Multiple Muscle Research Articles

The robotic approach to the passive interlocking mechanism in the hindlimb musculoskeletal system of Crocodylus porosus

Efficient locomotion in terrestrial vertebrates relies on intra-limb coordination that emerges through interaction with the environment and passive interlocking of the musculoskeletal system. These structures have been well investigated in some mammals and birds, but the presence of similar structures in other terrestrial vertebrates has been under appreciated. This study addresses the functionality of the passive interlocking system in reptilian hindlimb locomotion by dissecting Crocodylus porosus and constructing a robot. Based on the dissection, we hypothesized that the passive interlocking mechanism consisted of multiple muscles to maintain the semi-erect limb posture and support its weight. The mechanism is provided by the caudifemoralis longus muscle, along with its tendon and the gastrocnemius externus, acting as a passive element that interacts with the ground reaction force. Accordingly, the feasibility of the interlocking function was demonstrated by a robot implementing the hindlimb and pelvic musculoskeletal system of crocodilians. This study provides new insights into the locomotion mechanism of crocodilians and emphasizes the importance of passive interlocking in efficient locomotion in terrestrial vertebrates. The findings could have implications for developing biomimetic robots and understanding the evolution of terrestrial locomotion in vertebrates.

Omics-driven investigation of the biology underlying intrinsic submaximal working capacity and its trainability.

Submaximal exercise capacity is an indicator of cardiorespiratory fitness with clinical and public health implications. Submaximal exercise capacity and its response to exercise programs are characterized by heritability levels of about 40%. Using physical working capacity (power output) at a heart rate of 150 beats/min (PWC150) as an indicator of submaximal exercise capacity in subjects of the HERITAGE Family Study, we have undertaken multi-omics and in silico explorations of the underlying biology of PWC150 and its response to 20 wk of endurance training. Our goal was to illuminate the biological processes and identify panels of genes associated with human variability in intrinsic PWC150 (iPWC150) and its trainability (dPWC150). Our bioinformatics approach was based on a combination of genome-wide association, skeletal muscle gene expression, and plasma proteomics and metabolomics experiments. Genes, proteins, and metabolites showing significant associations with iPWC150 or dPWC150 were further queried for the enrichment of biological pathways. We compared genotype-phenotype associations of emerging candidate genes with reported functional consequences of gene knockouts in mouse models. We investigated the associations between DNA variants and multiple muscle and cardiovascular phenotypes measured in HERITAGE subjects. Two panels of prioritized genes of biological relevance to iPWC150 (13 genes) and dPWC150 (6 genes) were identified, supporting the hypothesis that genes and pathways associated with iPWC150 are different from those underlying dPWC150. Finally, the functions of these genes and pathways suggested that human variation in submaximal exercise capacity is mainly driven by skeletal muscle morphology and metabolism and red blood cell oxygen-carrying capacity.NEW & NOTEWORTHY Multi-omics and in silico explorations of the genes and underlying biology of submaximal exercise capacity and its response to 20 wk of endurance training were undertaken. Prioritized genes were identified: 13 genes for variation in submaximal exercise capacity in the sedentary state and 5 genes for the response level to endurance training, with no overlap between them. Genes and pathways associated with submaximal exercise capacity in the sedentary state are different from those underlying trainability.

Myopathy and Ophthalmologic Abnormalities in Association With Multiple Skeletal Muscle Mitochondrial DNA Deletions.

