scholarly journals Analysis of Increasing and Decreasing Isometric Finger Force Generation and the Possible Role of the Corticospinal System in This Process

Motor Control ◽  
2013 ◽  
Vol 17 (3) ◽  
pp. 221-237 ◽  
Author(s):  
Sheng Li
Keyword(s):  
Force Generation ◽  
Finger Force ◽  
Corticospinal System

Free radicals in hypoxic rat diaphragm contractility: no role for xanthine oxidase

2001 ◽  
Vol 281 (6) ◽  
pp. L1402-L1412 ◽  
Author(s):  
Leo M. A. Heunks ◽  
Herwin A. Machiels ◽  
Ronney de Abreu ◽  
Xiao Ping Zhu ◽  
Henricus F. M. van der Heijden ◽  
...  
Keyword(s):  
Free Radicals ◽  
Xanthine Oxidase ◽  
Power Output ◽  
Harmful Effect ◽  
Force Generation ◽  
Muscle Performance ◽  
Rat Diaphragm ◽  
Shortening Velocity ◽  
Contraction Pattern

Recent evidence indicates that hypoxia enhances the generation of oxidants. Little is known about the role of free radicals in contractility of the rat diaphragm during hypoxia. We hypothesized that antioxidants improve contractility of the hypoxic rat diaphragm and that xanthine oxidase (XO) is an important source of free radicals in the hypoxic diaphragm. The effects of N-acetylcysteine (NAC; 18 mM), Tiron (10 mM), and the XO inhibitor allopurinol (250 μM) were studied on isometric and isotonic force generation during hypoxia (Po 2 ∼7 kPa). NAC and Tiron decreased maximal force generation, slowed the shortening velocity, and decreased the power output. Fatigue rate was decreased in the presence of either NAC or Tiron. Allopurinol did not alter the contractility or fatigability of the diaphragm. During hyperoxia (Po 2 ∼85 kPa), neither NAC nor allopurinol affected the contractility or fatigability of the diaphragm. Thus free radicals play a significant role in diaphragm contractility during hypoxia. Whether antioxidants exert a beneficial or harmful effect on muscle performance depends on the contraction pattern of the muscle. Free radicals generated by XO do not play a role in diaphragm contractility during either hypoxia or hyperoxia.

scholarly journals Thrust Force Generated by Heaving Motion of a Plate: The Role of Vortex-Induced Force

2021 ◽  
Author(s):  
Kazuo Matsuuchi
Keyword(s):  
Vortex Shedding ◽  
Thrust Force ◽  
Unsteady Motion ◽  
Force Generation ◽  
Thrust Coefficient ◽  
Momentum Change ◽  
Vortex Element ◽  
Motion Characteristics ◽  
Vortex Systems

To understand the force acting on birds, insects, and fish, we take heaving motion as a simple example. This motion might deviate from the real one. However, since the mechanism of force generation is the vortex shedding due to the motion of an object, the heaving motion is important for understanding the force generated by unsteady motion. The vortices released from the object are closely related to the motion characteristics. To understand the force acting on an object, information about momentum change is necessary. However, in vortex systems, it is impossible to estimate the usual momentum. Instead of the momentum, the “virtual momentum,” or the impulse, is needed to generate the force. For calculating the virtual momentum, we traced all vortices over a whole period, which was carried out by using the vortex-element method. The force was then calculated based on the information on the vortices. We derived the thrust coefficient as a function of the ratio of the heaving to travelling velocity.

scholarly journals Phosphate has dual roles in cross-bridge kinetics in rabbit psoas single myofibrils

2021 ◽  
Vol 153 (3) ◽  
Author(s):  
Masataka Kawai ◽  
Robert Stehle ◽  
Gabriele Pfitzer ◽  
Bogdan Iorga
Keyword(s):  
Rate Constants ◽  
Striated Muscle ◽  
Intrinsic Rate ◽  
Isometric Tension ◽  
Force Generation ◽  
Skinned Fibers ◽  
Sinusoidal Analysis ◽  
Rabbit Psoas ◽  
Cross Bridge

