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The Journal of Neuroscience : the... Jul 2020Control of the body requires inhibiting complex actions, involving contracting and relaxing muscles. However, little is known of how voluntary commands to relax a muscle...
Control of the body requires inhibiting complex actions, involving contracting and relaxing muscles. However, little is known of how voluntary commands to relax a muscle are cancelled. Action inhibition causes both suppression of muscle activity and the transient excitation of antagonist muscles, the latter being termed active breaking. We hypothesized that active breaking is present when stopping muscle relaxations. Stop signal experiments were used to compare the mechanisms of active breaking for muscle relaxations and contractions in male and female human participants. In experiments 1 and 2, go signals were presented that required participants to contract or relax their biceps or triceps muscle. Infrequent Stop signals occurred after fixed delays (0-500 ms), requiring that participants cancelled go commands. In experiment 3, participants increased (contract) or decreased (relax) an existing isometric finger abduction depending on the go signal, and cancelled these force changes whenever Stop signals occurred (dynamically adjusted delay). We found that muscle relaxations were stopped rapidly, met predictions of existing race models, and had Stop signal reaction times that correlated with those observed during the stopping of muscle contractions, suggesting shared control mechanisms. However, stopped relaxations were preceded by transient increases in electromyography (EMG), while stopped contractions were preceded by decreases in EMG, suggesting a later divergence of control. Muscle state-specific active breaking occurred simultaneously across muscles, consistent with a central origin. Our results indicate that the later stages of action inhibition involve separate excitatory and inhibitory pathways, which act automatically to cancel complex body movements. The mechanisms of how muscle relaxations are cancelled are poorly understood. We showed in three experiments involving multiple effectors that stopping muscle relaxations involves transient bursts of EMG activity, which resemble cocontraction and have onsets that correlate with Stop signal reaction time. Comparison with the stopping of matched muscle contractions showed that active breaking was muscle state specific, being positive for relaxations and negative for contractions. The two processes were also observed to co-occur in agonist-antagonist pairs, suggesting separate pathways. The rapid, automatic activation of both pathways may explain how complex actions can be stopped at any stage of their execution.
Topics: Adult; Electromyography; Female; Fingers; Hamstring Muscles; Humans; Isometric Contraction; Male; Movement; Muscle Contraction; Muscle Relaxation; Muscle, Skeletal; Reaction Time
PubMed: 32611708
DOI: 10.1523/JNEUROSCI.0002-20.2020 -
Computers in Biology and Medicine Jun 2022This study develops a new hybrid active contraction model for myocardial dynamics abstracted from sarcomere by combining the phenomenologically active-stress based Hill...
This study develops a new hybrid active contraction model for myocardial dynamics abstracted from sarcomere by combining the phenomenologically active-stress based Hill model and the micro-structurally motivated active strain approach. This new model consists of a passive branch and a parallel active branch that consists of a serial passive element for active tension transmission and a contractile unit for active tension development. This rheology represents an additive decomposition of the total stress into a passive and active response. The active stress is formulated following the active strain approach based on the sliding filament theory by multiplicatively decomposing the stretch of the contractile element into a fictitious and an active part. The length-dependence and force-velocity are further incorporated in the active strain. We estimate the passive stiffness of the serial passive element using literature data, which is 250 kPa, then the active stress is computed from the serial passive element in the active branch because of its force transmission structure. This one-dimensional contraction model is further generalized to three dimensions for modelling myocardial dynamics. Our results demonstrate that the proposed active contraction model has a high descriptive capability for various experiments, including both isometric and isotonic contraction compared to existing active strain approaches. We also show that it can simulate physiologically accurate cardiac dynamics in humans. The excellent agreement with experimental data and a local sensitivity study highlight the importance of length-dependence and force-velocity in the active strain approach. Our results further show that there exists a tight interaction between the length-dependence and force-velocity relationships. This new hybrid model serves as a step forward in personalized cardiac modelling using an active-strain based contraction model and has the potential to understand the multi-scale coupling in active contraction according to the sliding filament theory.
