Innervation Of Muscle Research Articles

A new classification of the shoulder girdle muscles in domestic fowl based on their innervation from the brachial plexus.

Many studies have described the muscle anatomy of the domestic fowl (Gallus gallus domesticus), a commonly used animal in developmental experiments. However, some major differences in terminology existed among studies, making it difficult to precisely discuss the muscle homologies between domestic fowl and other animals. In this study, the innervations of shoulder girdle muscles in five sides of the domestic fowl were elucidated and the homology of the shoulder girdle muscles between domestic fowl and other tetrapods was discussed using terminology that conforms to Nomina Anatomica Avium (1993). Unlike previous descriptions, the supracoracoideus, being developed in domestic fowl, is thought to have a different muscular origin from the deltoid muscle. The coracobrachialis cranialis, coracobrachialis caudalis and coracobrachialis muscles, previously described as the coracobrachialis muscle group, had different innervations; the coracobrachialis cranialis should be grouped with the deltoid muscles, and the coracobrachialis caudalis appears to belong to the pectoral muscle group. I propose that the subcoracoscapularis in domestic fowl, keeping the reptilian form, is divided into the subcoracoideus and subscapularis muscles. Based on the innervation, the subscapularis in domestic fowl is homologous with the subscapularis in reptiles and a major part of the subscapularis in mammals. Unlike the descriptions in previous studies, the scapulohumeralis cranialis and caudalis in the domestic fowl in this study, being innervated by the common branch, were found to have a close relationship with the subcoracoscapularis muscle. Based on the observations in this study, a new classification of the shoulder girdle muscles in domestic fowl is proposed.

Engineering large and geometrically controlled vascularized nerve tissue in collagen hydrogels to restore large-sized volumetric muscle loss

Developing scalable vascularized and innervated tissue is a critical challenge for the successful clinical application of tissue-engineered constructs. Collagen hydrogels are extensively utilized in cell-mediated vascular network formation because of their naturally excellent biological properties. However, the substantial increase in hydrogel contraction induced by populated cells limits their long-term use. Previous studies attempted to mitigate this issue by concentrating collagen pre-polymer solutions or synthesizing covalently crosslinked collagen hydrogels. However, these methods only partially reduce hydrogel contraction while hindering blood vessel formation within the hydrogels. To address this challenge, we introduced additional support in the form of a supportive spacer to counteract the contraction forces of populated cells and prevent hydrogel contraction. This approach was found to promote cell spreading, resist hydrogel contraction, control hydrogel/tissue geometry, and even facilitate the engineering of functional blood vessels and host nerve growth in just one week. Subsequently, implanting these engineered tissues into muscle defect sites resulted in timely anastomosis with the host vasculature, leading to enhanced myogenesis, increased muscle innervation, and the restoration of injured muscle functionality. Overall, this innovative strategy expands the applicability of collagen hydrogels in fabricating large vascularized nerve tissue constructs for repairing volumetric muscle loss (∼63 %) and restoring muscle function.

A.F. Samoilov: from synapse to systemic organization of functions

One of the world’s leading physiologists of the late 19th — the first third of the 20th centuries, Doctor of Medicine, Professor, Head of the Department of Physiology of Kazan University, Lenin Prize winner, Honored Scientist of the RSFSR Alexander Filippovich Samoilov (1867, Odessa — 1930, Kazan) is known as one of the creators of the theory and practice of electrocardiography, introduction of this method into the clinic. In 1924, A. F. Samoilov proved the chemical nature of the transition of excitation from a nerve to a muscle. Many fundamental works of the scientist are devoted to spinal and central nervous mechanisms. As a student and follower of I. M. Sechenov, A. F. Samoilov proceeded to formulate the principles of systematic organization of functions in animals and humans based on the material of his works. The scientists studied the systems of coding characters in the notation of notes. On the example of the circular rhythm of muscle excitation described by him in 1929, A. F. Samoilov anticipated the model of an automatic self-regulating system and systemic social circular interaction.

