H-reflex Amplitude Research Articles

Evaluation of electrophysiological changes before and after pramipexole treatment in patients diagnosed with idiopathic restless legs syndrome

Background and purpose – Restless legs syndrome (RLS) is a neurological disorder characterized by an irresistible urge to move the legs, frequently accompanied by unpleasant sensations. In this study, we aimed to determine the changes in electrophysiological tests including Fwave responses and H-reflex parameters in patients with idiopathic RLS after pramipexole medication. Methods –This prospective study was conducted with twenty newly diagnosed, idiopathic RLS patients. The electrophysiological parameters, specifically F-wave duration (FWD), the duration of related compound muscle action potential (CMAPD), and FWD/ CMAPD ratio, the ratio of maximum H-reflex amplitude(H) to maximum M-response amplitude (M)(H/M) were recorded in patients with idiopathic RLS before and after pramipexole medication. Results – The results revealed significant improvements in specific electrophysiolo gical parameters after pramipexole use. We observed a significant decrease in FWD, CMAPD, and FWD/CMAPD values after pramipexole treatment suggesting a reduction in motor neuron excitability. We also obser ved a significant decrease in H/M ratio after pramipexole medication indicating reduced spinal motor neuron excitability. Conclusion – This study demonstrated significant improvement in specific electrophysiological parameters following pramipexole treatment in patients with idiopathic RLS. The findings provide better understanding of the effects of pramipexole on nerve function and may contribute to the development of a monitoring tool and lead to more targeted treatments and interventions for RLS, improving the overall management and care for patients’ outcomes and quality of life with this debilitating condition.

Spinally targeted paired associative stimulation with high-frequency peripheral component induces spinal level plasticity in healthy subjects

A novel variant of paired-associative stimulation (PAS) consisting of high-frequency peripheral nerve stimulation (PNS) and high-intensity transcranial magnetic stimulation (TMS) above the motor cortex, called high-PAS, can lead to improved motor function in patients with incomplete spinal cord injury. In PAS, the interstimulus interval (ISI) between the PNS and TMS pulses plays a significant role in the location of the intended effect of the induced plastic changes. While conventional PAS protocols (single TMS pulse often applied with intensity close to resting motor threshold, and single PNS pulse) usually require precisely defined ISIs, high-PAS can induce plasticity at a wide range of ISIs and also in spite of small ISI errors, which is helpful in clinical settings where precise ISI determination can be challenging. However, this also makes the determination of high-PAS level of plasticity induction more challenging and calls for more research on the mechanism of action of high-PAS. We sought to determine if the TMS-induced orthodromic activation in upper motor neurons and PNS-induced antidromic activation in lower motor neurons arriving simultaneously to the intervening synapses at the spinal cord level can be shown to induce acute changes at the targeted location, unlike an otherwise identical but cortically targeted equivalent. Ten healthy subjects participated in two separate sessions, where high-PAS induced activation was set to target spinal (SPINAL) or cortical (CORTICAL) levels with ISI manipulation between otherwise identically applied TMS and PNS pulses. The outcomes were assessed with motor-evoked potentials (MEPs) and Hoffmann (H)-reflex before (PRE), immediately after, and 30 and 60 min after (POST, POST30, POST60) the intervention. MEPs were significantly enhanced in both interventions. In the SPINAL but not in the CORTICAL session, maximal H-reflex amplitudes significantly increased at two timepoints, indicating an increase in spinal excitability. The H/M ratio (maximal H-reflex normalized to maximal M-wave) also showed a significant increase from PRE to POST30 timepoint in the SPINAL session when compared with the CORTICAL equivalent. These results confirm that spinally targeted high-PAS with individualized ISIs indeed has an effect at the spinal level in the sensorimotor system. High-PAS is a novel PAS variant that has shown promising results in motor rehabilitation of individuals with SCI and these new findings contribute to the understanding of its mechanism of action. This provides further evidence for high-PAS as an option for clinical settings to target plasticity at different levels of the corticospinal tract.

The H-reflex study of the flexor carpi radialis muscle in healthy individuals.

