing the strongest correlation with walking speed (r = 0.728). RTD in the KE and PF muscle groups of the more-involved limb was significantly correlated with single support time of the more-involved limb.

CONCLUSIONS

These data demonstrate that lower extremity strength is associated with walking ability after iSCI. Correlations for the muscle groups of the move-involved side were stronger compared to the less-involved limb. In addition, PF function is highlighted as a potential limiting factor to walking speed along with the importance of RTD.

Trunk strength and function using the multidirectional reach distance in individuals with non-traumatic spinal cord injury

CONTEXT

Trunk control is essential to engage in activities of daily living. Measuring trunk strength and function in persons with spinal cord injury (SCI) is difficult. Trunk function has not been studied in non-traumatic SCI (NTSCI).

OBJECTIVES

To characterize changes in trunk strength and seated functional reach in individuals with NTSCI during inpatient rehabilitation. To determine if trunk strength and seated reach differ between walkers and wheelchair users. To explore relationships between trunk and hip strength and seated functional reach.

DESIGN

Observational study.

SETTING

Two SCI rehabilitation facilities.

PARTICIPANTS

32 subacute inpatients (mean age 48.0 ± 15.4 years).

OUTCOME MEASURES

Isometric strength of trunk and hip and function (Multidirectional Reach Test: MDRT) were assessed at admission and within 2 weeks of discharge. Analysis of variance was conducted for admission measures (MDRT, hip and trunk strength) between walkers and wheelchair users. Changes in MDRT, hip and trunk strength were evaluated using parametric and non-parametric statistics. The level of association between changes in values of MRDT and strength was also examined.

RESULTS

Significant differences between walkers and wheelchair users were found for strength measures (P < 0.05) but not for MDRT. Left- and right-sided reaches increased in wheelchair users only (P < 0.05). Associations between changes in hip strength, trunk strength, and reach distance were found (R = 0.67-0.73).

CONCLUSION

In clinical settings, it is feasible and relevant to assess trunk, hip strength, and MRDT. Future studies require strategies to increase the number of participants assessed, in order to inform clinicians about relevant rehabilitation interventions.

Gait adaptation during walking on an inclined pathway following spinal cord injury

BACKGROUND

Individuals with incomplete spinal cord injury need to be assessed in different environments. The objective of this study was to compare lower-limb power generation in subjects with spinal cord injury and healthy subjects while walking on an inclined pathway.

METHODS

Eleven subjects with spinal cord injury and eleven healthy subjects walked on an inclined pathway at their natural gait speed and at slow gait speed (healthy subjects only). Ground reaction forces were recorded by force plates embedded in the inclined pathway and a 3-D motion analysis system recorded lower-limb motions. Data analysis included gait cycle parameters and joint peak powers. Differences were identified by student t-tests.

FINDINGS

Gait cycle parameters were lower in spinal cord injury subjects compared to healthy subjects at natural speed but similar at slow gait speed. Subjects with spinal cord injury presented lower power at the ankle, knee and hip compared to healthy subjects at natural gait speed while only the power generation at push-off remained lower when the two groups performed at similar speed.

INTERPRETATION

The most important differences are associated with the fact that individuals with spinal cord injury walk at a slower speed, except for the ankle power generation. This study demonstrated that, even with a good motor recovery, distal deficits remain and may limit the ability to adapt to uphill and downhill walking. Inclined pathways are indicated to train patients with spinal cord injury. Clinicians should focus on the speed of uphill and downhill walking and on the use of plantar flexors.

Short-term maximal-intensity resistance training increases volitional function and strength in chronic incomplete spinal cord injury: a pilot study

BACKGROUND AND PURPOSE

Recent research shows that individuals with an incomplete spinal cord injury (SCI) have a reserve of force-generating capability that is observable during repeated intermittent maximal volitional effort contractions. Previous studies suggest that increased neural drive contributes to the enhanced short-term force-generating capabilities. Whether this reserve can be harnessed with repeated training is unclear. The purpose of this pilot study was to investigate the effects of 4 weeks of maximal-intensity resistance training, compared with conventional progressive resistance training, on lower extremity function and strength in chronic incomplete SCI.

