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Philosophical Transactions of the Royal... May 2011Skeletal muscles are length- and velocity-sensitive force producers, constructed of a vast array of sarcomeres. Muscles come in a variety of sizes and shapes to... (Review)
Review
Skeletal muscles are length- and velocity-sensitive force producers, constructed of a vast array of sarcomeres. Muscles come in a variety of sizes and shapes to accomplish a wide variety of tasks. How does muscle design match task performance? In this review, we outline muscle's basic properties and strategies that are used to produce movement. Several examples are provided, primarily for human muscles, in which skeletal muscle architecture and moment arms are tailored to a particular performance requirement. In addition, the concept that muscles may have a preferred sarcomere length operating range is also introduced. Taken together, the case is made that muscles can be fine-tuned to perform specific tasks that require actuators with a wide range of properties.
Topics: Biomechanical Phenomena; Humans; Magnetic Resonance Imaging; Muscle Contraction; Muscle, Skeletal; Sarcomeres
PubMed: 21502118
DOI: 10.1098/rstb.2010.0316 -
The Journal of Biophysical and... Feb 1961
Topics: Muscle Fibers, Skeletal; Muscles; Myoblasts
PubMed: 13768451
DOI: 10.1083/jcb.9.2.493 -
Comprehensive Physiology Apr 2012Muscle plasticity is defined as the ability of a given muscle to alter its structural and functional properties in accordance with the environmental conditions imposed... (Review)
Review
Muscle plasticity is defined as the ability of a given muscle to alter its structural and functional properties in accordance with the environmental conditions imposed on it. As such, respiratory muscle is in a constant state of remodeling, and the basis of muscle's plasticity is its ability to change protein expression and resultant protein balance in response to varying environmental conditions. Here, we will describe the changes of respiratory muscle imposed by extrinsic changes in mechanical load, activity, and innervation. Although there is a large body of literature on the structural and functional plasticity of respiratory muscles, we are only beginning to understand the molecular-scale protein changes that contribute to protein balance. We will give an overview of key mechanisms regulating protein synthesis and protein degradation, as well as the complex interactions between them. We suggest future application of a systems biology approach that would develop a mathematical model of protein balance and greatly improve treatments in a variety of clinical settings related to maintaining both muscle mass and optimal contractile function of respiratory muscles.
Topics: Adaptation, Physiological; Diaphragm; Humans; Models, Biological; Motor Neurons; Muscle Contraction; Muscle Proteins; Respiratory Muscles; Systems Biology; Weight-Bearing
PubMed: 23798306
DOI: 10.1002/cphy.c110050 -
Scientific Reports Jan 2021Physiological cross-sectional area (PCSA), an important biomechanical variable, is an estimate of a muscle's contractile force potential and is derived from dividing...
Physiological cross-sectional area (PCSA), an important biomechanical variable, is an estimate of a muscle's contractile force potential and is derived from dividing muscle mass by the product of a muscle's average fascicle length and a theoretical constant representing the density of mammalian skeletal muscle. This density constant is usually taken from experimental studies of small samples of several model taxa using tissues collected predominantly from the lower limbs of adult animals. The generalized application of this constant to broader analyses of mammalian myology assumes that muscle density (1) is consistent across anatomical regions and (2) is unaffected by the aging process. To investigate the validity of these assumptions, we studied muscles of rabbits (Oryctolagus cuniculus) in the largest sample heretofore investigated explicitly for these variables, and we did so from numerous anatomical regions and from three different age-cohorts. Differences in muscle density and histology as a consequence of age and anatomical region were evaluated using Tukey's HSD tests. Overall, we observed that older individuals tend to have denser muscles than younger individuals. Our findings also demonstrated significant differences in muscle density between anatomic regions within the older cohorts, though none in the youngest cohort. Approximately 50% of the variation in muscle density can be explained histologically by the average muscle fiber area and the average percent fiber area. That is, muscles with larger average fiber areas and a higher proportion of fiber area tend to be denser. Importantly, using the age and region dependent measurements of muscle density that we provide may increase the accuracy of PCSA estimations. Although we found statistically significant differences related to ontogeny and anatomical region, if density cannot be measured directly, the specific values presented herein should be used to improve accuracy. If a single muscle density constant that has been better validated than the ones presented in the previous literature is preferred, then 1.0558 and 1.0502 g/cm would be reasonable constants to use across all adult and juvenile muscles respectively.
