EMG-EMG coherence during voluntary control of human standing tasks: a systematic scoping review

Motor control performance-related modulation of beta-band EEG-sEMG coherence differs between general and local muscular exercise-induced fatigue

PURPOSE

Exercise-induced fatigue can reduce motor control performance and increase the risk of sporting injuries, which are related to functional coupling within the corticomotoneuronal pathway. However, the differences in functional coupling caused by general and local muscular exercise-induced fatigue are unknown. This study aimed to investigate the effects of exercise-induced fatigue on the beta-band (16-30 Hz) functional coupling between the sensorimotor cortex (SM1) and muscles of the dominant lower limb under different fatigue protocols.

METHODS

Twenty-four healthy male participants were recruited to participate in randomized sessions of personalized constant speed running as general muscular exercise (GME) and maximum isokinetic ankle plantar-dorsiflexion as local muscular exercise (LME) to induce fatigue. These sessions were separated by 7 days. The electroencephalogram (EEG) signals of SM1 (e.g., FC1, FCz, and Cz) and surface electromyography signals (sEMG) of four muscles (soleus, SOL; medial gastrocnemius, MG; later gastrocnemius, and LG; tibialis anterior, TA) were simultaneously recorded before and after fatigue during the ankle plantar-dorsiflexion task, which were used for beta-band coherence analyses.

RESULTS

Following fatigue induced by GME, the EEG-sEMG coherence was significantly greater than that induced by LME (P < 0.04). Compared to pre-fatigue state, the coherence of FC1-SOL, FCz-SOL, and Cz-SOL increased significantly after general fatigue, while these coherences decreased significantly after local fatigue.

CONCLUSION

Fatigue induced by GME indicates an enhancement in beta-band functional coupling between the SM1 and muscles of the dominant lower limb, which is related to higher motor control performance. In contrast, fatigue induced by LME diminishes the functional coupling.

Analysis of Connectivity in Electromyography Signals to Examine Neural Correlations in the Activation of Lower Leg Muscles for Postural Stability: A Pilot Study

In quiet standing, the central nervous system implements a pre-programmed ankle strategy of postural control to maintain upright balance and stability. This strategy comprises a synchronized common neural drive delivered to synergistically grouped muscles. This study evaluated connectivity between EMG signals of the unilateral and bilateral homologous muscle pairs of the lower legs during various standing balance conditions using magnitude-squared coherence (MSC). The leg muscles examined included the right and left tibialis anterior (TA), medial gastrocnemius (MG), and soleus (S). MSC is a frequency domain measure that quantifies the linear phase relation between two signals and was analyzed in the alpha (8-13 Hz), beta (13-30 Hz), and gamma (30-100 Hz) neural frequency bands for feet together and feet tandem, with eyes open and eyes closed conditions. Results showed that connectivity in the beta and lower and upper gamma bands (30-100 Hz) was influenced by standing balance conditions and was indicative of a neural drive originating from the motor cortex. Instability was evaluated by comparing less stable standing conditions with a baseline-eyes open feet together stance. Changes in connectivity in the beta and gamma bands were found to be most significant in the muscle pairs of the back leg during a tandem stance regardless of dominant foot placement. MSC identified the MG:S muscle pair as significant for the right and left leg. The results of this study provided insight into the neural mechanism of postural control.

Synergy-Based Estimation of Balance Condition During Walking Tests

In the area of human-machine interface research, the continuous estimation of the Center of Pressure (COP) in the human body can assess users' balance conditions, thereby effectively enhancing the safety and diversity of studies. This paper aims to present a novel method for continuous synergy-based estimation of human balance states during walking, and simultaneously analyze the impact of various factors on the estimation results. Specifically, we introduce muscle synergy coherence features and analyze the variations of these features in different balance conditions. Furthermore, we fuse temporal features extracted by a bidirectional long short-term memory (BILSTM) network with spatial features derived from the analysis of muscle synergy coherence to continuously estimate the mediolateral COP and Ground Reaction Force (GRF) during human walking tests. Then, we analyze the influence of different electromechanical delay compensation (EMD) time, the number of synergies, and different walking speeds on the estimation results. Finally, we validate the estimation capability of the proposed method on data collected in real-world walking tests. The results indicate a significant correlation between the proposed muscle synergy coherence features and balance conditions. The network structure combining muscle synergy coherence features and BILSTM features enables accurate continuous estimation of COP ( ) and GRF ( ) during walking tests. Our research introduces a novel approach to the continuous estimation of balance conditions in human walking, with potential implications in various applications within human-machine engineering, such as exoskeletons and prosthetics.

