Distal Arm Muscles Research Articles

Objective Evaluation of Laparoscopic Experience Based on Muscle Electromyography and Accelerometry Performing Circular Pattern Cutting Tasks: A Pilot Study.

Purpose.The aim of this work is to present a new physical laparoscopy simulator with an electromyography (EMG)/accelerometry-based muscle activity recording system, EvalLap EMG-ACC, and perform objective evaluation of laparoscopic skills based on the quantification of muscle activity of participants with different levels of laparoscopic experience. Methods. EMG and ACC signals were obtained from 14 participants (6 experts, 8 medical students) performing circular pattern cutting tasks using a laparoscopic box trainer with the Trigno (Delsys Inc, Natick, MA) portable wireless system of 16 wireless sensors. Sensors were placed on the proximal and distal muscles of the upper extremities. Seven evaluation metrics were proposed and compared between skilled and novice surgeons. Results. The proximal and distal arm muscles (trapezius, deltoids, biceps, and forearms) were most active while executing laparoscopic tasks. Laparoscopic experience was associated with differences in EMG amplitude (), muscle activity (), hand acceleration (), user movement (), and muscle fatigue. For the cutting task, the deltoid, bicep, forearm EMG amplitude, and user movement significantly differed between experience groups. Conclusion. This pilot study demonstrates that different muscle groups are preferentially activated during laparoscopic tasks depending on the level of surgical experience. Expert surgeons showed less muscle activity compared with novices. EvalLap EMG-ACC represents a promising means to distinguish surgeons with basic cutting skills from those who have not yet developed these skills.

Effects of stimulus waveform on transcranial magnetic stimulation metrics in proximal and distal arm muscles

ObjectivesThe purpose of this study was to determine the effect of common transcranial magnetic stimulation (TMS) waveforms (monophasic and biphasic) on resting motor threshold (RMT), active motor threshold (AMT), and motor evoked potential (MEP) amplitudes in the biceps and first dorsal interosseous (FDI) because waveforms may affect motor targets differently. We also determined test-retest reliability. MethodsTen individuals participated in two sessions of TMS delivered to the motor cortex. Monophasic stimulation to induce a posterior–anterior current in the brain (monoPA) and biphasic posterior–anterior then anterior-posterior (biPA-AP) were applied in each session in random order. In each session, there were four blocks of measurements (2 muscles × 2 waveforms) of RMT, AMT and MEPs at the hotspot location. MEPs were normalized to the maximum EMG signal. ResultsRMTs and AMTs were lower for monoPA compared to biPA-AP stimulation for the biceps (p<0.01) and FDI (p<0.01). Normalized MEPs were greater for monoPA compared to biPA-AP stimulation in the FDI (p=0.01) and not different in the biceps (p=0.86). Motor thresholds were not different between sessions suggesting high reliability (p<0.01). Normalized MEPs had very low reliability across sessions in the FDI, and moderate reliability in the biceps. DiscussionPreliminary investigation suggests the effect of TMS waveform on motor thresholds is similar in upper limb proximal and distal muscles, but the effect differs per motor target for MEPs. Further, test–retest reliability of waveform effects was sensitive to target muscle. These findings may contribute to improve the efficacy and reliability of TMS for clinical use.

Increased muscle echointensity correlates with clinical disability and muscle strength in chronic inflammatory demyelinating polyneuropathy.

We evaluated muscle echointensity as a marker for secondary axonal damage in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) using ultrasonography. Findings were correlated with clinical disability and muscular strength. Eighty patients with CIDP (40 with typical and 40 with atypical CIDP) were examined clinically, including assessment of Medical Research Council (MRC) sum score and Inflammatory Neuropathy Cause and Treatment Overall Disability Sum Score (INCAT-ODSS). Echointensity in eight proximal and distal muscles of the arms and legs was evaluated by muscle ultrasonography using the Heckmatt scale. Alterations of echointensity occurred most frequently in the distal leg muscles, with a median (range) Heckmatt score of 1.5 (1-4). There were no differences between typical and atypical CIDP patients with regard to Heckmatt score. Alterations of echointensity correlated to disability and muscle strength. The arm score of the INCAT-ODSS correlated to Heckmatt score for the distal arm muscles (r=0.23, p=0.046) and the leg score of the INCAT-ODSS correlated to Heckmatt scores for the proximal (r=0.34, p=0.002) and distal leg muscles (r=0.33, p=0.004). MRC sum score, as well as individual MRC scores for arm and leg muscles, correlated to Heckmatt scores of the corresponding muscle groups (r=-0.25, p=0.02 for MRC sum score). Increased muscle echointensity, reflecting fibrosis and fatty infiltration due to secondary axonal damage, correlated to muscular strength and disability in a large cohort of CIDP patients. Alterations of echointensity occur in both typical and atypical CIDP patients and are pronounced in the distal leg muscles.