Topics: Age Factors; Aging; Animals; Biomechanical Phenomena; Female; Forelimb; Head; Hindlimb; Male; Models, Biological; Muscle Fibers, Skeletal; Muscle, Skeletal; Rabbits; Torso
PubMed: 33483576
DOI: 10.1038/s41598-021-81489-w -
Current Topics in Developmental Biology 2019Skeletal muscle powers all movement of the vertebrate body and is distributed in multiple regions that have evolved distinct functions. Axial muscles are ancestral... (Review)
Review
Skeletal muscle powers all movement of the vertebrate body and is distributed in multiple regions that have evolved distinct functions. Axial muscles are ancestral muscles essential for support and locomotion of the whole body. The evolution of the head was accompanied by development of cranial muscles essential for eye movement, feeding, vocalization, and facial expression. With the evolution of paired fins and limbs and their associated muscles, vertebrates gained increased locomotor agility, populated the land, and acquired fine motor skills. Finally, unique muscles with specialized functions have evolved in some groups, and the diaphragm which solely evolved in mammals to increase respiratory capacity is one such example. The function of all these muscles requires their integration with the other components of the musculoskeletal system: muscle connective tissue (MCT), tendons, bones as well as nerves and vasculature. MCT is muscle's closest anatomical and functional partner. Not only is MCT critical in the adult for muscle structure and function, but recently MCT in the embryo has been found to be crucial for muscle development. In this review, we examine the important role of the MCT in axial, head, limb, and diaphragm muscles for regulating normal muscle development, discuss how defects in MCT-muscle interactions during development underlie the etiology of a range of birth defects, and explore how changes in MCT development or communication with muscle may have led to the modification and acquisition of new muscles during vertebrate evolution.
Topics: Animals; Body Patterning; Connective Tissue; Evolution, Molecular; Gene Expression Regulation, Developmental; Humans; Mammals; Muscle Development; Muscle, Skeletal; Vertebrates
PubMed: 30797508
DOI: 10.1016/bs.ctdb.2018.12.004 -
The Journal of Physiology Sep 2013
Topics: History, 20th Century; History, 21st Century; Muscle Fatigue; Muscles; Physiology
PubMed: 24037136
DOI: 10.1113/jphysiol.2013.261354 -
Journal of Neurophysiology Jul 2018The mechanics, morphometry, and geometry of our joints, segments, and muscles are fundamental biomechanical properties intrinsic to human neural control. The goal of our...
The mechanics, morphometry, and geometry of our joints, segments, and muscles are fundamental biomechanical properties intrinsic to human neural control. The goal of our study was to investigate whether the biomechanical actions of individual neck muscles predict their neural control. Specifically, we compared the moment direction and variability produced by electrical stimulation of a neck muscle (biomechanics) to the preferred activation direction and variability (neural control). Subjects sat upright with their head fixed to a six-axis load cell and their torso restrained. Indwelling wire electrodes were placed into the sternocleidomastoid (SCM), splenius capitis (SPL), and semispinalis capitis (SSC) muscles. The electrically stimulated direction was defined as the moment direction produced when a current (2-19 mA) was passed through each muscle's electrodes. Preferred activation direction was defined as the vector sum of the spatial tuning curve built from root mean squared electromyogram when subjects produced isometric moments at 7.5% and 15% of their maximum voluntary contraction (MVC) in 26 three-dimensional directions. The spatial tuning curves at 15% MVC were well defined (unimodal, P < 0.05), and their preferred directions were 23°, 39°, and 21° different from their electrically stimulated directions for the SCM, SPL, and SSC, respectively ( P < 0.05). Intrasubject variability was smaller in electrically stimulated moment directions compared with voluntary preferred directions, and intrasubject variability decreased with increased activation levels. Our findings show that the neural control of neck muscles is not based solely on optimizing individual muscle biomechanics but, as activation increases, biomechanical constraints in part dictate the activation of synergistic neck muscles. NEW & NOTEWORTHY Biomechanics are an intrinsic part of human neural control. In this study, we found that the biomechanics of individual neck muscles cannot fully predict their neural control. Consequently, physiologically based computational neck muscle controllers cannot calculate muscle activation schemes based on the isolated biomechanics of muscles. Furthermore, by measuring biomechanics we showed that the intrasubject variability of the neural control was lower for electrical vs. voluntary activation of the neck muscles.
Topics: Adult; Biomechanical Phenomena; Evoked Potentials, Motor; Humans; Male; Movement; Muscle Contraction; Neck Muscles
PubMed: 29668386
DOI: 10.1152/jn.00512.2017 -
Journal of Anatomy Jan 2022Assessment of regional muscle architecture is primarily done through the study of animals, human cadavers, or using b-mode ultrasound imaging. However, there remain...