Topics: Elasticity; Humans; Muscle Contraction; Myocardial Contraction; Myocardium; Sarcomeres
PubMed: 35405401
DOI: 10.1016/j.compbiomed.2022.105417 -
Scientific Reports Oct 2023The skeletal muscle contraction is determined by cross-bridge formation between the myosin heads and the actin active sites. When the muscle contracts, it shortens,...
The skeletal muscle contraction is determined by cross-bridge formation between the myosin heads and the actin active sites. When the muscle contracts, it shortens, increasing its longitudinal shear elastic modulus ([Formula: see text]). Structurally, skeletal muscle can be considered analogous to the molecular receptors that form receptor-ligand complexes and exhibit specific ligand-binding dynamics. In this context, this work aims to apply elastography and the ligand-binding framework to approach the possible intrinsic mechanisms behind muscle synergism. Based on the short-range stiffness principle and the acoustic-elasticity theory, we define the coefficient [Formula: see text], which is directly related to the fraction saturation of molecular receptors and links the relative longitudinal deformation of the muscle to its [Formula: see text]. We show that such a coefficient can be obtained directly from [Formula: see text] estimates, thus calculating it for the biceps brachii, brachioradialis, and brachialis muscles during isometric elbow flexion torque (τ) ramps. The resulting [Formula: see text] curves were analyzed by conventional characterization methods of receptor-ligand systems to study the dynamical behavior of each muscle. The results showed that, depending on muscle, [Formula: see text] exhibits typical ligand-binding dynamics during joint torque production. Therefore, the above indicates that these different behaviors describe the longitudinal shortening pattern of each muscle during load sharing. As a plausible interpretation, we suggested that this could be related to the binding kinetics of the cross-bridges during their synergistic action as torque increases. Likewise, it shows that elastography could be useful to assess contractile processes at different scales related to the change in the mechanical properties of skeletal muscle.
Topics: Elasticity Imaging Techniques; Ligands; Muscle, Skeletal; Muscle Contraction; Elbow Joint; Isometric Contraction
PubMed: 37880279
DOI: 10.1038/s41598-023-45037-y -
Journal of Biomedicine & Biotechnology 2010
Topics: Animals; Humans; Muscle Contraction; Muscles
PubMed: 20798778
DOI: 10.1155/2010/780417 -
International Biomechanics Dec 2023Clinicians seek an accurate method to assess muscle contractility during activities to better guide treatment. We investigated application of a conductive electroactive...
Clinicians seek an accurate method to assess muscle contractility during activities to better guide treatment. We investigated application of a conductive electroactive polymer sensor as a novel wearable surface mechanomyography (sMMG) sensor for quantifying muscle contractility. The radial displacement of a muscle during a contraction is detected by the physically stretched dielectric elastomer component of the sMMG sensor which quantifies the changes in capacitance. The duration of muscle activation times for quadriceps, hamstrings, and gastrocnemius muscles demonstrated strong correlation between sMMG and EMG during a parallel squat activity and isometric contractions. A moderate to strong correlation was demonstrated between the sMMG isometric muscle activation times and force output times from a dynamometer. The potential wearable application of an electroactive polymer sensor to measure muscle contraction time is supported.
Topics: Electromyography; Polymers; Muscle Contraction; Muscle, Skeletal; Isometric Contraction
PubMed: 38419418
DOI: 10.1080/23335432.2024.2319068 -
Journal of Applied Physiology... May 1999The sliding filament and cross-bridge theories of muscle contraction provide discrete predictions of the tetanic force-length relationship of skeletal muscle that have... (Review)
Review
The sliding filament and cross-bridge theories of muscle contraction provide discrete predictions of the tetanic force-length relationship of skeletal muscle that have been tested experimentally. The active force generated by a maximally activated single fiber (with sarcomere length control) is maximal when the filament overlap is optimized and is proportionally decreased when overlap is diminished. The force-length relationship is a static property of skeletal muscle and, therefore, it does not predict the consequences of dynamic contractions. Changes in sarcomere length during muscle contraction result in modulation of the active force that is not necessarily predicted by the cross-bridge theory. The results of in vivo studies of the force-length relationship suggest that muscles that operate on the ascending limb of the force-length relationship typically function in stretch-shortening cycle contractions, and muscles that operate on the descending limb typically function in shorten-stretch cycle contractions. The joint moments produced by a muscle depend on the moment arm and the sarcomere length of the muscle. Moment arm magnitude also affects the excursion (length change) of a muscle for a given change in joint angle, and the number of sarcomeres arranged in series within a muscle fiber determines the sarcomere length change associated with a given excursion.