Increased oxygenation in the non-contracting forearm muscle during contralateral skilful hand movement.

What is the central question of this study? When performing skilful hand movement, motor command descends especially towards distal arm muscles. Does central command evoke a vascular response selectively in the distal arm muscles during skilful hand movement? What is the main finding and its importance? We found, using near-infrared spectroscopy, that unilateral skilful hand movement evoked a greater increase in oxygenation of the contralateral forearm muscle compared with that of the upper arm muscles. Mental imagery of the hand movement also increased oxygenation of the forearm muscle. These findings suggest that central command might contribute to the vasodilator response in the non-contracting forearm muscle during contralateral skilful hand movement. The human hand is a special organ to perform skilful movement in daily life. To meet metabolic demands of the working distal arm muscles, central command might evoke neurogenic vasodilatation in the muscles. Based on our previous demonstration that a centrally generated vasodilator signal is transmitted bilaterally to skeletal muscles during exercise, centrally induced vasodilatation might occur in the non-contracting distal arm muscles during contralateral skilful hand movement. To examine this possibility, we used near-infrared spectroscopy to measure the relative concentrations of oxygenated haemoglobin (Oxy-Hb; as an index of regional blood flow) in the non-contracting arm muscles during skilful hand movement (two-ball rotation) in 22 subjects. Two-ball rotation increased Oxy-Hb of both forearm and upper arm muscles, with little changes in perfusion pressure and cardiac output. The increased Oxy-Hb was greater in the forearm muscle than in the upper arm muscles. The increased Oxy-Hb of the forearm muscle during two-ball rotation was greater than that during one-armed cranking performed with no load. Mental imagery of two-ball rotation increased Oxy-Hb of the forearm and biceps muscles. The increases in Oxy-Hb of both forearm and upper arm muscles during two-ball rotation were reduced by decreasing the level of task difficulty. Intravenous administration of atropine attenuated the increases in Oxy-Hb of the arm muscles during two-ball rotation. It is likely that contralateral skilful hand movement evokes a selective increase in Oxy-Hb of the non-contracting forearm muscle via a sympathetic cholinergic mechanism and that the increase in oxygenation might be mediated, at least in part, by central command.

Cortical and Subcortical Effects of Transcutaneous Spinal Cord Stimulation in Humans with Tetraplegia.

An increasing number of studies supports the view that transcutaneous electrical stimulation of the spinal cord (TESS) promotes functional recovery in humans with spinal cord injury (SCI). However, the neural mechanisms contributing to these effects remain poorly understood. Here we examined motor-evoked potentials in arm muscles elicited by cortical and subcortical stimulation of corticospinal axons before and after 20 min of TESS (30 Hz pulses with a 5 kHz carrier frequency) and sham-TESS applied between C5 and C6 spinous processes in males and females with and without chronic incomplete cervical SCI. The amplitude of subcortical, but not cortical, motor-evoked potentials increased in proximal and distal arm muscles for 75 min after TESS, but not sham-TESS, in control subjects and SCI participants, suggesting a subcortical origin for these effects. Intracortical inhibition, elicited by paired stimuli, increased after TESS in both groups. When TESS was applied without the 5 kHz carrier frequency both subcortical and cortical motor-evoked potentials were facilitated without changing intracortical inhibition, suggesting that the 5 kHz carrier frequency contributed to the cortical inhibitory effects. Hand and arm function improved largely when TESS was used with, compared with without, the 5 kHz carrier frequency. These novel observations demonstrate that TESS influences cortical and spinal networks, having an excitatory effect at the spinal level and an inhibitory effect at the cortical level. We hypothesized that these parallel effects contribute to further the recovery of limb function following SCI.SIGNIFICANCE STATEMENT Accumulating evidence supports the view that transcutaneous electrical stimulation of the spinal cord (TESS) promotes recovery of function in humans with spinal cord injury (SCI). Here, we show that a single session of TESS over the cervical spinal cord in individuals with incomplete chronic cervical SCI influenced in parallel the excitability cortical and spinal networks, having an excitatory effect at the spinal level and an inhibitory effect at the cortical level. Importantly, these parallel physiological effects had an impact on the magnitude of improvements in voluntary motor output.