Modulation of lower limb muscle corticospinal excitability during various types of motor imagery

Motor imagery (MI) is used for rehabilitation and sports training. Previous studies focusing on the upper limb have investigated the effects of MI on corticospinal excitability in the muscles involved in the imagined movement (i.e., the agonist muscles). The present study focused on several lower-limb movements and investigated the influences of MI on corticospinal excitability in the lower limb muscles. Twelve healthy individuals (ten male and two female individuals) participated in this study. Motor-evoked potentials (MEP) from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and soleus (SOL) muscles were elicited through transcranial magnetic stimulation (TMS) to the primary motor cortex during MI of knee extension, knee flexion, ankle dorsiflexion, and ankle plantarflexion and at rest. The results showed that the RF MEPs were significantly increased during MI in knee extension, ankle dorsiflexion, and ankle plantarflexion but not in knee flexion, compared with those at rest. The TA MEPs were significantly increased during MI in knee extension and foot dorsiflexion, while MEPs were not significantly different during MI in knee flexion and foot dorsiflexion than those at rest. For the BF and SOL muscles, there was no significant MEP modulation in either MI. These results demonstrated that corticospinal excitability of the RF and TA muscles was facilitated during MI of movements in which they are active and during MI of lower-limb movements in which they are not involved. On the contrary, corticospinal excitability of the BF and SOL muscles was not facilitated by MI of lower-limb movements. These results suggest that facilitation of corticospinal excitability depends on the muscle and the type of lower-limb MI.

Cumulative Spike Train Estimation for Muscle Excitation Assessment From Surface EMG Using Spatial Spike Detection.

Estimating cumulative spike train (CST) of motor units (MUs) from surface electromyography (sEMG) is essential for the effective control of neural interfaces. However, the limited accuracy of existing estimation methods greatly hinders the further development of neural interface. This paper proposes a simple but effective approach for identifying CST based on spatial spike detection from high-density sEMG. Specifically, we use a spatial sliding window to detect spikes according to the spatial propagation characteristics of the motor unit action potential, focusing on the spikes of activated MUs in a local area rather than those of a specific MU. We validated the effectiveness of our proposed method through an experiment involving wrist flexion/extension and pronation/supination, comparing it with a recognized CST estimation method and an MU decomposition based method. The results demonstrated that the proposed method obtained higher accuracy on multi-DoF wrist torque estimation leveraging the estimated CST compared to the other three methods. On average, the correlation coefficient (R) and the normalized root mean square error (nRMSE) between the estimation results and recorded force were 0.96 0.03 and 10.1% 3.7%, respectively. Moreover, there was an extremely high interpretive extent between the CSTs of proposed method and the MU decomposition method. The outcomes reveal the superiority of the proposed method in identifying CSTs and can provide promising driven signals for neural interface.

A mechano- and heat-gated two-pore domain K+ channel controls excitability in adult zebrafish skeletal muscle.

TRAAK channels are mechano-gated two-pore-domain K+ channels. Up to now, activity of these channels has been reported in neurons but not in skeletal muscle, yet an archetype of tissue challenged by mechanical stress. Using patch clamp methods on isolated skeletal muscle fibers from adult zebrafish, we show here that single channels sharing properties of TRAAK channels, i.e., selective to K+ ions, of 56 pS unitary conductance in the presence of 5 mM external K+, activated by membrane stretch, heat, arachidonic acid, and internal alkaline pH, are present in enzymatically isolated fast skeletal muscle fibers from adult zebrafish. The kcnk4b transcript encoding for TRAAK channels was cloned and found, concomitantly with activity of mechano-gated K+ channels, to be absent in zebrafish fast skeletal muscles at the larval stage but arising around 1 mo of age. The transfer of the kcnk4b gene in HEK cells and in the adult mouse muscle, that do not express functional TRAAK channels, led to expression and activity of mechano-gated K+ channels displaying properties comparable to native zebrafish TRAAK channels. In whole-cell voltage-clamp and current-clamp conditions, membrane stretch and heat led to activation of macroscopic K+ currents and to acceleration of the repolarization phase of action potentials respectively, suggesting that heat production and membrane deformation associated with skeletal muscle activity can control muscle excitability through TRAAK channel activation. TRAAK channels may represent a teleost-specific evolutionary product contributing to improve swimming performance for escaping predators and capturing prey at a critical stage of development.