METHODS

Using a randomized crossover design, 5 individuals with chronic (> 1 year postinjury) SCI American Spinal Injury Association Impairment Scale classification C or D were tested before and after 4 weeks of both maximal-intensity training and progressive resistance training paradigms. Outcomes measures included the 6-Minute Walk Test, the Berg Balance Scale, and peak isometric torque for strength of lower extremity muscles.

RESULTS

Maximal-intensity resistance training was associated with an average increase of 12.19 ± 8.29 m on the 6-Minute Walk Test, 4 ± 1.9 points on the Berg Balance Scale, 4 ± 4.5 points on the lower extremity motor score), while no changes on the above scores were seen with conventional training. Furthermore, significant increases in peak volitional isometric torques (mean increase = 20 ± 8 Nm) were observed following maximal-intensity resistance training when compared with conventional training (mean increase = 0.12 ± 3 Nm, P = 0.03).

DISCUSSION AND CONCLUSIONS

Maximal-intensity training paradigm may facilitate rapid gains in volitional function and strength in persons with chronic motor-incomplete SCI, using a simple short-term training paradigm.

Exposure to acute intermittent hypoxia augments somatic motor function in humans with incomplete spinal cord injury

BACKGROUND

Neural plasticity may contribute to motor recovery following spinal cord injury (SCI). In rat models of SCI with respiratory impairment, acute intermittent hypoxia (AIH) strengthens synaptic inputs to phrenic motor neurons, thereby improving respiratory function by a mechanism known as respiratory long-term facilitation. Similar intermittent hypoxia-induced facilitation may be feasible in somatic motor pathways in humans.

OBJECTIVE

Using a randomized crossover design, the authors tested the hypothesis that AIH increases ankle strength in people with incomplete SCI.

METHODS

Ankle strength was measured in 13 individuals with chronic, incomplete SCI before and after AIH. Voluntary ankle strength was estimated using changes in maximum isometric ankle plantar flexion torque generation and plantar flexor electromyogram activity following 15 low oxygen exposures (Fio(2) = 0.09, 1-minute intervals). Results were compared with trials where subjects received sham exposure to room air.

RESULTS

AIH increased plantar flexion torque by 82 ± 33% (P < .003) immediately following AIH and was sustained above baseline for more than 90 minutes (P < .007). Increased ankle plantar flexor electromyogram activity (P = .01) correlated with increased torque (r(2) = .5; P < .001). No differences in plantar flexion strength or electromyogram activity were observed in sham experiments.

CONCLUSIONS

AIH elicits sustained increases in volitional somatic motor output in persons with chronic SCI. Thus, AIH has promise as a therapeutic tool to induce plasticity and enhance motor function in SCI patients.

Corticospinal tract integrity correlates with knee extensor weakness in chronic stroke survivors

OBJECTIVE

Muscle weakness develops rapidly after stroke, adversely affecting motor performance, and contributing to reduced functional ability. While the contributions of structural and functional alterations in skeletal muscle to post-stroke weakness have been well described, the relationship between motor pathway integrity, measured using both radiological and electrophysiological techniques, and post-stroke muscle weakness is not clear. This study sought to determine the role of corticospinal tract (CST) integrity on knee extensor weakness in chronic stroke survivors.

METHODS

Knee extensor strength and activation testing were performed at 90° of knee flexion using an interpolated triplet technique. CST integrity was evaluated using data obtained from Diffusion Tensor Imaging and transcranial magnetic stimulation.

RESULTS

Recordings in nine stroke subjects indicated substantial knee extensor weakness and activation deficits in the paretic legs of the stroke survivors. Regression analysis revealed that asymmetry in CST integrity was strongly related to between-leg differences in knee strength.

