Elisabeth Bravo-Esteban

Shared muscle synergies in human walking and cycling

The motor system may rely on a modular organization (muscle synergies activated in time) to execute different tasks. We investigated the common control features of walking and cycling in healthy humans from the perspective of muscle synergies. Three hypotheses were tested: 1) muscle synergies extracted from walking trials are similar to those extracted during cycling; 2) muscle synergies extracted from one of these motor tasks can be used to mathematically reconstruct the electromyographic (EMG) patterns of the other task; 3) muscle synergies of cycling can result from merging synergies of walking. A secondary objective was to identify the speed (and cadence) at which higher similarities emerged. EMG activity from eight muscles of the dominant leg was recorded in eight healthy subjects during walking and cycling at four matched cadences. A factorization technique [nonnegative matrix factorization (NNMF)] was applied to extract individual muscle synergy vectors and the respective activation coefficients behind the global muscular activity of each condition. Results corroborated hypotheses 2 and 3, showing that 1) four synergies from walking and cycling can successfully explain most of the EMG variability of cycling and walking, respectively, and 2) two of four synergies from walking appear to merge together to reconstruct one individual synergy of cycling, with best reconstruction values found for higher speeds. Direct comparison of the muscle synergy vectors of walking and the muscle synergy vectors of cycling (hypothesis 1) produced moderated values of similarity. This study provides supporting evidence for the hypothesis that cycling and walking share common neuromuscular mechanisms.

Impact of specific symptoms of spasticity on voluntary lower limb muscle function, gait and daily activities during subacute and chronic spinal cord injury

BACKGROUND Although the spasticity syndrome is an important sensorimotor disorder, the impact of grade of lower limb muscle hypertonia, spasm and clonus activity on voluntary muscle function, gait and daily activities has not been systematically analysed during subacute and chronic spinal cord injury (SCI). OBJECTIVE To determine the prevalence of spasticity signs and symptoms during SCI, and to assess their impact on motor function and activities. METHODS A descriptive transverse study of sixty-six subjects with SCI was performed by assessing injury characteristics, spasticity (modified Ashworth scale, Penn scale, SCATS scale) and motor function (lower limb manual muscle scores, WISCI II, spinal cord injury spasticity evaluation tool). RESULTS Most subjects with the spasticity syndrome presented lower limb hypertonia and spasms during both subacute and chronic SCI, interfering with daily life activities. Subjects with incomplete SCI and hypertonia revealed a loss of voluntary flexor muscle activity, while extensors spasms contributed strongly to loss of gait function. The Penn spasms scale no correlated with muscle function or gait. CONCLUSIONS Specific diagnosis of spasm activity during subacute SCI, and its impact on lower limb voluntary muscle activity, gait function and daily activities, is required to develop a more effective neurorehabilitation treatment strategy.

Oral administration of the p38α MAPK inhibitor, UR13870, inhibits affective pain behavior after spinal cord injury

&NA; OX‐42 positive–labeled cells and glutamate (mGluR5 and NR2B) receptors within the anterior cingulate cortex contribute to affective pain behavior after spinal cord injury. &NA; The p38&agr; mitogenous activated protein kinase (MAPK) cell signaling pathway is a key mechanism of microglia activation and has been studied as a target for neuropathic pain. The effect of UR13870, a p38&agr; MAPK inhibitor, on microglia expression in the anterior cingulate cortex (ACC) and spinal dorsal horn was addressed after T9 contusion spinal cord injury (SCI) in the rat, in addition to behavioral testing of pain‐related aversion and anxiety. Administration of intravenous UR13870 (1 mg/kg i.v.) and pregabalin (30 mg/kg i.v.) reduced place escape avoidance paradigm (PEAP) but did not affect open‐field anxiety behavior 42 days after SCI. PEAP behavior was also reduced in animals administered daily with oral UR13870 (10 mg/kg p.o.) and preserved spinal tissue 28 days after SCI. Although UR13870 (10 mg/kg p.o.) failed to reduce OX‐42 and glial fibrillar acid protein immunoreactivity within the spinal dorsal horn, a reduction toward the control level was observed close to the SCI site. In the anterior cingulate cortex (ACC), a significant increase in OX‐42 immunoreactivity was identified after SCI. UR13870 (10 mg/kg p.o.) treatment significantly reduced OX‐42, metabotropic glutamate type 5 receptor (mGluR5), and NMDA (N‐methyl‐d‐aspartate) 2B subunit receptor (NR2B) expression in the ACC after SCI. To conclude, oral treatment with a p38&agr; MAPK inhibitor reduces the affective behavioral component of pain after SCI in association with a reduction of microglia and specific glutamate receptors within the ACC. Nevertheless the role of neuroinflammatory processes within the vicinity of the SCI site in the development of affective neuropathic pain cannot be excluded.

