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BACKGROUND: Postural control imposes higher demands on the central neural system (CNS), and age-related declines or incomplete CNS development often result in challenges performing tasks like forward postural leaning. Studies on older adults suggest increased variability in center of pressure (COP), greater muscle co-activations, and reduced corticospinal control during forward leaning tasks. However, the understanding of these features in children remains unclear. Specifically, it is uncertain whether forward leaning poses greater challenges for young children compared to adults, given the ongoing maturation of CNS during development. Understanding the distinct neuromuscular patterns observed during postural leaning could help optimize therapeutic strategies aimed at improving postural control in pediatric populations. METHODS: 12 typically developing children (5.91 ±â€¯1.37 years) and 12 healthy young adults (23.16 ±â€¯1.52 years) participated in a dynamic leaning forward task aimed at matching a COP target in the anterior-posterior direction as steadily as possible. Participants traced a triangular trajectory involving forward leaning (FW phase) to 60 % of their maximum lean distance and backward returning (BW phase) to the neutral standing position. Surface electromyography (sEMG) from muscles including gastrocnemius medialis (GM), soleus (SOL), and tibialis anterior (TA) were collected during both phases. COP variability was assessed using the standard deviation (SD) of COP displacements. Muscle co-activation indexes (CI) for ankle plantar and dorsal flexors (SOL/TA, GM/TA) were derived from sEMG activities. Intermuscular coherence in the beta band (15-30 Hz) was also analyzed to evaluate corticospinal drive. RESULTS: Children exhibited a significantly greater SD of COP compared to young adults (p < 0.01) during the BW phase. They also demonstrated higher CI (p < 0.05) and reduced coherence of SOL/TA (p < 0.05) compared to young adults during this phase. No significant group differences were observed during the FW phase. Within the children's group, COP variability was significantly higher in the BW phase compared to the FW phase (p < 0.01). Moreover, children displayed greater CI (p < 0.01) and reduced coherence of SOL/TA (p < 0.01) during the BW phase compared to the FW phase. Conversely, no significant phase effects were observed in the adult group. Furthermore, sEMG measures were significantly correlated with COP variability (p < 0.05). CONCLUSIONS: The findings of this small study suggest that age-related differences in CNS development influence the modulation of corticospinal drive to ankle muscles (e.g., SOL/TA) during childhood, particularly supporting the existence of a separate pathway underlying the control of forward lean and backward returning.

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How cortical oscillations are involved in the coordination of functionally coupled muscles and how this is modulated by different movement contexts (static vs dynamic) remains unclear. Here, this is investigated by recording high-density electroencephalography (EEG) and electromyography (EMG) from different forearm muscles while healthy participants (n = 20) performed movement tasks (static and dynamic posture holding, and reaching) with their dominant hand. When dynamic perturbation was applied, beta band (15-35 Hz) activities in the motor cortex contralateral to the performing hand reduced during the holding phase, comparative to when there was no perturbation. During static posture holding, transient periods of increased cortical beta oscillations (beta bursts) were associated with greater corticomuscular coherence and increased phase synchrony between muscles (intermuscular coherence) in the beta frequency band compared to the no-burst period. This effect was not present when resisting dynamic perturbation. The results suggest that cortical beta bursts assist synchronisation of different muscles during static posture holding in healthy motor control, contributing to the maintenance and stabilisation of functional muscle groups. Theoretically, increased cortical beta oscillations could lead to exaggerated synchronisation in different muscles making the initialisation of movements more difficult, as observed in Parkinson's disease.

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Cortical motor neuron activity appears to drive lower motor neurons through two distinct frequency bands: the ß range (15-30 Hz) during weak muscle contractions and γ range (30-50 Hz) during strong contractions. It is unknown whether the frequency of cortical drive shifts continuously or abruptly between the ß and γ frequency bands as contraction strength changes. Intermuscular coherence (IMC) between synergistic arm muscles was used to assess how the frequency of common neuronal drive shifts with increasing contraction strength. Muscle activity was recorded by surface electromyography (EMG) from the biceps and brachioradialis in nine healthy adults performing 30-second isometric holds with added loads. IMC was calculated across the two muscle groups during the isometric contraction. Significant IMC was present in the 20 to 50 Hz range with all loads. Repeated measures ANOVA show the peak frequency of IMC increased significantly when load was added, from a peak of 32.7 Hz with no added load, to 35.3 Hz, 35.7 Hz, and 36.3 Hz with three-, five-, and ten-pound loads respectively. An increase in IMC frequency occurs in response to added load, suggesting that cortical drive functions over a range of frequencies as a function of an isometric contraction against load.