CONCLUSIONS

The results of this study suggest a strong link between CST integrity and lower extremity strength, and add to the growing evidence of substantial knee extensor weakness and activation impairments in stroke survivors.

SIGNIFICANCE

The findings from this study further our understanding of the anatomical and neurophysiological contributions to motor impairments after stroke, which may benefit clinicians and researchers in the field of stroke rehabilitation.

Repeated maximal volitional effort contractions in human spinal cord injury: initial torque increases and reduced fatigue

BACKGROUND

Substantial data indicate greater muscle fatigue in individuals with spinal cord injury (SCI) compared with healthy control subjects when tested by using electrical stimulation protocols. Few studies have investigated the extent of volitional fatigue in motor incomplete SCI.

METHODS

Repeated, maximal volitional effort (MVE) isometric contractions of the knee extensors (KE) were performed in 14 subjects with a motor incomplete SCI and in 10 intact subjects. Subjects performed 20 repeated, intermittent MVEs (5 seconds contraction/5 seconds rest) with KE torques and thigh electromyographic (EMG) activity recorded.

RESULTS

Peak KE torques declined to 64% of baseline MVEs with repeated efforts in control subjects. Conversely, subjects with SCI increased peak torques during the first 5 contractions by 15%, with little evidence of fatigue after 20 repeated efforts. Increases in peak KE torques and the rate of torque increase during the first 5 contractions were attributed primarily to increases in quadriceps EMG activity, but not to decreased knee flexor co-activation. The observed initial increases in peak torque were dependent on the subject's volitional activation and were consistent on the same or different days, indicating little contribution of learning or accommodation to the testing conditions. Sustained MVEs did not elicit substantial increases in peak KE torques as compared to repeated intermittent efforts.

CONCLUSIONS

These data revealed a marked divergence from expected results of increased fatigability in subjects with SCI, and may be a result of complex interactions between mechanisms underlying spastic motor activity and changes in intrinsic motoneuron properties.

Temporal characteristics of lower extremity moment generation in children with cerebral palsy

Lower extremity weakness has been documented in children with cerebral palsy (CP). However, the temporal characteristics of moment generation have not been characterized, and they may be important to function. This study tested ankle, knee, and hip flexion and extension moment generation capabilities in children with CP and in able-bodied children. Maximum voluntary isometric contractions (MVIC), the maximum rates of moment development and relaxation, and the time to produce and reduce the moments were quantified. Relationships between the temporal measures, Gross Motor Function Measure-66 (GMFM-66), and MVICs were also examined. Children with CP had significantly reduced MVICs, maximum development, and relaxation rates, and increased times to produce and reduce moments. The maximum rates of moment development and relaxation at some joints were correlated with the GMFM-66 and MVICs. These results suggest that both the magnitude and temporal characteristics of moment generation need to be targeted during therapeutic interventions for children with CP.

Adaptation of postural responses during different standing perturbation conditions in individuals with incomplete spinal cord injury

Incomplete spinal cord injury (ISCI) frequently disrupts afferent and efferent neural pathways underlying co-requisite voluntary and involuntary muscle activation required for functional standing and walking. To understand involuntary postural control mechanisms necessary for standing, we compared eight individuals with ISCI to eight controls with no impairment. The aim of this study was to investigate anticipatory and reactive balance responses in individuals with ISCI. The ability to adapt to changes in balance conditions was assessed by monitoring automatic postural responses (APRs) during a series of expected and unexpected changes in perturbation direction (backward translation versus toes-up rotation). Both groups were able to modulate appropriately within one or two trials following an unexpected change in condition. Onset times of anterior tibialis and medial gastrocnemius (MG) were significantly slower in the ISCI group during expected and unexpected conditions. These findings demonstrate that persons with mild to moderate lower extremity sensorimotor deficits are able to generate and adapt APRs to a rapid and unexpected contextual change during a simple standing balance task.