Tibialis Anterior muscle coherence during controlled voluntary activation in patients with spinal cord injury: diagnostic potential for muscle strength, gait and spasticity

BackgroundCoherence estimation has been used as an indirect measure of voluntary neurocontrol of residual motor activity following spinal cord injury (SCI). Here intramuscular Tibialis Anterior (TA) coherence estimation was performed within specific frequency bands for the 10-60 Hz bandwidth during controlled ankle dorsiflexion in subjects with incomplete SCI with and without spasticity.MethodsIn the first cohort study 15 non-injured and 14 motor incomplete SCI subjects were recruited to evaluate TA coherence during controlled movement. Specifically 15-30 Hz EMG was recorded during dorsiflexion with: i) isometric activation at 50, 75 and 100% of maximal voluntary torque (MVT), ii) isokinetic activation at 60 and 120°/s and iii) isotonic dorsiflexion at 50% MVT. Following identification of the motor tasks necessary for measurement of optimal TA coherence a second cohort was analyzed within the 10-16 Hz, 15-30 Hz, 24-40 Hz and 40-60 Hz bandwidths from 22 incomplete SCI subjects, with and without spasticity.ResultsIntramuscular 40-60 Hz, but not 15-30 Hz TA, coherence calculated in SCI subjects during isometric activation at 100% of MVT was lower than the control group. In contrast only isometric activation at 100% of MVT 15-30 Hz TA coherence was higher in subjects with less severe SCI (AIS D vs. AIS C), and correlated functionally with dorsiflexion MVT. Higher TA coherence was observed for the SCI group during 120°/s isokinetic movement. In addition 15-30 Hz TA coherence calculated during isometric activation at 100% MVT or 120°/s isokinetic movement correlated moderately with walking function and time from SCI, respectively. Spasticity symptoms correlated negatively with coherence during isometric activation at 100% of MVT in all tested frequency bands, except for 15-30 Hz. Specifically, 10-16 Hz coherence correlated inversely with passive resistive torque to ankle dorsiflexion, while clinical measures of muscle hypertonia and spasm severity correlated inversely with 40-60 Hz.ConclusionAnalysis of intramuscular 15-30 Hz TA coherence during isometric activation at 100% of MVT is related to muscle strength and gait function following incomplete SCI. In contrast several spasticity symptoms correlated negatively with 10-16 Hz and 40-60 Hz TA coherence during isometric activation at 100% MVT. Validation of the diagnostic potential of TA coherence estimation as a reliable and comprehensive measure of muscle strength, gait and spasticity should facilitate SCI neurorehabilation.

Hybrid therapy of walking with Kinesis overground robot for persons with incomplete spinal cord injury

Rehabilitation of walking ability is one of the most important objectives after a spinal cord injury. Robotic and neuroprosthetic technologies hold a considerable potential for driving walking rehabilitation therapies. However, new developments are needed in order to improve the walking rehabilitation interventions based in these technologies.We recently presented a cooperative control strategy of Kinesis, a lower limb exoskeleton for providing hybrid therapy of walking (Del-Ama, 2014). Its design aimed to actively manage muscle fatigue caused by surface electrical stimulation, and to implement the assist-as-needed control paradigm in which both stimulation and robotic controller cooperate with the residual functionality of the user. In this article we present three case studies for investigating the feasibility of the hybrid therapy of walking delivered with Kinesis in patients with incomplete spinal cord injury. Besides, the adaptability features of Kinesis stimulation-robot cooperative control are assessed, characterizing the behavior of the cooperative controller while providing hybrid therapy of walking.Patients with incomplete spinal cord injury participated in the experiments. The protocol consisted of walking with Kinesis during 6?min. Three configurations of the cooperative controller were tested for each patient in separate sessions in order to investigate its adaptability features. The immediate impact of the hybrid therapy of walking was assessed through several variables that represent the physiological impact, user-exoskeleton physical interaction, stimulation intensity and user subjective perception of the hybrid therapy of walking.Results show that the cooperative controller of Kinesis adapted to patient functional deficits and voluntary actions during walking, modulating stimulation and robotic assistance, which was the aim of the controller design. Nevertheless, no noticeable differences were observed in the comparison between compliant and trajectory exoskeleton control. Further work is envisioned regarding several aspects of hybrid walking control: stimulation control based on muscle activation estimate, improved semi-automatic control of walking, and improved muscle fatigue monitoring. The hybrid walking therapy was tolerated by the patients without adverse effects, along with a tolerable physical demand. This shows a potential for walking rehabilitation in motor incomplete SCI patients, guaranteeing further research on this topic. We investigate the feasibility of providing the hybrid therapy of walking with Kinesis hybrid exoskeleton.We compare and investigate the role of the stimulation and the compliant robot control.Three case studies are presented. The cooperative controller of Kinesis adapted to patients and voluntary actions.No noticeable differences were observed between compliant and trajectory control.

