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Journal of Neurophysiology Oct 2022It is important to understand the effects of rapid changes in weight on neuromuscular functions of combat athletes. The purpose of this case study was to investigate...
It is important to understand the effects of rapid changes in weight on neuromuscular functions of combat athletes. The purpose of this case study was to investigate time-course changes in muscle strength, muscle size, and neural input during rapid weight loss in a professional boxer. One professional male boxer (26 yr) participated in two matches during measurements: welterweight (66.6 kg; weight loss: WL) and super welterweight (69.85 kg; control: CON). His muscle contraction properties and body composition were measured from 6 wk (baseline) before the matches to 1 wk after them. Maximal voluntary isometric knee extension torque, muscle cross-sectional area (mCSA) of the vastus lateralis using ultrasound, and high-density surface electromyography of the vastus lateralis during submaximal ramp-up contraction were measured. Individual motor units were identified, and modified discharge rates were calculated from a regression line between the recruitment threshold and discharge rates at 60%-70% of maximum torque according to the baseline value. His body weights for WL and CON decreased from 70.80 and 71.42 kg at the baseline to 68.75 and 71.36 kg immediately before the matches, respectively. Muscle strength changed little for either match. For WL, skeletal muscle mass and mCSA decreased, but there was no decrease for CON. The modified motor unit discharge rate for WL increased immediately before the match compared with other periods but did not change for CON. After rapid weight loss, neural input increased to compensate for lost muscle mass, and muscle strength was maintained. This case study found that neural input to muscle, which was evaluated by high-density surface electrocardiography, increased to compensate for the decline of body weight and muscle mass and to maintain muscle strength during rapid weight loss, while neuromuscular characteristics were not markedly changed during no significant weight loss.
Topics: Electromyography; Humans; Isometric Contraction; Male; Muscle Contraction; Muscle Strength; Muscle, Skeletal; Quadriceps Muscle; Weight Loss
PubMed: 36129200
DOI: 10.1152/jn.00307.2022 -
Journal of Electromyography and... Apr 2022The spatial distributions of muscle innervation zone (IZ) and muscle fiber conduction velocity (CV) were examined in nine healthy young male participants. High-density...
The spatial distributions of muscle innervation zone (IZ) and muscle fiber conduction velocity (CV) were examined in nine healthy young male participants. High-density surface electromyography (EMG) was collected from the biceps brachii muscle when subjects performed isometric elbow flexions at 20% to 80% of the maximal voluntary contraction (MVC). A total of 9498 samples of IZs were identified and CVs were calculated using the Radon transform. The center and width of IZ sample distribution were compared within four different force levels and six medial to lateral electrode column positions using repeated measures ANOVA and multiple comparison tests. Significant shifts of IZ center were observed in the medial columns (Columns 5, 6, and 7) compared with the lateral columns (Columns 3 and 4) (p < 0.05). Similarly, significant differences in the IZ width were found in Column 7 and 8 compared to Column 3 (p < 0.05). In contrast, muscle CV was unaffected by column position. Instead, muscle CV was faster at 40% and 80% MVC compared to 20% MVC (p < 0.05). The findings of this study add further insights into the physiological properties of the biceps brachii muscle.
Topics: Arm; Electromyography; Humans; Isometric Contraction; Male; Muscle Contraction; Muscle Fibers, Skeletal; Muscle, Skeletal
PubMed: 35176686
DOI: 10.1016/j.jelekin.2022.102637 -
Proceedings of the National Academy of... Jan 2020Fluid fills intracellular, extracellular, and capillary spaces within muscle. During normal physiological activity, intramuscular fluid pressures develop as muscle...
Fluid fills intracellular, extracellular, and capillary spaces within muscle. During normal physiological activity, intramuscular fluid pressures develop as muscle exerts a portion of its developed force internally. These pressures, typically ranging between 10 and 250 mmHg, are rarely considered in mechanical models of muscle but have the potential to affect performance by influencing force and work produced during contraction. Here, we test a model of muscle structure in which intramuscular pressure directly influences contractile force. Using a pneumatic cuff, we pressurize muscle midcontraction at 260 mmHg and report the effect on isometric force. Pressurization reduced isometric force at short muscle lengths (e.g., -11.87% of P at 0.9 L), increased force at long lengths (e.g., +3.08% of P at 1.25 L), but had no effect at intermediate muscle lengths ∼1.1-1.15 L This variable response to pressurization was qualitatively mimicked by simple physical models of muscle morphology that displayed negative, positive, or neutral responses to pressurization depending on the orientation of reinforcing fibers representing extracellular matrix collagen. These findings show that pressurization can have immediate, significant effects on muscle contractile force and suggest that forces transmitted to the extracellular matrix via pressurized fluid may be important, but largely unacknowledged, determinants of muscle performance in vivo.
