Passive Force Generation Research Articles

Quantifying Plantar Flexor Muscles Stiffness During Passive and Active Force Generation Using Shear Wave Elastography in Individuals With Chronic Stroke

ObjectivesThis study aims to investigate the mechanical properties of paretic and healthy plantar flexor muscles and assesses the spatial distribution of stiffness between the gastrocnemius medialis (GM) and lateralis (GL) during active force generation. MethodsShear wave elastography measurements were conducted on a control group (CNT, n=14; age= 59.9 ± 10.6 years; BMI= 24.5 ± 2.5 kg/m2) and a stroke survivor group (SSG, n = 14; age = 63.2 ± 9.6 years; BMI = 23.2 ± 2.8 kg/m2). Shear modulus within the GM and GL was obtained during passive ankle mobilization at various angles of dorsiflexion (P0= 0°; P1= 10°; P2= 20°; P3= -20° and P4= -30°) and during different levels of maximal voluntary contraction (MVC) (100%, 30%, 50%, 70%). Muscle activation of GM, GL, and tibialis anterior was also evaluated. ResultsThe results revealed a significant increase in passive stiffness within the paretic plantar flexor muscles under high tension during passive mobilization (p<0.05). Yet, during submaximal and maximal MVC, the paretic plantar flexors exhibited decreased active stiffness levels (p<0.05). A notable discrepancy was found between the stiffness of the GM and GL muscles, with the GM demonstrating greater stiffness from 0° of dorsiflexion in the SSG (p<0.05), and from 10° of dorsiflexion in the CNT (p<0.05). No significant difference in stiffness was observed between the GM and GL muscles during active conditions. ConclusionStroke affects the mechanical properties differently depending on the state of muscle activation. Notably, the distribution of stiffness among synergistic plantar flexor muscles varied in passive condition, while remaining consistent in active condition.

Diabetes disturbs functional adaptation of the remote myocardium after ischemia/reperfusion

Diabetes mellitus type 2 is associated with adverse clinical outcome after myocardial infarction. To better understand the underlying causes we here investigated sarcomere protein function and its calcium-dependent regulation in the non-ischemic remote myocardium (RM) of diabetic mice (db/db) after transient occlusion of the left anterior descending coronary artery. Before and 24 h after surgery db/db and non-diabetic db/+ underwent magnetic resonance imaging followed by histological and biochemical analyses of heart tissue. Intracellular calcium transients and sarcomere function were measured in isolated cardiomyocytes. Active and passive force generation was assessed in skinned fibers and papillary muscle preparations. Before ischemia and reperfusion (I/R), beat-to-beat calcium cycling was depressed in diabetic cardiomyocytes. Nevertheless, contractile function was preserved owing to increased myofilament calcium sensitivity and higher responsiveness of myocardial force production to β-adrenergic stimulation in db/db compared to db/+. In addition, protein kinase C activity was elevated in db/db hearts leading to strong phosphorylation of the titin PEVK region and increased titin-based tension of myofilaments. I/R impaired the function of whole hearts and RM sarcomeres in db/db to a larger extent than in non-diabetic db/+, and we identified several reasons. First, the amplitude and the kinetics of cardiomyocyte calcium transients were further reduced in the RM of db/db. Underlying causes involved altered expression of calcium regulatory proteins. Diabetes and I/R additively reduced phospholamban S16-phosphorylation by 80% (P < 000.1) leading to strong inhibition of the calcium ATPase SERCA2a. Second, titin stiffening was only observed in the RM of db/+, but not in the RM of db/db. Finally, db/db myofilament calcium sensitivity and force generation upon β-adrenergic stimulation were no longer enhanced over db/+ in the RM. The findings demonstrate that impaired cardiomyocyte calcium cycling of db/db hearts is compensated by increased myofilament calcium sensitivity and increased titin-based stiffness prior to I/R. In contrast, sarcomere function of the RM 24 h after I/R is poor because both these compensatory mechanisms fail and myocyte calcium handling is further depressed.