Modulation of thermal somatosensory thresholds within local and remote spinal dermatomes following cervical repetitive magnetic stimulation

BACKGROUND Repetitive magnetic stimulation (rMS) modulates thermal somatosensory function at both low (0.2-1.0Hz) and high (5.0-20.0Hz) frequencies within the conditioned dermatome. However the effects of 1Hz and 20Hz cervical (C6-C7) rMS on thermosensory thresholds and contact heat evoked potentials (CHEPs) tested within local and remote spinal dermatomes are not known. METHODS Thirty healthy subjects participated in the study. Warm and cold detection threshold, heat and cold pain thresholds, and Cz/Fz CHEPs were evaluated within the C6, T10 and extrasegmental V3 control dermatome, before and after random assignment of subjects to sham, 1 or 20Hz C6-C7 rMS. RESULTS Following both 1 and 20Hz cervical rMS, warm detection threshold increased within the local C6 dermatome. Furthermore 1Hz cervical rMS increased warm detection threshold within the remote T10 dermatome, but not within the V3-trigeminal control area. Cervical rMS failed to modulate cold detection threshold, heat and cold pain threshold or Cz/Fz CHEP amplitude from the dermatomal test sites. CONCLUSION Both 1 and 20Hz cervical rMS modulated warm detection threshold within the locally conditioned C6 dermatome. The concomitant increase in warm detection threshold within the T10 dermatome following 1Hz rMS provides evidence for remote neuromodulation of thermosensory function via intraspinal control mechanisms.

Muscle Synergies in Cycling after Incomplete Spinal Cord Injury: Correlation with Clinical Measures of Motor Function and Spasticity

Background: After incomplete spinal cord injury (iSCI), patients suffer important sensorimotor impairments, such as abnormal locomotion patterns and spasticity. Complementary to current clinical diagnostic procedures, the analysis of muscle synergies has emerged as a promising tool to study muscle coordination, which plays a major role in the control of multi-limb functional movements. Objective: Based on recent findings suggesting that walking and cycling share similar synergistic control, the analysis of muscle synergies during cycling might be explored as an early descriptor of gait-related impaired control. This idea was split into the following two hypotheses: (a) iSCI patients present a synergistic control of muscles during cycling; (b) muscle synergies outcomes extracted during cycling correlate with clinical measurements of gait performance and/or spasticity. Methods: Electromyographic (EMG) activity of 13 unilateral lower limb muscles was recorded in a group of 10 healthy individuals and 10 iSCI subjects during cycling at four different cadences. A non-negative matrix factorization (NNMF) algorithm was applied to identify synergistic components (i.e., activation coefficients and muscle synergy vectors). Reconstruction goodness scores (VAF and r2) were used to evaluate the ability of a given number of synergies to reconstruct the EMG signals. A set of metrics based on the similarity between pathologic and healthy synergies were correlated with clinical scales of gait performance and spasticity. Results: iSCI patients preserved a synergistic control of muscles during cycling. The similarity with the healthy reference was consistent with the degree of the impairment, i.e., less impaired patients showed higher similarities with the healthy reference. There was a strong correlation between reconstruction goodness scores at 42 rpm and motor performance scales (TUG, 10-m test and WISCI II). On the other hand, the similarity between the healthy and affected synergies presented correlation with some spasticity symptoms measured by Penn, Modified Ashworth and SCATS scales. Conclusion: Overall, the results of this study support the hypothesis that the analysis of muscle synergies during cycling can provide detailed quantitative assessment of functional motor impairments and symptoms of spasticity caused by abnormal spatiotemporal muscle co-activation following iSCI.