Topics: Animals; Humans; Muscle Contraction; Muscle, Skeletal
PubMed: 10233103
DOI: 10.1152/jappl.1999.86.5.1445 -
Nutrients Aug 2019Exercise has beneficial effects on our health by stimulating metabolic activation of skeletal muscle contraction. Caffeine is a powerful metabolic stimulant in the...
Exercise has beneficial effects on our health by stimulating metabolic activation of skeletal muscle contraction. Caffeine is a powerful metabolic stimulant in the skeletal muscle that has ergogenic effects, including enhanced muscle power output and endurance capacity. In the present study, we aim to characterize the metabolic signatures of contracting muscles with or without caffeine stimulation using liquid chromatography-mass spectrometry and capillary electrophoresis coupled to mass spectrometry. Isolated rat epitrochlearis muscle was incubated in the presence or absence or of 3 mM caffeine for 30 min. Electrical stimulation (ES) was used to induce tetanic contractions during the final 10 min of incubation. Principal component analysis and hierarchical clustering analysis detected 184 distinct metabolites across three experimental groups-basal, ES, and ES with caffeine (ES + C). Significance Analysis of Microarray identified a total of 50 metabolites with significant changes in expression, and 23 metabolites significantly changed between the ES and ES + C groups. Changes were observed in metabolite levels of various metabolic pathways, including the pentose phosphate, nucleotide synthesis, β-oxidation, tricarboxylic acid cycle, and amino acid metabolism. In particular, D-ribose 5-phosphate, IMP, O-acetylcarnitine, butyrylcarnitine, L-leucine, L-valine, and L-aspartate levels were higher in the ES + C group than in the ES group. These metabolic alterations induced by caffeine suggest that caffeine accelerates contraction-induced metabolic activations, thereby contributing to muscle endurance performance and exercise benefits to our health.
Topics: Animals; Caffeine; Electric Stimulation; Male; Metabolomics; Muscle Contraction; Muscle, Skeletal; Rats; Rats, Sprague-Dawley
PubMed: 31394740
DOI: 10.3390/nu11081819 -
PLoS Computational Biology Jun 2023In vitro studies using isolated or skinned muscle fibers suggest that the sigmoidal relationship between the intracellular calcium concentration and force production may...
In vitro studies using isolated or skinned muscle fibers suggest that the sigmoidal relationship between the intracellular calcium concentration and force production may depend upon muscle type and activity. The goal of this study was to investigate whether and how the calcium-force relationship changes during force production under physiological conditions of muscle excitation and length in fast skeletal muscles. A computational framework was developed to identify the dynamic variation in the calcium-force relationship during force generation over a full physiological range of stimulation frequencies and muscle lengths in cat gastrocnemius muscles. In contrast to the situation in slow muscles such as the soleus, the calcium concentration for the half-maximal force needed to drift rightward to reproduce the progressive force decline, or sag behavior, observed during unfused isometric contractions at the intermediate length under low-frequency stimulation (i.e., 20 Hz). The slope at the calcium concentration for the half-maximal force was required to drift upward for force enhancement during unfused isometric contractions at the intermediate length under high-frequency stimulation (i.e., 40 Hz). The slope variation in the calcium-force relationship played a crucial role in shaping sag behavior across different muscle lengths. The muscle model with dynamic variations in the calcium-force relationship also accounted for the length-force and velocity-force properties measured under full excitation. These results imply that the calcium sensitivity and cooperativity of force-inducing crossbridge formation between actin and myosin filaments may be operationally altered in accordance with the mode of neural excitation and muscle movement in intact fast muscles.