Adapting Mechanisms for In-Pipe Inspection Robots: A Review

In-pipe inspection robots have proven useful in examining the inside of pipes without affecting their structure, therefore, the interest in researching these robots has constantly increased over time. There are many different types of inspection robots, but the most commonly used are the wall pressed type. This paper proposes a review of the wall pressed type inspection robots in terms of adapting mechanisms. By adapting mechanism is meant a simple linkage or a combination of linkages, with an active or passive force generation system used to adapt the robot to variations in pipe diameter. The characteristics of the different adaptation mechanisms are compared and analyzed regarding the type of linkages used, how the pressure force on the pipe wall is obtained, and the possibility of ensuring the movement through inclined or vertical pipes with elbows and branches.

SUMOylation does not affect cardiac troponin I stability but alters indirectly the development of force in response to Ca2.

Post-translational modification of the myofilament protein troponin I by phosphorylation is known to trigger functional changes that support enhanced contraction and relaxation of the heart. We report for the first time that human troponin I can also be modified by SUMOylation at lysine 177. Functionally, TnI SUMOylation is not a factor in the development of passive and maximal force generation in response to calcium, however this modification seems to act indirectly by preventing SUMOylation of other myofilament proteins to alter calcium sensitivity and cooperativity of myofilaments. Utilising a novel, custom SUMO site-specific antibody that recognises only the SUMOylated form of troponin I, we verify that this modification occurs in human heart and that it is upregulated during disease.

Nicotinic-acid derivative BGP-15 improves diastolic function in a rabbit model of atherosclerotic cardiomyopathy.

The small molecule BGP-15 has been reported to alleviate symptoms of heart failure and improve muscle function in murine models. Here, we investigated the acute and chronic effects of BGP-15 in a rabbit model of atherosclerotic cardiomyopathy. Rabbits were maintained on standard chow (control) or atherogenic diet (hypercholesterolemic) for 16 weeks. BGP-15 was administered intravenously (once) or orally (for 16 weeks), to assess acute and chronic effects. Cardiac function was evaluated by echocardiography, endothelium-dependent vasorelaxation was assessed and key molecules in the protein kinase G (PKG) pathway were examined by enzyme-linked immunosorbent assay (ELISA) and western blot. Passive force generation was investigated in skinned cardiomyocytes. Both acute and chronic BGP-15 treatments improved the diastolic performance of the diseased heart. However, vasorelaxation and serum lipid markers were unaffected. Myocardial cyclic guanosine monophosphate (cGMP) levels were elevated in the BGP-15-treated group, along with preserved PKG activity and increased phospholamban Ser16-phosphorylation. PDE5 expression decreased in the BGP-15-treated group and PDE1 was inhibited. Cardiomyocyte passive tension reduced in BGP-15-treated rabbits, the ratio of titin N2BA/N2B isoforms increased and PKG-dependent N2B-titin phosphorylation elevated. BGP-15 treatment improves diastolic function, reduces cardiomyocyte stiffness and restores titin compliance in a rabbit model of atherosclerotic cardiomyopathy by increasing the activity of the cGMP-PKG pathway. As BGP-15 has been proven to be safe, it may be clinically useful in the treatment of diastolic dysfunction.

Modeling and Development of Passively Adaptive Assistive Tools for the Assembly of Press-Fit Components

Abstract This article discusses passive mechanical architectures for accuracy correction during assembly operations. A specific solution for passive force generation with thresholds is presented. Then, the kinematics of several rotational and translational mechanisms is presented. Afterwards, a case study is introduced and the design of a prototype is presented together with some tests performed on a spark plug assembly task.

Running economy - a comprehensive review for passive force generation.

Running economy is considered a major determinant of distance running performance. Enhancing the body’s ability for passive force generation could have a positive effect on running economy by minimizing the energy cost required for the propulsion of the body. Thus, the purpose of this comprehensive review was to provide a list of modifiable factors that promote this ability. The interest was focused on lower-limb stiffness, as it is a factor of great influence and at the same time can be modified with training and specific biomechanical adjustments. Although it appears that no clear instructions can be provided to athletes and coaches, it should be noted that careful consideration of the runners’ anthropometric, physiological, and biomechanical characteristics are necessary for optimal performance results.