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Spinocerebellar ataxias (SCAs) are familial neurodegenerative diseases involving the cerebellum and spinocerebellar tracts. While there is variable involvement of corticospinal tracts (CST), dorsal root ganglia, and motor neurons in SCA3, SCA6 is characterized by a pure, late-onset ataxia. Abnormal intermuscular coherence in the beta-gamma frequency range (IMCßγ) implies a lack of integrity of CST or the afferent input from the acting muscles. We test the hypothesis that IMCßγ has the potential to be a biomarker of disease activity in SCA3 but not SCA6. Intermuscular coherence between biceps brachii and brachioradialis muscles was measured from surface EMG waveforms in SCA3 (N = 16) and SCA6 (N = 20) patients and in neurotypical subjects (N = 23). IMC peak frequencies were present in the ß range in SCA patients and in the γ range in neurotypical subjects. The difference between IMC amplitudes in the γ and ß ranges was significant when comparing neurotypical control subjects to SCA3 (p < 0.01) and SCA6 (p = 0.01) patients. IMCßγ amplitude was smaller in SCA3 patients compared to neurotypical subjects (p < 0.05), but not different between SCA3 and SCA6 patients or between SCA6 and neurotypical subjects. IMC metrics can differentiate SCA patients from normal controls.

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The foot core system is essential for upright stability. However, aging-induced changes in the foot core function remain poorly understood. The present study aimed to examine age-related differences in postural stability from the perspective of foot core capacity and neuromuscular control during quiet standing. Thirty-six older and 25 young adults completed foot core capacity tests including toe flexion strength, muscle ultrasonography, and plantar cutaneous sensitivity. The center of pressure (COP) and electromyography (EMG) of abductor hallucis (ABH), peroneus longus (PL), tibialis anterior (TA) and medial gastrocnemius (GM) were simultaneously recorded during double-leg and single-leg standing (SLS). EMG data were used to calculate muscle synergy and intermuscular coherence across three frequency bands. Compared to young adults, older adults exhibited thinner hallucis flexors, weaker toe strength, and lower plantar cutaneous sensitivity. The ABH thickness and plantar cutaneous sensitivity were negatively associated with the COP mean peak velocity in older adults, but not in young adults. Besides, older adults had higher cocontraction of muscles spanning the arch (ABH-PL) and ankle (TA-GM), and had lower beta- and gamma-band coherence of the ABH-PL and TA-PL during SLS. Foot core capacities became compromised with advancing age, and the balance control of older adults was susceptible to foot core than young adults in balance tasks. To compensate for the weakened foot core, older adults may adopt arch and ankle stiffening strategies via increasing muscle cocontraction. Furthermore, coherence analysis indicated that aging may increase the demand for cortical brain resources during SLS.

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Asymmetrically impaired standing control is a prevalent disability among stroke patients; however, most of the neuromuscular characteristics are unclear. Therefore, the main purpose of this study was to investigate between-limb differences in intermuscular coherence during quiet standing. Consequently, 15 patients who had sub-acute stroke performed a quiet standing task without assistive devices, and electromyography was measured on the bilateral tibialis anterior (TA), soleus (SL), and medial gastrocnemius (MG). The intermuscular coherence of the unilateral synergistic (SL-MG) pair and unilateral antagonist (TA-SL and TA-MG) pairs in the delta (0-5 Hz) and beta (15-35 Hz) bands were calculated and compared between the paretic and non-paretic limbs. The unilateral synergistic SL-MG coherence in the beta band was significantly greater in the non-paretic limb than in the paretic limb (p = 0.017), while unilateral antagonist TA-MG coherence in the delta band was significantly greater in the paretic limb than in the non-paretic limb (p < 0.01). During quiet standing, stroke patients showed asymmetry in the cortical control of the plantar flexor muscles, and synchronous control between the antagonistic muscles was characteristic of the paretic limb. This study identified abnormal muscle activity patterns and asymmetrical cortical control underlying impaired standing balance in patients with sub-acute stroke using an intermuscular coherence analysis.

