Muscle synergies reveal impaired trunk muscle coordination strategies in individuals with thoracic spinal cord injury

Spinal cord injury (SCI) can result in paralysis of trunk muscles, which can affect sitting balance. The objective of this study was to analyze trunk muscle coordination of individuals with thoracic SCI and compare it to able-body individuals. A total of 27 individuals were recruited and subdivided into: (a) high thoracic SCI; (b) low thoracic SCI; and (c) able-body groups. Participants were seated and asked to lean their trunk in eight directions while trunk muscle activity was recorded. Muscle coordination was assessed using the non-negative matrix factorization (NMF) method to extract muscle modules, which are the synergistic trunk muscle activations, and their directional activation patterns. Our results showed that individuals with SCI used less muscle modules, more co-contractions, and less directional tuning, compared to able-bodied people. These results suggest impaired and simplified muscle coordination due to the loss of supraspinal input after SCI. Observed variability in muscle coordination within SCI groups also suggests that other mechanisms such as spasticity and muscle stretch reflexes or individual factors such as experience and training contributed to the postural muscle synergies. Overall, muscle coordination deficits revealed impaired neuromuscular strategies which provide implications for rehabilitation of trunk muscles during sitting balance after SCI.     

Use of muscle synergies and wavelet transforms to identify fatigue during squatting

The objective of this study was to supplement continuous wavelet transforms with muscle synergies in a fatigue analysis to better describe the combination of decreased firing frequency and altered activation profiles during dynamic muscle contractions. Nine healthy young individuals completed the dynamic tasks before and after they squatted with a standard Olympic bar until complete exhaustion. Electromyography (EMG) profiles were analyzed with a novel concatenated non-negative matrix factorization method that decomposed EMG signals into muscle synergies. Muscle synergy analysis provides the activation pattern of the muscles while continuous wavelet transforms output the temporal frequency content of the EMG signals. Synergy analysis revealed subtle changes in two-legged squatting after fatigue while differences in one-legged squatting were more pronounced and included the shift from a general co-activation of muscles in the pre-fatigue state to a knee extensor dominant weighting post-fatigue. Continuous wavelet transforms showed major frequency content decreases in two-legged squatting after fatigue while very few frequency changes occurred in one-legged squatting. It was observed that the combination of methods is an effective way of describing muscle fatigue and that muscle activation patterns play a very important role in maintaining the overall joint kinetics after fatigue.     

Combining muscle synergies and biomechanical analysis to assess gait in stroke patients

The understanding of biomechanical deficits and impaired neural control of gait after stroke is crucial to prescribe effective customized treatments aimed at improving walking function. Instrumented gait analysis has been increasingly integrated into the clinical practice to enhance precision and inter-rater reliability for the assessment of pathological gait. On the other hand, the analysis of muscle synergies has gained relevance as a novel tool to describe the neural control of walking. Since muscle synergies and gait analysis capture different but equally important aspects of walking, we hypothesized that their combination can improve the current clinical tools for the assessment of walking performance.To test this hypothesis, we performed a complete bilateral, lower limb biomechanical and muscle synergies analysis on nine poststroke hemiparetic patients during overground walking. Using stepwise multiple regression, we identified a number of kinematic, kinetic, spatiotemporal and synergy-related features from the paretic and non-paretic side that, combined together, allow to predict impaired walking function better than the Fugl-Meyer Assessment score. These variables were time of peak knee flexion, VAF_total values, duration of stance phase, peak of paretic propulsion and range of hip flexion. Since these five variables describe important biomechanical and neural control features underlying walking deficits poststroke, they may be feasible to drive customized rehabilitation therapies aimed to improve walking function.This paper demonstrates the feasibility of combining biomechanical and neural-related measures to assess locomotion performance in neurologically injured individuals.     