Children with developmental coordination disorder are less able to fine-tune muscle activity in anticipation of postural perturbations than typically developing counterparts.

The majority of children with developmental coordination disorder (DCD) struggle with static and dynamic balance, yet there is limited understanding of the underlying neuromechanical mechanisms that underpin poor balance control in these children. Eighteen children with DCD and seven typically developing (TD) children aged 7-10 years stood with eyes open on a moveable platform progressively translated antero-posteriorly through three frequencies (0.1, 0.25 and 0.5 Hz). Myoelectric activity of eight leg muscles, whole-body 3D kinematics and centre of pressure were recorded. At each frequency, postural data were divided into transition-state and steady-state cycles. Data were analyzed using a linear mixed model with follow-up Tukey's pairwise comparisons. At the slowest frequency, children with DCD behaved like age-matched TD controls. At the fastest frequency, children with DCD took a greater number of steps, had a greater centre of mass variability, had a greater centre of pressure area, and tended to activate their muscles earlier and for longer than TD children. Children with DCD did not alter their postural response following prolonged exposure to platform movement, however they made more, non-structured postural adjustments in the medio-lateral direction as task difficulty increased. At the faster oscillation frequencies, children with DCD adopted a different muscle recruitment strategy to TD children. Activating their muscles earlier and for longer may suggest that children with DCD attempt to predict and react to postural disturbances, however the resulting anticipatory muscle excitation patterns do not seem as finely tuned to the perturbation as those demonstrated by TD children. Future work should examine the impact of balance training interventions on the muscle recruitment strategies of children with DCD, to ensure optimal interventions can be prescribed.

Modulation of sarcopenia phenotypes by glutathione peroxidase 4 overexpression in mice.

Our laboratory previously showed lipid hydroperoxides and oxylipin levels are elevated in response to loss of skeletal muscle innervation and are associated with muscle pathologies. To elucidate the pathological impact of lipid hydroperoxides, we overexpressed glutathione peroxidase 4 (GPx4), an enzyme that targets reduction of lipid hydroperoxides in membranes, in adult CuZn superoxide dismutase knockout (Sod1KO) mice that show accelerated muscle atrophy associated with loss of innervation. The gastrocnemius muscle from Sod1KO mice shows reduced mitochondrial respiration and elevated oxidative stress (F2 -isoprostanes and hydroperoxides) compared to wild-type (WT) mice. Overexpression of GPx4 improved mitochondrial respiration and reduced hydroperoxide generation in Sod1KO mice, but did not attenuate the muscle loss that occurs in Sod1KO mice. In contrast, contractile force generation is reduced in EDL muscle in Sod1KO mice relative to WT mice, and overexpression of GPx4 restored force generation to WT levels in Sod1KO mice. GPx4 overexpression also prevented loss of muscle contractility at the single fibre level in fast-twitch fibres from Sod1KO mice. Muscle fibres from Sod1KO mice were less sensitive to both depolarization and calcium at the single fibre level and exhibited a reduced activation by S-glutathionylation. GPx4 overexpression in Sod1KO mice rescued the deficits in both membrane excitability and calcium sensitivity of fast-twitch muscle fibres. Overexpression of GPx4 also restored the sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO gastrocnemius muscles. These data suggest that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and in maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia. KEY POINTS: Knockout of CuZn superoxide dismutase (Sod1KO) induces elevated oxidative stress with accelerated muscle atrophy and weakness. Glutathione peroxidase 4 (GPx4) plays a fundamental role in the reduction of lipid hydroperoxides in membranes, and overexpression of GPx4 improves mitochondrial respiration and reduces hydroperoxide generation in Sod1KO mice. Muscle contractile function deficits in Sod1KO mice are alleviated by the overexpression of GPx4. GPx4 overexpression in Sod1KO mice rescues the impaired muscle membrane excitability of fast-twitch muscle fibres and improves their calcium sensitivity. Sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO muscles is decreased, and it is restored by the overexpression of GPx4. Our results confirm that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia.

