Synergy Structure Research Articles

New Reinforcing Approach for Biobased UV-Curing Resins: Hybrid Lignocellulose Fillers with Improved Synergy and Wood Structure Mimics

Lignocellulosic fillers have been widely investigated for various polymer resin applications since they have great potential for using wood biomass and recycled plastics. However, besides cellulose nanocrystals (CNC) and nanofibrils (CNF), not much of the other lignocellulose has been used for UV-curing resins. Even more so, none has been used in hybrid lignocellulose combination compositions. In the present work, the effects of hybrid lignocellulose fillers such as lignin (LN)/CNC/CNF/hemicellulose (HC) with ratio-varying compositions on UV-curing biobased resins have been investigated for wood-mimic material coating applications. The hybrid filler effects on the macromolecular chain network, surface morphology, thermomechanical properties, and thermostability were carefully studied. A combination of scanning electron microscopy, DMA Cole–Cole plot, contact angle, etc., allowed getting a sense of hybrid filler distribution and interaction within the polymer matrix. It was identified that an increase in the HC content of up to 38% contributes to more even particle distribution and achieves a maximum double bond conversion rate of about 80%. HC also contributes to porous surface structure, while CNC smooths surface morphology, and, in turn, CNF increases defects. Thermomechanical testing revealed the unique benefit of hybrid reinforcement, showing higher results than single-filler compositions despite the general decrease after incorporation of 5 wt % LN. The storage modulus showed a fourfold increase for 5 wt % LN composition. The observed enormous property enhancement has been attributed to the benefits of hybrid fillers, which mitigate characteristic radical scavenging properties of LN and strongly reduce general filler aggregation, allowing more even filler dispersion while also improving filler–matrix interface synergy. Seventeen different compositions clearly, in comparison to single fillers, show the benefit of hybrid lignocellulosic reinforcement and testify to the ability to precisely tune up material performance and achieve wood structure-mimicking coating materials.

Bionic Aerogel with a Lotus Leaf-like Structure for Efficient Oil-Water Separation and Electromagnetic Interference Shielding.

Increasing pollution from industrial wastewater containing oils or organic solvents poses a serious threat to both the environment and human health. Compared to complex chemical modifications, bionic aerogels with intrinsic hydrophobic properties exhibit better durability and are considered as ideal adsorbents for oil-water separation. However, the construction of biomimetic three-dimensional (3D) structures by simple methods is still a great challenge. Here, we prepared biomimetic superhydrophobic aerogels with lotus leaf-like structures by growing carbon coatings on Al2O3 nanorod-carbon nanotube hybrid backbones. Thanks to its multicomponent synergy and unique structure, this fascinating aerogel can be directly obtained through a simple conventional sol-gel and carbonization process. The aerogels exhibit excellent oil-water separation (22 g·g-1), recyclability (over 10 cycles) and dye adsorption properties (186.2 mg·g-1 for methylene blue). In addition, benefiting from the conductive porous structure, the aerogels also demonstrate outstanding electromagnetic interference (EMI) shielding capabilities (~40 dB in X-band). This work presents fresh insights for the preparation of multifunctional biomimetic aerogels.

"Fine synergies" describe motor adaptation in people with drop foot in a way that supplements traditional "coarse synergies".

Synergy analysis via dimensionality reduction is a standard approach in biomechanics to capture the dominant features of limb kinematics or muscle activation signals, which can be called "coarse synergies." Here we demonstrate that the less dominant features of these signals, which are often explicitly disregarded or considered noise, can nevertheless exhibit "fine synergies" that reveal subtle, yet functionally important, adaptations. To find the coarse synergies, we applied non-negative matrix factorization (NMF) to unilateral EMG data from eight muscles of the involved leg in ten people with drop-foot (DF), and of the right leg of 16 unimpaired (control) participants. We then extracted the fine synergies for each group by removing the coarse synergies (i.e., first two factors explaining 85% of variance) from the data and applying Principal Component Analysis (PCA) to those residuals. Surprisingly, the time histories and structure of the coarse EMG synergies showed few differences between DF and controls-even though the kinematics of drop-foot gait is evidently different from unimpaired gait. In contrast, the structure of the fine EMG synergies (as per their PCA loadings) showed significant differences between groups. In particular, loadings for Tibialis Anterior, Peroneus Longus, Gastrocnemius Lateralis, Biceps and Rectus Femoris, Vastus Medialis and Lateralis muscles differed between groups ( ). We conclude that the multiple differences found in the structure of the fine synergies extracted from EMG in people with drop-foot vs. unimpaired controls-not visible in the coarse synergies-likely reflect differences in their motor strategies. Coarse synergies, in contrast, seem to mostly reflect the gross features of EMG in bipedal gait that must be met by all participants-and thus show few differences between groups. However, drawing insights into the clinical origin of these differences requires well-controlled clinical trials. We propose that fine synergies should not be disregarded in biomechanical analysis, as they may be more informative of the disruption and adaptation of muscle coordination strategies in participants due to drop-foot, age and/or other gait impairments.

