Effects of adenosine triphosphate concentration on motor force regulation during skeletal muscle contraction

We employ a mechanical model of sarcomere to quantitatively investigate how adenosine triphosphate (ATP) concentration affects motor force regulation during skeletal muscle contraction. Our simulation indicates that there can be negative cross-bridges resisting contraction within the sarcomere and higher ATP concentration would decrease the resistance force from negative cross-bridges by promoting their timely detachment. It is revealed that the motor force is well regulated only when ATP concentration is above a certain level. These predictions may provide insights into the role of ATP in regulating coordination among multiple motors.

Predictors of residual force enhancement in voluntary contractions of elbow flexors

Background:The steady-state increase in muscle force generating potential following a lengthening contraction is called residual force enhancement(RFE).In this study,we aimed to test for differences in torque,electromyographic activity(EMG),and the associated neuromuscular efficiency(NME)between isometric voluntary contractions of elbow flexors preceded and not preceded by a lengthening contraction.The dependence of such differences on(i)stretch amplitude,(ii)the region of the force-length(FxL)relationship where contraction occurs,and(iii)the individual's ability to produce(negative)work during the stretch was investigated.Methods:Sixteen healthy adults participated in the study.Elbow flexor torque,angle,and biceps brachii EMG for purely isometric contractions(reference contractions)and for isometric contractions preceded by active stretches of 20°and 40°were measured at the ascending,plateau,and descending regions of subject-specific FxL curves.All contractions were performed in an isokinetic dynamometer.Two-factor(stretch×FxL region)repeated measures analysis of variance ANOVAs was used to analyze the effect of active stretch on EMG,torque,and NME across conditions.The relationships between mechanical work during stretch-calculated as the torque-angular displacement integral-and the changes in EMG,torque,and NME were analyzed using Pearson correlation.Results:In general,torque,EMG,and NME following active stretches differed from the values observed for the purely isometric reference contractions.While although the detailed effects of active stretch on torque and EMG differed between regions of the FxL relationship,NME increased by about 19%for all muscle lengths.Up to 30%of the interindividual variability in torque generating potential change in response to active stretching was accounted for by differences in(negative)work capacity between subjects.Conclusion:Our results suggest that(i)RFE contributes to"flatten"the elbow flexor torque-angle relationship,favoring torque production at lengths where the purely isometric torques are reduced substantially,and(ii)RFE contributes to a reduction in energy cost of torque production during isometric contractions for the entire operating range.

Assessment of Human Skeletal Muscle Contraction and Force by Diffusion Tensor Imaging

We aimed to investigate the association between mobility and skeletal muscle strength by using magnetic resonance diffusion tensor imaging (DTI). This study included 20 healthy male volunteers (mean age, 21.8 ± 1.1 years). The maximum voluntary strength (MVC) of each participant was measured with the ankle joint in plantar and dorsal flexion using an instrument for measuring muscle strength. Moreover, magnetic resonance imaging (MRI) was performed with the ankle joint at rest, in plantar flexion, and in dorsal flexion. For imaging, a 1.5-T MRI device was used, and a diffusion-weighted stimulated echo-planar imaging pulse sequence. Tensor eigenvalues (λ), fractional anisotropy (FA), and the apparent diffusion coefficient (ADC) were calculated from data obtained by DTI. The resulting MRI data were compared to the data on muscle mobility or strength and statistically analyzed. Regarding changes in DTI indices during muscle movements, anisotropy of the tibialis anterior was significantly increased from rest to plantar flexion (P < 0.01), whereas no significant change was observed in dorsal flexion (n.s.). In contrast, the extent of significant changes in anisotropy of the medial gastrocnemius (mGC) and soleus (SOL) was small at plantar flexion (mGC, P < 0.01;SOL, n.s.), whereas the indices were significantly increased at dorsal flexion (P < 0.01). Regarding the correlation between MVC of each skeletal muscle and the DTI indices, FA and λ3 were significantly correlated in movements involving the muscles, whereas no significant correlation was observed in movements not involving them. Changes in intramuscular water molecules by elongation and contraction of the skeletal muscle fibers could be assumed to affect changes in diffusional anisotropy. When muscles contract, the space between myocytes was reduced and they might become increasingly dense. Moreover, diffusional anisotropy increased with increasing MVC, whereas ADC remained unchanged. DTI was suggested to produce measurements similar to the degree of muscle strength.