Assessment of regional muscle architecture is primarily done through the study of animals, human cadavers, or using b-mode ultrasound imaging. However, there remain several limitations to how well such measurements represent in vivo human whole muscle architecture. In this study, we developed an approach using diffusion tensor imaging and magnetic resonance imaging to quantify muscle fibre lengths in different muscle regions along a muscle's length and width. We first tested the between-day reliability of regional measurements of fibre lengths in the medial (MG) and lateral gastrocnemius (LG) and found good reliability for these measurements (intraclass correlation coefficient [ICC] = 0.79 and ICC = 0.84, respectively). We then applied this approach to a group of 32 participants including males (n = 18), females (n = 14), young (24 ± 4 years) and older (70 ± 2 years) adults. We assessed the differences in regional muscle fibre lengths between different muscle regions and between individuals. Additionally, we compared regional muscle fibre lengths between sexes, age groups, and muscles. We found substantial variability in fibre lengths between different regions within the same muscle and between the MG and the LG across individuals. At the group level, we found no difference in mean muscle fibre length between males and females, nor between young and older adults, or between the MG and the LG. The high variability in muscle fibre lengths between different regions within the same muscle, possibly expands the functional versatility of the muscle for different task requirements. The high variability between individuals supports the use of subject-specific measurements of muscle fibre lengths when evaluating muscle function.
Topics: Animals; Diffusion Tensor Imaging; Female; Magnetic Resonance Imaging; Male; Muscle Fibers, Skeletal; Muscle, Skeletal; Reproducibility of Results
PubMed: 34411299
DOI: 10.1111/joa.13539 -
Journal of Biomedicine & Biotechnology 2010Inherited neuromuscular disorders affect approximately one in 3,500 children. Structural muscular defects are most common; however functional impairment of skeletal and... (Review)
Review
Inherited neuromuscular disorders affect approximately one in 3,500 children. Structural muscular defects are most common; however functional impairment of skeletal and cardiac muscle in both children and adults may be caused by inborn errors of energy metabolism as well. Patients suffering from metabolic myopathies due to compromised energy metabolism may present with exercise intolerance, muscle pain, reversible or progressive muscle weakness, and myoglobinuria. In this review, the physiology of energy metabolism in muscle is described, followed by the presentation of distinct disorders affecting skeletal and cardiac muscle: glycogen storage diseases types III, V, VII, fatty acid oxidation defects, and respiratory chain defects (i.e., mitochondriopathies). The diagnostic work-up and therapeutic options in these disorders are discussed.
Topics: Energy Metabolism; Humans; Metabolism, Inborn Errors; Muscles; Myopathies, Structural, Congenital
PubMed: 20589068
DOI: 10.1155/2010/340849 -
NMR in Biomedicine Mar 2017The mechanical functions of muscles involve the generation of force and the actuation of movement by shortening or lengthening under load. These functions are... (Review)
Review
The mechanical functions of muscles involve the generation of force and the actuation of movement by shortening or lengthening under load. These functions are influenced, in part, by the internal arrangement of muscle fibers with respect to the muscle's mechanical line of action. This property is known as muscle architecture. In this review, we describe the use of diffusion tensor (DT)-MRI muscle fiber tracking for the study of muscle architecture. In the first section, the importance of skeletal muscle architecture to function is discussed. In addition, traditional and complementary methods for the assessment of muscle architecture (brightness-mode ultrasound imaging and cadaver analysis) are presented. Next, DT-MRI is introduced and the structural basis for the reduced and anisotropic diffusion of water in muscle is discussed. The third section discusses issues related to the acquisition of skeletal muscle DT-MRI data and presents recommendations for optimal strategies. The fourth section discusses methods for the pre-processing of DT-MRI data, the available approaches for the calculation of the diffusion tensor and the seeding and propagating of fiber tracts, and the analysis of the tracking results to measure structural properties pertinent to muscle biomechanics. Lastly, examples are presented of how DT-MRI fiber tracking has been used to provide new insights into how muscles function, and important future research directions are highlighted. Copyright © 2016 John Wiley & Sons, Ltd.
Topics: Algorithms; Animals; Diffusion Tensor Imaging; Forecasting; Humans; Image Enhancement; Image Interpretation, Computer-Assisted; Muscle Fibers, Skeletal; Muscle, Skeletal; Reproducibility of Results; Sensitivity and Specificity
PubMed: 27257975
DOI: 10.1002/nbm.3563