Spatial and Temporal Muscle Synergies Provide a Dual Characterization of Low-dimensional and Intermittent Control of Upper-limb Movements

Muscle synergy analysis investigates the neurophysiological mechanisms that the central nervous system employs to coordinate muscles. Several models have been developed to decompose electromyographic (EMG) signals into spatial and temporal synergies. However, using multiple approaches can complicate the interpretation of results. Spatial synergies represent invariant muscle weights modulated with variant temporal coefficients; temporal synergies are invariant temporal profiles that coordinate variant muscle weights. While non-negative matrix factorization allows to extract both spatial and temporal synergies, the comparison between the two approaches was rarely investigated targeting a large set of multi-joint upper-limb movements. Spatial and temporal synergies were extracted from two datasets with proximal (16 subjects, 10M, 6F) and distal upper-limb movements (30 subjects, 21M, 9F), focusing on their differences in reconstruction accuracy and inter-individual variability. We showed the existence of both spatial and temporal structure in the EMG data, comparing synergies with those from a surrogate dataset in which the phases were shuffled preserving the frequency content of the original data. The two models provide a compact characterization of motor coordination at the spatial or temporal level, respectively. However, a lower number of temporal synergies are needed to achieve the same reconstruction R2: spatial and temporal synergies may capture different hierarchical levels of motor control and are dual approaches to the characterization of low-dimensional coordination of the upper-limb. Last, a detailed characterization of the structure of the temporal synergies suggested that they can be related to intermittent control of the movement, allowing high flexibility and dexterity. These results improve neurophysiology understanding in several fields such as motor control, rehabilitation, and prosthetics.

Muscle activation patterns and muscle synergies reflect different modes of coordination during upper extremity movement.

A core issue in motor control is how the central nervous system generates and selects the muscle activation patterns necessary to achieve a variety of behaviors and movements. Extensive studies have verified that it is the foundation to induce a complex movement by the modular combinations of several muscles with a synergetic relationship. However, a few studies focus on the synergetic similarity and dissimilarity among different types of movements, especially for the upper extremity movements. In this study, we introduced the non-negative matrix factorization (NMF) method to explore the muscle activation patterns and synergy structure under 6 types of movements, involving the hand open (HO), hand close (HC), wrist flexion (WF), wrist extension (WE), supination (SU), and pronation (PR). For this, we enrolled 10 healthy subjects to record the electromyography signal for NMF calculation. The results showed a highly modular similarity of the muscle synergy among subjects under the same movement. Furthermore, Spearman's correlation analysis indicated significant similarities among HO-WE, HO-SU, and WE-SU (p < 0.001). Additionally, we also found shared synergy and special synergy in activation patterns among different movements. This study confirmed the theory of modular structure in the central nervous system, which yields a stable synergetic pattern under the same movement. Our findings on muscle synergy will be of great significance to motor control and even to clinical assessment techniques.