Beta-Band Cortico-Muscular Phase Coherence in Hemiparetic Stroke

Following a stroke, compensation for the loss of ipsilesional corticospinal and corticobulbar projections, results in increased reliance on contralesional motor pathways during paretic arm movement. Better understanding outcomes of post-stroke contralesional cortical adaptation outcomes may benefit more targeted post-stroke motor rehabilitation interventions. This proof-of-concept study involves eight healthy controls and ten post-stroke participants. Electroencephalographic (EEG) and deltoid electromyographic (EMG) data were collected during an upper-limb task. Phase coupling between beta-band motor cortex EEG and deltoid EMG was assessed using the Multi-Phase Locking Value (M-PLV) method. Different from classic cortico-muscular coherence, M-PLV allows for the calculation of dynamic phase coherence and delays, and is not affected by the non-stationary nature of EEG/EMG signals. Nerve conduction delay from the contralateral motor cortex to the deltoid muscle of the paretic arm was estimated. Our results show the ipsilateral (contralesional) motor cortex beta-band phase coherence behavior is altered in stroke participants, with significant differences in ipsilateral EEG-EMG coherence values, ipsilateral time course percentage above the significance threshold, and ipsilateral time course area above the significance threshold. M-PLV phase coherence analysis provides evidence for post-stroke contralesional motor adaptation, highlighting its increased role in the paretic shoulder abduction task. Nerve conduction delay between the motor cortices and deltoid muscle is significantly higher in stroke participants. Beta-band M-PLV phase coherence analysis shows greater phase-coherence distribution convergence between the ipsilateral (contralesional) and contralateral (ipsilesional) motor cortices in stroke participants, which is interpretable as evidence of maladaptive neural adaptation resulting from a greater reliance on the contralesional motor cortices.

Neurobiological Insights Into Cerebral Palsy: A Review of the Mechanisms and Therapeutic Strategies

BACKGROUND

Cerebral palsy (CP) is a common neurodevelopmental disorder characterized by impaired mobility and posture caused by brain injury or abnormal development. CP relates to a variety of neurological mechanisms and pathways that impact the type and severity of motor disability, as well as comorbidities. The heterogeneity in clinical phenotype, pathogenesis, and etiology poses significant challenges for effective therapeutic intervention.

OBJECTIVES

The review aims to provide a comprehensive analysis of the neurobiological mechanisms underlying CP and evaluate current and prospective therapeutic strategies, highlighting the necessity for targeted interventions to address the disorder's multifaceted nature.

METHODS

A thorough literature review was conducted, focusing on studies published in peer-reviewed journals that explore the pathophysiological mechanisms, clinical interventions, and therapeutic strategies for CP.

RESULTS

The pathogenesis of CP involves a complex interplay of genetic, environmental, and perinatal factors leading to brain injury. Inflammatory processes, oxidative stress, and excitotoxicity are critical in CP development. Current therapeutic approaches primarily focus on symptom management through physical and occupational therapy, as well as pharmacological interventions. Emerging therapies, including anti-inflammatory agents, antioxidants, and neuroprotective and neurotrophic agents, show potential but require further validation. Notably, although steroids provide anti-inflammatory benefits, their use in pediatric patients raises concerns regarding long-term adverse effects such as osteoporosis.

CONCLUSION

Despite advances in understanding CP's neurobiological underpinnings, effective therapeutic targets remain elusive. A comprehensive approach addressing CP's heterogeneity is essential. Future research should emphasize in-depth evaluations of the efficacy and safety of therapeutic agents, particularly in pediatric populations, to develop targeted and effective treatments for CP.

Intermuscular Coherence during Quiet Standing in Sub-Acute Patients after Stroke: An Exploratory Study

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.

Increased EMG-EMG coherence in the theta and alpha bands during bimanual force modulation

During the execution of movements, error correction processes have been inferred by EEG activation at oscillation frequencies in the theta (4-8 Hz) and alpha (8-12 Hz) bands. The current study examined whether evidence for error detection and correction could be found at the muscular level through the use of EMG-EMG coherence, which quantifies the amount of synchronous EMG activity between limbs in the frequency domain. Participants (n = 13) performed a bimanual force production task involving either wrist flexors or extensors under conditions in which the force was to be held constant or continuously modulated. As predicted, the modulation of changing force output resulted in significantly greater force variability and increased EMG-EMG coherence throughout the theta and alpha band for both flexor and extensor responses. These results are consistent with EEG activation frequencies associated with error correction, motor reprogramming and sustained attention and indicate that evidence for these cortical processes can also be observed at the muscular level in the form of correlated EMG frequency content between limbs.