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PURPOSE: This study aimed to identify the contribution of the common synaptic drives to motor units during obstacle avoidance, using coherence analysis between a-pair electromyography (EMG) signals (EMG-EMG coherence). MATERIALS AND METHODS: Fourteen healthy volunteers walked on a treadmill with and without obstacle avoidance. During obstacle gait, subjects were instructed to step over an obstacle with their right leg while walking that would randomly and unpredictably appear. Surface EMG signals were recorded from the following muscles of the right leg: the proximal and distal ends of tibialis anterior (TAp and TAd), biceps femoris (BF), semitendinosus (ST), lateral gastrocnemius (LG), and medial gastrocnemius (MG). Beta-band (13-30 Hz) EMG-EMG coherence was analysed. RESULTS: Beta-band EMG-EMG coherence of TAp-TAd during swing phase and BF-ST during pre and initial swing phase when stepping over an obstacle were significantly higher compared to normal gait (both p < 0.05). Beta-band EMG-EMG coherence of TAp-TAd, BF-ST, and LG-MG during stance phase were not significantly different between the two gait conditions (all p > 0.05). CONCLUSIONS: The present findings suggest increased common synaptic drives to motor units in ankle dorsiflexor and knee flexor muscles during obstacle avoidance. It also may reflect an increased cortical contribution to modify the gait patterns to avoid an obstacle.

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Objective. Muscle network modeling maps synergistic control during complex motor tasks. Intermuscular coherence (IMC) is key to isolate synchronization underlying coupling in such neuromuscular control. Model inputs, however, rely on electromyography, which can limit the depth of muscle and spatial information acquisition across muscle fibers.Approach. We introduce three-dimensional (3D) muscle networks based on vibrational mechanomyography (vMMG) and IMC analysis to evaluate the functional co-modulation of muscles across frequency bands in concert with the longitudinal, lateral, and transverse directions of muscle fibers. vMMG is collected from twenty subjects using a bespoke armband of accelerometers while participants perform four hand gestures. IMC from four superficial muscles (flexor carpi radialis, brachioradialis, extensor digitorum communis, and flexor carpi ulnaris) is decomposed using matrix factorization into three frequency bands. We further evaluate the practical utility of the proposed technique by analyzing the network responses to various sensor-skin contact force levels, studying changes in quality, and discriminative power of vMMG.Main results. Results show distinct topological differences, with coherent coupling as high as 57% between specific muscle pairs, depending on the frequency band, gesture, and direction. No statistical decrease in signal strength was observed with higher contact force.Significance. Results support the usability vMMG as a tool for muscle connectivity analyses and demonstrate the use of IMC as a new feature space for hand gesture classification. Comparison of spectrotemporal and muscle network properties between levels of force support the robustness of vMMG-based network models to variations in tissue compression. We argue 3D models of vMMG-based muscle networks provide a new foundation for studying synergistic muscle activation, particularly in out-of-clinic scenarios where electrical recording is impractical.

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Introduction: Activation of the unaffected hemisphere contributes to motor function recovery post stroke in patients with severe upper limb motor paralysis. Transcranial direct current stimulation (tDCS) has been used in stroke rehabilitation to increase the excitability of motor-related areas. tDCS has been reported to improve upper limb motor function; nonetheless, its effects on corticospinal tract excitability and muscle activity patterns during upper limb exercise remain unclear. Additionally, it is unclear whether simultaneously applied bihemispheric tDCS is more effective than anodal tDCS, which stimulates only one hemisphere. This study examined the effects of bihemispheric tDCS training on corticospinal tract excitability and muscle activity patterns during upper limb movements in a patient with subacute stroke. Methods: In this single-case retrospective study, the Fugl-Meyer Assessment, Box and Block Test, electromyography, and intermuscular coherence measurement were performed. Intermuscular coherence was calculated at 15-30 Hz, which reflects corticospinal tract excitability. Results: The results indicated that bihemispheric tDCS improved the Fugl-Meyer Assessment, Box and Block Test, co-contraction, and intermuscular coherence results, as compared with anodal tDCS. Discussion: These results reveal that upper limb training with bihemispheric tDCS improves corticospinal tract excitability and muscle activity patterns in patients with subacute stroke.