This study aimed to investigate the physiological and anatomical factors influencing the flexor carpi radialis (FCR) H-reflex and to establish reference values for FCR H-reflex parameters in relation to these factors. The FCR H-reflexes, elicited by median nerve stimulation, were assessed in 80 healthy individuals both at rest and during isometric voluntary contraction (IVC). Multiple linear regression analyses were performed with H-reflex parameters as the dependent variables, while age, gender, height, arm length, and weight were included as independent variables. The FCR H-reflex was recorded bilaterally in nearly all healthy individuals (76 out of 80) during IVC, while it could be obtained in only 35% (28 out of 80) of these individuals at rest. During IVC, the maximum H-reflex amplitude (Hmax) and its ratio to the maximum M-response amplitude (Hmax/Mmax ratio) were significantly increased (p < 0.001). However, there were no changes in H-reflex latency, latency difference, conduction velocity (HRCV), or amplitude ratio (p > 0.05). In both conditions, age and arm length were the most important factors affecting H-reflex latency (p < 0.001), while HRCV was influenced only by age (p < 0.01). Women exhibited shorter H-reflex latencies (p < 0.01), and both Hmax amplitude and Hmax/Mmax ratio were higher in women during IVC (p < 0.05). The H-reflex amplitude ratio during IVC showed a tendency to decrease with age (p < 0.05). These findings suggest that FCR H-reflexes are more reliably elicited during IVC, and that both physiological and anatomical factors should be considered when assessing H-reflex abnormalities.

Neural interference effects on lateral vestibulospinal tract excitability by noisy galvanic vestibular stimulation

ObjectiveNoisy galvanic vestibular stimulation (GVS) using weak random noise waveforms enhances postural stability by modulating vestibular-related neural networks. This study aimed to investigate the neural interference mechanisms of noisy GVS on lateral vestibulospinal tract (LVST) excitability. MethodsTwenty-six healthy volunteers were randomly divided into two groups: balance training combined with noisy GVS and sham GVS. Participants performed 10-minute balance training while standing on a soft foam surface with their eyes closed while adapting to each electrical stimulus. LVST excitability was assessed by measuring the soleus H-reflex following square-wave pulse GVS. Postural stability was measured by assessing the center of foot pressure sway while standing on a foam surface with eyes closed. ResultsThe noisy GVS group showed significantly increased post-intervention H-reflex amplitude. The sham GVS group showed no significant difference in H-reflex amplitude pre- and post-intervention. The average sway velocity in the noisy and sham GVS groups significantly decreased in the medial–lateral direction of the center of foot pressure. ConclusionsNoisy GVS may enhance LVST excitability and decrease body sway via vestibular system interference during holding upright, which relies heavily on vestibular sensations. SignificanceThese findings may help understand the neural mechanisms of noisy GVS in neurorehabilitation.

Frequency-dependent effects of superimposed NMES on spinal excitability in upper and lower limb muscles

Superimposing neuromuscular electrical stimulation (NMES) on voluntary contractions has proven to be highly effective for improving muscle strength and performance. These improvements might involve specific adaptations occurring at cortical and spinal level. The effects of NMES on corticospinal activation seem to be frequency dependent and differ between upper and lower limb muscles. The aim of this study was to investigate acute responses in spinal excitability, as measured by H-reflex amplitude of flexor carpi radialis (FCR) and soleus (SOL) muscles, after NMES superimposed on voluntary contractions (NMES + ISO) at two different pulse frequencies (40 and 80 Hz). Conditions involved fifteen intermittent contractions at submaximal level. Before and after each condition, H-reflexes were elicited in FCR and SOL muscles.H-reflex amplitudes increased in FCR and SOL following both NMES + ISO at 40 and 80 Hz. The potentiation of the H-reflex was greater following the 40 Hz condition compared to 80 Hz, although no differences between muscles emerged.These findings indicated that superimposing NMES has an excitatory effect on spinal motoneurons in both upper and lower limb muscles with an overall greater response after low frequency NMES. Such facilitation could be associated to enhanced somatosensory stimuli conjunctly with higher supraspinal downward commands.

Synaptic dynamics linked to widespread elevation of H-reflex before peripheral denervation in amyotrophic lateral sclerosis.