Ankle paresis in incomplete spinal cord injury: relation to corticospinal conductivity and ambulatory capacity

There is limited data on the relation of corticospinal tract conductivity to clinical measures in incomplete spinal cord injury. This study examined the relationship of muscle strength to corticospinal tract input assessed by motor evoked potentials (MEPs) during static and dynamic conditions and to gait. Dorsiflexor strength was established by manual muscle test, maximal voluntary contraction, and maximal movement velocity, the latter being acquired during auditory-paced ankle movements. MEPs were elicited during isometric contractions with constant or continuously increasing ankle joint torque. Gait was assessed by quantifying its speed and independence. Linear regression analyses showed that maximal movement velocity was related to the MEP latencies and amplitudes in the dynamic condition (R(2)(adj.) = 0.62) and to the MEP latencies in the static condition (R(2)(adj.) = 0.45). Maximal voluntary contraction was only related to the MEP latencies in the static (R(2)(adj.) = 0.45) and the dynamic condition (R(2)(adj.) = 0.21), whereas manual muscle test did not show any relationship to the MEPs. In incomplete spinal cord injury patients, the dynamic measure maximal movement velocity might be a useful clinical assessment of corticospinal tract function. Clinical studies on recovery and repair of corticospinal tract function in spinal lesions could substantially benefit from implementing dynamic measures in the clinical assessment protocol.

Changes in corticospinal function and ankle motor control during recovery from incomplete spinal cord injury

Little is known about the mechanisms that underlie motor recovery after incomplete spinal cord injury (iSCI) in humans. This study assessed changes in corticospinal tract (CST) function by measuring motor-evoked potentials (MEPs) and ankle motor control at 1, 3, and 6 months after acute iSCI. In 12 iSCI patients and matched controls, MEPs (evoked at 20% of maximal voluntary contraction [MVC]) were combined with a comprehensive ankle motor assessment protocol that measured ankle dorsiflexor strength (MVC, manual muscle testing, maximal movement velocity [MMV]), dexterity (the ability to accurately time ankle dorsiflexion movements) and gait (speed, walking aids). In the first 6 months after iSCI, all measures of muscle strength, gait and the MEP amplitudes significantly increased. The level of background electromyography (EMG) at 20% MVC remained stable, although absolute MVC increased. The MEP latencies were significantly delayed and remained unchanged during the first 6 months after iSCI. In addition, dexterity was preserved throughout rehabilitation. The percentage increase in MEP amplitude was significantly related only to the percentage improvement in MMV. The finding of unchanged CST conductivity, as assessed by MEP latencies in acute iSCI patients recovering motor function, is in accordance with previous studies in human SCI on this issue. The increased MEP facilitation at stable background EMG might indicate improved synchronization of the descending volley and/or responsiveness of motoneurons to supra-spinal input. The absence of a relationship between MEP amplitudes and recovery of ambulation and muscle strength implies that plastic changes in spinal neural circuits and preserved motor units might have contributed to the functional improvement.

Effects of intense exercise in chronic spinal cord injury

BACKGROUND

Exercise has beneficial effects on muscle and motor function after spinal cord injury (SCI). Little is known regarding effects of prolonged intense exercise (IE) in humans with chronic SCI.

DESIGN

Prospective, non-randomized, controlled observational study. The intervention was either a multimodal IE program (n=21) or a control (CTL) intervention consisting of self-regulated exercise (n=8).

OBJECTIVE

Measure sensorimotor function over 6 months in relation to an IE program.

SETTING

Single outpatient center.

SUBJECTS

Subjects with chronic SCI (n=29 total), mainly ASIA Impairment Scale A and B, injury levels C4-T11.