In this study, we aimed to study the role of inorganic phosphate (Pi) in the production of oscillatory work and cross-bridge (CB) kinetics of striated muscle. We applied small-amplitude sinusoidal length oscillations to rabbit psoas single myofibrils and muscle fibers, and the resulting force responses were analyzed during maximal Ca2+ activation (pCa 4.65) at 15°C. Three exponential processes, A, B, and C, were identified from the tension transients, which were studied as functions of Pi concentration ([Pi]). In myofibrils, we found that process C, corresponding to phase 2 of step analysis during isometric contraction, is almost a perfect single exponential function compared with skinned fibers, which exhibit distributed rate constants, as described previously. The [Pi] dependence of the apparent rate constants 2πb and 2πc, and that of isometric tension, was studied to characterize the force generation and Pi release steps in the CB cycle, as well as the inhibitory effect of Pi. In contrast to skinned fibers, Pi does not accumulate in the core of myofibrils, allowing sinusoidal analysis to be performed nearly at [Pi] = 0. Process B disappeared as [Pi] approached 0 mM in myofibrils, indicating the significance of the role of Pi rebinding to CBs in the production of oscillatory work (process B). Our results also suggest that Pi competitively inhibits ATP binding to CBs, with an inhibitory dissociation constant of ∼2.6 mM. Finally, we found that the sinusoidal waveform of tension is mostly distorted by second harmonics and that this distortion is closely correlated with production of oscillatory work, indicating that the mechanism of generating force is intrinsically nonlinear. A nonlinear force generation mechanism suggests that the length-dependent intrinsic rate constant is asymmetric upon stretch and release and that there may be a ratchet mechanism involved in the CB cycle.

Muscle Force Generation and Age: The Role of Sex Hormones

1993 ◽  
pp. 129-141 ◽  
Author(s):  
S. K. Phillips ◽  
J. L. Rowbury ◽  
S. A. Bruce ◽  
R. C. Woledge
Keyword(s):  
Sex Hormones ◽  
Muscle Force ◽  
Force Generation

scholarly journals Molecular mechanisms of genetic damages of the myocardium in cardiomyopathy

2010 ◽  
Vol 56 (3) ◽  
pp. 319-328
Author(s):  
A.G. Hasanov ◽  
T.V. Bershova ◽  
E.N. Basargina ◽  
M.I. Bakanov
Keyword(s):  
Extracellular Matrix ◽  
Molecular Mechanisms ◽  
Genetic Factors ◽  
Cytoskeletal Proteins ◽  
Matrix Proteins ◽  
Force Generation ◽  
Cardiac Cell ◽  
Cell Dysfunction ◽  
Thick Filaments

The review highlighted problems of reorganization of myocardical contractile and cytoskeletal proteins in cardiomyopathy (CM). The role of the genetic factors coding contractile proteins, proteins of thin and thick filaments, and also extracellular matrix proteins in processes of formation and development of hypertrophic (HCM) and dilated (DCM) cardiomyopathy are analyzed. The mechanisms responsible for the changes in cardiac proteins on regulation involved into force generation, its transfer, recycling ATP, impairments in transmembranal signals, that finally lead to cardiac cell dysfunction determining various manifestations of CM are considered.

The Nature of Finger Enslaving: New Results and Their Implications

Motor Control ◽  
2021 ◽  
Vol 25 (4) ◽  
pp. 680-703
Author(s):  
Valters Abolins ◽  
Mark L. Latash
Keyword(s):  
Motor Control ◽  
Connective Tissue ◽  
Finger Force ◽  
Neural Factors ◽  
Cortical Excitation

We present a review on the phenomenon of unintentional finger action seen when other fingers of the hand act intentionally. This phenomenon (enslaving) has been viewed as a consequence of both peripheral (e.g., connective tissue links and multifinger muscles) and neural (e.g., projections of corticospinal pathways) factors. Recent studies have shown relatively large and fast drifts in enslaving toward higher magnitudes, which are not perceived by subjects. These and other results emphasize the defining role of neural factors in enslaving. We analyze enslaving within the framework of the theory of motor control with spatial referent coordinates. This analysis suggests that unintentional finger force changes result from drifts of referent coordinates, possibly reflecting the spread of cortical excitation.