Changes in shear wave propagation within skeletal muscle during active and passive force generation

Muscle force can be generated actively through changes in neural excitation, and passively through externally imposed changes in muscle length. Disease and injury can disrupt force generation, but it can be challenging to separate passive from active contributions to these changes. Ultrasound elastography is a promising tool for characterizing the mechanical properties of muscles and the forces that they generate. Most prior work using ultrasound elastography in muscle has focused on the group velocity of shear waves, which increases with increasing muscle force. Few studies have quantified the phase velocity, which depends on the viscoelastic properties of muscle. Since passive and active forces within muscle involve different structures for force transmission, we hypothesized that measures of phase velocity could detect changes in shear wave propagation during active and passive conditions that cannot be detected when considering only group velocity. We measured phase and group velocity in the human biceps brachii during active and passive force generation and quantified the differences in estimates of shear elasticity obtained from each of these measurements. We found that measures of group velocity consistently overestimate the shear elasticity of muscle. We used a Voigt model to characterize the phase velocity and found that the estimated time constant for the Voigt model provided a way to distinguish between passive and active force generation. Our results demonstrate that shear wave elastography can be used to distinguish between passive and active force generation when it is used to characterize the phase velocity of shear waves propagating in muscle.

Calcium Dependent Properties of Ig 80–83 of N2A Titin

Titin is a giant elastic protein responsible for passive force generation in muscles. In addition, numerous studies have implicated a role for titin in active muscle. Recent work on muscles from mdm mice, suggests that during muscle activation, the N2A region of titin binds to actin thereby increasing titin and active muscle stiffness. Atomic force microscopy (AFM) can be used to measure the elastic properties of a titin construct, specifically by unfolding and refolding of its constituent immunoglobulin (Ig) domains. We hypothesized that the Ig domains from the N2A region of titin (Ig 80–83) exhibit different elastic properties in the presence and absence of calcium. To test this hypothesis, we stretched a N2A‐like construct consisting of Ig 80–83 and a Halo‐tag domain at different pulling velocities, in the presence and absence of calcium. Our results suggest a non‐linear unfolding energy landscape for serially linked Ig 80–83 domains in the presence of calcium. We also found, while calcium increased the persistence length of unfolded Ig domains in the N2A‐like construct, its contour length did not change. Increase in persistence length indicates an increase in the stiffness of the N2A domain, which supports the hypothesis that titin stiffness increases in the presence of calcium. These results differ from previous studies without calcium and indicate unique properties of Ig domains specific to the N2A region of titin.Support or Funding InformationAPS IOSP Fellowship Awarded to B. Thompson, NSF IOS‐1451650 Awarded to J. MonroyThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Medial gastrocnemius and soleus muscle-tendon unit, fascicle, and tendon interaction during walking in children with cerebral palsy.

This study investigates the invivo function of the medial gastrocnemius and soleus muscle-tendon units (MTU), fascicles, and tendons during walking in children with cerebral palsy (CP) and an equinus gait pattern. Fourteen children with CP (9 males, 5 females; mean age 10y 6mo, standard deviation [SD] 2y 11mo; GMFCS level I=8, II=6), and 10 typically developing (6 males, 4females; mean age 10y, SD 2y 1mo) undertook full body 3D gait analysis and simultaneous B-mode ultrasound images of the medial gastrocnemius and soleus fascicles during level walking. Fascicle lengths were analysed using a semi-automated tracking algorithm and MTUs using OpenSim. Statistical parametric mapping (two-sample t-test) was used to compare differences between groups (p<0.05). In the CP group medial gastrocnemius fascicles lengthened during mid-stance gait and remained longer into late-stance compared to the typically developing group (p<0.001). CP medial gastrocnemius fascicles shortened less during stance (1.16mm [SD 1.47mm]) compared to the typically developing group (4.48mm [SD 1.94mm], p<0.001). In the CP group the medial gastrocnemius and soleus MTU and tendon were longer during early- and mid-stance (p<0.001). Ankle power during push-off (p=0.015) and positive work (p<0.002) and net work (p<0.001) were significantly lower in the CP group. Eccentric action of the CP medial gastrocnemius muscle fascicles during mid-stance walking is consistent with reduced volume and neuromuscular control of impaired muscle. Reduced ankle push-off power and positive work in the children with CP may be attributed to reduced active medial gastrocnemius fascicle shortening. These findings suggest a reliance on passive force generation for forward propulsion during equinus gait.