RESULTS

Baseline neurological assessments (for example, ASIA motor score, 39+/-3 vs 42+/-5, IE vs CTL, P>0.5, mean+/-s.e.m.) did not differ between the two groups. During the 6 months, IE subjects averaged 7.3+/-0.7 h per week exercise, not significantly different from CTL subjects (5.2+/-1.3 h per week, P>0.1). However, after 6 months, IE subjects showed significantly greater motor gains than CTL subjects in the main outcome measure, ASIA motor score (change of 4.8+/-1.0 vs -0.1+/-0.5 points, P=0.0001). The main outcome measure was calculated by ASIA motor score. These IE subject ASIA motor gains correlated with number of exercise hours per week (r=0.53, P<0.02), and with type of specific IE components, particularly load bearing.

CONCLUSIONS

Multimodal IE can significantly improve motor function in subjects with chronic SCI. An organized program may provide greater motor benefits than a self-regulated program; load bearing might be of particular value. IE might have therapeutic value in chronic SCI, and as an adjunct to other restorative therapies.

Non-invasive assessment of lower extremity muscle composition after incomplete spinal cord injury

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

(1) To quantify intramyocellular lipid (IMCL) content of the soleus muscle. (2) To assess the T(2) relaxation rates in the lower extremity skeletal muscles in persons with incomplete spinal cord injury (SCI).

SETTING

Academic Institution, Florida.

METHODS

Eight subjects (42+/-10 years old; 70+/-12 kg; 176+/-10 cm) with chronic (17+/-9 months post injury) motor SCI (C4-T12; ASIA C or D) and eight matched healthy controls were tested. Localized unsuppressed proton spectroscopy (H-MRS) was performed to estimate total lipid content and individual lipid components; IMCL and extramyocellular lipid (EMCL) from the soleus muscle. T(2)-weighted imaging of lower extremity muscles yielded muscle T(2) rates.

RESULTS

The IMCL content of the soleus muscle was 3.3 times higher in the patient group as compared to controls (P=0.002; 0.0401 (0.0234-0.0849) versus 0.0123 (0.0090-0.0175)). Similarly, EMCL measures were 4.5 times higher as compared to the controls (P=0.002). Significant differences were observed in the T(2) relaxation times of the soleus and gastrocnemius muscles (P<0.05).

CONCLUSION

The increased levels of IMCL might interfere with the glucose uptake in skeletal muscle; potentially predisposing persons with incomplete SCI to the development of peripheral insulin resistance. Marked elevations in the T(2) relaxation times of the locomotor muscles are reflective of an altered muscle composition.

Locomotor training and muscle function after incomplete spinal cord injury: case series

BACKGROUND/OBJECTIVE

To determine whether 9 weeks of locomotor training (LT) results in changes in muscle strength and alterations in muscle size and activation after chronic incomplete spinal cord injury (SCI).

STUDY DESIGN

Longitudinal prospective case series.

METHODS

Five individuals with chronic incomplete SCI completed 9 weeks of LT. Peak isometric torque, torque developed within the initial 200 milliseconds of contraction (Torque 200), average rate of torque development (ARTD), and voluntary activation deficits were determined using isokinetic dynamometry for the knee-extensor (KE) and plantar-flexor (PF) muscle groups before and after LT. Maximum muscle cross-sectional area (CSA) was measured prior to and after LT.

RESULTS

Locomotor training resulted in improved peak torque production in all participants, with the largest increases in the more-involved PF (43.9% +/- 20.0%), followed by the more-involved KE (21.1% +/- 12.3%). Even larger improvements were realized in Torque 200 and ARTD (indices of explosive torque), after LT. In particular, the largest improvements were realized in the Torque 200 measures of the PF muscle group. Improvements in torque production were associated with enhanced voluntary activation in both the KE and ankle PF muscles and an increase in the maximal CSA of the ankle PF muscles.

CONCLUSION

Nine weeks of LT resulted in positive alterations in the KE and PF muscle groups that included an increase in muscle size, improved voluntary activation, and an improved ability to generate both peak and explosive torque about the knee and ankle joints.