Abnormal cutaneous flexor reflex activity during controlled isometric plantarflexion in human spinal cord injury spasticity syndrome

Study design:Although abnormal cutaneous reflex (CR) activity has been identified during gait after incomplete spinal cord injury (SCI), this activity has not been directly compared in subjects with and without the spasticity syndrome.Objectives:Characterisation of CR activity during controlled rest and ‘ramp and hold’ phases of controlled plantarflexion in subjects with and without the SCI spasticity syndrome.Design:Transverse descriptive study with non-parametric group analysis.Setting:SCI rehabilitation hospital.Methods:Tibialis Anterior (TA) reflexes were evoked by innocuous cutaneous plantar sole stimulation during rest and ramp and hold phases of plantarflexion torque in non-injured subjects (n=10) and after SCI with (n=9) and without (n=10) hypertonia and/or involuntary spasm activity. Integrated TA reflex responses were analysed as total (50–300 ms) or short (50–200 ms) and long-latency (200–300 ms) activity.Results:Total and long-latency TA activity was inhibited in non-injured subjects and the SCI group without the spasticity syndrome during plantarflexion torque but not in the SCI spasticity group. Furthermore, loss of TA reflex inhibition during plantarflexion correlated with time after SCI (ρ=0.79, P=0.009). Moreover, TA reflex activity inversely correlated with maximum plantarflexion torque in the spasticity group (ρ=−0.75, P=0.02), despite similar non-reflex TA electromyographic activity during plantarflexion after SCI in subjects with (0.11, 0.08–0.13 mV) or without the spasticity syndrome (0.09, 0.07–0.12 mV).Conclusions:This reflex testing procedure supports previously published evidence for abnormal CR activity after SCI and may characterise the progressive disinhibition of TA reflex activity during controlled plantarflexion in subjects diagnosed with the spasticity syndrome.

Knee Muscle Fatigue Estimation during Isometric Artificially Elicited Contractions in Incomplete Spinal Cord Injured Subjects

Muscle fatigue due to functional electrical stimulation still prevents its widespread use as a gait rehabilitation tool for Spinal Cord Injured subjects. Although there is an active research towards optimization of pulse parameters to delay muscle fatigue, changes in stimulated muscle’s performance during repeated contractions due to fatigue have not been yet determined. A study of muscle fatigue of knee extensors and flexors of incomplete SCI during isometric contractions is presented. The outcome of this study is the proposal of objective criteria for detecting muscle fatigue from initial changes has been extracted. Also a comparison between flexors and extensors knee muscle fatigue models is given.

Longitudinal Estimation of Intramuscular Tibialis Anterior Coherence during Subacute Spinal Cord Injury: Relationship with Neurophysiological, Clinical and Functional Measures

Tibialis Anterior (TA) electromyographic coherence estimation is assumed to reflect common supraspinal descending input spinal motoneurons, related to corticospinal tract activity. This study documented residual voluntary motor recovery at 2 week intervals during subacute spinal cord injury (SCI) with intramuscular TA EMG coherence estimation within the 10-60Hz bandwidth, assessed during controlled maximal isometric and isokinetic dorsiflexion. Several clinical and functional lower limb measures (muscular testing, dorsiflexion maximal voluntary torque and gait function measured with the WISCI II) and neurophysiological measures (TA motor evoked potentials, MEPs) were also recorded. Total and TA muscle strength, voluntary torque generation and gait function improved during subacute SCI, in addition to 40-60Hz, but not 15-30Hz intramuscular TA coherence. TA MEPs failed to reflect significant recovery of function. The SCI spasticity syndrome non-specifically reduced 15-30Hz TA coherence and was detected as high TA coherence values during fast isokinetic movement in all frequency bands. To conclude, longitudinal assessment of adaptive and maladaptive motor plasticity during subacute SCI can be detected with TA EMG coherence estimation during controlled movement, providing orientative diagnostic information during neurorehabilitation.