Changes in Hoffmann reflex (H-reflex) exhibit heterogeneity among patients with amyotrophic lateral sclerosis (ALS), likely due to phenotype diversity. Current knowledge primarily focuses on soleus H-reflex, which may demonstrate an initial increase before subsequent decline throughout the disease course. The main objective was to investigate other muscles, to determine whether H-reflex changes could be associated with patient phenotype (onset site, functional disabilities). Additional experiments were performed to elucidate the neurophysiological mechanisms underlying H-reflex modifications. In age- and sex-matched groups of control subjects and patients, we compared H-reflex recruitment curves in soleus, quadriceps, and forearm flexors. Additionally, we examined H-reflex and motor evoked potential (MEP) recruitment curves in quadriceps. Last, to assess potential changes in monosynaptic excitatory postsynaptic potentials (EPSPs) of both peripheral and cortical origins, we analyzed peristimulus time histograms (PSTHs) and peristimulus frequencygrams (PSFs) of single motor units, along with H-reflex occurrence after paired-pulse stimuli. The ratio between maximal amplitudes of H-reflex and direct motor response increased in all muscles, irrespective of disease onset, and was found positively correlated with exaggerated osteotendinous reflexes and spasticity but depressed in patients on riluzole. This finding was accompanied by a reduction in MEP size and no changes in PSTH, PSF, and paired-pulse H-reflex probability. It is speculated that spinal interneurons may compensate for potential depression of monosynaptic EPSPs in ALS. From a clinical perspective, although the added value of H-reflex to osteotendinous reflex evaluation may be limited, it can serve as a valuable quantitative biomarker of pyramidal dysfunction in clinical trials.NEW & NOTEWORTHY Without significant evidence of peripheral denervation, H-reflex enhancement appears to be a widespread phenomenon, regardless of disease onset site. This increase is likely associated with a decrease in inhibitory control over presynaptic transmission of the synapse between muscle group Ia afferents and motoneurons. Although the link to exaggerated osteotendinous reflexes and spasticity implies a restricted role in identifying a pyramidal syndrome, its quantitative aspect positions the H-reflex as a valuable biomarker in clinical trials.

Association of H-reflex parameters and peroneal nerve conduction velocity with dynamic balance and agility in university athletes: a cross-sectional study

Abstract Athletic performance parameters encompass a wide range of physical, physiological, and biomechanical measures that are crucial for evaluating and optimising athletes’ capabilities. There are various intrinsic factors that can contribute to athletic skills, which subsequently impact overall performance. Thus, there is a need to explore significant intrinsic factors associated with athletic parameters, that can provide insights into the physiological mechanisms underlying performance. In this study, we examined the potential relationship of two such intrinsic factors, namely the H-reflex and the peroneal nerve conduction velocity, with athletic skills like dynamic balance and agility. Forty-five university-level athletes of all genders playing for different teams of Jamia Millia Islamia University, New Delhi, India were selected. All athletes underwent tibial H-reflex, peroneal NCV, mSEBT (for dynamic balance), and agility T-test evaluations. The Pearson correlation coefficient was calculated to evaluate the association of nerve function parameters (H-reflex and NCV) with athletic performance parameters (dynamic balance and agility). Results showed that H-reflex amplitude showed a significant negative correlation with both dynamic balance scores (Dominant Leg [DL]: r = −0.321 and ; Non-dominant leg [NDL]: r = −0.397 and ) and T-test scores (DL: r = −0.342; NDL: r = −0.321, ), respectively. The peroneal NCV was significantly positively correlated with dynamic balance (DL: r = 0.438 and ; NDL: r = 0.418 and ) and agility scores (DL: r = 0.639 and ; NDL: r = 0.641 and ) in athletes. In conclusion, significant associations were found between H-reflex and Peroneal nerve conduction velocity and key athletic performance parameters like dynamic balance and agility among university athletes. This implies that neural function is closely linked with athletic skills and performance. Registered in Clinical Trials Registry-India (CTRI) under registration number: REF/2023/11/075394.

Neurophysiological Assessment of H-Reflex Alterations in Compressive Radiculopathy.