Selective activation of neuromuscular compartments within the human trapezius muscle

Task-dependent differences in relative activity between “functional” subdivisions within human muscles are well documented. Contrary, independent voluntary control of anatomical subdivisions, termed neuromuscular compartments is not observed in human muscles. Therefore, the main aim of this study was to investigate whether subdivisions within the human trapezius can be independently activated by voluntary command using biofeedback guidance. Bipolar electromyographical electrodes were situated on four subdivisions of the trapezius muscle. The threshold for “active” and “rest” for each subdivision was set to >12% and <1.5% of the maximal electromyographical amplitude recorded during a maximal voluntary contraction. After 1 h with biofeedback from each of the four trapezius subdivisions, 11 of 15 subjects learned selective activation of at least one of the four anatomical subdivisions of the trapezius muscle. All subjects managed to voluntarily activate the lower subdivisions independently from the upper subdivisions. Half of the subjects succeeded to voluntarily activate both upper subdivisions independently from the two lower subdivisions. These findings show that anatomical subdivisions of the human trapezius muscle can be independently activated by voluntary command, indicating neuromuscular compartmentalization of the trapezius muscle. The independent activation of the upper and lower subdivisions of the trapezius is in accordance with the selective innervation by the fine cranial and main branch of the accessory nerve to the upper and lower subdivisions. These findings provide new insight into motor control characteristics, learning possibilities, and function of the clinically relevant human trapezius muscle.     

Patterns of leg muscle recruitment vary between novice and highly trained cyclists

This study compared patterns of leg muscle recruitment and coactivation, and the relationship between muscle recruitment, coactivation and cadence, in novice and highly trained cyclists. Electromyographic (EMG) activity of tibialis anterior (TA), tibialis posterior (TP), peroneus longus (PL), gastrocnemius lateralis (GL) and soleus (SOL) was recorded using intramuscular fine-wire electrodes. Four experimental conditions of varying cadence were investigated. Differences were evident between novice and highly trained cyclists in the recruitment of all muscles. Novice cyclists were characterized by greater individual variance, greater population variance, more extensive and more variable muscle coactivation, and greater EMG amplitude in periods between primary EMG bursts. Peak EMG amplitude increased linearly with cadence and was not different at individual preferred cadence in either novice or highly trained cyclists. However, EMG amplitude in periods between primary EMG bursts, as well as the duration of primary EMG bursts, increased with increasing cadence in novice cyclists but were not influenced by cadence in highly trained cyclists. Our findings suggest that muscle recruitment is highly skilled in highly trained cyclists and less refined in novice cyclists. More skilled muscle recruitment in highly trained cyclists is likely a result of neuromuscular adaptations due to repeated performance of the cycling movement in training and competition.     

No evidence of expertise-related changes in muscle synergies during rowing

The purpose of the present study was to determine whether expertise in rowing is driven by a specific structure in muscular coordination. We compared seven experienced rowers and eight untrained (i.e., inexperienced) subjects during rowing on an ergometer. Both surface electromyography activity and mechanical patterns (forces exerted at the handle and the foot-stretcher) were recorded during a high intensity rowing exercise. A non-negative matrix factorization was applied to 23 electromyographic patterns to differentiate muscle synergies. Results showed that expertise was not associated with different dimensionality in the electromyographic data and that three muscle synergies were sufficient to explain the majority of the variance accounted for (i.e., >90% of the total variance) in the two populations. The synergies extracted were similar in the two populations, with identical functional roles. While the temporal organization of the propulsive synergies was very similar, slight differences were found in the composition of the muscle synergies (muscle synergy vectors) between the two populations. The results suggests that rowing expertise would not require the development of novel muscle synergies but would imply intrinsic synergies already used in different behaviors. Performance in rowing is more probably linked to adjustments in the mechanical output of the muscle synergies rather than to differences in the shape and timing of their activations.     

