Specific Nature of Training on Skeletal Muscles
Atko Viru in Adaptation in Sports Training, 2017
The principle of specific adaptation to various kinds of muscular activity was first formulated and argued by N. N. Yakovlev. The most prominent result of training for improved strength is hypertrophy of skeletal muscles. Each exercise determines the degree of activity of various organs, different type of muscles, and motor units. The plasma membrane of skeletal muscles has been frequently implicated in the process of fatigue. The cross-sectional area of thigh muscles remained essentially unchanged during about 6 months of strenuous bicycling. Intra-animal comparisons revealed that no differences existed in the total fiber number or the incidence of fibers with bifurcations between enlarged and contralateral muscles. The protein content of the Sarcoplasmic Reticulum increased in rat muscles as a result of swimming training when the exercise intensity was gradually elevated by increasing additional loads, but not when the exercise intensity remained modest even if its duration was gradually prolonged.
Skeletal Muscle
Nassir H. Sabah in Neuromuscular Fundamentals, 2020
A skeletal muscle consists of muscle fibers comprising mainly myosin thick filaments and actin thin filaments. A contractile force is generated through sliding of these filaments, with respect to one another, as a result of cross-bridge cycling in the presence of a high concentration of calcium ions. This concentration increases because of a massive influx from the terminal cisternae caused by the depolarization of the muscle action potential but is quickly restored to normal by an efficient ion pump. The muscle fibers of a motor unit are all innervated by one motoneuron and belong to one of three types of fiber: Type I, Type IIA, or Type IIB, which differ in their speed of contraction and their resistance to fatigue. The arrangement of muscle fibers in a muscle results in four types of muscle: parallel, convergent, pennate, or sphincter muscles. There are three types of receptors in skeletal muscle: Golgi tendon organs that respond to the force of contraction, secondary muscle spindle receptors that respond to the amount of stretch, and primary muscle spindle receptors that respond to amount of stretch and its rate of change. The muscle spindle receptors are on intrafusal muscle fibers innervated by γ-motoneurons.
Skeletal Muscle
Manoj Ramachandran, Tom Nunn in Basic Orthopaedic Sciences, 2018
Skeletal muscle cells are of mesodermal origin. Many muscle fibres grouped together are termed fascicles. The major contractile proteins in skeletal muscle are actin and myosin. Actin is a globular protein that is a chief constituent of the thin filaments of the sarcomere. Myosin molecules have six distinct subunits: two heavy chains and four light chains. Surrounding each myofibril is an intracytoplasmic membranous sac called the sarcoplasmic reticulum. Voltage-sensitive membrane proteins in the T-tubule, known as modified dihydropyridinereceptors, are mechanically coupled with ryanodine receptors of the sarcoplasmic reticulum. The myotendinous junction is the area where insertion of every skeletal muscle fibre into its tendon occurs. Control of muscle contraction is by recruitment of motor units. Muscle cell damage by, for example, physical trauma leads to release of inflammatory mediators and damaged cellular components. Electromyography (EMG) is the recording of electrical activity in skeletal muscle.
Glucose metabolism and metabolic flexibility in cultured skeletal muscle cells is related to exercise status in young male subjects
Published in Archives of Physiology and Biochemistry, 2018
Jenny Lund, Daniel S. Tangen, Håvard Wiig, Hans K. Stadheim, Siw A. Helle, Jesper B. Birk, Thorsten Ingemann-Hansen, Arild C. Rustan, G. Hege Thoresen, Jørgen F. P. Wojtaszewski, Eili T. Kase, Jørgen Jensen
We hypothesised that skeletal muscles of healthy young people have a large variation in oxidative capacity and fibre-type composition, and aimed therefore to investigate glucose metabolism in biopsies and myotubes isolated from musculus vastus lateralis from healthy males with varying degrees of maximal oxygen uptake. Trained and intermediary trained subjects showed higher carbohydrate oxidation in vivo. Fibre-type distribution in biopsies and myotubes did not differ between groups. There was no correlation between fibre-type I expression in biopsies and myotubes. Myotubes from trained had higher deoxyglucose accumulation and fractional glucose oxidation (glucose oxidation relative to glucose uptake), and were also more sensitive to the suppressive action of acutely added oleic acid to the cells. Despite lack of correlation of fibre types between skeletal muscle biopsies and cultured cells, myotubes from trained subjects retained some of their phenotypes in vitro with respect to enhanced glucose metabolism and metabolic flexibility.
Modeling and simulation of musculoskeletal system of human lower limb based on tensegrity structure
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Zhanxi Wang, Chaoran Yang, Kang Feng, Xiansheng Qin
In this paper, a mechanical model of the skeletal muscle of human lower limb system is established by using the Hill muscle model and kinetic equation of the movement of lower extremities according to the attachment positions of skeletal muscle. State vector and neural control are delineated by the direct configuration method. Changes of gait and skeletal muscle stress during walking process are analyzed with energy consumption as objective function. Results illustrate that simulation data are in good agreement with actual walking gait data. Feasibility and correctness of the designed model and control behavior of skeletal muscle tension structure are also verified.
Proteomic study of skeletal muscle in obesity and type 2 diabetes: progress and potential
Published in Expert Review of Proteomics, 2018
Introduction: Skeletal muscle is the major site of insulin-stimulated glucose uptake and imparts the beneficial effects of exercise, and hence is an important site of insulin resistance in obesity and type 2 diabetes (T2D). Despite extensive molecular biology-oriented research the molecular mechanisms underlying insulin resistance in skeletal muscle remain to be established. Areas covered: The proteomic capabilities have greatly improved over the last decades. This review summarizes the technical challenges in skeletal muscle proteomics studies as well as the results of quantitative proteomic studies of skeletal muscle in relation to obesity, T2D, and exercise. Expert commentary: Current available proteomic studies contribute to the view that insulin resistance in obesity and T2D is associated with increased glycolysis and reduced mitochondrial oxidative metabolism in skeletal muscle, and that the latter can be improved by exercise. Future proteomics studies should be designed to markedly intensify the identification of abnormalities in metabolic and signaling pathways in skeletal muscle of insulin-resistant individuals to increase the understanding of the pathogenesis of T2D, but more importantly to identify multiple novel targets of treatment of which at least some can be safely targeted by novel drugs to treat and prevent T2D and reduce risk of cardiovascular disease.