Establishing a molecular diagnosis of mitochondrial diseases due to pathogenic mitochondrial DNA (mtDNA) variants can be difficult because of varying levels of tissue heteroplasmy, and identifying these variants is important for clinical management. Here, we present clinical and molecular findings in 8 adult patients with classical features of mitochondrial ophthalmologic and/or muscle disease and multiple mtDNA deletions isolated to muscle. The patients were identified via a retrospective review of patients seen in both a tertiary ophthalmology center and a genetics clinic with a clinical diagnosis of chronic progressive external ophthalmoplegia, optic nerve abnormalities, and/or mitochondrial myopathy. Age at onset of symptoms ranged from 18 to 61 years. Ocular manifestations included bilateral optic neuropathy in one patient, bilateral optic disc cupping without optic neuropathy in 2 patients, ptosis in 4 patients, and ocular motility deficits in 2 patients. Five patients had generalized weakness. Pathogenic variants in mtDNA were not found in the blood or buccal sample from any patient, but 7 of 8 patients had multiple mtDNA deletions identified in muscle tissue. One patient had a single mtDNA deletion identified in the muscle. Heteroplasmy was less than 15% for all of the identified deletions, with the exception of one deletion that had a heteroplasmy of 50%-60%. None of the patients were found to have a nuclear gene variant known to be associated with mitochondrial DNA maintenance. mtDNA deletions were identified in adult patients with ophthalmologic and/or musle abnormalities and may underlie their clinical presentations.

Poster (Knowledge Generation) ID 1985240

Background Following a spinal cord injury, there is a significant loss of monoamines below the lesion. In the rat model, exogenous administration of the serotonin precursor, 5-hydroxytryptophan (5HTP), increases neural excitability through augmentation of spinal serotonin levels. To determine whether this compensatory mechanism can be harnessed to restore serotonergic modulation in humans after SCI, participants visited the lab on four occasions where they received i) placebo, ii) carbidopa, iii) 50mg 5HTP+carbidopa, or iv) 100mg 5HTP+carbidopa in a randomized, crossover design. Cutaneomuscular reflexes (CMR) were obtained pre-drug and 30, 60, 90 and 120-min post-drug intake. Surface electromyography was also recorded during a pedalling movement pre- and post-drug. Results Nine participants with chronic, complete SCI (35.3±5.5 years) and four participants with chronic, incomplete SCI (47.0±19.7years) were enrolled. Following ingestion of 100mg 5HTP only, the short polysynaptic and long-lasting reflex components of the CMR were significantly increased by ∼ 86±61% and 58±17% respectively in individuals with complete SCI. No significant changes were noted in the cohort of individuals with incomplete SCI. Integrated EMG during pedalling was increased in multiple lower extremity muscles during the extension and flexion phases of the cycle following both 50-mg (82±15% and 51±7%) and 100-mg 5HTP (140±27% and 130±16%) in individuals with more severe injuries, but not in those with incomplete injuries. Conclusion Ingestion of 5HTP facilitates neural excitability and induces rhythmic muscle activity in previously inactive muscles during an assisted pedalling movement in individuals with chronic, complete SCI. This has significant clinical implications for rehabilitation after SCI.

A Dynamic Elbow Testing Apparatus for Simulating Elbow Joint Motion in Varying Shoulder Positions

To develop and evaluate the capabilities of a dynamic elbow testing apparatus that simulates unconstrained elbow motion throughout the range of humerothoracic (HTA) abduction. Elbow flexion was generated by six computer-controlled electromechanical actuators that simulated muscle action, while six degree-of-freedom joint motion was measured using an optical tracking device. Repeatability of joint kinematics was assessed at four HTA angles (0°, 45°, 90°, 135°) and with two muscle force combinations (A1-biceps brachialis, brachioradialis and A2-biceps, brachioradialis). Repeatability was determined by comparing kinematics at every 10° of flexion over five flexion-extension cycles (0° to 100°). Multiple muscle force combinations can be used at each HTA angle to generate elbow flexion. Trials showed that the testing apparatus produced highly repeatable joint motion at each HTA angle and with varying muscle force combinations. The intraclass correlation coefficient was greater than 0.95 for all conditions. Repeatable smooth cadaveric elbow motion was created that mimicked the invivo situation. These results suggest that the dynamic elbow testing apparatus can be used to characterize elbow biomechanics in cadaver upper extremities.