Does Resting Motor Threshold Predict Motor Hand Recovery After Stroke?

Background: Resting Motor threshold (rMT) is one of the measurement obtained by Transcranial Magnetic Stimulation (TMS) that reflects corticospinal excitability. As a functional marker of the corticospinal pathway, the question arises whether rMT is a suitable biomarker for predicting post-stroke upper limb function. To that aim, we conducted a systematic review of relevant studies that investigated the clinical significance of rMT in stroke survivors by using correlations between upper limb motor scores and rMT.Methods: Studies that reported correlations between upper limb motor function and rMT as a measure of corticospinal excitability in distal arm muscle were identified via a literature search in stroke patients. Two authors extracted the data using a home-made specific form. Subgroup analyses were carried out with patients classified with respect to time post-stroke onset (early vs. chronic stage) and stroke location (cortical, subcortical, or cortico-subcortical). Methodological quality of the study was also evaluated by a published checklist.Results: Eighteen studies with 22 groups (n = 508 stroke patients) were included in this systematic review. Mean methodological quality score was 14.75/24. rMT was often correlated with motor function or hand dexterity (n = 15/22, 68%), explaining on average 31% of the variance of the motor score. Moreover, the results did not seem impacted if patients were examined at the early or chronic stages of stroke. Two findings could not be properly interpreted: (i) the fact that the rMT is an independent predictor of motor function as several confounding factors are well-established, and, (ii) whether the stroke location impacts this prediction.Conclusion: Most of the studies found a correlation between rMT and upper limb motor function after stroke. However, it is still unclear if rMT is an independent predictor of upper limb motor function when taking into account for age, time post stroke onset and level of corticospinal tract damage as confounding factors. Clear-cut conclusions could not be drawn at that time but our results suggest that rMT could be a suitable candidate although future investigations are needed.Systematic Review Registration Number: (https://www.crd.york.ac.uk/prospero/): ID 114317.

Crossed corticospinal facilitation between arm and trunk muscles in humans.

A voluntary contraction of muscles with one arm increases the excitability of corticospinal projections to the contralateral resting arm, a phenomenon known as crossed facilitation. Although many motor tasks engage simultaneous activation of the arm and trunk, interactions between corticospinal projections targeting these segments remain largely unknown. Using transcranial magnetic stimulation over the trunk representation of the primary motor cortex, we examined motor-evoked potentials (MEPs) in the resting erector spinae (ES) muscle when the contralateral arm remained at rest or performed 20% of isometric maximal voluntary contraction (MVC) into index finger abduction, thumb abduction, elbow flexion, and elbow extension. We found that MEP size in the ES increased during all voluntary contractions, with greater facilitation occurring during elbow flexion and index finger abduction. To further examine the origin of changes in MEP size, we measured short-interval intracortical inhibition (SICI) and cervicomedullary MEPs (CMEPs) in the ES muscle during elbow flexion and index finger abduction and when the arm remained at rest. Notably, SICI decreased and CMEPs remained unchanged in the ES during both voluntary contractions compared with rest, suggesting a cortical origin for the effects. Our findings reveal crossed facilitatory interactions between trunk extensor and proximal and distal arm muscles, particularly for elbow flexor and index finger muscles, likely involving cortical mechanisms. These interactions might reflect the different role of these muscles during functionally relevant arm and trunk movements. NEW & NOTEWORTHY Many of the tasks of daily life involve simultaneous activation of the arm and trunk. We found that responses in the erector spinae muscles evoked by motor cortical stimulation increased in size during elbow flexion and extension and during index finger abduction and thumb abduction. Crossed facilitation with the trunk was more pronounced during elbow flexion and index finger abduction. These results might reflect the different role of these muscles during arm and trunk movements.

Measurement of motor-evoked potential resting threshold and amplitude of proximal and distal arm muscles in healthy adults. A reliability study.