Study of the Contact Force in Free-form Surfaces Compliant EDM Polishing by Robot

With an elastic negative pole being driven by ultra so nic vibration and being moved along the surface of work-piece compliantly by ro bot, a new kind of effective EDM, the compliant EDM, cuts the electrically condu ctive materials away and polishes work-piece of free-form surface. The study o f the contact force between the end of polishing tool and the surface of work-p iece is the key for the compliant EDM to study its cutting mechanism and to make better use of it. This paper makes a model for the contact force and verifies i t by experiments and simulation based on the theory of elastic body kinetics and dynamic stress concentration. The research work shows that this contact force i s caused by both the electrical impulsion of EDM and the mechanical force of ult rasonic vibration, the discharge frequency of compliant EDM has a much more clos er connection with the vibration frequency of polishing tool rather than the fre quency of ultrasonic vibration.

Residual force enhancement in human skeletal muscles:A systematic review and meta-analysis

Objective:We reviewed and appraised the existing evidence of in vivo manifestations of residual force enhancement in human skeletal muscles and assessed,through a meta-analysis,the effect of an immediate history of eccentric contraction on the subsequent torque capacity of voluntary and electrically evoked muscle contractions.Methods:Our search was conducted from database inception to May 2020.Descriptive information was extracted from,and quality was assessed for,45 studies.Meta-analyses and metaregressions were used to analyze residual torque enhancement and its dependence on the angular amplitude of the preceding eccentric contraction.Results:Procedures varied across studies with regards to muscle group tested,angular stretch amplitude,randomization of contractions,time window analyzed,and verbal command.Torque capacity in isometric(constant muscle tendon unit length and joint angle)contractions preceded by an eccentric contraction was typically greater compared to purely isometric contractions,and this effect was greater for electrically evoked muscle contractions than voluntary contractions.Residual torque enhancement differed across muscle groups for the voluntary contractions,with a significant enhancement in torque observed for the adductor pollicis,ankle dorsiflexors,ankle plantar flexors,and knee extensors,but not for the elbow and knee flexors.Meta-regressions revealed that the angular amplitude of the eccentric contraction(normalized to the respective joints full range of motion)was not associated with the residual torque enhancement observed.Conclusion:There is evidence of residual torque enhancement for most,but not all,muscle groups,and residual torque enhancement is greater for electrically evoked than for voluntary contractions.Contrary to our hypothesis,and contrary to generally accepted findings on isolated muscle preparations,residual torque enhancement in voluntary and electrically evoked contractions does not seem to depend on the angular amplitude of the preceding eccentric contraction.