Topics: Animals; Biomechanical Phenomena; Body Fluids; Collagen; Extracellular Matrix; Hamstring Muscles; Hydrostatic Pressure; Isometric Contraction; Models, Biological; Muscle Contraction; Muscle, Skeletal; Rana catesbeiana
PubMed: 31879350
DOI: 10.1073/pnas.1914433117 -
Physiological Reviews Jul 2023The local environment surrounding airway smooth muscle (ASM) cells has profound effects on the physiological and phenotypic properties of ASM tissues. ASM is continually... (Review)
Review
The local environment surrounding airway smooth muscle (ASM) cells has profound effects on the physiological and phenotypic properties of ASM tissues. ASM is continually subjected to the mechanical forces generated during breathing and to the constituents of its surrounding extracellular milieu. The smooth muscle cells within the airways continually modulate their properties to adapt to these changing environmental influences. Smooth muscle cells connect to the extracellular cell matrix (ECM) at membrane adhesion junctions that provide mechanical coupling between smooth muscle cells within the tissue. Membrane adhesion junctions also sense local environmental signals and transduce them to cytoplasmic and nuclear signaling pathways in the ASM cell. Adhesion junctions are composed of clusters of transmembrane integrin proteins that bind to ECM proteins outside the cell and to large multiprotein complexes in the submembranous cytoplasm. Physiological conditions and stimuli from the surrounding ECM are sensed by integrin proteins and transduced by submembranous adhesion complexes to signaling pathways to the cytoskeleton and nucleus. The transmission of information between the local environment of the cells and intracellular processes enables ASM cells to rapidly adapt their physiological properties to modulating influences in their extracellular environment: mechanical and physical forces that impinge on the cell, ECM constituents, local mediators, and metabolites. The structure and molecular organization of adhesion junction complexes and the actin cytoskeleton are dynamic and constantly changing in response to environmental influences. The ability of ASM to rapidly accommodate to the ever-changing conditions and fluctuating physical forces within its local environment is essential for its normal physiological function.
Topics: Muscle Contraction; Muscle, Smooth; Myocytes, Smooth Muscle; Phenotype; Integrins
PubMed: 36796098
DOI: 10.1152/physrev.00020.2022 -
Communications Biology Dec 2023Assessing gastrointestinal motility lacks simultaneous evaluation of intraluminal pressure (ILP), circular muscle (CM) and longitudinal muscle (LM) contraction, and...
Assessing gastrointestinal motility lacks simultaneous evaluation of intraluminal pressure (ILP), circular muscle (CM) and longitudinal muscle (LM) contraction, and lumen emptying. In this study, a sophisticated machine was developed that synchronized real-time recordings to quantify the intricate interplay between CM and LM contractions, and their timings for volume changes using high-resolution cameras with machine learning capability, the ILP using pressure transducers and droplet discharge (DD) using droplet counters. Results revealed four distinct phases, B, N, D, and A, distinguished by pressure wave amplitudes. Fluid filling impacted LM strength and contraction frequency initially, followed by CM contraction affecting ILP, volume, and the extent of anterograde, retrograde, and segmental contractions during these phases that result in short or long duration DD. This comprehensive analysis sheds light on peristalsis mechanisms, understand their sequence and how one parameter influenced the other, offering insights for managing peristalsis by regulating smooth muscle contractions.
Topics: Animals; Mice; Peristalsis; Gastrointestinal Motility; Muscle Contraction; Intestine, Small
PubMed: 38062160
DOI: 10.1038/s42003-023-05631-2 -
PeerJ 2022Muscular co-contraction of antagonistic muscle pairs is often observed in human movement, but it is considered inefficient and it can currently not be predicted in...
Muscular co-contraction of antagonistic muscle pairs is often observed in human movement, but it is considered inefficient and it can currently not be predicted in simulations where muscular effort or metabolic energy are minimized. Here, we investigated the relationship between minimizing effort and muscular co-contraction in systems with random uncertainty to see if muscular co-contraction can minimize effort in such system. We also investigated the effect of time delay in the muscle, by varying the time delay in the neural control as well as the activation time constant. We solved optimal control problems for a one-degree-of-freedom pendulum actuated by two identical antagonistic muscles, using forward shooting, to find controller parameters that minimized muscular effort while the pendulum remained upright in the presence of noise added to the moment at the base of the pendulum. We compared a controller with and without feedforward control. Task precision was defined by bounding the root mean square deviation from the upright position, while different perturbation levels defined task difficulty. We found that effort was minimized when the feedforward control was nonzero, even when feedforward control was not necessary to perform the task, which indicates that co-contraction can minimize effort in systems with uncertainty. We also found that the optimal level of co-contraction increased with time delay, both when the activation time constant was increased and when neural time delay was added. Furthermore, we found that for controllers with a neural time delay, a different trajectory was optimal for a controller with feedforward control than for one without, which indicates that simulation trajectories are dependent on the controller architecture. Future movement predictions should therefore account for uncertainty in dynamics and control, and carefully choose the controller architecture. The ability of models to predict co-contraction from effort or energy minimization has important clinical and sports applications. If co-contraction is undesirable, one should aim to remove the cause of co-contraction rather than the co-contraction itself.
Topics: Humans; Muscle, Skeletal; Uncertainty; Movement; Muscle Contraction; Standing Position
PubMed: 35415011
DOI: 10.7717/peerj.13085 -
Mathematical Biosciences Sep 2019Smooth muscle contraction regulates the size of the blood vessel lumen which directly affects the mechanical response of the vessel. Folding in arteries has been...