The Effects of Exercise-Induced Muscle Damage on Antagonist Muscles in Upper Limb Reaching Tasks

Coordination and control of multiple muscle groups are critical when adapting to movement disruptions, such as altered goals or pathways. Humans use sensory information from internal and external sources to engage in online movement control. Proprioception, mainly obtained from sensors in the muscles such as muscle spindles, is an important source of sensory information. After intense or unusual exercise, exercise-induced muscle damage (EIMD) can occur within 24 to 48 hours. EIMD can also increase noise in the signals generated by the sensory organs in the muscles and may influence online movement control.
 The objective of the study is to investigate the effects of EIMD on upper-limb movement control.
 Four right-handed, neurologically healthy, female participants (aged 20-21, M = 0.5) took part in the pilot experiment, they had normal, or corrected-to-normal vision, and participated in less than 5 hours of structured strength training weekly. The study consisted of familiarization and baseline testing, an exercise protocol, and a muscle damage assessment. In each session, a maximal voluntary contraction of the biceps brachii was assessed using a dynamometer. This dynamometer was also used for the EIMD-inducing protocol. To test the effects of EIMD on online control, participants completed a series of reaching tasks using the Kinarm Exoskeleton Robot. During some reaches, participants were required to correct their movement to either a force or target perturbation.
 Our pilot data shows that our protocol successfully induced muscle damage, as well as less antagonistic muscle (bicep) activation during reaching tasks. This suggests reduced biceps muscle contribution to movement control post-exercise. A decrease in movement time could signify learning and requires further exploration. We are hopeful that with further data collection, we will establish that participants are less accurate and have reduced flexor muscle activity in responses to both types of perturbations, compared to baseline.

Applying an Artificial Neuromolecular System to the Application of Robotic Arm Motion Control in Assisting the Rehabilitation of Stroke Patients-An Artificial World Approach.

Stroke patients cannot use their hands as freely as usual. However, recovery after a stroke is a long road for many patients. If artificial intelligence can assist human arm movement, it is believed that the possibility of stroke patients returning to normal hand movement can be significantly increased. In this study, the artificial neuromolecular system (ANM system) developed by our laboratory is used as the core motion control system to learn to control the mechanical arm, produce similar human rehabilitation actions, and assist patients in transiting between different activities. The strength of the ANM system lies in its ability to capture and process spatiotemporal information by exploiting the dynamic information processing inside neurons. Five experiments are conducted in this research: continuous learning, dimensionality reduction, moving problem domains, transfer learning, and fault tolerance. The results show that the ANM system can find out the arm movement trajectory when people perform different rehabilitation actions through the ability of continuous learning and reduce the activation of multiple muscle groups in stroke patients through the learning method of reducing dimensions. Finally, using the ANM system can reduce the learning time and performance required to switch between different actions through transfer learning.

Molecular logic of synaptic diversity between Drosophila tonic and phasic motoneurons

Although neuronal subtypes display unique synaptic organization and function, the underlying transcriptional differences that establish these features are poorly understood. To identify molecular pathways that contribute to synaptic diversity, single-neuron Patch-seq RNA profiling was performed on Drosophila tonic and phasic glutamatergic motoneurons. Tonic motoneurons form weaker facilitating synapses onto single muscles, while phasic motoneurons form stronger depressing synapses onto multiple muscles. Super-resolution microscopy and invivo imaging demonstrated that synaptic active zones in phasic motoneurons are more compact and display enhanced Ca2+ influx compared with their tonic counterparts. Genetic analysis identified unique synaptic properties that mapped onto gene expression differences for several cellular pathways, including distinct signaling ligands, post-translational modifications, and intracellular Ca2+ buffers. These findings provide insights into how unique transcriptomes drive functional and morphological differences between neuronal subtypes.

Human upper extremity motor cortex activity shows distinct oscillatory signatures for stereotyped arm and leg movements.