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Beta-band (15-30 Hz) synchronization between the EMG signals of active limb muscles can serve as a non-invasive assay of corticospinal tract integrity. Tasks engaging a single limb often primarily utilize one corticospinal pathway, although bilateral neural circuits can participate in goal-directed actions involving multi-muscle coordination and utilization of feedback. Suboptimal utilization of such circuits after CNS injury can result in unintended mirror movements and activation of pathological synergies. Accordingly, it is important to understand how the actions of one limb (e.g., a less-affected limb after strokes) influence the opposite corticospinal pathway for the rehabilitation target. Certain unimanual actions decrease the excitability of the "unengaged" corticospinal tract, presumably to prevent mirror movement, but there is no direct way to predict the extent to which this will occur. In this study, we tested the hypothesis that task-dependent changes in beta-band drives to muscles of one hand will inversely correlate with changes in the opposite corticospinal tract excitability. Ten participants completed spring pinching tasks known to induce differential 15-30 Hz drive to muscles. During compressions, transcranial magnetic stimulation single pulses to the ipsilateral M1 were delivered to generate motor-evoked potentials in the unengaged hand. The task-induced changes in ipsilateral corticospinal excitability were inversely correlated with associated changes in EMG-EMG coherence of the task hand. These results demonstrate a novel connection between intermuscular coherence and the excitability of the "unengaged" corticospinal tract and provide a springboard for further mechanistic studies of unimanual tasks of varying difficulty and their effects on neural pathways relevant to rehabilitation.

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Introduction: Knowledge about the mechanics and physiological features of balance for healthy individuals enhances understanding of impairments of balance related to neuropathology secondary to aging, diseases of the central nervous system (CNS), and traumatic brain injury, such as concussion. Methods: We examined the neural correlations during muscle activation related to quiet standing from the intermuscular coherence in different neural frequency bands. Electromyography (EMG) signals were recorded from six healthy participants (fs = 1,200 Hz for 30 s) from three different muscles bilaterally: anterior tibialis, medial gastrocnemius, and soleus. Data were collected for four different postural stability conditions. In decreasing order of stability these were feet together eyes open, feet together eyes closed, tandem eyes open, and tandem eyes closed. Wavelet decomposition was used to extract the neural frequency bands: gamma, beta, alpha, theta, and delta. Magnitude-squared-coherence (MSC) was computed between different muscle pairs for each of the stability conditions. Results and discussion: There was greater coherence between muscle pairs in the same leg. Coherence was greater in lower frequency bands. For all frequency bands, the standard deviation of coherence between different muscle pairs was always higher in the less stable positions. Time-frequency coherence spectrograms also showed higher intermuscular coherence for muscle pairs in the same leg and in less stable positions. Our data suggest that coherence between EMG signals may be used as an independent indicator of the neural correlates for stability.

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Maintaining balance is thought to primarily occur sub-consciously. Occasionally, however, individuals will direct conscious attention towards balance, e.g., in response to a threat to balance. Such conscious movement processing (CMP) increases the reliance on attentional resources and may disrupt balance performance. However, the underlying changes in neuromuscular control remain poorly understood. We investigated the effects of CMP (manipulated using verbal instructions) on neural control of posture in twenty-five adults (11 females, mean age = 23.9, range = 18-33). Participants performed 90-s, bipedal stance balance trials in high- and low-CMP conditions, during both stable (solid surface) and unstable (foam) task conditions. Postural sway amplitude, frequency and complexity were used to assess postural control. Surface EMG was recorded bilaterally from lower leg muscles (Soleus, Tibialis Anterior, Gastrocnemius Medialis, Peroneus Longus) and intermuscular coherence (IMC) was assessed for 12 muscle pairs across four frequency bands. We observed significantly increased sway amplitude, and decreased sway frequency and complexity in the high- compared to the low-CMP conditions. All sway variables increased in the unstable compared to the stable conditions. We observed reduced beta band IMC between several muscle pairs during high- compared to low-CMP, but these findings did not remain significant after controlling for multiple comparisons. Finally, IMC significantly increased in the unstable conditions for most muscle combinations and frequency bands. In all, results tentatively suggest that CMP-induced changes in sway outcomes may be facilitated by reduced beta-band IMC, but these findings need to be replicated before they can be interpreted more conclusively.