Spasticity may defend skeletal muscle size and composition after incomplete spinal cord injury

DESIGN

Cross-sectional.

OBJECTIVES

(1) To determine the effects of the level of spinal cord injury (SCI) on skeletal muscle, intramuscular fat (IMF) cross-sectional areas (CSAs) and relative IMF; (2) to determine the relation, if any, of spasticity to each of these variables after incomplete SCI.

SETTINGS

In-patient study at the Shepherd Center, Atlanta, GA, USA.

METHODS

Thirteen individuals with incomplete SCI were classified according to their level of injury into a high level of injury group (HLI, C5-C7, n=8) and a low level of injury group (LLI, T12-L2, n=5). Spasticity was determined for thigh muscles using a modified Ashworth scale at 6 weeks post-injury. T1-weighted magnetic resonance (MR) images were taken 6 weeks post-injury to measure thigh skeletal muscle and IMF CSAs.

RESULTS

Spasticity was significantly evident in the HLI group compared to the LLI group (P=0.023). Six weeks post-injury, muscle CSA was 103+/-18 cm(2) in the HLI group and 80+/-20 cm(2) in the LLI group (P=0.042). Relative IMF was 3.6+/-2.0% in HLI and 7.5+/-4.0% in LLI (P=0.021). Additionally, spasticity accounted for 54% of the variability in muscle CSA for all subjects (r (2)=0.54, P=0.006).

CONCLUSIONS

Spasticity may be an important factor in defending skeletal muscle size and indirectly preventing IMF accumulation early after incomplete SCI.

Impact of varying pulse frequency and duration on muscle torque production and fatigue

Neuromuscular electrical stimulation (NMES) involves the use of electrical current to facilitate contraction of skeletal muscle. However, little is known concerning the effects of varying stimulation parameters on muscle function in humans. The purpose of this study was to determine the extent to which varying pulse duration and frequency altered torque production and fatigability of human skeletal muscle in vivo. Ten subjects underwent NMES-elicited contractions of varying pulse frequencies and durations as well as fatigue tests using stimulation trains of equal total charge, yet differing parametric settings at a constant voltage. Total charge was a strong predictor of torque production, and pulse trains with equal total charge elicited identical torque output. Despite similar torque output, higher- frequency trains caused greater fatigue. These data demonstrate the ability to predictably control torque output by simultaneously controlling pulse frequency and duration and suggest the need to minimize stimulation frequency to control fatigue.

Resistance training and locomotor recovery after incomplete spinal cord injury: a case series

STUDY DESIGN

Longitudinal intervention case series.

OBJECTIVE

To determine if a 12-week resistance and plyometric training program results in improved muscle function and locomotor speed after incomplete spinal cord injury (SCI).

SETTING

University research setting.

METHODS

Three ambulatory individuals with chronic (18.7+/-2.2 months post injury) motor incomplete SCI completed 12 weeks of lower extremity resistance training combined with plyometric training (RPT). Muscle maximum cross-sectional area (max-CSA) of the knee extensor (KE) and plantar flexor (PF) muscle groups was determined using magnetic resonance imaging (MRI). In addition, peak isometric torque, time to peak torque (T (20-80)), torque developed within the initial 220 ms of contraction (torque(220)) and average rate of torque development (ARTD) were calculated as indices of muscle function. Maximal as well as self-selected gait speeds were determined pre- and post-RPT during which the spatio-temporal characteristics, kinematics and kinetics of gait were measured.

RESULTS

RPT resulted in improved peak torque production in the KE (28.9+/-4.4%) and PF (35.0+/-9.1%) muscle groups, as well as a decrease in T(20-80), an increased torque(220) and an increase ARTD in both muscle groups. In addition, an increase in self-selected (pre-RPT=0.77 m/s; post-RPT=1.03 m/s) and maximum (pre-RPT=1.08 m/s; post-RPT=1.47 m/s) gait speed was realized. Increased gait speeds were accompanied by bilateral increases in propulsion and hip excursion as well as increased lower extremity joint powers.