The Features of Synergetic Interaction of Lower Extremities’ Skeletal Muscles under the Spinal Cord Electrical Stimulation

The aim of the work was to study the neural basis of the synergetic interaction of the lower extremities’ skeletal muscles during locomotor activity. It was supposed to determine the relationship of the locomotor-related neuronal networks with the centers regulating the spatiotemporal modes of muscle interaction in the structure of the step cycle and its periods. The subjects walked the treadmill both, under normal conditions and during spinal cord percutaneous electrical stimulation. The parameters of the synergies extracted using the principal component method were analyzed. The reorganization of neuronal activity of spinal locomotor-related networks, similar to adaptive processes that compensate for motor deficits in people with pathologies of the nervous system, has been revealed. Percutaneous electrical stimulation changed the reciprocal relations of bilateral lower extremities muscles in the structure of synergetic modules, mainly during the swing phase. The synergy structure demonstrated combined temporal profiles with several peaks of activity. During stimulation, the formation of a basic profile with a clear outline of the main fluctuations was revealed. The spatiotemporal structure of muscle synergy patterns during stance phase turned out to be more stable, which is probably due to an increase in afferentation from the foot support-sensetive zones, which creates optimal conditions for initiating the central generators of locomotor pattern.

Modular organization of locomotor networks in people with severe spinal cord injury.

Previous studies support modular organization of locomotor circuitry contributing to the activation of muscles in a spatially and temporally organized manner during locomotion. Human spinal circuitry may reorganize after spinal cord injury; however, it is unclear if reorganization of spinal circuitry post-injury affects the modular organization. Here we characterize the modular synergy organization of locomotor muscle activity expressed during assisted stepping in subjects with complete and incomplete spinal cord injury (SCI) of varying chronicity, before any explicit training regimen. We also investigated whether the synergy characteristics changed in two subjects who achieved independent walking after training with spinal cord epidural stimulation. To capture synergy structures during stepping, individuals with SCI were stepped on a body-weight supported treadmill with manual facilitation, while electromyography (EMGs) were recorded from bilateral leg muscles. EMGs were analyzed using non-negative matrix factorization (NMF) and independent component analysis (ICA) to identify synergy patterns. Synergy patterns from the SCI subjects were compared across different clinical characteristics and to non-disabled subjects (NDs). Results for both NMF and ICA indicated that the subjects with SCI were similar among themselves, but expressed a greater variability in the number of synergies for criterion variance capture compared to NDs, and weaker correlation to NDs. ICA yielded a greater number of muscle synergies than NMF. Further, the clinical characteristics of SCI subjects and chronicity did not predict any significant differences in the spatial synergy structures despite any neuroplastic changes. Further, post-training synergies did not become closer to ND synergies in two individuals. These findings suggest fundamental differences between motor modules expressed in SCIs and NDs, as well as a striking level of spatial and temporal synergy stability in motor modules in the SCI population, absent the application of specific interventions.

The Number and Structure of Muscle Synergies Depend on the Number of Recorded Muscles: A Pilot Simulation Study with OpenSim.

The muscle synergy approach is used to evaluate motor control and to quantitatively determine the number and structure of the modules underlying movement. In experimental studies regarding the upper limb, typically 8 to 16 EMG probes are used depending on the application, although the number of muscles involved in motor generation is higher. Therefore, the number of motor modules may be underestimated and the structure altered with the standard spatial synergy model based on the non-negative matrix factorization (NMF). In this study, we compared the number and structure of muscle synergies when considering 12 muscles (an "average" condition that represents previous studies) and 32 muscles of the upper limb, also including multiple muscle heads and deep muscles. First, we estimated the muscle activations with an upper-limb model in OpenSim using data from multi-directional reaching movements acquired in experimental sessions; then, spatial synergies were extracted from EMG activations from 12 muscles and from 32 muscles and their structures were compared. Finally, we compared muscle synergies obtained from OpenSim and from real experimental EMG signals to assess the reliability of the results. Interestingly, we found that on average, an additional synergy is needed to reconstruct the same R2 level with 32 muscles with respect to 12 muscles; synergies have a very similar structure, although muscles with comparable physiological functions were added to the synergies extracted with 12 muscles. The additional synergies, instead, captured patterns that could not be identified with only 12 muscles. We concluded that current studies may slightly underestimate the number of controlled synergies, even though the main structure of synergies is not modified when adding more muscles. We also show that EMG activations estimated with OpenSim are in partial (but not complete) agreement with experimental recordings. These findings may have significative implications for motor control and clinical studies.