Stepping and arm swing are stereotyped movements that require coordination across multiple muscle groups. It is not known whether the encoding of these stereotyped movements in the human primary motor cortex is confined to the limbs' respective somatotopy. We recorded subdural electrocorticography activities from the hand/arm area in the primary motor cortex of 6 subjects undergoing deep brain stimulation surgery for essential tremor and Parkinson's disease who performed stepping (all patients) and arm swing (n = 3 patients) tasks. We show stepping-related low frequency oscillations over the arm area. Furthermore, we show that this oscillatory activity is separable, both in frequency and spatial domains, from gamma band activity changes that occur during arm swing. Our study contributes to the growing body of evidence that lower extremity movement may be more broadly represented in the motor cortex, and suggest that it may represent a way to coordinate stereotyped movements across the upper and lower extremities.

A Procedure for Measuring Anterior Scalene Morphology and Quality with Ultrasound Imaging: An Intra- and Inter-rater Reliability Study.

Ultrasound (US) imaging is an essential tool for clinicians because of its cost-effectiveness and accessibility for assessing multiple muscle metrics including muscle quality, size and shape. Although previous studies highlighted the importance of the anterior scalene muscle (AS) in patients with neck pain, studies analyzing the reliability of US measurements for this muscle are lacking. This study aimed to develop a protocol for assessing AS muscle shape and quality measured with US and investigating its intra- and inter-examiner reliability. Through use of a linear transducer, B-mode images of the anterolateral neck region at the C7 level were acquired in 28 healthy volunteers by two examiners (one experienced and one novel). Cross-sectional area, perimeter, shape descriptors and mean echo-intensity were measured twice by each examiner in randomized order. Intra-class correlation coefficients (ICCs), standard errors of measurement and minimal detectable changes were calculated. Results indicated no muscle side-to-side asymmetries (p > 0.05). Gender differences were found for muscle size (p < 0.01), but muscle shape and brightness were comparable (p > 0.05). Intra-examiner reliability was good to excellent for all metrics for the experienced and (ICC >0.846) and novel (ICC >780) examiners. Although inter-examiner reliability was good for most of the metrics (ICC >0.709), the estimates for assessing solidity and circularity were unacceptable (ICC <0.70). This study found that the described ultrasound procedure for locating and measuring anterior scalene muscle morphology and quality is highly reliable in asymptomatic individuals.

Gait asymmetry in children with Duchenne muscular dystrophy: evaluated through kinematic synergies and muscle synergies of lower limbs

BackgroundGait is a complex, whole-body movement that requires the coordinated action of multiple joints and muscles of our musculoskeletal system. In the context of Duchenne muscular dystrophy (DMD), a disease characterized by progressive muscle weakness and joint contractures, previous studies have generally assumed symmetrical behavior of the lower limbs during gait. However, such a symmetric gait pattern of DMD was controversial. One aspect of this is criticized, because most of these studies have primarily focused on univariate variables, rather than on the coordination of multiple body segments and even less investigate gait symmetry under a motor synergy of view.MethodsWe investigated the gait pattern of 20 patients with DMD, compared to 18 typical developing children (TD) through 3D Gait Analysis. Kinematic and muscle synergies were extracted with principal component analysis (PCA) and non-negative matrix factorization (NNMF), respectively. The synergies extracted from the left and right sides were compared with each other to obtain a symmetry value. In addition, bilateral spatiotemporal variables of gait, such as stride length, percentage of stance and swing phase, step length, and percentage of double support phase, were used for calculating the symmetry index (SI) to evaluate gait symmetry as well.ResultsCompared with the TD group, the DMD group walked with decreased gait velocity (both p < 0.01), stride length (both p < 0.01), and step length (both p < 0.001). No significant difference was found between groups in SI of all spatiotemporal parameters extracted between the left and right lower limbs. In addition, the DMD group exhibited lower kinematic synergy symmetry values compared to the TD group (p < 0.001), while no such significant group difference was observed in symmetry values of muscle synergy.ConclusionsThe findings of this study suggest that DMD influences, to some extent, the symmetry of synergistic movement of multiple segments of lower limbs, and thus kinematic synergy appears capable of discriminating gait asymmetry in children with DMD when conventional spatiotemporal parameters are unchanged.