前交叉韧带重建后肌肉等长发力率及与功能表现的关系

背景:前交叉韧带重建后肌肉功能的恢复通常评估肌肉的最大力量,最近的研究认为还应考虑神经肌肉功能,比如肌肉等长发力率,即在肌肉等长收缩条件下测量不同时间间隔的力-时间曲线斜率。目的:阐述前交叉韧带重建后患者肌肉等长发力率的研究现状与不足,分析术后不同时间内股四头肌和腘绳肌等长发力率的缺陷程度;等长发力率对术后患者功能表现的影响,为优化前交叉韧带重建后康复、减少患者二次损伤以及降低膝骨关节炎发生率提供重要信息。方法:检索中国知网、维普、万方和PubMed数据库,以“前交叉韧带,发力率”为中文检索词,以“anterior cruciate ligament,rate of force development,rate of torque development”为英文检索词,按照纳入和排除标准最终纳入69篇文献。结果与结论:(1)大多数研究发现前交叉韧带重建后半年内患者双侧肌肉等长发力率存在缺陷,双侧腘绳肌早期等长发力率(即肌肉收缩100 ms时间段内任意时间间隔的力-时间曲线斜率)在半年后有显著改善,但双侧股四头肌早期等长发力率长期缺陷,表明术后股四头肌神经肌肉功能长期受损。(2)有关晚期等长发力率(肌肉收缩100 ms后时间段内任意时间间隔的力-时间曲线斜率)的相关研究较少,无法得出确切结论。(3)关于着陆运动(跳跃落地和侧切等)和日常生活活动(走、跑),股四头肌早期等长发力率比等长峰值力矩相关性更强,运动过程中生物力学的异常改变被认为是患者二次损伤以及创伤性膝骨关节炎发生的重要风险因素,积极改善股四头肌早期等长发力率可能会降低二次损伤以及创伤性膝骨关节炎的发生率。(4)目前仅有很少的证据表明,全身振动训练能改善前交叉韧带重建后患者股四头肌早期等长发力率,建议今后在术后早期阶段应用神经肌肉电刺激干预股四头肌和腘绳肌,而在术后晚期阶段实施爆发力、高阻力训练,这可能会改善患者等长发力率。(5)短时间产生足够的肌肉力量才能有效保护前交叉韧带,而腘绳肌等长发力率与功能表现的关系尚不清楚,这可能会提供有关预防患者二次损伤的信息。(6)作者建议将等长发力率作为指导康复以及恢复运动的评估指标之一,除了关注对称性的改善以及与正常人的差异,还要考虑腘绳肌与股四头肌力量的比值,合适的比值范围才能保证肌肉快速发力时的平衡,这可能会降低再次损伤的发生,但比值的正常范围尚不清楚。(7)未来研究要考虑移植物类型和膝关节屈曲角度对等长发力率的影响,以尽可能找出患者存在的神经肌肉功能障碍,帮助患者更好地康复。

合同履行绿色义务的性质与效力——《民法典》第509条第3款释论

《民法典》第509条第3款规定的合同履行中的绿色义务,引起了巨大理论争议,也带来了司法实践难题。将该条款解释为倡导性条款,还是解释为有约束力的法定义务条款,其意义完全不同。为推进生态文明建设,结合民法绿色原则和立法体系进行分析,应当明确该条款的法定义务属性,通过对合同自由的适当限制,实现对当事人行为的环保约束。具体来说,合同履行的绿色义务具有附随义务属性,违反该义务可能导致损害赔偿、强制履行等责任,债权人也可能因而享有合同解除权;同时,该义务具有不真正义务属性,虽不能强制执行,但可能导致对方当事人减少价款请求权。上述两种定性虽有区别但并非相互排斥,应当由法官在司法裁判中结合案情决定采用不同的解释路径,以确定合同履行绿色义务的具体内容和边界,并依据社会共同价值、参酌习惯等,认定违反该义务的法律效果,体现绿色义务对合同当事人的现实约束力。

关于魔力弹簧的收缩时间和上端运动问题

针对有关魔力弹簧研究中的几个问题进行探讨和澄清.建立了预收缩力弹簧的模型,推出其形变规律.根据质心运动定理,导出这种弹簧自由下落时,收缩到原长所用的时间、其上端的运动方程和速度公式.研究表明,对于通常演示所用的魔力弹簧,在自由下落时的收缩阶段,其上端不是作匀速直线运动.

中国民法语境下“合同效力”的层次性

从《民法典》与《民法典合同编通则解释》就行政审批对合同效力的影响、无权处分的法律后果等所作的规定看,“合同效力”在我国民法上具有明显的层次性。广义的合同效力与广义的合同拘束力属同义语,是法律对当事人合意的认可和保护,其前提是合同具备有效要件,即“依法成立”。因此,合同无效与合同不成立并无实质区别。但是,为了准确描述合同已依法成立但未生效的法律状态,我国民法有时是在狭义上使用合同拘束力的概念,并将其与狭义的合同效力概念区别开来:前者指当事人于合同依法成立后不得擅自撤销或者解除合同,并不得违反诚信原则恶意阻止条件成就或消极对待报批义务;后者则指当事人一方得基于合同请求对方履行约定的义务,即履行效力。此外,由于我国民法上的买卖合同不仅包含当事人发生债权债务关系的意思,而且包含当事人移转所有权的意思,因此,还应将买卖合同的效力进一步区分为履行效力与移转效力。“合同效力”的此种层次性,既是现代交易阶段化的必然产物,也是中国民法体系特色的重要表现。