Hexachlorocyclotriphosphazene functionalized lignin as a sustainable and effective flame retardant for epoxy resins

Lignin, a low-cost and abundant polyphenol biomass, has considerable potential to develop sustainable flame retardants for polymers due to its aromatic skeleton and high char-forming capability after combustion. In order to integrate phosphorous and nitrogen elements, herein lignin was facilely modified by hexachlorocyclotriphosphazene through a one-step nucleophilic substitution reaction. The functionalized lignin (Lig-HCCP) was used as an additive to improve the flame retardancy of epoxy resins. The effects of Lig-HCCP with different loading levels on the curing behaviors, rheological characteristics, as well as thermal, mechanical, and flame-retardant properties of the resulting epoxy composites were studied in detail. Notably, the epoxy composite containing 20 wt% Lig-HCCP showed the highest limited oxygen index (LOI) of 28.2% and achieved a UL-94 V-0 rating in the vertical burning test. Furthermore, the results of cone calorimeter tests indicated that the peak heat release rate, heat release rate, and total smoke production of the epoxy composite were decreased by 58.9%, 38.5%, and 63.1%, respectively, compared with the control resin. The flame retardant mechanisms could be ascribed to the P-N synergy and abundant aromatic structures in Lig-HCCP, which contributed to the formation of intumescent and compact char layers. This work demonstrates a simple and promising approach to utilize lignin feedstocks for value-added flame retardants.

External walking environment differentially affects muscle synergies in children with cerebral palsy and typical development.

Despite external environmental changes in walking, such as manipulating gait speed, previous studies have shown that the underlying muscle synergy structures (synergy weights or vectors) rarely vary. The purpose of this study is to examine if external environmental changes to the walking task influence muscle synergies in children with cerebral palsy (CP) and/or typical development (TD). To identify muscle synergies, we extracted muscle synergies from eight children with CP and eight age-matched TD in three treadmill walking conditions, e.g., baseline (adjusted to individual comfortable walking speed), variable speed (VS), or restricted foot width (RW). Then, we grouped similar muscle synergies using k-mean clustering and discriminant analyses from all datasets of individual synergy structures. Proportion tests exhibited six clusters of muscle synergies predominantly arising from children with CP and four clusters from children with TD. Also, the proportion of muscle synergies was significantly different in four of the CP-preferred clusters across conditions. Specifically, the proportion of the baseline condition was significantly different from VS and RW conditions in one and two clusters, respectively. The proportion was significantly different between VS and RW conditions in four clusters. Cadence and step lengths differed across conditions but not groups which makes the group differences in proportion even more notable. In contrast, step width, while significantly lower in CP, did not differ across conditions. Our findings demonstrate that muscle synergies in children with CP are more sensitive to changes in the external walking environment than in typically developing children.

Dual-phase synergy with electron redistribution during NiFe-LDH/Ni3S4 hollow nanoprisms for enhanced oxygen evolution

Electron redistribution and hollow structure construction are effective strategies to design efficient oxygen evolution reaction (OER) catalysts. In this work, NiFe-LDH/Ni3S4 hollow nanoprisms (HNPs) with dual-phase synergy were fabricated as active and durable electrocatalysts. Benefitting from the strong electron transfer between Ni3S4 and NiFe-LDH, the OER activity is enhanced. In addition, the well-designed hollow and porous nanostructure not only provide larger surface areas and more active sites, but also facilitate the efficiency of mass transport. Thanks to the electronic synergy and hollow structure, LDH/Ni3S4 HNPs exhibit low overpotential of 223 ​mV at 10 ​mA ​cm−2, small Tafel slope of 49 ​mV dec−1, as well as great durability for 20 ​h in alkaline condition. The outstanding electrocatalytic performance making it as a competitive candidate for OER.

Motor Synergy Structure Variability in Different Intensity Locomotions

Motor Synergy Structure Variability in Different Intensity Locomotions

Upper Limb Sensory-Motor Control During Exposure to Different Mechanical Environments in Multiple Sclerosis Subjects With No Clinical Disability.