Effect of lower body, core and upper body kinematic chain exercise protocol on throwing performance among university shot put athletes: A pilot study

A coordinated sequence of movements is required to generate maximum power and velocity in shot put. Kinematic chains emphasize the interactions between various body segments during a movement. They suggest that force production and transfer are optimized by coordinating multiple joints and muscle groups. In previous research, the kinematic chain has been attributed to shot put performance. Few studies have examined the effects of a comprehensive kinematic chain exercise protocol on throwing performance among shot put athletes, particularly at universities. Pilot study investigating lower body, core, and upper body kinematic chain exercise protocol on university shot put athletes' throwing performance. A total of twenty-four young athletes specializing in shotput, with an average age of 19.87 years and a standard deviation of 1.31 years, were divided into two groups, namely the experimental group and the control group, using a random assignment method, the experimental group, consisting of 12 participants, underwent an 8-week kinematic chain training program alongside their regular training sessions. On the other hand, the control group, also consisting of 12 participants, only participated in their regular training sessions without any additional intervention. Pre- and post-training assessments were conducted to measure shotput throwing performance, preference for throwing style, and the participants' satisfaction with the exercise protocol, using a questionnaire. The athletes who took part in the kinematic chain program demonstrated a significant improvement in throwing distance compared to the control group (p = 0.01). Additionally, the athletes in the experimental group reported higher levels of satisfaction with the exercise protocol (p = 0.005). These findings indicate that incorporating an 8-week Lower Body, Core and Upper Body kinematic chain exercise protocol into regular training sessions can lead to more pronounced improvements in sport-specific throwing performance among young shotput athletes.

Multidisciplinary treatment for infective endocarditis complicated with systemic multiple abscess due to Panton-Valentine leukocidin producing community-acquired methicillin-resistant Staphylococcus aureus and Candida albicans: a case report

BackgroundInfective endocarditis resulting from community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a rare, but often fatal heart disorder. Here, we report a case of multidisciplinary treatment for infective endocarditis with systemic multiple abscesses due to Panton-Valentine leukocidin (PVL) producing CA-MRSA and Candida albicans.Case presentationThe patient suffered from infective endocarditis, destructive thyroiditis, hemorrhagic cerebral infarction due to mycotic embolism, lung abscess, multiple skeletal muscle abscess, and disseminate intravascular coagulopathy. Aggressive medical treatment as well as mechanical circulatory support was required before the curative surgical treatment. Blood cultures were positive for MRSA and Candida albicans. Genomic analysis of MRSA revealed Staphylococcal Cassette Chromosome mec IVc and also the virulence gene encoding PVL.ConclusionsCA-MRSA strains have higher pathogenicity and are more destructive to tissue than healthcare-associated MRSA strains because of the toxins they produce, including PVL. Multidisciplinary treatment including aggressive surgery was required to rescue the patient.

Three-dimensional motion of the toes with simulated contraction of individual toe flexors and extensors: A cadaver study

BackgroundThe primary motion of the toes is flexion and extension. The motion results from activity of multiple muscles, and toe disorders may result from muscle dysfunction. The relationships of specific muscles related to toe function is underreported. The purpose of this study was to quantitatively evaluate three-dimensional toe motion resulting from specific muscle contraction using cadavers. MethodsThree-dimensional joint movements of the 1st, 2nd, and 5th toe were produced by applying traction of individual muscles using six Thiel-embalmed cadaver legs. The traction increments were 3 mm, 6 mm, and 9 mm, during which the angle of the distal bone with respect to the proximal bone of each toe joint was measured using a magnetic tracking system. ResultsAs tendon traction distance increased, the angular measure of the distal bone with respect to the proximal bone at each toe joint increased linearly and three-dimensionally. The flexor hallucis brevis significantly pronated and abducted the 1st toe compared to the extensor hallucis longus and brevis. The flexor digitorum brevis significantly supinated and adducted the 2nd toe compared to the flexor digitorum longus and quadratus plantae, while the extensor digitorum brevis demonstrated significant pronation and abduction compared to the extensor digitorum longus. ConclusionsThree intrinsic muscles produced significant toe motion in frontal and horizontal planes. Our results revealed that there was a proportional relationship between tendon excursion and joint angle, and an antagonistic relationship of muscles acting on the toes. These results can be considered regarding pathogenesis of toe disorders or deformity and regarding treatment such as exercise therapy or tendon transfer. Level of evidenceV, cadaveric study.