This study aimed to investigate changes in the H-reflex recruitment curve in compressive radiculopathy, specifically assessing differences between symptomatic and asymptomatic limbs in patients with unilateral S1 radiculopathy through derived parameters. A total of 24 volunteers (15 male and 9 female, aged between 22 and 60 years) with confirmed nerve root compression in the L5/S1 segment participated. Nerve root compression was verified through clinical MRI examination and attributed to disc protrusion, spinal canal stenosis, or isthmic spondylolisthesis of L5/S1. Analysis revealed no difference in M-wave threshold intensity between symptomatic and non-symptomatic limbs. However, the H-reflex exhibited a trend toward increased threshold intensity in the symptomatic limb. Notably, a significant decrease in the slope of the H-reflex was observed on the symptomatic side, and the maximal H-reflex amplitude proved to be markedly different between the two limbs. The Hmax/Mmax ratio demonstrated a significant decrease in the symptomatic limb, indicating reduced effectiveness of signal translation. In conclusion, our findings emphasize the importance of H-reflex parameters in evaluating altered recruitment curves, offering valuable insights for neurological examinations. The observed differences in maximal values of M-wave, H-reflex, and their ratio in affected and unaffected limbs can enhance the diagnostic process for lumbosacral unilateral radiculopathy and contribute to a standardized approach in clinical assessments.

Effects of Multimodal Physical Therapy on Pain, Disability, H-reflex, and Diffusion Tensor Imaging Parameters in Patients With Lumbosacral Radiculopathy Due to Lumbar Disc Herniation: A Preliminary Trial.

Background Lumbosacral radiculopathy (LSR) due to lumbar disc herniation (LDH) is a condition caused by mechanical compression of nerve roots. Various physical therapy interventions have been proposed for the conservative management of LSR due to LDH. However, the study of physical therapy interventions in a multimodal form is lacking. Additionally, the effect of physical therapy on diffusion tensor imaging (DTI) parameters of the compressed nerve root has not been studied. This study aimed to investigate the effects of multimodal physical therapy (MPT) on pain, disability, soleus H-reflex, and DTI parameters of the compressed nerve root in patients with chronic unilateral LSR due to LDH. Methods A prospective preliminary pre-postclinical trial with a convenience sample was conducted. A total of 14 patients with chronic unilateral LSR due to paracentral L4-L5 or L5-S1 LDH were recruited for the study. Participants received a total of 18 sessions of a six-weekMPT program that consisted of electrophysical agents, manual therapy interventions, and core stability exercises. Electrophysical agents involved interferential current and hot pack. Manual therapy interventions included myofascial release, side posture positional distraction, passive spinal rotation mobilization, and high-velocity low-amplitude manipulation. Visual analog scale (VAS), Roland-Morris Disability Questionnaire (RMDQ), soleus H-reflex amplitude, side-to-side amplitude (H/H) ratio, fractional anisotropy (FA), and apparent diffusion coefficient (ADC) of the compressed nerve root were measured at baseline and post-intervention. Results There were significant improvements in VAS, RMDQ, H/H ratio, FA, and ADC of the compressed nerve root. Furthermore,significant improvement was found in the affected side compared with the contralateral side in H-reflex amplitude. Conclusions The observations of this preliminary trial suggest that MPT is a successful intervention in patients with chronic unilateral LSR due to LDH. Regarding DTI parameters of the compressed nerve root, FA increased and ADC decreased. Future studies with a control group, large sample sizes, and longer follow-up periods are needed.

Are Surface Electromyography Parameters Indicative of Post-Activation Potentiation/Post-Activation Performance Enhancement, in Terms of Twitch Potentiation and Voluntary Performance? A Systematic Review.

The aim was to identify if surface electromyography (sEMG) parameters are indicative of post-activation potentiation (PAP)/post-activation performance enhancement (PAPE), in terms of twitch potentiation and voluntary performance. Three databases were used in April 2024, with the following inclusion criteria: (a) original research, assessed in healthy human adults, and (b) sEMG parameters were measured. The exclusion criteria were (a) studies with no PAP/PAPE protocol and (b) non-randomized control trials. The following data were extracted: study characteristics/demographics, PAP/PAPE protocols, sEMG parameters, twitch/performance outcomes, and study findings. A modified physiotherapy evidence database (PEDro) scale was used for quality assessment. Fifteen randomized controlled trials (RCTs), with a total of 199 subjects, were included. The M-wave amplitude (combined with a twitch torque outcome) was shown to generally be indicative of PAP. The sEMG amplitudes (in some muscles) were found to be indicative of PAPE during ballistic movements, while a small decrease in the MdF (in certain muscles) was shown to reflect PAPE. Changes in the Hmax/Mmax ratio were found to contribute (temporally) to PAP, while the H-reflex amplitude was shown to be neither indicative of PAP nor PAPE. This review provides preliminary findings suggesting that certain sEMG parameters could be indicative of PAP/PAPE. However, due to limited studies, future research is warranted.