CONCLUSIONS

The combination of lower extremity RPT can attenuate existing neuromuscular impairments and improve gait speed in persons after incomplete SCI.

Skeletal muscle atrophy and increased intramuscular fat after incomplete spinal cord injury

STUDY DESIGN

Cross-sectional and longitudinal design.

OBJECTIVES

(1) To quantify skeletal muscle cross-sectional area (CSA) after correcting for intramuscular fat (IMF) in thigh muscle groups 6 weeks after incomplete spinal cord injury (SCI), (2) to monitor the changes in muscle CSA and IMF after 3 months from the initial measurement.

SETTING

Academic institution Athens, GA, USA.

METHODS

Six incomplete SCI patients (28+/-4 years, 178+/-5 cm and 78+/-6 kg, mean+/-SE, C7 to L3, American Spinal Injury Association B or C) were tested at 5+/-1 weeks and 3 months after the initial measurement. T1-weighted magnetic resonance images were taken of both thighs. Six able-bodied (AB) controls were matched in age, sex, height and weight (29+/-4 years, four male and two female subjects, 179+/-5 cm and 77+/-6 kg).

RESULTS

At 6 weeks post-injury, muscle CSA was 82+/-4 cm(2) in incomplete SCI and 123+/-21 cm(2) in AB controls (P=0.04). IMF CSA was 5.2+/-1.3 and 2.3+/-0.6 cm(2) in incomplete SCI and AB controls, respectively (P=0.03). Relative IMF was three-fold higher (P=0.03) in the SCI group versus AB controls (5.8+/-1.4 versus 2.0+/-0.6%). After 3 months, IMF increased 26% in the SCI group compared to the initial measurement (P=0.02).

CONCLUSIONS

Skeletal muscle atrophy is associated with greater IMF accumulation in SCI group 6 weeks post-injury compared to AB controls. Moreover, IMF continues to increase over time in incomplete SCI.

Lower-extremity muscle cross-sectional area after incomplete spinal cord injury

OBJECTIVES

(1) To quantify skeletal muscle size in lower-extremity muscles of people after incomplete spinal cord injury (SCI), (2) to assess differences in muscle size between involved lower limbs, (3) to determine the impact of ambulatory status (using wheelchair for community mobility vs not using a wheelchair for community mobility) on muscle size after incomplete SCI, and (4) to determine if differential atrophy occurs among individual muscles after incomplete SCI.

DESIGN

Case-control study.

SETTING

University research setting.

PARTICIPANTS

Seventeen people with incomplete SCI and 17 age-, sex-, weight-, and height-matched noninjured controls.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Maximum cross-sectional area (CSA) of individual lower-extremity muscles (soleus, medial gastrocnemius, lateral gastrocnemius, tibialis anterior, quadriceps femoris, hamstrings) as assessed by magnetic resonance imaging.

RESULTS

Overall, subjects with incomplete SCI had significantly smaller (24%-31%) average muscle CSA in affected lower-extremity muscles as compared with control subjects (P<.05). Mean differences were highest in the thigh muscles ( approximately 31%) compared with the lower-leg muscles ( approximately 25%). No differences were noted between the self-reported more- and less-involved limbs within the incomplete SCI group. Dichotomizing the incomplete SCI group showed significantly lower muscle CSA values in both the wheelchair (range, 21%-39%) and nonwheelchair groups (range, 24%-38%). In addition, the wheelchair group exhibited significantly greater plantarflexor muscle atrophy compared with the dorsiflexors, with maximum atrophy in the medial gastrocnemius muscle (39%).

CONCLUSIONS

Our results suggest marked and differential atrophic response of the affected lower-extremity muscles that is seemingly affected by ambulatory status in people with incomplete SCI.