Infantile Hypertrophic Pyloric Stenosis: Review of Pathophysiology, Clinical Presentation, Treatment and Outcomes

Infantile hypertrophic pyloric stenosis (IHPS) is considered one of the most common pediatric surgical conditions. Presentation is most common between the ages of 2 to 12 weeks with a mean and median age of 5 weeks. IHPS has been reported to be more common in males than females (5:1) and in first-born children (30-40%). Throughout history, the etiology of this condition has been studied, discovering multiple genetic and environmental factors, such as newborns with increased acid secretion, nitric oxide synthase deficiency, poor innervation of the pyloric muscle, smoking during pregnancy, neonatal use of macrolides and cesarean section; however, the exact cause remains uncertain. The classic clinical presentation begins with a recent history of severe, nonbilious projectile vomiting immediately after feeding and a strong, persistent appetite. During abdominal examination, palpation of the "pyloric olive" in the epigastrium by an experienced doctor is considered a pathognomonic sign. Laboratory tests may show low chloride, potassium, and hydrogen ion levels, leading to metabolic alkalosis due to persistent vomiting. Ultrasound is the gold standard imaging study if history and physical examination are insufficient to diagnose IHPS with a reported sensitivity and specificity of up to 98% and 100% by allowing evaluation of pyloric morphology and behavior. Pyloromyotomy is considered the definitive treatment for infantile hypertrophic pyloric stenosis, but should not be performed until the baby is adequately resuscitated. Patients typically experience positive outcomes after pyloromyotomy, with low morbidity and mortality rates. Most cases recover quickly and without complications.

Effects of natural products on functional constipation: analysis of active ingredient and mechanism.

Constipation is a prevalent clinical ailment of the gastrointestinal system, yet its pathogenesis remains ambiguous. Despite the availability of numerous treatment modalities, they are insufficient in resolving the issue for patients. This work conducted a comprehensive review of the existing literature pertaining to the utilization of natural products for the treatment of constipation, with a focus on the efficacy of natural products in treating constipation, and to provide a comprehensive summary of their underlying mechanisms of action. Upon conducting a thorough review of the extant literature, we found that natural products can effectively treat constipation as modern synthetic drugs and compounded drugs with acetylcholinesterase (AChE) effects, rich in fiber and mucus, and the effects of increasing the tension of the ileum and gastrointestinal tract muscle, mediating signaling pathways, cytokine, excitability of the smooth muscle of the gastrointestinal tract, and regulating the homeostasis of intestinal flora. However, there is a wide variety of natural products, and there are still relatively few studies; the composition of natural products is complex, and the mechanism of action of natural products cannot be clarified. In the future, we need to further improve the detailed mechanism of natural products for the treatment of constipation.

Late Results of Early End-to-End Repair in Sciatic Nerve Injuries.