Posttranslational Arginylation Regulates Striated Muscle Function.

In this article, we propose the hypothesis that the posttranslational arginylation of proteins, a process catalyzed by the enzyme arginyl-tRNA-transferase, regulates active and passive force generation in striated muscles. Specifically, we propose that proteins essential for muscle contraction and force production are regulated by arginylation, including myosin heavy chain, troponin, actin, and titin filaments.

Prolonged controlled mechanical ventilation in humans triggers myofibrillar contractile dysfunction and myofilament protein loss in the diaphragm

BackgroundProlonged controlled mechanical ventilation (CMV) in humans and experimental animals results in diaphragm fibre atrophy and injury. In animals, prolonged CMV also triggers significant declines in diaphragm myofibril contractility. In...

Reduced passive force in skeletal muscles lacking protein arginylation.

Arginylation is a posttranslational modification that plays a global role in mammals. Mice lacking the enzyme arginyltransferase in skeletal muscles exhibit reduced contractile forces that have been linked to a reduction in myosin cross-bridge formation. The role of arginylation in passive skeletal myofibril forces has never been investigated. In this study, we used single sarcomere and myofibril measurements and observed that lack of arginylation leads to a pronounced reduction in passive forces in skeletal muscles. Mass spectrometry indicated that skeletal muscle titin, the protein primarily linked to passive force generation, is arginylated on five sites located within the A band, an important area for protein-protein interactions. We propose a mechanism for passive force regulation by arginylation through modulation of protein-protein binding between the titin molecule and the thick filament. Key points are as follows: 1) active and passive forces were decreased in myofibrils and single sarcomeres isolated from muscles lacking arginyl-tRNA-protein transferase (ATE1). 2) Mass spectrometry revealed five sites for arginylation within titin molecules. All sites are located within the A-band portion of titin, an important region for protein-protein interactions. 3) Our data suggest that arginylation of titin is required for proper passive force development in skeletal muscles.

Exploiting elasticity: Modeling the influence of neural control on mechanics and energetics of ankle muscle–tendons during human hopping

We present a simplified Hill-type model of the human triceps surae-Achilles tendon complex working on a gravitational–inertial load during cyclic contractions (i.e. vertical hopping). Our goal was to determine the role that neural control plays in governing muscle, or contractile element (CE), and tendon, or series elastic element (SEE), mechanics and energetics within a compliant muscle–tendon unit (MTU). We constructed a 2D parameter space consisting of many combinations of stimulation frequency and magnitude (i.e. neural control strategies). We compared the performance of each control strategy by evaluating peak force and average positive mechanical power output for the system (MTU) and its respective components (CE, SEE), force–length (F–L) and –velocity (F–V) operating point of the CE during active force production, average metabolic rate for the CE, and both MTU and CE apparent efficiency. Our results suggest that frequency of stimulation plays a primary role in governing whole-MTU mechanics. These include the phasing of both activation and peak force relative to minimum MTU length, average positive power, and apparent efficiency. Stimulation amplitude was primarily responsible for governing average metabolic rate and within MTU mechanics, including peak force generation and elastic energy storage and return in the SEE. Frequency and amplitude of stimulation both played integral roles in determining CE F–L operating point, with both higher frequency and amplitude generally corresponding to lower CE strains, reduced injury risk, and elimination of the need for passive force generation in the CE parallel elastic element (PEE).