Functional muscle synergies to support the knee against moment specific loads while weight bearing

ObjectiveExternally applied abduction and rotational loads are major contributors to the knee joint injury mechanism; yet, how muscles work together to stabilize the knee against these loads remains unclear. Our study sought to evaluate lower limb functional muscle synergies in healthy young adults such that muscle activation can be directly related to internal knee joint moments.MethodsConcatenated non-negative matrix factorization extracted muscle and moment synergies of 22 participants from electromyographic signals and joint moments elicited during a weight-bearing force matching protocol.ResultsTwo synergy sets were extracted: Set 1 included four synergies, each corresponding to a general anterior, posterior, medial, or lateral force direction. Frontal and transverse moments were coupled during medial and lateral force directions. Set 2 included six synergies, each corresponding to a moment type (extension/flexion, ab/adduction, internal/external rotation). Hamstrings and quadriceps dominated synergies associated with respective flexion and extension moments while quadriceps-hamstring co-activation was associated with knee abduction. Rotation moments were associated with notable contributions from hamstrings, quadriceps, gastrocnemius, and hip ab/adductors, corresponding to a general co-activation muscle synergy.ConclusionOur results highlight the importance of muscular co-activation of all muscles crossing the knee to support it during injury-inducing loading conditions such as externally applied knee abduction and rotation. Functional muscle synergies can provide new insight into the relationship between neuromuscular control and knee joint stability by directly associating biomechanical variables to muscle activation.     

乡村地区生态系统服务权衡与协同关系——以湖州市为例

湖州是中国"美丽乡村"发源地,十多年来乡村面貌发生较大改变,从而对其生境维持、文化保护带来压力,定量评估湖州乡村的生态系统服务及相关关系对其可持续发展具有重要意义。基于Thornthwaite Memorial模型、Miami模型、InVEST模型、水量平衡法、Maxent模型等方法对该区域2010-2018年粮食供给、碳贮存、水源涵养、文化服务等四项生态系统服务进行时空演变分析,探究不同生态系统服务间的权衡与协同关系。结果表明：(1)在2010-2018年,湖州市乡村地区粮食供给在波动中下降,一级区以东、西部的平原耕地为主;碳贮存均值与总量年际变化极小,中、西部的高山林地碳储量最高;水源涵养均值呈现先增后减的小幅波动,空间分布特点与碳贮存相似;文化服务能力逐年增强,一级区向景点区域集聚并扩张。(2)在权衡与协同分析中,水源涵养与碳贮存、粮食供给之间以协同效应为主,文化服务与水源涵养、粮食供给、碳贮存之间以权衡效应为主,粮食供给与碳贮存之间由权衡效应向协同效应转变,各服务间相关关系总体逐渐增强且存在空间差异性。(3)热点区域识别研究显示,Ⅰ类热点区主要为提供粮食供给的耕地,占比多且略有增强;Ⅱ类热点区主要为提供碳贮存、水源涵养的林地,总体有所减少;Ⅲ类热点区主要为提供碳贮存、水源涵养,以及粮食供给或文化服务的林地和耕地,占比较多并不断扩大;Ⅳ类热点区、非热点区分别位于山地-平原过渡区、靠近城镇区域,均占比极少且变化小。研究结果以期为揭示乡村地区生态系统供给、调节、文化服务间的关系,优化乡村经济结构与发展模式,推进乡村的合理规划和可持续发展提供参考。     

Reciprocal aiming precision and central adaptations as a function of mechanical constraints

The present study investigated the influence of mechanical constraints (load and movement velocity) on the movement accuracy during a reciprocal aiming precision task. Seven participants had to point rhythmically and alternatively (with flexion–extension of the right elbow) a cursor at two targets as accurately as possible. Two loads (applied to the limb effectors; 500 and 2500 g), two movement frequencies (1.25 and 1.75 Hz) as well as two target sizes (1 and 5 cm) were manipulated. Surface EMG activity of both biceps brachii and triceps brachii was recorded. Attentional demands, reflecting the central cost associated with the performance of aiming movements was assessed using a dual-task paradigm (via a probe reaction time task – RT). While the results demonstrated a significant degradation of pointing accuracy with mechanical loading (mean absolute error – AE for 500 g load: 0.32 mm ± 0.64; mean AE for 2500 g load: 0.51 ± 0.74 mm), no significant effect of movement frequency was found. For the two mechanical constraints, the mental effort to meet the task demands remained the same (mean RT_−500g: 370 ± 123 ms; mean RT_−2500g: 395 ± 119 ms). Electromyographic activity of both biceps brachii and triceps brachii muscles evidenced neural adaptations to changes in mechanical constraints. Put together, the present findings suggest that the cause of the observed loss of movement accuracy may probably result from more peripheral alterations such as an impairment of the afferent information processing.     