论不动产抵押合同未登记的法律效果——以《担保制度解释》第46条为中心

未登记的不动产抵押合同不产生担保效力,无法类推适用赠与合同规则。《担保制度解释》第46条第1款明确了债权人的登记请求权,债权人可自由行使登记请求权和违约损害赔偿请求权,协助登记应属债权人的不真正义务;第2款不可归责于抵押人的事由应属不可抗力规则的适用,该款后半句明确了债权人的代偿请求权;第3款抵押人损害赔偿的范围应为债务人未受清偿部分,且受到约定担保范围、可预见性规则、抵押权顺位规则、抵押权行使期间规则以及与有过失规则的限制。抵押人和债务人之间在责任承担上应属连带责任关系。

双边市场中的销售人员激励合同设计

与传统企业类似,平台企业需要雇佣销售人员开展促销活动,但与传统企业不同,平台企业两边的用户存在交叉网络效应。构建平台企业雇佣销售人员进行促销的委托代理模型,研究交叉网络效应对于销售激励合同设计和平台利润的影响。研究发现,如果代理人的工资与直接销售挂钩,即平台仅对销售人员直接施加努力的一边进行补偿,则交叉网络效应的增强不见得总是有利于平台利润的提高。但是,如果将平台另一边的销售量也纳入激励合同,则代理人需要在平台两边都分担风险,这将促使代理人提高努力水平,也有利于增加平台利润。研究揭示了,双边市场中的激励合同设计不但需要考虑平台两边用户由于交叉网络效应导致的溢出效应和风险传导,还需要考虑平台的费用设定。

浅析《节约用水条例》实施对节水产业发展的机遇与挑战

《节约用水条例》是我国首部全面规范节约用水的行政法规,规定国家要完善鼓励和支持节水产业发展、科技创新的政策措施,这为节水产业发展提供了制度保障。梳理了《节约用水条例》中节水产业发展的相关规定,分析了《节约用水条例》实施对节水产业带来的机遇以及对高耗水产业、农村居民和农业生产用水的挑战。从完善节水产业政策、发展节水产业技术、健全节水产业发展市场、强化节水产业监管等方面提出了节水产业发展政策建议,可为加快形成节水产业新质生产力、推动节水产业高质量发展提供参考。

健康青年男性和女性盆底肌群的MRI三维重建与有限元分析

研究磁共振成像(MRI)对健康男性和女性盆底组织结构三维重建的方法及意义。选取健康青年男性及女性各1人,进行MRI扫描,观察盆底部分组织结构,应用医学图像处理软件ITK-SNAP进行三维重建,建立盆底肌群的三维几何模型,并实现任意角度观察和精确定位测量分析。在此基础上,应用有限元程序ANSYS workbench,建立计算模型,并对计算结果进行拟合分析,得到耻骨直肠肌收缩力与肛直角角度变化的相关性,研究结果可为今后开展盆底相关疾病的研究提供参考依据。

再论违约金的规制模式:异化与回归

我国民法上违约金规则系糅合了法国民法和德国民法关于违约金规则的立法范式,亦即对违约金的定义采德国模式,而违约金司法酌减规则的规制对象则与法国法相同。但经过司法实践的演化,违约金司法酌减规则业已异化为以补偿债权人为内核的数字型酌减模式,由此引致民法规范体系的不融贯、规则的适用无法实现其规范意涵的局面,严重影响了以交换正义为目的的合同法律制度价值的实现。因此,应当重新审视违约金作为合意产物的本质,让违约金的规制模式回归于合同效力控制规则的道路上,并根据合意特性的不同,从合意度和均衡度两个方面检视违约金的效力。值此情形,并不会因违约金的给付而给当事人带来风险。由此,注重违约金规制模式的本土化改造,以新的立法实践和司法实践回应当下的时代课题,方能推动具有鲜明中国特色、实践特色的民法理论体系的发展。

突发公共卫生事件下粤港澳大湾区海上货运的法律风险及其应对

发生突发公共卫生事件时海上货物运输会面临更多的风险和不确定性;我国“一国两制”的现状,又使粤港澳大湾区内的海上货运合同纠纷呈现出区别于单一法域下之合同纠纷的特殊性。文章结合相关国际公约、通则及惯例等,对部分国家和地区的法律中有关“不可抗力”“合同落空”及相关概念与规定作了综合的法理分析,探讨了突发公共卫生事件下粤港澳大湾区海上货运履约之风险规避的法律依据和应对之策。