Multiple sclerosis (MS) is an autoimmune and neurodegenerative disease resulting in motor impairments associated with muscle weakness and lack of movement coordination. The goal of this work was to quantify upper limb motor deficits in asymptomatic MS subjects with a robot-based assessment including performance and muscle synergies analysis. A total of 7 subjects (MS: 3 M−4 F; 42 ± 10 years) with clinically definite MS according to McDonald criteria, but with no clinical disability, and 7 age- and sex-matched subjects without a history of neurological disorders participated in the study. All subjects controlled a cursor on the computer screen by moving their hand or applying forces in 8 coplanar directions at their self-selected speed. They grasped the handle of a robotic planar manipulandum that generated four different environments: null, assistive or resistive forces, and rigid constraint. Simultaneously, the activity of 15 upper body muscles was recorded. Asymptomatic MS subjects generated less smooth and less accurate cursor trajectories than control subjects in controlling a force profile, while the end-point error was significantly different also in the other environments. The EMG analysis revealed different muscle activation patterns in MS subjects when exerting isometric forces or when moving in presence of external forces generated by a robot. While the two populations had the same number and similar structure of muscle synergies, they had different activation profiles. These results suggested that a task requiring to control forces against a rigid environment allows better than movement tasks to detect early sensory-motor signs related to the onset of symptoms of multiple sclerosis and to differentiate between stages of the disease.

Exploiting the trade-offs of electron transfer in MOF-derived single Zn/Co atomic couples for performance-enhanced zinc-air battery

Dual-metal single-atom catalysts (DACs) with an intrinsic synergy and multiple coordination structures are flourishing for oxygen reduction reaction (ORR), on the basis of optimization and regulation of the electron configuration for active centers. Herein, a two-step strategy consisting of cavity confinement and post-adsorption is developed to prepare a nitrogen-doped carbon catalyst co-supported by high-density ZnN4 and CoN4 sites (denoted as ZnCo-NC-II) through metal-organic framework (MOF) engineering. Structural characterization incorporated with density functional theory (DFT) calculation demonstrates that electrons are transferred from Zn (donors) to nearby Co (acceptors) through the conjugated graphene π-bond. The optimized Co d-band center achieves a moderate adsorption strength between O2 and CoN4 active sites. So, the rate-determining step (RDS) for the *OOH formation is accelerated. Therefore, ZnCo-NC-II exhibits a distinguished ORR activity with a half-wave potential (E1/2) of 0.86 and 0.79 V (vs RHE) in alkaline and acid media, respectively. The zinc-air battery built with the ZnCo-NC-II catalyst shows excellent electrochemical performance for an immediate practical application. Our work is conducive to an atomic-level clarification on both the composition and design and thereof the synergistic catalytic mechanism with dual-metal sites.

Muscle synergies are modified with improved task performance in skill learning

How do muscle synergies change as motor skills are learned? The purpose of this study was to investigate the relationship between synergy number and skill acquisition, and to examine learning-related changes in synergy structure and activation patterns. We performed muscle synergy analysis using non-negative matrix factorization to identify muscle synergies from activation patterns of ten major leg muscles before and after recreational cyclists learned a novel one-legged pedal force aiming task (Park, Van Emmerik, & Caldwell, 2021). Synergy number was defined as the smallest number of factors from the matrix factorization algorithm that could explain more than the predefined threshold values. Improvements in pedal force direction after practice occurred without a change in the number of muscle synergies (four), suggesting that task constraints (e.g. the need for smooth pedaling motion) in this novel targeting task may limit the CNS to the same number of muscle synergies before and after practice. Improved task performance while continuing to satisfy multiple biomechanical tasks was obtained with changes in structure (muscle weightings) for one synergy, and activation amplitudes without changes in timing or pattern for three synergies. In each crank cycle quadrant, multiple synergies were altered in either structure or activation amplitude, suggesting that the cooperative changes may be essential for improving task performance while producing a smooth pedaling motion. Changes in both synergy structure and activation levels could be muscle coordination strategies in motor skill learning.