Mechanisms of sciatic nerve injury include gunshot injury, sharps injury, injection injury, contusion, femoral fracture injury, and iatrogenic injury due to fracture surgery. Regardless of the type of injury, patients undergoing sciatic nerve repair have poor motor and sensory outcomes. In this study, we compared the late outcomes of a group of patients in whom the author performed an early end-to-end anastomosis for sciatic nerve sharps injury and another group of patients with a similar injury who were not operated on but left to natural history. The sciatic nerve, comprising two primary divisions with distinct muscle innervations, was subject to separate examinations. Group 1 (n=10, study group) underwent tibial division anastomosis, while Group 2 (n=12, control group) received no surgical intervention involving the tibial division. Similarly, Group 3 (n=11, study group) underwent peroneal division anastomosis, while Group 4 (n=14, control group) encompassed subgroups that did not undergo peroneal division surgery. In Group 1, the rate of gain in plantar flexion muscle strength was significantly higher (p < 0.05) compared to Group 2. Furthermore, the sensory examination gain level ratio within the tibial domain was significantly greater (p < 0.05) in Group 1 than in Group 2. Additionally, Group 1 exhibited a significantly higher rate (p < 0.05) of detection of regeneration and reinnervation findings in electromyography (EMG) compared to Group 2. When evaluating the long-term outcomes following early end-to-end anastomoses of the sciatic nerve, it becomes evident that while significant improvements are observed when compared to individuals without anastomosis, the positive impact of surgical interventions on motor and sensory gains in daily life remains limited. Nevertheless, we contend that early surgical intervention holds potential advantages in terms of patient management.

Cluster analysis of multiple impairment measures in evidence-based classification for para-alpine sit skiers.

The International Paralympic Committee has been promoting the development of evidence-based classification to reduce the subjectivity in current decision-making systems. The current study aimed to evaluate the validity of the impairment and performance tests for para-alpine sit skiing classification, and whether cluster analysis of the measures would produce a valid classification structure. Thirty-eight para-alpine sit skiers with different disabilities completed seven tests. During these tests, isometric trunk strength, trunk muscle excitation, trunk range of movement (ROM), and simulated skiing performance (board tilt angle) were assessed. Correlations between the measures and the board tilt angle were calculated. To group athletes, K-means cluster analysis was performed according to how much the impairment measures affected the board tilting. There were significant correlations between all measures and the maximal board tilt angle (r = 0.35-0.81, p < 0.05). The cluster analysis revealed that the introduction of ROM and muscle excitation was an effective supplement to strength measures in improving the classification accuracy (53%-79%). It produced four clusters with strong structures (mean silhouette coefficient = 0.81) and large and significant inter-cluster differences in most measures and performance between clusters (p < 0.05). The cluster analysis produced classes comprising athletes with similar degrees of activity limitation. All tests reported can help establish a more transparent classification system for para-alpine sit skiers. This study also provides a reference for evidence-based classification systems in other Para sports.

Evaluation of nerve innervation distribution of orbicularis oculi muscle for botulinum neurotoxin application using Sihler's method

BackgroundBlepharospasm is the involuntary and forced closure of the eyelids due to spasm-like contraction of the orbicularis oculi muscle around the eye. The study aimed to reveal the nerve innervation of the orbicularis oculi muscle for Botulinum neurotoxin (BoNT) treatment of blepharospasm by Sihler’s staining technique. MethodsThis study used six cephalus (12 orbicularis oculi muscles) with an average age of 69,6 (62−88) years. Then, the orbicularis oculi muscles were removed by dissection, and Sihler's staining technique was applied to the muscles. The limit for dissection of the muscle is the orbital opening level, where the nerves enter the muscle, and the muscle attaches to the bone. ResultsIn the region above the palpebral fissure, the nerves entering the muscle were densely located in the superolateral quadrant between 9 and 12 o′clock in the right eye and between 12 and 3 o′clock in the left eye. In the region under the palpebral fissure, the nerves’ density in the orbicularis oculi muscle was higher between 4 and 7 o′clock in the right eye and between 5 and 8 o′clock in the left eye. ConclusionThis study unveiled the nerve branches associated with the orbicularis oculi muscle. It pinpointed precise crossing points of these nerve branches, which can be targeted for applying BoNT in treating blepharospasm. Consequently, by utilizing minimal BoNT, it is anticipated that the quantity of toxin administered will decrease, leading to more efficient outcomes and reduced expenses. Furthermore, this approach can aid in averting potential undesired complications during BoNT administration.