Recessive and dominant mutations in COL12A1 cause a novel EDS/myopathy overlap syndrome in humans and mice

Collagen VI-related myopathies are disorders of connective tissue presenting with an overlap phenotype combining clinical involvement from the muscle and from the connective tissue. Not all patients displaying related overlap phenotypes between muscle and connective tissue have mutations in collagen VI. Here, we report a homozygous recessive loss of function mutation and a de novo dominant mutation in collagen XII (COL12A1) as underlying a novel overlap syndrome involving muscle and connective tissue. Two siblings homozygous for a loss of function mutation showed widespread joint hyperlaxity combined with weakness precluding independent ambulation, while the patient with the de novo missense mutation was more mildly affected, showing improvement including the acquisition of walking. A mouse model with inactivation of the Col12a1 gene showed decreased grip strength, a delay in fiber-type transition and a deficiency in passive force generation while the muscle seems more resistant to eccentric contraction induced force drop, indicating a role for a matrix-based passive force-transducing elastic element in the generation of the weakness. This new muscle connective tissue overlap syndrome expands on the emerging importance of the muscle extracellular matrix in the pathogenesis of muscle disease.

Abstract 253: Modeling of Pathologic Hypertophy with Cardiac Microtissues

Introduction: Pathological myocyte hypertrophy and fibroblast activation are key features of myocardial remodeling in hypertension and heart failure. Crosstalk between myocytes and fibroblasts contributes to the structural, mechanical, and electrical remodeling involved in various forms of heart failure. Replicating these responses in traditional 2D cell culture conditions has proven difficult. In this study, we utilized a novel platform to examine the cellular crosstalk and biological processes that underlie functional and structural changes in the 3D engineered tissues when exposed to pathological factors. We hypothesized that engineered cardiac tissues can report structural and functional responses to pathologic biochemical stimuli. Methods: These studies employ microfabricated polydimethylsiloxane (PDMS) templates to engineer arrays of 3D cardiac microtissues (CMT). Cantilevers within templates provide physiologically-relevant biomechanical loading to the CMTs, promote the appropriate organization of neonatal rat cardiac myocytes and fibroblasts, and report active and passive force generation in real time. Data was collected using fluorescent and confocal microscopy. Results: CMTs in a controlled mechanical environment demonstrate mechanical and structural changes within 24 hours of exposure to a cocktail of factors involved in maladaptive remodeling, including Transforming Growth Factor-β, Endothelin-1, and Angiotensin II. Analysis of 40 microtissues revealed that the percent change in passive tension was 45% higher (16.4 ± 10.3% vs. 61.1 ± 11.8%, p&lt;0.01) and in active tension 170% higher (24.9 ± 9.5% vs.196.1 ± 76.0%, p&lt;0.001) in treated CMTs compared to untreated CMTs. The percentage change in cross-sectional area of CMTs treated with pathological factors was 35% higher (-24.5 ± 15.6% vs.11.6 ± 7.9%, p&lt;0.001) than untreated samples. Conclusions: These findings demonstrate that the CMT model can be used to study and dissect the dynamics of pathological hypertrophy. Ongoing experiments are examining the distinct contributions of the pathologic growth factors, the relative contributions of fibroblasts and cardiomyocytes to the pathologic growth response, and the interactions between biomechanical and humoral inputs.

Deformations Within Moving Kinetochores Reveal Different Sites of Active and Passive Force Generation

Kinetochores mediate chromosome segregation at mitosis. They are thought to contain both active, force-producing and passive, frictional interfaces with microtubules whose relative locations have been unclear. We inferred mechanical deformation within single kinetochores during metaphase oscillations by measuring average separations between fluorescently labeled kinetochore subunits in living cells undergoing mitosis. Inter-subunit distances were shorter in kinetochores moving toward poles than in those moving away. Inter-subunit separation decreased abruptly when kinetochores switched to poleward movement and decreased further when pulling force increased, suggesting that active force generation during poleward movement compresses kinetochores. The data revealed an active force-generating interface within kinetochores and a separate passive frictional interface located at least 20 nanometers away poleward. Together, these interfaces allow persistent attachment with intermittent active force generation.