基于服务簇的东北地区生态系统服务权衡与协同

生态系统服务簇是多种生态系统服务的组合,能够表征生态系统服务间权衡与协同关系,可为制定有效的区域社会-生态系统管理方案提供科学依据。研究采用全局Moran′s I指数、主成分分析、聚类分析等方法,系统阐明了东北地区6种生态系统服务的组成、权衡与协同、作用机制和区域差异。结果表明:(1)6种生态系统服务均表现出显著的正空间自相关(Moran′s I>0),即各生态系统服务存在空间聚类分布,而非随机分布;(2)聚类分析将东北地区划分为南部经济-生态协调区、东北部森林生态平衡区、西部防风固沙区和中部粮食生产区四个生态功能区;(3)水源涵养、固碳和土壤保持服务之间具有极显著的协同关系(r=0.73,r=0.70,r=0.80),而防风固沙和土壤保持服务之间存在极显著的权衡关系(r=-0.22);(4)东北部森林生态平衡区和南部经济-生态协调区的固碳能力显著高于西部防风固沙区和中部粮食生产区,中部粮食生产区的食物供给服务和生物多样性服务则较高。开展基于服务簇的生态系统服务权衡与协同的研究,有助于针对每种生态功能服务簇制定相应的管理方案,促进各个生态功能区经济、社会、资源与生态环境的全面协调...     

北方重点生态功能区生态系统服务权衡与协同

北方地区作为我国最重要的生态屏障区,也是我国荒漠化发展最快、生态极为脆弱、受风沙危害最严重的区域。分析了北方地区6个国家重点生态功能区生态系统结构变化和防风固沙、土壤保持、水源涵养、牧草供给等生态系统关键服务多年变化状况,从而客观科学地评价典型生态功能区生态保护效果,总结目前存在的主要生态问题,为重点生态功能区监管和考核提供科学地决策依据。结果表明：1）草地面积除阴山北麓有所增加以外,其他功能区皆减少;荒漠面积在东部三个功能区有所增加,而在西部三个功能区有所减少;草地植被覆盖度皆有所提高,增幅0.4%-7%。2）防风固沙服务除呼伦贝尔有所提升以外,其他功能区皆呈现下降态势;水源涵养在西部塔里木河与阿尔金先上升后下降,中部阴山北麓和科尔沁有所提高,而东部浑善达克与呼伦贝尔呈持续上升态势;各功能区的土壤保持呈现不同程度提升,而牧草供给皆有所下降。3）除呼伦贝尔和浑善达克南端以外,牧草供给与防风固沙服务之间以协同关系为主;除科尔沁西北部和呼伦贝尔东端以外,牧草供给与水源涵养、土壤保持服务之间以协同关系为主。通过生态系统类型变化及供给与调节服务相关关系分析可以看出,生态功能区开垦导致草地减少的现象需要遏制,出现权衡关系的东部区域也是生态保护与生产利用矛盾较大的农牧交错带,需要成为后续保护和修复的重点区域。     

Finger joint coordination during tapping

We investigated finger joint coordination during tapping by characterizing joint kinematics and torques in terms of muscle activation patterns and energy profiles. Six subjects tapped with their index finger on a computer keyswitch as if they were typing on the middle row of a keyboard. Fingertip force, keyswitch position, kinematics of the metacarpophalangeal (MCP) and the proximal and distal interphalangeal (IP) joints, and intramuscular electromyography of intrinsic and extrinsic finger muscles were measured simultaneously. Finger joint torques were calculated based on a closed-form Newton–Euler inverse dynamic model of the finger. During the keystroke, the MCP joint flexed and the IP joints extended before and throughout the loading phase of the contact period, creating a closing reciprocal motion of the finger joints. As the finger lifted, the MCP joint extended and the interphalangeal (IP) joints flexed, creating an opening reciprocal motion. Intrinsic finger muscle and extrinsic flexor activities both began after the initiation of the downward finger movement. The intrinsic finger muscle activity preceded both the IP joint extension and the onset of extrinsic muscle activity. Only extrinsic extensor activity was present as the finger was lifted. While both potential energy and kinetic energy are present and large enough to overcome the work necessary to press the keyswitch, the motor control strategies utilize the muscle forces and joint torques to ensure a successful keystroke.     