Topics: Calcium; Muscle Contraction; Muscle, Skeletal; Muscle Fibers, Skeletal; Isometric Contraction
PubMed: 37289805
DOI: 10.1371/journal.pcbi.1011178 -
Journal of Applied Physiology... Aug 2022The purpose was to investigate whether postactivation potentiation (PAP) mitigates power (i.e., torque × angular velocity) loss during dynamic fatiguing contractions...
The purpose was to investigate whether postactivation potentiation (PAP) mitigates power (i.e., torque × angular velocity) loss during dynamic fatiguing contractions and subsequent recovery by enhancing either muscle torque or angular velocity in human plantar flexors. In 12 participants, electrically stimulated (1, 10, and 50 Hz) dynamic contractions were done during a voluntary isotonic fatiguing protocol until a 75% loss in voluntary peak power, and throughout 30 min of recovery. At the initial portion of fatigue (20% decrease), power responses of evoked low frequencies (1 and 10 Hz) were enhanced due to PAP (156% and 137%, respectively, < 0.001), whereas voluntary maximal efforts were depressed due to fatiguing mechanisms. Following the fatiguing task, prolonged low-frequency force depression (PLFFD) was evident by reduced 10:50 Hz peak power ratios (21%-24%) from 3 min onward during the 30-min recovery ( < 0.005). Inducing PAP with maximal voluntary dynamic contractions during PLFFD enhanced the peak power responses of low frequencies (1 and 10 Hz) by 128%-160%, < 0.01. This PAP response mitigated the effects of PLFFD as the 1:50 ( < 0.05) and 10:50 ( > 0.4) Hz peak power ratios were greater or not different from the prefatigue (baseline) values. In addition, PAP enhanced peak torque more than peak angular velocity during both baseline and fatigue measurements ( < 0.03). These results indicate that PAP can ameliorate PLFFD acutely when evaluated during concentric isotonic contractions and that peak torque is enhanced to a greater degree compared with peak angular velocity at baseline and in a fatigued state. Postactivation potentiation (PAP) enhanced stimulated low frequencies (1 and 10 Hz) during muscle fatigue development when assessed with power (torque × angular velocity) in a voluntary isotonic fatiguing task. Following the task during 30 min of recovery, prolonged low-frequency force depression (PLFFD) was evident, and inducing PAP with brief maximal contractions during this state ameliorated the effects of PLFFD. PAP enhanced peak torque more than peak angular velocity during both baseline and fatiguing conditions.
Topics: Animals; Electric Stimulation; Fishes; Humans; Isometric Contraction; Isotonic Contraction; Muscle Contraction; Muscle Fatigue; Muscle, Skeletal; Torque
PubMed: 35796610
DOI: 10.1152/japplphysiol.00214.2022 -
Therapeutic Advances in Respiratory... Jun 2008Bronchial asthma as such exists because airway smooth muscle (ASM) contracts excessively in response to various stimuli. After several decades during which research was... (Review)
Review
Bronchial asthma as such exists because airway smooth muscle (ASM) contracts excessively in response to various stimuli. After several decades during which research was mainly focused on airway inflammation, increasing attention is now being paid to a possible abnormal behaviour of ASM. Thus, ASM is regarded as a major target for anti-asthma treatments. This review first describes the mechanisms of ASM contraction and airway hyperresponsiveness, through cellular, animal and human models. The developments of new drugs targeting extra and/or intracellular pathway of ASM contraction are discussed.
Topics: Animals; Anti-Asthmatic Agents; Asthma; Drugs, Investigational; Humans; Muscle Contraction; Muscle Relaxation; Muscle, Smooth
PubMed: 19124365
DOI: 10.1177/1753465808091154