Biohybrid tensegrity actuator driven by selective contractions of multiple skeletal muscle tissues

Biohybrid robots are robots composed of both biological and artificial materials that can exhibit the unique characteristics commonly found in living organisms. Skeletal muscle tissues can be utilized as their actuators due to their flexibility and ON/OFF controllability, but previous muscle-driven robots have been limited to one-degree of freedom (DOF) or planar motions due to their design. To overcome this limitation, we propose a biohybrid actuator with a tensegrity structure that enables multiple muscle tissues to be arranged in a 3D configuration with balanced tension. By using muscle tissues as tension members of tensegrity structure, the contraction of muscle tissues can cause the movement of the actuator in multiple-DOFs. We demonstrate the fabrication of the biohybrid tensegrity actuator by attaching three cultured skeletal muscle tissue made from C2C12 cells and fibrin-based hydrogel to an actuator skeleton using a snap-fit mechanism. When we applied an electric field of more than 4 V mm−1 to the skeletal muscle tissue, the fabricated actuator had a structure to tilt in multiple directions through the selective displacement of about 0.5 mm in a specific direction caused by the contractions of muscle tissue, resulting in 3D multi-DOF tilting motion. We also show that the actuator possesses superior characteristics of tensegrity structure such as stability and robustness by assessing the response of the actuator to external force. This biohybrid tensegrity actuator provides a useful platform for the development of muscle-driven biohybrid robots with complex and flexible movements.

Ex vivo adult stem cell characterization from multiple muscles in ambulatory children with cerebral palsy during early development of contractures

Cerebral palsy (CP) is one of the most common conditions leading to lifelong childhood physical disability. Literature reported previously altered muscle properties such as lower number of satellite cells (SCs), with altered fusion capacity. However, these observations highly vary among studies, possibly due to heterogeneity in patient population, lack of appropriate control data, methodology and different assessed muscle.In this study we aimed to strengthen previous observations and to understand the heterogeneity of CP muscle pathology. Myogenic differentiation of SCs from the Medial Gastrocnemius (MG) muscle of patients with CP (n = 16, 3–9 years old) showed higher fusion capacity compared to age-matched typically developing children (TD, n = 13). Furthermore, we uniquely assessed cells of two different lower limb muscles and showed a decreased myogenic potency in cells from the Semitendinosus (ST) compared to the MG (TD: n = 3, CP: n = 6). Longitudinal assessments, one year after the first botulinum toxin treatment, showed slightly reduced SC representations and lower fusion capacity (n = 4). Finally, we proved the robustness of our data, by assessing in parallel the myogenic capacity of two samples from the same TD muscle.In conclusion, these data confirmed previous findings of increased SC fusion capacity from MG muscle of young patients with CP compared to age-matched TD. Further elaboration is reported on potential factors contributing to heterogeneity, such as assessed muscle, CP progression and reliability of primary outcome parameters.

Benign Metastasizing Leiomyoma

Benign metastasizing leiomyoma is a rare condition usually seen in reproductive age women which presented with multiple benign smooth muscle tumors in extra uterine sites, which display unusual growth pattern. In this report, a case of benign metastasizing leiomyoma is discussed.