Baseline Has no Effect on Change in Forward Shoulder Posture, Range of Motion, and Muscle Excitation Following Myofascial Release: A Velocity-dependent Investigation

Baseline Has no Effect on Change in Forward Shoulder Posture, Range of Motion, and Muscle Excitation Following Myofascial Release: A Velocity-dependent Investigation

Division of neuromuscular compartments and localization of the center of the intramuscular nerve-dense region in pelvic wall muscles based on Sihler's staining.

The innervation of the pelvic wall muscles is not very clear. This study aimed to reveal the division of neuromuscular compartments and localize the surface position and depth of the center of the intramuscular nerve-dense region (CINDR) of the pelvic wall muscles based on Sihler's staining. Twenty-four adult cadavers were used. To localize the CINDR of the pelvic wall muscles, horizontal (H) and longitudinal (L) reference lines were drawn, and Sihler's staining was used to reveal the intramuscular nerve distribution. The CINDR projection points (P and P' points) behind and in front of the body surface, the positions of the P points projected onto the H and L lines (PH and PL points), and the depth of CINDR were determined by spiral computed tomography scanning. The piriformis and obturator internus muscles can be divided into two and three neuromuscular compartments, respectively. The PH of CINDR of the piriformis muscle was located at 22.61 ± 2.66% of the H line, the PL was at 28.53 ± 6.08% of the L line, and the puncture depth of the piriformis muscle was at 24.64 ± 2.16% of the PP' line. The PH of CINDR of the obturator internus muscle was at 16.49 ± 1.20% of the H line, the PL was at 10.94 ± 1.09% of its L line, and the puncture depth was 6.26 ± 0.38cm. These findings may guide the design of the compartmentalized transplantation of the pelvic wall muscles and improve the target localization efficiency and efficacy for injecting botulinum toxin A to treat pelvic wall muscle spasm.

Corticospinal excitability during observation of basketball free-throw movement: Effects of video playback speed and stimulus timing.

Transcranial magnetic stimulation studies have indicated that action observation (AO) modulates corticospinal excitability. Although a few previous studies have shown that the AO of simple motor movements at a slow playback speed facilitates corticospinal excitability more than that at normal playback speed, it is unclear if this effect occurs during the AO of sport-related complex movements. Therefore, we investigated the changes in the motor evoked potential (MEP) amplitudes of the flexor carpi radialis (FCR) and abductor digiti minimi (ADM) muscles during the AO of a basketball free-throw movement at three different playback speeds (100%, 75%, and 50% speeds). Additionally, we evaluated the effects of stimulus timing (holding the ball vs. releasing the ball for shooting) and motor expertise (expert basketball players vs. novices) on the MEP amplitude during the AO. Our results demonstrated that regardless of motor expertise, the MEP amplitude of the FCR muscle was significantly smaller in the 50% speed condition than in the 100% condition. In the ADM muscle, the MEP amplitude was significantly larger when the ball was held after dribbling than when the ball was released. Therefore, it is suggested that corticospinal excitability in specific muscles during the observation of complex whole-body movements is influenced by video playback speed and stimulus timing.

Orally administered boldine reduces muscle atrophy and promotes neuromuscular recovery in a rodent model of delayed nerve repair.

Peripheral nerve injury often results in poor functional recovery due to a prolonged period of muscle denervation. In particular, absent axonal contact, denervated muscle can undergo irrevocable atrophy and diminished receptiveness for reinnervation over time, ultimately reducing the likelihood for meaningful neuromuscular recovery. While innovative surgical approaches can minimize the harmful effects of denervation by re-routing neighboring-otherwise uninjured-axons, there are no clinically-available approaches to preserve the reinnervation capacity of denervated muscles. Blocking intramuscular connexin hemichannel formation has been reported to improve muscle innervation in vitro and prevent atrophy in vivo. Therefore, the current study investigated the effects of orally administered boldine, a connexin hemichannel inhibitor, on denervated-related muscle changes and nerve regeneration in a rat model of delayed peripheral nerve repair. We found that daily boldine administration significantly enhanced an evoked response in the tibialis anterior muscle at 2 weeks after common peroneal nerve transection, and decreased intramuscular connexin 43 and 45 expression, intraneural Schwann cell expression of connexin 43, and muscle fiber atrophy up to 4 weeks post transection. Additional animals underwent a cross nerve repair procedure (tibial to common peroneal neurorrhaphy) at 4 weeks following the initial transection injury. Here, we found elevated nerve electrophysiological activity and greater muscle fiber maturation at 6 weeks post repair in boldine treated animals. These findings suggest that boldine may be a promising pharmacological approach to minimize the deleterious effects of prolonged denervation and, with further optimization, may improve levels of functional recovery following nerve repair.