PurposeReliability of motor-evoked potential threshold and amplitude measurement of upper limb muscles is important when detecting changes in cortical excitability. The objective of this study was to investigate intra-rater, test–retest reliability and minimal detectable change of resting motor threshold and amplitude of a proximal and distal upper limb muscles, anterior deltoid and distal extensor digitorum communis in healthy adults.MethodTo measure motor-evoked potential responses, transcranial magnetic stimulation was interfaced with electromyography and neuronavigation equipment. Two measurements were conducted on day 1 and a third measurement three days later. Reliability was analysed using intraclass correlation coefficients.ResultsTwenty participants completed the study. Excellent intra-rater (intraclass correlation coefficient = 0.91 (extensor digitorum), 0.94 (anterior deltoid)) and good to excellent test–retest reliability (intraclass correlation coefficient = 0.69 (anterior deltoid), 0.84 (extensor digitorum)) was found for resting motor threshold. Minimal detectable change for resting motor threshold was found at 10.95% (extensor digitorum) and 16.35% (anterior deltoid) between first and third measurements. Motor-evoked potential amplitude of extensor digitorum communis had fair to good intra-rater (intraclass correlation coefficient = 0.50) and test–retest reliability (intraclass correlation coefficient = 0.65).ConclusionsOur results suggest that resting motor threshold is a reliable neurophysiological measure even for proximal shoulder muscles. Future research should further explore the reliability of motor-evoked potential amplitude before integration into neurological rehabilitation.

Human-like distal-dominant gradient in the target muscles of transient corticomotoneuronal direct connections in juvenile rodents

Background: It has long been believed that the monosynaptic corticomotoneuronal (CM) connections linking motor cortex directly to spinal motoneurons are the privilege of higher primates that plays an important role in the cortical control of skilled hand movement. CM-connections had been considered to be sparse or absent in non-primates however we recently reported a functional direct connection between motor cortex and the cervical motoneurons in infant rats. It is further known in higher primates that the direct CM-connections were most pronounced for distal arm muscles and especially finger muscles easily linked to the ability to perform skilled movements of fingers.

Central command increases muscular oxygenation of the non-exercising arm at the early period of voluntary one-armed cranking.

This study aimed to examine whether central command increases oxygenation in non‐contracting arm muscles during contralateral one‐armed cranking and whether the oxygenation response caused by central command differs among skeletal muscles of the non‐exercising upper limb. In 13 male subjects, the relative changes in oxygenated‐hemoglobin concentration (Oxy‐Hb) of the non‐contracting arm muscles [the anterior deltoid, triceps brachii, biceps brachii, and extensor carpi radialis (ECR)] were measured during voluntary one‐armed cranking (intensity, 35–40% of maximal voluntary effort) and mental imagery of the one‐armed exercise for 1 min. Voluntary one‐armed cranking increased (P < 0.05) the Oxy‐Hb of the triceps, biceps, and ECR muscles to the same extent (15 ± 4% of the baseline level, 17 ± 5%, and 16 ± 4%, respectively). The greatest increase in the Oxy‐Hb was observed in the deltoid muscle. Intravenous injection of atropine (10–15 μg/kg) and/or propranolol (0.1 mg/kg) revealed that the increased Oxy‐Hb of the arm muscles consisted of the rapid atropine‐sensitive and delayed propranolol‐sensitive components. Mental imagery of the exercise increased the Oxy‐Hb of the arm muscles. Motor‐driven passive one‐armed cranking had little influence on the Oxy‐Hb of the arm muscles. It is likely that central command plays a role in the initial increase in oxygenation in the non‐contracting arm muscles via sympathetic cholinergic vasodilatation at the early period of one‐armed cranking. The centrally induced increase in oxygenation may not be different among the distal arm muscles but may augment in the deltoid muscle.