Different descending pathways mediate early and late portions of lower limb responses to transcranial magnetic stimulation.

Although recent studies in nonhuman primates have provided evidence that transcranial magnetic stimulation (TMS) activates cells within the reticular formation, it remains unclear whether descending brain stem projections contribute to the generation of TMS-induced motor evoked potentials (MEPs) in skeletal muscles. We compared MEPs in muscles with extensive direct corticomotoneuronal input (first dorsal interosseous) versus a prominent role in postural control (gastrocnemius) to determine whether the amplitudes of early and late MEPs were differentially modulated by cortical suppression. Suprathreshold TMS was applied with and without a preceding suprathreshold TMS pulse at two interstimulus intervals (50 and 80 ms). H reflexes in target muscles were also tested with and without TMS conditioning. Early and late gastrocnemius MEPs were differentially modulated by cortical inhibition, the amplitude of the early MEP being significantly reduced by cortical suppression and the late MEP facilitated. The amplitude of H reflexes in the gastrocnemius was reduced within the cortical silent period. Early MEPs in the first dorsal interosseous were also reduced during the silent period, but late MEPs were unaffected. Independent modulation of early and late MEPs in the gastrocnemius muscle supports the idea that the MEP is generated by multiple descending pathways. Suppression of the early MEP is consistent with transmission along the fast-conducting corticospinal tract, whereas facilitation of the late MEP suggests transmission along a corticofugal, potentially cortico-reticulospinal, pathway. Accordingly, differences in late MEP modulation between the first dorsal interosseous and gastrocnemius reflect an increased role of corticofugal pathways in the control of postural muscles.NEW & NOTEWORTHY Early and late portions of the response to transcranial magnetic stimulation (TMS) in a lower limb postural muscle are modulated independently by cortical suppression, late motor evoked potentials (MEPs) being facilitated during cortical inhibition. These results suggest a cortico-brain stem transmission pathway for late portions of the TMS-induced MEP.

Role of BoNT-A in patient with post COVID-19 spasticity, assessed by H-reflex

Background. COVID-19 is a pandemic disease due to viral infection. It spread throughout the world, and the association of COVID-19 with neuroendocrine system is a well-known fact especially while the connection between the endocrine and immune system neuroinflammation play a crucial role in pathophysiology. Therapeutic indication of Botulinum-neurotoxin-A (BoNT-A) is used in the treatment of focal post-stroke spasticity (PSS) and in re-habilitation which is regarded as a safe and effective type of treatment. Objective. To assess spasticity after COVID-19 infection. Methods. Thirty patients diagnosed as post-COVID-19 stroke spasticity were enrolled, their age ranged from (30-60 years). They had focal spasticity of lower extremities. BoNT-A was given in day 0 and 4 weeks later, in the gastrocnemius and soleus muscle. H-reflex was recorded from soleus muscles at 1st presentation and 4 weeks after injection of BoNT-A. Muscle power was assessed by Medical Research Council scale (MRC) and MAS. Results. The amplitude and latency of H-reflex record from soleus muscles and the H/M ratio showed a statistically significant difference between pre- and post-therapy with BoNT-A injection in cases with post COVID-19 spasticity. There was a significant increase in MRC scale but, MAS scale showed a significant reduction after injection of BoNT-A. Conclusion. Post COVID spasticity is a well-known complication after COVID-19 infection, there was clinical improvement in PSS post BoNT-A injections, which was assessed clinically by MAS and MRC scale, neurophysiological the H-reflex was correlated negatively regarding latency, while there was no correlation regarding H-reflex amplitude or Hmax/Mmax ratio and MAS.

Soleus H-reflex amplitude modulation during walking remains physiological during transspinal stimulation in humans.