Direction-specific recruitment of rotator cuff muscles during bench press and row

Recent studies indicate that rotator cuff (RC) muscles are recruited in a reciprocal, direction-specific pattern during shoulder flexion and extension exercises. The main purpose of this study was to determine if similar reciprocal RC recruitment occurs during bench press (flexion-like) and row (extension-like) exercises. In addition, shoulder muscle activity was comprehensively compared between bench press and flexion; row and extension; and bench press and row exercises. Electromyographic (EMG) activity was recorded from 9 shoulder muscles sites in 15 normal volunteers. All exercises were performed at 20, 50 and 70% of subjects’ maximal load. EMG data were normalized to standard maximal voluntary contractions. Infraspinatus activity was significantly higher than subscapularis during bench press, with the converse pattern during the row exercise. Significant differences in activity levels were found in pectoralis major, deltoid and trapezius between the bench press and flexion exercises and in lower trapezius between the row and extension exercises. During bench press and row exercises, the recruitment pattern in each active muscle did not vary with load. During bench press and row exercises, RC muscles contract in a reciprocal direction-specific manner in their role as shoulder joint dynamic stabilizers to counterbalance antero-posterior translation forces.     

黄河上游流域生态系统服务变化及其权衡协同关系

黄河上游是我国重要的生态屏障和生态功能区,研究其生态系统服务的时空演化及其权衡协同关系对实现黄河流域生态保护和高质量发展具有重要意义。基于土地利用、土壤、气象等数据,借助InVEST模型、相关性分析以及空间自相关分析等方法,定量分析了2000-2020年黄河上游生态系统服务的时空演化特征及其权衡与协同关系。结果表明:(1)黄河上游各项生态系统服务整体表现为"西南高,东北低"的分布格局,高值区主要分布于流域西南部,低值区主要分布于流域东北部;(2)研究期内,黄河上游各项生态系统服务均呈现波动变化的趋势,产水量和土壤保持呈现整体减少趋势,生境质量与碳储量呈现增加的趋势;(3)各项生态系统服务两两之间均存在不同程度的相关关系,产水量与生境质量、碳储量呈现此消彼长的权衡关系,产水量-土壤保持、生境质量-碳储量与土壤保持-碳储量之间呈现协同关系;(4)在空间分布格局上,各项生态系统服务间的权衡与协同关系表现出显著的空间异质性与尺度效应,不同分区之间差异较大。本文可为科学管理区域生态系统,促进流域可持续发展提供参考。     

滦河流域土壤保持和水质净化服务及其权衡与协同关系

滦河流域是京津冀地区重要的生态屏障和水源涵养区,但流域内仍存在水土流失、河流水质不达标等问题。基于实测资料及loadest模型等工具率定InVEST模型参数,定量评估了滦河流域各生态区2005、2010和2015年土壤保持和水质净化服务及其时空变化特征,采用相关分析和基于网格的Moran′I指数分析了两项服务的作用机理和权衡与协同关系的时空分异,并探讨了气候和土地利用变化对二者的影响。结果表明：2005年、2010年、2015年滦河流域年均土壤保持强度为136.45 t/hm²,时间上呈现出先强增后微减的特点,空间格局表现为由西北向东南增加;流域总氮(TN)、总磷(TP)年均输出量分别为1526.73 t/a和82.89 t/a,输出量逐年增加且集中在流域中下游,流域整体水质净化能力有所减弱。流域内水体中TN、TP浓度与泥沙入河量具有显著相关性,土壤保持和水质净化服务关系整体上由协同向权衡转变,空间上的差异性表现为林地、草地集中区域(生态区A)多以协同关系为主,而农牧带交错地区(生态区B)多以权衡关系为主。建议未来滦河流域开展生态建设和管理工作时应统筹考虑土壤保持...     