Rhythmic wrist movements facilitate the soleus H-reflex and non-voluntary air-stepping in humans

Neural coupling between the upper and lower limbs during human walking is supported by modulation of cross-limb reflexes and the presence of rhythmic activity in the proximal arm muscles. Nevertheless, the involvement of distal arm muscles in cyclic movements and sensorimotor neuromodulation is also suggested given their step-synchronized activation in many locomotor-related tasks (e.g., swimming, skiing, climbing, cycling, crawling, etc.). Here we investigated the effect of rhythmic wrist movements, separately and in conjunction with arm swinging, on the characteristics of non-voluntary cyclic leg movements evoked by muscle vibration in a gravity neutral position and on the soleus H-reflex of the stationary legs. For the H-reflex modulation, five conditions were compared: stationary arms, voluntary alternating upper limb swinging, combined upper limb and wrist motion, wrist movements only and motion of the upper limbs with addition of load. Rhythmic wrist movements significantly facilitated the amplitude of non-voluntary leg oscillations, including ankle joint oscillations, and the H-reflex. The latter effect was related to rhythmicity of wrist motion rather than to a simple extra tension in the upper limb muscles (a kind of the Jendrassik manoeuvre) since adding resistance to arm oscillations (without flexion-extension in the wrist joint) had an opposite inhibitory effect on the H-reflex. Our results further support the existence of connections between the distal parts of the upper and lower extremities at the neural level, suggesting that wrist joint movements can be an important component of motor neurorehabilitation.

Hereditary motor and sensory neuropathy, caused by mutations in the NEFL gene in a family from Karachaevo-Cherkessia

The clinical and genetic features of hereditary motor and sensory neuropathy (HMSN; Charcot–Marie–Tooth disease, CMT) caused by newly identified missense mutation s.65G&gt;T (p.Pro22His) in NEFL gene located on the chromosome 8р21.2 are described. The disease was diagnosed in a large family from Ust-Dzhegutinsky district of the Karachay-Cherkess Republic with the segregation of the disease in four generations. The prevalence of the HMSN in that district was found to be 1:4340 persons, including 1:3376 among Karachays. The clinical picture of the disease was characterized by onset at the age of 11–14 years, weakness in foot muscles and steppage gait. The specific features in the majority of patients were the absence of major sensory disturbances, as well as long-term preserved distal arm muscles. Nerve conduction velocity in the median nerve varied from 30 to 42 m/s, which corresponds to values in patients with CMT2E, previously described.

Interlimb Reflexes Induced by Electrical Stimulation of Cutaneous Nerves after Spinal Cord Injury.

Whether interlimb reflexes emerge only after a severe insult to the human spinal cord is controversial. Here the aim was to examine interlimb reflexes at rest in participants with chronic (>1 year) spinal cord injury (SCI, n = 17) and able-bodied control participants (n = 5). Cutaneous reflexes were evoked by delivering up to 30 trains of stimuli to either the superficial peroneal nerve on the dorsum of the foot or the radial nerve at the wrist (5 pulses, 300 Hz, approximately every 30 s). Participants were instructed to relax the test muscles prior to the delivery of the stimuli. Electromyographic activity was recorded bilaterally in proximal and distal arm and leg muscles. Superficial peroneal nerve stimulation evoked interlimb reflexes in ipsilateral and contralateral arm and contralateral leg muscles of SCI and control participants. Radial nerve stimulation evoked interlimb reflexes in the ipsilateral leg and contralateral arm muscles of control and SCI participants but only contralateral leg muscles of control participants. Interlimb reflexes evoked by superficial peroneal nerve stimulation were longer in latency and duration, and larger in magnitude in SCI participants. Interlimb reflex properties were similar for both SCI and control groups for radial nerve stimulation. Ascending interlimb reflexes tended to occur with a higher incidence in participants with SCI, while descending interlimb reflexes occurred with a higher incidence in able-bodied participants. However, the overall incidence of interlimb reflexes in SCI and neurologically intact participants was similar which suggests that the neural circuitry underlying these reflexes does not necessarily develop after central nervous system injury.

Who is who after spinal cord injury and repair? Can the brain stem descending motor pathways take control of skilled hand motor function?