Designing of CoP4/FeP4 with hollow nanocages as bifunctional catalysts for overall water splitting

Efficient and stable electrocatalysts are essential for water splitting. Feasible structural design can facilitate electron transport and increase specific surface area. Herein, the porous CoP4/FeP4 hollow cubes are synthesized by two steps: synthesizing the Co–Fe prussian blue analogues via co-precipitation and phosphating it by calcination. The construction of heterojunction in CoP4/FeP4 not only accelerates electronic transmission but also provides active sites, which acts synergistically on the oxygen and hydrogen evolution reactions. Therefore, the CoP4/FeP4 hollow cubes with the exist of mesoporous exhibit the promising performance for water splitting. The enhanced performance that basically originates from bimetallic synergy and unique morphological structure is acquired with a low overpotential of 270 mV at 10 mA cm−2 and the Tafel slope of 42.4 mV dec−1 towards the oxygen evolution reaction (OER). Electrolyzer with two-electrode system assemble by utilizing the CoP4/FeP4 hybrid as anode and cathode exhibits a cell voltage of 1.74 V to achieve 10 mA cm−2 for overall water splitting. This study that provides a simple strategy to design and construct the heterogeneous interface may promote the development of non-noble metal for HER and OER.

How incentive synergy and organizational structures shape innovation ambidexterity

PurposeOrganizational incentives and structures play a crucial role in realizing explorative and exploitative innovations in firms. Existing studies have neglected the role of trade-off mechanisms between the two on innovation ambidexterity. This study aims to investigate these trade-off mechanisms and their position on innovation ambidexterity.Design/methodology/approachGiven the limited theoretical understanding, the authors conducted a case study with a sample of two Chinese firms with abundant interview and secondary data.FindingsThe results show that firms can develop innovation ambidexterity at two levels, namely, the time and space levels, using incentive synergy as well as organizational structures. Furthermore, the authors explain the role of the trade-off between incentive synergy and organizational structure in promoting a balance between explorative and exploitative innovation.Originality/valueThe authors propose trade-off mechanisms between incentive synergy and organizational structure and explore how trade-off mechanisms can play a role in promoting a balance of explorative and exploitative innovation at both time and space levels.

Estimation of Time-Frequency Muscle Synergy in Wrist Movements.

Muscle synergy analysis is a kind of modularized decomposition of muscles during exercise controlled by the central nervous system (CNS). It can not only extract the synergistic muscles in exercise, but also obtain the activation states of muscles to reflect the coordination and control relationship between muscles. However, previous studies have mainly focused on the time-domain synergy without considering the frequency-specific characteristics within synergy structures. Therefore, this study proposes a novel method, named time-frequency non-negative matrix factorization (TF-NMF), to explore the time-varying regularity of muscle synergy characteristics of multi-channel surface electromyogram (sEMG) signals at different frequency bands. In this method, the wavelet packet transform (WPT) is used to transform the time-scale signals into time-frequency dimension. Then, the NMF method is calculated in each time-frequency window to extract the synergy modules. Finally, this method is used to analyze the sEMG signals recorded from 8 muscles during the conversion between wrist flexion (WF stage) and wrist extension (WE stage) movements in 12 healthy people. The experimental results show that the number of synergy modules in wrist flexion transmission to wrist extension (Motion Conversion, MC stage) is more than that in the WF stage and WE stage. Furthermore, the number of flexor and extensor muscle synergies in the frequency band of 0–125 Hz during the MC stage is more than that in the frequency band of 125–250 Hz. Further analysis shows that the flexion muscle synergies mostly exist in the frequency band of 140.625–156.25 Hz during the WF stage, and the extension muscle synergies appear in the frequency band of 125–156.25 Hz during the WE stage. These results can help to better understand the time-frequency features of muscle synergy, and expand study perspective related to motor control in nervous system.

The Effects of Fatigue on Muscle Synergies in the Shoulders of Baseball Players.