Smooth muscle contraction regulates the size of the blood vessel lumen which directly affects the mechanical response of the vessel. Folding in arteries has been observed in arteries during excessive contraction, known as a coronary artery spasm. The interplay of muscle contraction, geometry, and material responses and their effects on stability can be understood through mathematical models. Here, we consider a three-layer cross-sectional model of a coronary artery with anisotropic properties and intimal thickening, and perform a linear stability analysis to investigate the circumferential folding patterns that emerge due to muscle contraction. Our model shows that a critical level of contractile activity yields a uniform strain distribution across the arterial wall. When the muscle is contracted above this critical level, the tissue behaves isotropically and it is more prone to circumferential instability. This theoretical framework could serve as a valuable tool to understand the relationship between arterial lumen morphology and wall contraction in health and disease.
Topics: Biomechanical Phenomena; Coronary Vessels; Humans; Models, Biological; Muscle Contraction; Muscle, Smooth, Vascular; Tunica Intima
PubMed: 31276682
DOI: 10.1016/j.mbs.2019.108223 -
Exercise and Sport Sciences Reviews Jan 2023The rate at which an individual can develop force during rapid voluntary contractions can be influenced by both the neural drive to a muscle and its intrinsic...
The rate at which an individual can develop force during rapid voluntary contractions can be influenced by both the neural drive to a muscle and its intrinsic musculotendinous properties. We hypothesize that the maximal rate of force development across human individuals is mainly attributable to the rate of motor unit recruitment.
Topics: Humans; Muscle Contraction; Motor Neurons; Muscle, Skeletal; Recruitment, Neurophysiological; Electromyography; Isometric Contraction
PubMed: 36123735
DOI: 10.1249/JES.0000000000000306 -
The Review of Scientific Instruments Mar 2023Surface electromyography (sEMG) is considered an established means for controlling prosthetic devices. sEMG suffers from serious issues such as electrical noise, motion...
Surface electromyography (sEMG) is considered an established means for controlling prosthetic devices. sEMG suffers from serious issues such as electrical noise, motion artifact, complex acquisition circuitry, and high measuring costs because of which other techniques have gained attention. This work presents a new optoelectronic muscle (OM) sensor setup as an alternative to the EMG sensor for precise measurement of muscle activity. The sensor integrates a near-infrared light-emitting diode and phototransistor pair along with the suitable driver circuitry. The sensor measures skin surface displacement (that occurs during muscle contraction) by detecting backscattered infrared light from skeletal muscle tissue. With an appropriate signal processing scheme, the sensor was able to produce a 0-5 V output proportional to the muscular contraction. The developed sensor depicted decent static and dynamic features. In detecting muscle contractions from the forearm muscles of subjects, the sensor showed good similarity with the EMG sensor. In addition, the sensor displayed higher signal-to-noise ratio values and better signal stability than the EMG sensor. Furthermore, the OM sensor setup was utilized to control the rotation of the servomotor using an appropriate control scheme. Hence, the developed sensing system can measure muscle contraction information for controlling assistive devices.
Topics: Humans; Upper Extremity; Electromyography; Muscle, Skeletal; Muscle Contraction; Hand; Isometric Contraction
PubMed: 37012764
DOI: 10.1063/5.0130394 -
Journal of Neurophysiology Aug 2022The nematode uses rhythmic muscle contractions (pumps) of the pharynx, a tubular feeding organ, to filter, transport, and crush food particles. A number of feeding...
The nematode uses rhythmic muscle contractions (pumps) of the pharynx, a tubular feeding organ, to filter, transport, and crush food particles. A number of feeding mutants have been identified, including those with slow pharyngeal pumping rate, weak muscle contraction, defective muscle relaxation, and defective grinding of bacteria. Many aspects of these pharyngeal behavioral defects and how they affect pharyngeal function are not well understood. For example, the behavioral deficits underlying inefficient particle transport in "slippery" mutants have been unclear. Here we use high-speed video microscopy to describe pharyngeal pumping behaviors and particle transport in wild-type animals and in feeding mutants. Different "slippery" mutants exhibit distinct defects including weak isthmus contraction, failure to trap particles in the anterior isthmus, and abnormal timing of contraction and relaxation in pharyngeal compartments. Our results show that multiple deficits in pharyngeal timing or contraction can cause defects in particle transport. The nematode uses rhythmic contractions of its pharynx (feeding organ) to filter, transport, and crush food bacteria. Genetic analyses have identified mutants with defective pharyngeal motions, but many details of these movements and how they affect feeding are poorly understood. We use high-speed video microscopy to describe pharyngeal pumping behaviors and particle transport in feeding mutants. We find that multiple deficits in pharyngeal timing or contraction can cause defects in particle transport.
Topics: Animals; Caenorhabditis elegans; Feeding Behavior; Microscopy, Video; Muscle Contraction; Pharynx
PubMed: 35730757
DOI: 10.1152/jn.00444.2021