Left Hindquarter Amputation due to High-Grade Pleomorphic Sarcoma of the Groin: A Case Report

Introduction:Hindquarter amputation or known as hemipelvectomy is a surgical technique that is primarily used for the eradication of malignant primary soft tissue and bone tumors of the pelvis, hip, and upper thigh regions. Occasionally, hindquarter amputation has been employed in the treatment of severe trauma, metastases, and infection. This case report aims to give a lesson in the case of the High-Grade Pleomorphic Sarcoma of the Groin because this is a very rare case and most patients are not willing to undergo amputation.Case Presentation: A 54-year-old male patient came with a complaint of a lump in the thigh. Initially, the lump was as big as a marble and has been getting bigger since last year. The size of the lump was approximately 30 x 30 x 30 cmConclusions: The most common indications for amputation in patients with the primary localized disease were extensive involvement of the limb-girdle, multiple muscle compartment involvement, multifocality, and unsuitability for limb-sparing surgery, typically due to lack of a salvage option. Hindquarter amputation was used as a treatment for 13% of all pelvic bone sarcomas where there is a realistic chance of control of symptoms or long-term survival.comas.

Muscle coordination patterns in regulation of medial gastrocnemius activation during walking

The ankle plantar flexion in the late stance phase is referred to as the ankle push-off. When the ankle push-off force is enhanced, compensatory adjustments occur in the adjacent phases. The muscle control that achieves these compensatory movements remains unknown, although they are expected to be coordinately regulated across multiple muscles and phases. Muscle synergy is used as a quantification technique for muscle coordination, and this analysis enables the comparison of synchronized activity between multiple muscles. Therefore, this study aimed to elucidate the tuning of muscle synergies in muscle activation adjustment of push-off. It is hypothesized that muscle activation adjustment of push-off is performed in the muscle synergy related to ankle push-off and in the muscle synergy that activates during the adjacent push-off phase. Eleven healthy men participated, and participants manipulated the activity of the medial gastrocnemius during walking through visual feedback. Two conditions were compared as experimental conditions: increasing the muscle activity to 1.6 times that during normal walking (High) and matching it with that during normal walking (Normal). Twelve muscle activities in the trunk and lower limb and kinematic data were recorded. Muscle synergies were extracted by the non-negative matrix factorization. No significant difference was observed in the number of synergies (High: 3.5 ± 0.8, Normal: 3.7 ± 0.9, p = 0.21) and muscle synergy activation timing and duration between the High and Normal conditions (p > 0.27). However, significant differences were observed in the peak muscle activity during the late stance phase of the rectus femoris (RF), biceps femoris (BF) between conditions (RF at High: 0.32 ± 0.21, RF at Normal: 0.45 ± 0.17, p = 0.02; BF at High: 0.16 ± 0.01, BF at Normal: 0.08 ± 0.06 p = 0.02). Although the quantification of force exertion has not been conducted, the modulation of RF and BF activation could have occurred due to the attempts to help knee flexion. Muscle synergies during normal walking are therefore maintained, and slight adjustments in the amplitude of muscle activity occurred for each muscle.

Axonal mapping of the motor cranial nerves.

Basic behaviors, such as swallowing, speech, and emotional expressions are the result of a highly coordinated interplay between multiple muscles of the head. Control mechanisms of such highly tuned movements remain poorly understood. Here, we investigated the neural components responsible for motor control of the facial, masticatory, and tongue muscles in humans using specific molecular markers (ChAT, MBP, NF, TH). Our findings showed that a higher number of motor axonal population is responsible for facial expressions and tongue movements, compared to muscles in the upper extremity. Sensory axons appear to be responsible for neural feedback from cutaneous mechanoreceptors to control the movement of facial muscles and the tongue. The newly discovered sympathetic axonal population in the facial nerve is hypothesized to be responsible for involuntary control of the muscle tone. These findings shed light on the pivotal role of high efferent input and rich somatosensory feedback in neuromuscular control of finely adjusted cranial systems.