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Despite its importance, abnormal interactions between the proximal and distal upper extremity muscles of stroke survivors and their impact on functional task performance has not been well described, due in part to the complexity of upper extremity tasks. In this pilot study, we elucidated proximal-distal interactions and their functional impact on stroke survivors by quantitatively delineating how hand and arm movements affect each other across different phases of functional task performance, and how these interactions are influenced by stroke. Fourteen subjects, including nine chronic stroke survivors and five neurologically-intact subjects participated in an experiment involving transport and release of cylindrical objects between locations requiring distinct proximal kinematics. Distal kinematics of stroke survivors, particularly hand opening, were significantly affected by the proximal kinematics, as the hand aperture decreased and the duration of hand opening increased at the locations that requires shoulder abduction and elbow extension. Cocontraction of the extrinsic hand muscles of stroke survivors significantly increased at these locations, where an increase in the intermuscular coherence between distal and proximal muscles was observed. Proximal kinematics of stroke survivors was also affected by the finger extension, but the cocontraction of their proximal muscles did not significantly increase, suggesting the changes in the proximal kinematics were made voluntarily. Our results showed significant proximal-to-distal interactions between finger extension and elbow extension/shoulder abduction of stroke survivors exist during their functional movements. Increased cocontraction of the hand muscles due to increased neural couplings between the distal and proximal muscles appears to be the underlying mechanism.

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Background: Stroke alters muscle co-activation and notably leads to exaggerated antagonist co-contraction responsible for impaired motor function. However, the mechanisms underlying this exaggerated antagonist co-contraction remain unclear. To fill this gap, the analysis of oscillatory synchronicity in electromyographic signals from synergistic muscles, also called intermuscular coherence, was a relevant tool. Objective: This study compares functional intermuscular connectivity between muscle pairs of the paretic and non-paretic upper limbs of stroke subjects and the dominant limb of control subjects, concomitantly between two muscle pairs with a different functional role, through an intermuscular coherence analysis. Methods: Twenty-four chronic stroke subjects and twenty-four healthy control subjects were included. Subjects performed twenty elbow extensions while kinematic data and electromyographic activity of both flexor and extensor elbow muscles were recorded. Intermuscular coherence was analyzed in the beta frequency band compared to the assessment of antagonist co-contraction. Results: Intermuscular coherence was higher in the stroke subjects' paretic limbs compared to control subjects. For stroke subjects, the intermuscular coherence of the antagonist-antagonist muscle pair (biceps brachii-brachioradialis) was higher than that of the agonist-antagonist muscle pair (triceps brachii-brachioradialis). For the paretic limb, intermuscular coherence of the antagonist-antagonist muscle pair presented a negative relationship with antagonist co-contraction. Conclusion: Differences in intermuscular coherence between the paretic limbs of stroke subjects and control subjects suggest a higher common central drive during movement. Furthermore, results highlight the association between stroke-related alteration of intermuscular functional connectivity and the alteration of motor function.