The soleus H-reflex modulation pattern was investigated during stepping following transspinal stimulation over the thoracolumbar region at 15, 30, and 50Hz with 10kHz carry-over frequency above and below the paresthesia threshold. The soleus H-reflex was elicited by posterior tibial nerve stimulation with a single 1 ms pulse at an intensity that the M-wave amplitudes ranged from 0 to 15% of the maximal M-wave evoked 80ms after the test stimulus, and the soleus H-reflex was half the size of the maximal H-reflex evoked on the ascending portion of the recruitment curve. During treadmill walking, the soleus H-reflex was elicited every 2 or 3 steps, and stimuli were randomly dispersed across the step cycle which was divided in 16 equal bins. For each subject and condition, the soleus M-wave and H-reflex were normalized to the maximal M-wave. The soleus background electromyographic (EMG) activity was estimated as the linear envelope for 50ms duration starting at 100ms before posterior tibial nerve stimulation for each bin. The gain was determined as the slope of the relationship between the soleus H-reflex and the soleus background EMG activity. The soleus H-reflex phase-dependent amplitude modulation remained unaltered during transspinal stimulation, regardless frequency, or intensity. Similarly, the H-reflex slope and intercept remained the same for all transspinal stimulation conditions tested. Locomotor EMG activity was increased in knee extensor muscles during transspinal stimulation at 30 and 50Hz throughout the step cycle while no effects were observed in flexor muscles. These findings suggest that transspinal stimulation above and below the paresthesia threshold at 15, 30, and 50Hz does not block or impair spinal integration of proprioceptive inputs and increases activity of thigh muscles that affect both hip and knee joint movement. Transspinal stimulation may serve as a neurorecovery strategy to augment standing or walking ability in upper motoneuron lesions.

Neuromuscular Electrical Stimulation Does Not Influence Spinal Excitability in Multiple Sclerosis Patients

(1) Background: Neuromuscular electrical stimulation (NMES) has beneficial effects on physical functions in Multiple sclerosis (MS) patients. However, the neurophysiological mechanisms underlying these functional improvements are still unclear. This study aims at comparing acute responses in spinal excitability, as measured by soleus Hoffmann reflex (H-reflex), between MS patients and healthy individuals, under three experimental conditions involving the ankle planta flexor muscles: (1) passive NMES (pNMES); (2) NMES superimposed onto isometric voluntary contraction (NMES+); and (3) isometric voluntary contraction (ISO). (2) Methods: In total, 20 MS patients (MS) and 20 healthy individuals as the control group (CG) took part in a single experimental session. Under each condition, participants performed 15 repetitions of 6 s at 20% of maximal voluntary isometric contraction, with 6 s of recovery between repetitions. Before and after each condition, H-reflex amplitudes were recorded. (3) Results: In MS, H-reflex amplitude did not change under any experimental condition (ISO: p = 0.506; pNMES: p = 0.068; NMES+: p = 0.126). In CG, H-reflex amplitude significantly increased under NMES+ (p = 0.01), decreased under pNMES (p &lt; 0.000) and was unaltered under ISO (p = 0.829). (4) Conclusions: The different H-reflex responses between MS and CG might reflect a reduced ability of MS patients in modulating spinal excitability.

Do soleus responses to transcutaneous spinal cord stimulation show similar changes to H-reflex in response to Achilles tendon vibration?

Recently, the use of transcutaneous spinal cord stimulation (TSCS) has been proposed as a viable alternative to the H-reflex. The aim of the current study was to investigate to what extent the two modes of spinal cord excitability investigation would be similarly sensitive to the well-known vibration-induced depression. Fourteen healthy participants (8 men and 6 women; age: 26.7±4.8years) were engaged in the study. The right soleus H-reflex and TSCS responses were recorded at baseline (PRE), during right Achilles tendon vibration (VIB) and following 20min of vibration exposure (POST-VIB). Care was taken to match H-reflex and TSCS responses amplitude at PRE and to maintain effective stimulus intensities constant throughout time points. The statistical analysis showed a significant effect of time for the H-reflex, with VIB (13±5% of maximal M-wave (Mmax) and POST-VIB (36±4% of Mmax) values being lower than PRE-values (48±6% of Mmax). Similarly, TSCS responses changed over time, VIB (9±5% of Mmax) and POST-VIB (27±5% of Mmax) values being lower than PRE-values (46±6% of Mmax). Pearson correlation analyses revealed positive correlation between H-reflex and TSCS responses PRE-to-VIB changes, but not for PRE- to POST-VIB changes. While the sensitivity of TSCS seems to be similar to the gold standard H-reflex to highlight the vibratory paradox, both responses showed different sensitivity to the effects of prolonged vibration, suggesting slightly different pathways may actually contribute to evoked responses of both stimulation modalities.

Neural Adjustments during Repeated Braking and Throttle Actions on a Motorcycle Setup.