Over the last years, anatomical, electrophysiological and genetic studies have carefully dissected the pathways connecting the brain and the spinal cord. Lawrence and Kuypers (1968) described the organization of the descending motor pathways in the non-human primate spinal cord. Although there are some differences between species regarding the precise anatomical location of each spinal pathway and the selective connectivity onto spinal interneurons and motoneurons, the pattern of organization described is conserved among the mammalian spinal cord (Courtine et al., 2007). Based on their description, the major descending motor pathways are grouped depending on their anatomical origin and their terminal distribution pattern in the spinal grey matter. The motor cortex projects corticospinal axons to the spinal cord, which mostly run in the contralateral cord and innervate the mid and dorsal grey matter neurons. On the other hand, the spinal pathways originating in the brain stem are subdivided in the lateral and ventromedial systems. The ventromedial system fibers originate in the reticular formation and the vestibular complex, and terminate in the ventral and medial parts of the ventral horn grey matter. In contrast, the lateral system fibers originate in the red nucleus and preferentially terminate in the dorsal and lateral parts of the dorsal and medial grey matter (Figure 1). Together with the corticospinal fibers, the lateral brain-stem system contacts interneurons related to motorneurons of distal muscles, whereas on the other hand, the ventromedial system pathways contact interneurons related to motoneurons of proximal muscles. Functionally, the corticospinal and lateral brain stem pathways are involved in the control of distal arm and hand muscles involved in skilled forelimb movements. The ventral brainstem pathways are mostly involved in the control of the proximal musculature of the trunk and limbs involved in posture and locomotion. Behavioral and electrophysiological studies mostly performed in cats and non-human primates corroborate these anatomical findings (Lemon, 2012). Furthermore, rodents with injuries in discrete areas of the spinal cord selectively impair specific motor functions, evidencing the functional specificity of each spinal pathway and the spinal networks that they innervate (Schucht et al., 2002; Anderson et al., 2007)

Selective Effects of Arm Proximal and Distal Muscles Fatigue on Force Coordination in Manipulation Tasks

ABSTRACT. Effects of muscle fatigue on force coordination and task performance of various manipulation tasks are explored. Grip force (GF; normal force component acting at the digits-object contact area) and load force (LF; tangential component that lifts and holds objects) were recorded prior to and after fatiguing the distal (DAM; i.e., GF producing) and proximal arm muscles (PAM; LF producing). Results reveal a deterioration of GF scaling (i.e., averaged GF-LF ratio), GF-LF coupling (their correlation), and task performance (ability to exert a prescribed LF pattern) associated with DAM, but not PAM fatigue. Deteriorated force coordination clearly increases the likelihood of dropping an object; however, the observed selective effects of DAM and PAM fatigue represent a novel finding deserving of further research.

Activation and intermuscular coherence of distal arm muscles during proximal muscle contraction

In the human upper extremity (UE), unintended effects of proximal muscle activation on muscles controlling the hand could be an important aspect of motor control due to the necessary coordination of distal and proximal segments during functional activities. This study aimed to elucidate the effects of concurrent activation of elbow muscles on the coordination between hand muscles performing a grip task. Eleven healthy subjects performed precision grip tasks while a constant extension or flexion moment was applied to their elbow joints, inducing a sustained submaximal contraction of elbow muscles to counter the applied torque. Activation of four hand muscles was measured during each task condition using surface electromyography (EMG). When concurrent activation of elbow muscles was induced, significant changes in the activation levels of the hand muscles were observed, with greater effects on the extrinsic finger extensor (23.2 % increase under 30 % elbow extensor activation; p = 0.003) than extrinsic finger flexor (14.2 % increase under 30 % elbow flexor activation; p = 0.130). Elbow muscle activation also induced involuntary changes in the intrinsic thumb flexor activation (44.6 % increase under 30 % elbow extensor activation; p = 0.005). EMG-EMG coherence analyses revealed that elbow muscle activation significantly reduced intermuscular coherence between distal muscle pairs, with its greatest effects on coherence in the β-band (13-25 Hz) (average of 17 % decrease under 30 % elbow flexor activation). The results of this study provide evidence for involuntary, muscle-specific interactions between distal and proximal UE muscles, which may contribute to UE motor performance in health and disease.

Electrical activity of the distal muscles of the hand in men having high or low output alpha-frequencies while performing usual manual movements in response to sensory signals.