Titin and diaphragm dysfunction in mechanically ventilated rats

PurposeDiaphragm weakness induced by mechanical ventilation may contribute to difficult weaning from the ventilator. For optimal force generation the muscle proteins myosin and titin are indispensable. The present study investigated if myosin and titin loss or dysfunction are involved in mechanical ventilation-induced diaphragm weakness.MethodsMale Wistar rats were either assigned to a control group (n = 10) or submitted to 18 h of mechanical ventilation (MV, n = 10). At the end of the experiment, diaphragm and soleus muscle were excised for functional and biochemical analysis.ResultsMaximal specific active force generation of muscle fibers isolated from the diaphragm of MV rats was lower than controls (128 ± 9 vs. 165 ± 13 mN/mm2, p = 0.02) and was accompanied by a proportional reduction of myosin heavy chain concentration in these fibers. Passive force generation upon stretch was significantly reduced in diaphragm fibers from MV rats by ca. 35%. Yet, titin content was not significantly different between control and MV diaphragm. In vitro pre-incubation with phosphatase-1 decreased passive force generation upon stretch in diaphragm fibers from control, but not from MV rats. Mechanical ventilation did not affect active or passive force generation in the soleus muscle.ConclusionsMechanical ventilation leads to impaired diaphragm fiber active force-generating capacity and passive force generation upon stretch. Loss of myosin contributes to reduced active force generation, whereas reduced passive force generation is likely to result from a decreased phosphorylation status of titin. These impairments were not discernable in the soleus muscle of 18 h mechanically ventilated rats.Electronic supplementary materialThe online version of this article (doi:10.1007/s00134-012-2504-5) contains supplementary material, which is available to authorized users.

Deformations Within Moving Kinetochores Reveal Different Sites of Active and Passive Force Generation

Deformations Within Moving Kinetochores Reveal Different Sites of Active and Passive Force Generation

The cytoskeleton and the cellular transduction of mechanical strain in the heart: a special issue

There is a fundamental requirement for all cells to communicate and process information with regard to their surroundings and this is accomplished by vast array of signals that, at its basis, are all based on four principal physical processes: electricity, force, chemical reaction, and light. Mechanical strain sensing in muscle is unique in that forces are both generated by the muscle cells itself (“insideout” pathway) as well as acted upon these cells from the exterior (“outside-in” pathway). These mechanisms are critically important in the heart to alter its form and function and meet varied hemodynamic demands. Accordingly, this special issue of Pfluger s Archiv European Journal of Physiology is focused on the cellular transduction of mechanical strain in the heart. The issue is composed of invited reviews written by world leaders in their respective fields of research. A well-known example of acute strain regulation in cardiac tissue is the Frank–Starling Law of the heart [9]. Interestingly, although this basic beat-to-beat regulatory mechanism has been appreciated for over a century, the cellular mechanisms that underlie this strain transduction system have only been identified in recent decades as being caused by (a) an immediate change in cardiac cell contractility that is secondary to changes in contractile protein Ca sensitivity [11, 12], and (b) a slower change in cardiac cell contractility that develops over the course of several beats that is secondary to changes in intracellular Ca homeostasis [1, 17]. However, the molecular mechanisms and cellular signal transduction processes that underlie these cellular regulatory systems are still under intense investigation [9]. In this issue, this area of research is reviewed by contributions from the groups of Campbell [5], Cazorla [6], Cingolani [7], Peter Kohl [2], Landesberg [23], and McDonald [16]. Cardiac muscle cells are dynamic; increased mechanical load induces a hypertrophic response, while reduced load elicits the reverse response [21]. The cellular signal transduction processes responsible for this tight, long term, regulatory system that leads to remodeling of the sarcomeric architecture in the cardiac muscle cell are varied and complex. In addition, the cardiac cell is integrated into the extracellular scaffolding and force transmission system formed by the extracellular matrix, which itself is a dynamic structure that is subject to regulation and remodeling. This rapidly expanding area of research is reviewed in this special issue by contributions from the groups of Borg [3], Kresh [13], Parker [15], and Russell [8]. Among the several cytoskeletal protein structures that play a role in the cellular transduction system, the giant sarcomeric protein titin (the “fourth filament”) is particularly intriguing. Titin’s role as the predominant contributor to passive force generation within the physiological range in striated muscle is now well established [14]. However, recent observations indicate a far greater role of this giant protein in a vast array of cellular functions, including the response to cellular strain in myofilament length dependent activation, protein turnover, hypertrophic responses, and modulation of cardiac function in cardiac pathologies such P. P. de Tombe (*) Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Ave, Maywood, IL 60153-5500, USA e-mail: pdetombe@lumc.edu