The aim of the study was to assess neuromuscular changes during an intermittent fatiguing task designed to replicate fundamental actions and ergonomics of road race motorcycling. Twenty-eight participants repeated a sequence of submaximal brake-pulling and gas throttle actions, interspaced by one maximal brake-pulling, until failure. During the submaximal brake-pulling actions performed at 30% MVC, force fluctuations, surface EMG, maximal M-wave (Mmax) and H-reflex were measured in the flexor digitorum superficialis. At the end of the task, the MVC force and associated EMG activity decreased (P<0.001) by 46% and 26%, respectively. During the task, force fluctuation and EMG activity increased gradually (106% and 61%, respectively) with respect to the pre-fatigue state (P≤0.029). The Mmax first phase did not change (P≥0.524), whereas the H-reflex amplitude, normalized to Mmax, increased (149%; P≤0.039). Noteworthy, the relative increase in H-reflex amplitude was correlated with the increase in EMG activity during the task (r=0.63; P<0.001). During the 10-min recovery, MVC force and EMG activity remained depressed (P≤0.05) whereas H-reflex amplitude and force fluctuation returned to pre-fatigue values. In conclusion, contrarily to other studies, our results bring forward that when mimicking motorcycling brake-pulling and gas throttle actions, supraspinal neural mechanisms primarily limit the duration of the performance.

The Hmax/Mmax Ratio as a Diagnostic Tool in Assessing Spasticity in a Patient with Hereditary Spastic Paraplegia

Hereditary spastic paraplegia (HSP) refers to a group of inherited diseases caused by progressive degeneration of the corticospinal tracts. We report a case of an HSP patient with ankle spasticity treated with an intrathecal baclofen (ITB) pump, for whom the Hmax/Mmax ratio was used as a diagnostic tool for spasticity. A man in his early 30s who was born without any complications and developed normally in childhood was diagnosed with HSP when he was 29 years old. Equinus gait pattern and bilateral genu recurvatum improved after manual therapy and botulinum toxin injections in both gastrocnemius muscles; however, after a few months, his gait disturbance became more severe as a natural course of the disease. To treat ankle spasticity and clonus, he was considered a suitable candidate for an ITB therapy. However, as spasticity is a finding that is easy to recognize but difficult to evaluate, we conducted electrophysiological testing, including H-reflex and the ratio of H-reflex amplitude to compound muscle action potential amplitude. The Hmax/Mmax ratio was 75.2% on the right side and 65.2% on the left side before an ITB pump, and 37.6% on the right side and 47.0% on the left side after an ITB pump. This case illustrates the usefulness of testing electrophysiological parameters such as the Hmax/Mmax ratio to measure spasticity objectively in late-onset HSP patients. The Hmax/Mmax ratio is also a good tool for measuring the degree of improvement in spasticity after ITB or additional treatment in these patients.

Comparison of acute responses in spinal excitability between older and young people after neuromuscular electrical stimulation.

This study aims at comparing acute responses in spinal excitability, as measured by H-reflex, between older and young individuals, following a single session of NMES superimposed onto voluntary isometric contractions of the ankle plantar-flexor muscles (NMES+), with respect to passive NMES (pNMES) and voluntary isometric contractions only (ISO). Thirty-two volunteers, 16 older (OLDER) and 16 young (YOUNG), were asked to sustain a constant force at 20% of maximal voluntary isometric contraction (MVIC) of the ankle plantar-flexor muscles in the dominant limb during each of the 3 conditions (NMES+ , pNMES and ISO). Fifteen repetitions of 6s were performed, with a resting interval of 6s between repetitions. Before and after each condition, soleus H-reflexes were elicited by percutaneous electrical stimulation of the posterior tibial nerve and H-reflex amplitudes recorded by surface EMG. In OLDER, H-reflex amplitude did not change following any experimental condition (ISO: p = 0.203; pNMES: p = 0.542; NMES+: p = 0.431) compared to baseline. On the contrary, in YOUNG, H-reflex amplitudes significantly increased (p < 0.000) and decreased (p = 0.001) following NMES+ and pNMES, respectively, while there was no significant change in reflex responses following ISO (p = 0.772). The lack of change in H-reflex responses following either NMES+ or pNMES might reflect a reduced ability of older people in modulating spinal excitability after the conditions. Specifically, an age-related alteration in controlling mechanisms at presynaptic level was suggested.