Human functional capabilities largely depend upon genetic qualities of person's nervous system. The registration of the spontaneous electroencephalogram (EEG) is among the physiological techniques allowing making a direct estimation of specific features of the nervous system, in particular, the human brain activity. Research is dedicated to the study of distal muscles of the hand, in particular, its functional ability in men with a high or low background EEG α-frequency being in quiescent state or while performing usual manual movements in response to sensory signals. A test group consisting of 104 healthy men from the ages of 19 to 21 was divided into two groups according to the magnitude of their individual α- frequency (IAF) median - groups with high (n = 53, IA≥10,04 Hz) and low (n = 51, IAF≤10,03 Hz) levels of IAF. Subjects' psychodynamic properties of their nervous processes have been evaluated as well as any background and level of changes in the average amplitude of EMG while performing usual manual movements in response to sensory signals and intergroup differences were studied. It has been found that higher levels of speed and accuracy of the sensorimotor response in men with a high IAF are associated with increased lateral and reciprocal significant differences both in the background muscle activity and efficiency of the distal arm muscles primarily functioning as flexors. But on the contrary, the inverse dynamics appears in men having the low-frequency which is correlated with a lower mobility and balanced nervous processes in their sensorimotor response. The establishment of such common factors in the experiments groups is an important step towards defining prognostic criteria for the functionality of motor area based on EMG activity of the distal muscles of the hand.

FRI0491-HPR Qualitative differences in the muscle activities in the forearm flexor and extensor muscles in healthy men and women in different ages

BackgroundBalance between flexor and extensor muscle activity is essential for optimal function. This has been demonstrated previously for the lower extremity, trunk and shoulder function, but information on the relationship...

Posture-related modulations in motor cortical excitability of the proximal and distal arm muscles

The effect of postural orientation on the motor corticospinal excitability (MCE) of proximal and distal upper extremity (UE) muscles was investigated. In a crossover design, recruitment curves (RCs), short interval cortical inhibition (SICI) and intracortical facilitation (ICF) of resting anterior deltoid (AD) and first dorsal interosseus (FDI) was assessed in two postures: sitting and standing. Six healthy adults without contraindications to transcranial magnetic stimulation (TMS) participated in the study. TMS was applied over the motor cortical representation of FDI and AD at intensities ranging from 90% to 200% of resting motor threshold (RMT) in increments of 10%. SICI and ICF were assessed for each muscle using a conditioning stimulus (80% RMT) preceding a test stimulus (120% RMT) with an interstimulus interval of 2ms and 15ms, respectively. For AD, but not FDI, there was a significant and consistent increase in RC slope during standing compared to sitting. For FDI, there was no difference in ICF and SICI between sitting and standing. However, for AD, while there was no difference in ICF between the two postures, there was a clear trend for SICI to decrease (p=0.06) in standing compared to sitting. These results indicate that postural change from sitting to standing, affects the MCE of proximal but not distal muscles. While this indicates the role of proximal UE muscles in postural control, it also implies that rehabilitation protocols for enhancing proximal arm motor function may be advantaged if administered in a standing posture.

Impaired crossed facilitation of the corticospinal pathway after cervical spinal cord injury

In uninjured humans, it is well established that voluntary contraction of muscles on one side of the body can facilitate transmission in the contralateral corticospinal pathway. This crossed facilitatory effect may favor interlimb coordination and motor performance. Whether this aspect of corticospinal function is preserved after chronic spinal cord injury (SCI) is unknown. Here, using transcranial magnetic stimulation, we show in patients with chronic cervical SCI (C(5)-C(8)) that the size of motor evoked potentials (MEPs) in a resting intrinsic hand muscle remained unchanged during increasing levels of voluntary contraction with a contralateral distal or proximal arm muscle. In contrast, MEP size in a resting hand muscle was increased during the same motor tasks in healthy control subjects. The magnitude of voluntary electromyography was negatively correlated with MEP size after chronic cervical SCI and positively correlated in healthy control subjects. To examine the mechanisms contributing to MEP crossed facilitation we examined short-interval intracortical inhibition (SICI), interhemispheric inhibition (IHI), and motoneuronal behavior by testing F waves and cervicomedullary MEPs (CMEPs). During strong voluntary contractions SICI was unchanged after cervical SCI and decreased in healthy control subjects compared with rest. F-wave amplitude and persistence and CMEP size remained unchanged after cervical SCI and increased in healthy control subjects compared with rest. In addition, during strong voluntary contractions IHI was unchanged in cervical SCI compared with rest. Our results indicate that GABAergic intracortical circuits, interhemispheric glutamatergic projections between motor cortices, and excitability of index finger motoneurons are neural mechanisms underlying, at least in part, the lack of crossed corticospinal facilitation observed after SCI. Our data point to the spinal motoneurons as a critical site for modulating corticospinal transmission after chronic cervical SCI.