罗马法上的信义原则

信义指守信、遵守诺言,即言出必行或言行一致。罗马人以信义为荣,罗马式信义不同于希腊式或布匿式信义,是罗马人的一项生活原则,也被视作罗马男性美德“坚韧不拔”的一个方面。有些信义关系具有法律特征,有些不具备。罗马法承认不要式法律行为的效力,遵循完全债务合同的严格拘束力,其秉承的诚实信用原则具有信义与正直的双重面向。在信义的类型上,除合同信义外,还包括一种誓言信义。从罗马法的信义原则中发展出罗马高级官员受其所颁布告示的约束和法不溯及既往这两条重要规则。此外,在古罗马人的生活中还存在着为数众多的持续性信义关系,其体现在解放自由人与其庇主之间、庇主与门客之间、古罗马财政官与其上级官员之间、朋友之间以及友好合作协议中,但这些信义关系并不都具有法律上的特征。了解了信义原则的这些具体体现,便能更好地理解罗马法。

生效法律文书确定的债权依法转让的效力问题

生效法律文书确定的债权依法转让的效力问题事关人民法院是否支持第三人申请变更、追加其为申请执行人。对生效法律文书确定的债权依法转让的效力的认定,应当通过审查程序加以确认。只有生效法律文书确定的债权转让的形式及原因合法有效的,人民法院才能支持第三人申请变更、追加其为申请执行人的请求。

论不可抗力与情事变更的区分与衔接

不论是情事变更这一术语还是不可抗力这一术语,其在使用的过程中往往包含了两层含义,第一层含义是客观事实,第二层含义是法律规则,将这两层含义进行区分是论述其关系的前提。在客观事实层面,应当从因果关系的角度来理解不可抗力事件和情事变更事实之间的关系,不可抗力事件是可能导致情事变更事实的原因之一。在法律规则层面,两者的功能定位截然不同,分别作用于合同运行的不同阶段。情事变更规则作用于原给付阶段,处理是否要继续履行合同的问题;不可抗力规则作用于次给付阶段,处理债务不履行责任的问题。目前,我国的不可抗力规则可以细分为不可抗力解除规则和不可抗力免责规则,但在法定解除制度中独立规定不可抗力解除规则并无重要意义。不可抗力规则的作用应当是责任免除。情事变更规则作用于合同履行阶段,其可以产生变更或解除合同的法律效果,该规则的作用在于使合同关系恢复到均衡状态,而不是免除违约责任。

借名买房司法裁判问题探析

房屋交易类型日益多元复杂,借名买房问题由来已久。因借名买房产生的法律纠纷多、案件争议大、社会关注度高、司法裁决难。从近年来中国裁判文书网借名买房案件裁判结果来看,房屋产权判决归出名人或归借名人的比例日趋偏高。学界、实务界观点纷呈,缺乏权威且有针对性的法律解读,适用不同的法律、法规及相关司法解释会导致同类案不同判。司法实践中判定借名买房的房屋归借名人所有虽具一定合理性,但潜在危机不可小觑,一是挑战民法典不动产物权登记生效的原则规定,二是增加治理房地产资源浪费及因房贷等诱发的社会群体事件难度。借名买房现象一时难以根除,亟需统一认识并依法合理规制,既需保护当事人合法权益,更应树立司法权威,将借名买房涉案房屋判处归出名人所有符合当下司法实践需求。

配筋和预应力下拱坝动力特性的模型试验研究

通过坝体横缝配筋和施加拱向预应力的拱坝模型振动台试验,研究了不同配筋率和预应力的变化对拱坝动力特性的影响。通过振动台输入的几组典型动荷载(白噪声和谐波荷载等),来观测模型拱坝的动力反应,并进行相应的有限元分析。结果表明:在配置横缝钢筋之后,拱坝的动力性能出现明显的改变,固有频率得到明显提高;施加预应力之后,坝体的固有频率也得到一定的改变,而动载下的缝开度则明显减小。相比较而言,预应力增加对减小横缝的开度反应更为有效,而配筋的增加则对改善拱坝的整体性作用更加有效。