Methods for automated delineation and assessment of EMG responses evoked by peripheral nerve stimulation in diagnostic and closed-loop therapeutic applications

Objective. Surface electromyography measurements of the Hoffmann (H-) reflex are essential in a wide range of neuroscientific and clinical applications. One promising emerging therapeutic application is H-reflex operant conditioning, whereby a person is trained to modulate the H-reflex, with generalized beneficial effects on sensorimotor function in chronic neuromuscular disorders. Both traditional diagnostic and novel realtime therapeutic applications rely on accurate definitions of the H-reflex and M-wave temporal bounds, which currently depend on expert case-by-case judgment. The current study automates such judgments. Approach. Our novel wavelet-based algorithm automatically determines temporal extent and amplitude of the human soleus H-reflex and M-wave. In each of 20 participants, the algorithm was trained on data from a preliminary 3 or 4 min recruitment-curve measurement. Output was evaluated on parametric fits to subsequent sessions’ recruitment curves (92 curves across all participants) and on the conditioning protocol’s subsequent baseline trials (∼1200 per participant) performed near H max. Results were compared against the original temporal bounds estimated at the time, and against retrospective estimates made by an expert 6 years later. Main results. Automatic bounds agreed well with manual estimates: 95% lay within ±2.5 ms. The resulting H-reflex magnitude estimates showed excellent agreement (97.5% average across participants) between automatic and retrospective bounds regarding which trials would be considered successful for operant conditioning. Recruitment-curve parameters also agreed well between automatic and manual methods: 95% of the automatic estimates of the current required to elicit H max fell within of the retrospective estimate; for the ‘threshold’ current that produced an M-wave 10% of maximum, this value was . Significance. Such dependable automation of M-wave and H-reflex definition should make both established and emerging H-reflex protocols considerably less vulnerable to inter-personnel variability and human error, increasing translational potential.

Functional Activity of Reciprocal Inhibition of α-Motor Neurons of Antagonistic Muscles in Different Types of Muscle Contractions of Submaximal and Maximal Force

INTRODUCTION: Currently, the results of investigation of different types of spinal inhibition in isometric voluntary contraction of muscles have been published. There are separate reports devoted to the role of recurrent and presynaptic inhibition in the regulation of isometric and anisometric voluntary contractions of submaximal and maximal strength.&#x0D; AIM: To evaluate the effect of the type and strength of muscle contraction with and without performing Jendrassik maneuver on the manifestation of reciprocal inhibition of -motor neurons of antagonistic muscles of the lower leg.&#x0D; MATERIALS AND METHODS: The study involved 8 healthy men aged 2022 years. Reciprocal inhibition was evaluated by suppression of the amplitude of testing H-reflex of m. soleus in conditioning stimulation of n. peroneus profundus, and of testing stimulation of n. tibialis with 3 msec interval between stimuli. Reciprocal inhibition was recorded in concentric, eccentric and isometric contractions with 50% and 100% of maximal voluntary contraction (MVC) with and without Jendrassic maneuver.&#x0D; RESULTS: In performing concentric, eccentric and isometric contractions of lower leg muscles with increase in strength from 50% to 100% of MVC, the activity of reciprocal inhibition decreased. Reciprocal inhibition was most evident in concentric contraction with 50% of MVC strength, less evident in eccentric contraction and was lowest in isometric contraction. With the maximal strength, reciprocal inhibition was most expressed in isometric contraction, less expressed in concentric contraction and was weakest in eccentric contraction. With Jendrassik maneuver, reduction of reciprocal inhibition was more expressed in different types of MVCs in comparison with parameters obtained with 50% of MVC. Using Jendrassic maneuver with 50% and 100% of MVC effort, strongest reciprocal inhibition was recorded in isometric contraction, weaker inhibition in concentric contraction and weakest in eccentric contraction. The effect of Jendrassik maneuver was manifested by weakening of reciprocal inhibition in concentric and eccentric contraction of submaximal force, and by its enhancement in isometric contraction.&#x0D; CONCLUSION: Variability of manifestation of reciprocal inhibition of -motor neurons of antagonistic muscles of lower leg in different types of muscle contractions of submaximal and maximal strength is associated with the fact that the pool of segmental motor neurons of m. soleus is controlled not only by a wide spectrum of excitatory cortico- and reticulospinal influences, but also by other kinds of inhibition, thus providing coordinated motor actions.