Dissecting the functions of multiple interactions of STAC3 in skeletal muscle excitation–contraction coupling

Dissecting the functions of multiple interactions of STAC3 in skeletal muscle excitation–contraction coupling

Using the Neuromuscular Junction Cellular Response to Predict Functional Recovery after Nerve Grafting in a Mouse Experimental Model.

Functional recovery following peripheral nerve injury worsens with increasing time of denervation before repair. Denervated muscle undergoes progressive atrophy that limits the extent to which motor endplates can be reinnervated. The aims of this study were to assess nerve injuries reconstructed at different time points and to identify various neural and muscle-based markers to predict functional outcome, including an in-depth look at the neuromuscular junction (NMJ). Adult wild-type C57BL/6J mice underwent surgery on the sciatic nerve and were divided into 5 groups: (1) nerve cut and repaired, (2) acute (nerve cut and immediately repaired with a 1-cm autograft), (3) subacute (nerve grafted 2 weeks after injury), (4) delayed (nerve grafted 4 weeks after injury), (5) nerve cut and capped. Functional recovery was measured by treadmill and electrodiagnostic tests. Nerves were harvested for histologic evaluation, and leg muscles, for histologic evaluation and NMJ immunofluorescent staining of motor endplate innervation and terminal Schwann cells (tSCs). The delayed graft group performed worst in nearly all parameters. The subacute graft group shared more similarities with the acute group, especially the tSC response (subacute, 48%; acute, 51%) and motor endplate innervation pattern (subacute, 75%; acute, 72%). The only parameters to elucidate differences were muscle weight and motor endplate fragmentation. Traditional axon count failed to capture differences among the 3 groups. The tSC activity and NMJ innervation pattern can be used as predictive markers of functional recovery that capture differences among acute, subacute, and delayed nerve injuries. The tSC activity at the NMJ displayed by immunohistochemical methods can accurately reflect target muscle innervation over time. This can be used as a predictor of reinnervation when timing of nerve reconstruction is delayed, which can be a critically needed tool in clinical scenarios.

Consistent control information driven musculoskeletal model for multiday myoelectric control

Objective. Musculoskeletal model (MM)-based myoelectric interface has aroused great interest in human-machine interaction. However, the performance of electromyography (EMG)-driven MM in long-term use would be degraded owing to the inherent non-stationary characteristics of EMG signals. Here, to improve the estimation performance without retraining, we proposed a consistent muscle excitation extraction approach based on an improved non-negative matrix factorization (NMF) algorithm for MM when applied to simultaneous hand and wrist movement prediction. Approach. We added constraints and L 2-norm regularization terms to the objective function of classic NMF regarding muscle weighting matrix and time-varying profiles, through which stable muscle synergies across days were identified. The resultant profiles of these synergies were then used to drive the MM. Both offline and online experiments were conducted to evaluate the performance of the proposed method in inter-day scenarios. Main results. The results demonstrated significantly better and more robust performance over several competitive methods in inter-day experiments, including machine learning methods, EMG envelope-driven MM, and classic NMF-based MM. Furthermore, the analysis of control information on different days revealed the effectiveness of the proposed method in obtaining consistent muscle excitations. Significance. The outcomes potentially provide a novel and promising pathway for the robust and zero-retraining control of myoelectric interfaces.