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BACKGROUND: Intermuscular synchronization is one of the fundamental aspects of maintaining a stable posture and is of great importance in the aging process. This study aimed to assess muscle synchronization and postural stabilizer asymmetry during quiet standing and the limits of stability using wavelet analysis. Intermuscular synchrony and antagonistic sEMG-sEMG (surface electromyography) coherence asymmetry were evaluated in the tibialis anterior and soleus muscles. METHODS: The study involved 20 elderly (aged 65 ± 3.6) and 20 young (aged 21 ± 1.3) subjects. The task was to perform a maximum forward bend in a standing position. The prone test was divided into three phases: quiet standing (10 s), dynamic learning, and maintenance of maximum leaning (20 s). Wavelet analysis of coherence was performed in the delta and beta bands. RESULTS: Young subjects modulated interface coherences to a greater extent in the beta band. Analysis of postural stability during standing tasks showed that only the parameter R2b (the distance between the maximal and minimal position central of pressure), as an indicator for assessing the practical limits of stability, was found to be significantly associated with differences in aging. CONCLUSION: The results showed differences in the beta and delta band oscillations between young and older subjects in a postural task involving standing quietly and leaning forward.

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The interplay between biarticular and monoarticular muscles of the knee and hip joints during bipedal squats (SQBP ) requires adequate central-nervous control mechanisms to enable smooth and dynamic movements. Here, we investigated motor control between M. vastus medialis (VM), M. vastus lateralis (VL), and M. rectus femoris (RF) in 12 healthy male recreational athletes during SQBP with three load levels (50%, 62.5%, and 75% of 3-repetition maximum) following a standardized strength training protocol (3 sets of 10 repetitions). To quantify differences in motor control mechanisms in both time and frequency domains, we analyzed (1) muscle covariation via correlation analyses, as well as (2) common neural input via intermuscular coherence (IMC) between RF, VM, and VL. Our results revealed significantly higher gamma IMC between VM-VL compared with RF-VL and RF-VM for both legs. Correlation analyses demonstrated significantly higher correlation coefficients during ascent periods compared with descent periods across all analyzed muscle pairs. However, no load-dependent modulation of motor control could be observed. Our study provides novel evidence that motor control during SQBP is characterized by differences in common input between biarticular and monoarticular muscles. Additionally, muscle activation patterns show higher similarity during ascent compared with descent periods. Future research should aim to validate and extend our observations as insights into the underlying control mechanisms offer the possibility for practical implications to optimize training concepts in elite sports and rehabilitation.

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OBJECTIVE: To determine the electrodiagnostic characteristics of facial onset sensory and motor neuronopathy (FOSMN). METHODS: Electrophysiological data from 10 FOSMN patients in Newcastle-upon-Tyne and Sydney were reviewed. Relevant literature was reviewed. RESULTS: Findings on standard electrophysiological assessment were in broad agreement with those published: blink reflexes were abnormal in all but one patient; sensory nerve action potentials were reduced but compound muscle action potentials preserved; mixed acute and chronic neurogenic change was identified on needle electromyography in bulbar and cervico-thoracic muscles in approximately 50% of patients. Upper limb somatosensory evoked potential (SEP) central conduction times were increased (n = 4) and progressed on repeat testing (n = 3). Upper motor neuron dysfunction was revealed by several measures [ipsilateral motor evoked potentials (MEPs) (n = 1); reduced short interval intra-cortical inhibition on threshold-tracking transcranial magnetic stimulation (n = 2); absent beta-band intermuscular coherence (n = 3)]. CONCLUSIONS: Electrodiagnostic investigation of FOSMN should include blink reflex testing, SEPs and tests of upper motor neuron function. The combination of progressive lower motor neuron disease and upper motor neuron disease on neurophysiological investigation provides further support for the contention that FOSMN is a rare variant of motor neurone disease. SIGNIFICANCE: These findings will aid the neurologist and neurophysiologist in making a confident diagnosis of FOSMN, thus expediting appropriate care.