Muscle synergies are defined as the central nervous system's organizational structure for movement. Muscle synergies change after muscular fatigue, with certain synergies assuming the primary role to compensate for fatigue within another muscle synergy. Owing to the high eccentric forces imposed upon the external rotators (ie, posterior rotator cuff), pitchers that continue to throw while fatigued are at a significantly higher risk of shoulder and/or elbow injury; however, the neuromuscular compensation strategies of baseball players in response to fatigue are currently unknown. Players would utilize the same muscle synergy structure following external rotation (ER) fatigue; however, muscle coefficients of nonfatigued muscles would increase (ie, compensate for the external rotators) after fatigue. Cross-sectional study conducted in a controlled, laboratory setting. Nine players from an intercollegiate competitive club baseball team voluntarily participated in this study. Surface electromyography was used on 14 muscles of the glenohumeral and scapulothoracic joints of the dominant arm during a reaching protocol. Players completed a baseline reaching protocol (prefatigue), then an ER fatigue protocol until maximum concentric ER was reduced by 40%, and finally repeated the same reaching protocol (postfatigue). Principal component analysis was used to extract muscle synergies, the variance accounted for (VAF) of each synergy, and muscle coefficients. Prefatigue was compared with postfatigue using paired t tests for all dependent variables. Four muscle synergies were extracted for both pre- and postfatigue. The VAF for the ER/abduction synergy decreased significantly (prefatigue, 34.6%; postfatigue, 32.4%; P = 0.03), showing a decreased reliance on ER/abduction during the reaching task after fatigue. Within synergy 1, the pectoralis major muscle coefficient (-0.489 vs -0.552; P = 0.01; effect size = 1.68) decreased significantly from prefatigue to postfatigue, indicating that the pectoralis major assumed more of an antagonist role during ER/abduction. Within synergy 2 (forward reaching), there were no significant changes in VAF or muscle coefficients observed. For the third synergy, muscle coefficients increased for the serratus anterior (P = 0.02) and middle deltoid (P = 0.01), whereas in the fourth synergy, the pectoralis major (P = 0.01) increased and teres major (P = 0.01) and biceps brachii (P = 0.05) muscle coefficients decreased. The decreased VAF of the ER/abduction synergy after fatigue indicate that other muscles within that synergy could not fully compensate to maintain function. Interestingly, the changes in muscle coefficients suggest that players relied less on the internal rotation (IR) synergy and more on the cross-body synergy following fatigue. This may be due to imbalances between ER and IR while maintaining balance between cross-abduction and adduction. Clinicians may consider implementing low-load, high-repetition training programs to develop posterior shoulder endurance and prolong the onset of muscular fatigue.

Individuals with Chronic Mild-to-Moderate Traumatic Brain Injury Exhibit Decreased Neuromuscular Complexity During Gait

Background Synergy analysis provides a means of quantifying the complexity of neuromuscular control during gait. Prior studies have shown evidence of reduced neuromuscular complexity during gait in individuals with neurological disorders associated with stroke, cerebral palsy, and Parkinson’s disease. Objective The purpose of this study was to investigate neuromuscular complexity during gait in individuals who experienced a prior traumatic brain injury (TBI) that resulted in chronic balance deficits. Methods We measured and analyzed lower extremity electromyographic data during treadmill and overground walking for 44 individuals with residual balance deficits from a mild-to-moderate TBI at least 1 year prior. We also tested 20 unimpaired controls as a comparison. Muscle synergies were calculated for each limb using non-negative matrix factorization of the activation patterns for 6 leg muscles. We quantified neuromuscular complexity using Walk-DMC, a normalized metric of the total variance accounted for by a single synergy, in which a Walk-DMC score of 100 represents normal variance accounted for. We compared group average synergy structures and inter-limb similarity using cosine similarity. We also quantified each individual’s gait and balance using the Sensory Organization Test, the Dynamic Gait Index, and the Six-Minute Walk Test. Results Neuromuscular complexity was diminished for individuals with a prior TBI. Walk-DMC averaged 92.8 ± 12.3 for the TBI group during overground walking, which was significantly less than seen in controls (100.0 ± 10.0). Individuals with a prior TBI exhibited 13% slower overground walking speeds than controls and reduced performance on the Dynamic Gait Index (18.5 ± 4.7 out of 24). However, Walk-DMC measures were insufficient to stratify variations in assessments of gait and balance performance. Group average synergy structures were similar between groups, although there were considerable between-group differences in the inter-limb similarity of the synergy activation vectors. Conclusions Individuals with gait and balance deficits due to a prior TBI exhibit evidence of decreased neuromuscular complexity during gait. Our results suggest that individuals with TBI exhibit similar muscle synergy weightings as controls, but altered control of the temporal activation of these muscle weightings.