Clot-On-A-Chip: A Microfluidic Device To Study Platelet Aggregation and Contractility Under Shear

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 2363-2363 ◽  
Author(s):  
Lucas Ting ◽  
Shirin Feghhi ◽  
Ari Karchin ◽  
Wes Tooley ◽  
Nathan J White ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Board Of Directors ◽  
Microfluidic Device ◽  
Platelet Function ◽  
Research Funding ◽  
Force Generation ◽  
Advisory Committees ◽  
Equity Ownership ◽  
Contractile Forces

Abstract Introduction In primary hemostasis, platelets adhere, activate, and aggregate at the wall of an injured vessel to form a hemostatic plug for the cessation of bleeding. After activation, platelets generate myosin-driven contractile forces to compact the size of the plug in order to reduce the space between platelets and prevent their disaggregation. Hemodynamic shear can be a major effector of platelet function in hemostasis, but its effect on the ability of platelets to produce contractile forces is an open question. Studying the dynamics of platelet aggregation and platelet force generation under hemodynamic shear can provide important insights into hemostasis and thrombosis. Method We have developed a microfluidic device that uses microscale blocks to induce platelet aggregation and microscale posts to measure platelet forces in a hemostatic plug. Whole human blood in heparin or citrate is pumped through a microfabricated chip containing microchannels with arrays of blocks and posts arranged along the bottom of a microchannel (Fig. 1). The surface of the blocks and posts are pre-coated with von Willebrand factor and type I collagen to allow for platelet adhesion. As blood is passes over a block, its rectangular shape induces a high shear rate that causes platelets to aggregate on its surface. A flexible micropost is situated behind each block. As platelets aggregate between the block and post, their contractile forces causes the post to bend toward the block. The deflection of the post is recorded under fluorescence microscopy and analyzed using quantitative image analysis of the videos. Since a microscale post bends like a cantilever beam, its deflection can be used to quantify the forces of platelets. Results Blebbistatin, a myosin inhibitor, was used to confirm that deflection of the posts by the platelets in heparinized blood was due to myosin activity. When blood was incubated with 2-MeSAMP, a P2Y12 antagonist, platelets were able to aggregate, but their ability to generate contractile forces was substantially reduced. This finding indicates that ADP activation is needed for platelet contractility under shear. The rate of hemodynamic shear was found to influence platelet function, for the rate of platelet aggregation and force generation were found to increase for blood sheared from 2000 to 12,000 s-1. Moreover, platelet aggregation and contractile forces were reduced when glycoprotein Ib-V-IX complex and integrin αIIbβ3 were inhibited with antibody AK2 and antibody fragment c7E3 Fab, respectively. When citrated blood was incubated with tissue plasminogen activator, platelets aggregate and produced contractile forces that increased steadily within the first ten minutes, but then the forces began to subside. Conclusions Our device can be used to study the role of hemodynamic shear in platelet function and gives insights into the role of platelet forces during hemostasis. Its microscale dimensions also allow us the study the biomechanics involved in the formation of a hemostatic plug during its early stages of growth and stability. Disclosures: White: Vidacare Corp: Honoraria; Stasys Medical Corp: Consultancy, Equity Ownership, Membership on an entity’s Board of Directors or advisory committees, Patents & Royalties; NIH: Research Funding; Coulter Foundation: Research Funding; Washington State Life Sciences Discovery Fund: Research Funding. Sniadecki:Stasys Medical Corporation: Equity Ownership, Founder Other, Membership on an entity’s Board of Directors or advisory committees.

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