粤港澳大湾区生态系统服务时空演化及其权衡与协同特征

打造国际一流湾区和世界级城市群的粤港澳大湾区,生态保护、环境优化与城市发展、经济开放具有同等重要地位,掌握其城镇化过程中生态系统及其服务变化状况有助于科学合理、有针对性的制定生态保护修复相关政策。基于2000—2015年粤港澳大湾区生态系统宏观格局变化,分析了大湾区生态系统生产力、水源涵养、土壤保持服务的时空演化特征,进而探讨了供给与调节服务之间的权衡与协同关系。结果表明:(1)森林与农田是大湾区的主体生态系统,面积占大湾区国土面积的54.1%和22.8%,近15年由于城镇面积快速增长(增幅达68.6%),导致森林、农田、湿地面积不断减少。(2)基于净初级生产力的供给服务量和土壤保持量整体上均呈现轻度增加趋势,特别是江门、肇庆等生态服务主要提供区域;东南部最高、北部次之、中部偏低的水源涵养量,除西北部呈现增加趋势以外,其它区域皆呈现减少趋势;城镇扩张是生态系统供给、调节服务明显减少的主要影响因素。(3)大湾区生态系统供给服务与水源涵养、土壤保持调节服务之间的相关关系均以协同为主,然而,在大湾区东北部和南部的广州、惠州、江门等区域呈现明显的权衡关系,提示大湾区发展过程中,需要在这些呈现权...     

黄土丘陵沟壑区典型小流域生态系统服务权衡与协同关系研究

黄土高原植被恢复状况制约生态系统服务的提升,本研究依托中国科学院水利部水土保持研究所安塞国家科学野外观测站的基础土壤、植被、气象和水文等数据,在黄土丘陵沟壑区选取纸坊沟和坊塌2个典型小流域,通过购买1998、2008和2018年遥感影像,采用InVEST(Integrated Valuation of Ecosystem Services and Tradeoffs)模型对生态服务(碳储量、土壤保持量、生境质量和产水量)进行评估,探究植被恢复过程中生态系统服务的协同效应和权衡关系。通过对比得知：随着植被的恢复,坊塌和纸坊沟各生态服务(碳储量、土壤保持量、生境质量和产水量)均得到了大幅度的提升,其中2008—2018年增加幅度较小,而1998—2008年增加幅度较大,主要原因在于该阶段(1998—2008年)是退耕还林还草的初始10年,林地及草地面积增长较多,而后10年为退耕的延续阶段,退耕面积增长减缓。从1998—2018年,受自然因素和人为因素的影响,坊塌和纸坊沟流域生态系统服务表现出协同和权衡关系。对于坊塌流域,2008年生态系统服务主要表现为协同关系,1998、2018年以权衡关...     

Effects of training and weight support on muscle activation in Parkinson’s disease

The aim of this study was to investigate the effect of high-intensity locomotor training on knee extensor and flexor muscle activation and adaptability to increased body-weight (BW) support during walking in patients with Parkinson’s disease (PD). Thirteen male patients with idiopathic PD and eight healthy participants were included. The PD patients completed an 8-week training program on a lower-body, positive-pressure treadmill. Knee extensor and flexor muscles activation during steady treadmill walking (3 km/h) were measured before, at the mid-point, and after training. Increasing BW support decreased knee extensor muscle activation (normalization) and increased knee flexor muscle activation (abnormal) in PD patients when compared to healthy participants. Training improved flexor peak muscle activation adaptability to increased (BW) support during walking in PD patients. During walking without BW support shorter knee extensor muscle off-activation time and increased relative peak muscle activation was observed in PD patients and did not improve with 8 weeks of training. In conclusion, patients with PD walked with excessive activation of the knee extensor and flexor muscles when compared to healthy participants. Specialized locomotor training may facilitate adaptive processes related to motor control of walking in PD patients.