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OBJECTIVE: Although adolescent idiopathic scoliosis is thought to be an orthopedic disorder, sensorimotor deficits resulting in asymmetric neural drive to the axial musculature have been proposed as contributing factors. Asymmetry in the vestibular control of spinal motoneurons can cause spine deformation reminiscent of idiopathic scoliosis in animal models. METHODS: To examine the neural control of axial muscles, we compared common oscillatory drive to bilateral lumbar muscles between 19 participants with adolescent idiopathic scoliosis and 19 healthy adolescents. We measured right and left paraspinal muscle activity during steady isometric back extensions at 15% or 30% of their maximum voluntary contraction. RESULTS: The variance in exerted force and symmetry in bilateral muscle activation were similar between groups. We estimated the strength of common oscillations between muscle motoneuron pools using intermuscular coherence. Compared to controls, participants with adolescent idiopathic scoliosis exhibited smaller intermuscular coherence between paraspinal muscles in the alpha and beta bands. To identify the cause of the observed decreased in intermuscular coherence, we quantified variability of electromyography power ratio and relative activation timing between the paraspinal muscle. Intermuscular phase between muscle oscillations across the alpha band demonstrated larger variability in adolescent with idiopathic scoliosis. The variability of the ratio of lumbar muscles power was similar between groups in the alpha and beta bands. CONCLUSION: Our results suggest that altered bilateral control of axial muscles characterized by increased variability in the timing of alpha oscillations may be linked to spine deformation in adolescents. SIGNIFICANCE: Our findings provide a new perspective on neural factors associated with a common spine deformation, adolescent idiopathic scoliosis.

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Cardiorespiratory or aerobic exercise immediately after practice of an upper-extremity motor skill task can facilitate skill consolidation, as demonstrated by enhanced performances at 24 h and 7-day retention tests. The purpose of this study was to examine the effect of acute cardiorespiratory exercise on motor skill consolidation when skill practice involved low and high levels of contextual interference introduced through repetitive and interleaved practice schedules, respectively. Forty-eight young healthy adults were allocated to one of four groups who performed either repetitive or interleaved practice of a pinch grip motor sequence task, followed by either a period of seated rest or a bout of high-intensity interval cycling. At pre- and post-practice and 24 h and 7-day retention tests, we assessed motor skill performance and ß-band (15-35 Hz) intermuscular coherence using surface electromyography (EMG) collected from the abductor pollicis brevis and first dorsal interosseous. At the 7-day retention test, off-line consolidation was enhanced in the cardiorespiratory exercise relative to the rest group, but only among individuals who performed interleaved motor skill practice (p = 0.02). Similarly, at the 7-day retention test, ß-band intermuscular coherence increased to a greater extent in the exercise group than in the rest group for those who performed interleaved practice (p = 0.02). Under the present experimental conditions, cardiorespiratory exercise preferentially supported motor skill consolidation and change in intermuscular coherence when motor skill practice involved higher rather than lower levels of contextual interference.

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Natural manipulation tasks in air consist of two kinematic components: a grasping component, with activation of the hand muscles, and a lifting component, with activation of the proximal muscles. However, it remains unclear whether the synchronized motor commands to the hand/proximal arm muscles are divergently controlled during the task. Therefore, we examined how intermuscular coherence was modulated depending on the muscle combinations during grip and lift (G&L) tasks. Electromyograms (EMGs) were recorded from the biceps brachii (BB), triceps brachii (TB), flexor digitorum superficialis (FDS), and extensor digitorum communis (EDC) muscles. The participants were required to maintain G&L tasks involving a small cubical box with the thumb and index and middle fingers. Consequently, we found that the beta-rhythm coherence (15-35 Hz) in BB-TB, BB-FDS, and TB-EDC pairs during G&L was significantly larger than that during the isolated task with cocontraction of the two target muscles but not BB-EDC, TB-FDS, and FDS-EDC (task and muscle pair specificities). These increases in beta-rhythm coherence were also observed in intramuscular EMG recordings. Furthermore, the results from the execution of several mimic G&L tasks revealed that the separated task-related motor signals and combinations between the motor signals/sensations of the fingertips or object load had minor contributions to the increase in the coherence. These results suggest that during G&L the central nervous system regulates synchronous drive onto motoneurons depending on the muscle pairs and that the multiple combination effect of the sensations of touch/object load and motor signals in the task promotes the synchrony of these pairs.NEW & NOTEWORTHY Natural manipulation in air consists of two kinematic components: grasping, with activation of hand muscles, and lifting, with activation of proximal muscles. We show that during the maintenance of object manipulation in air the central nervous system regulates the synchronous drive onto human motoneuron pools depending on the hand/proximal muscle pairs and that the multiple combination effect of the sensations of touch/object load and motor signals in the task promotes the synchrony of these pairs.

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