Muscle tissue and its adaptation to physical loads

Muscle tissue and its adaptation to physical loads

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Category: Scientific fitness Created: 09 April 2014

Topic: “physiology”. The structure of the muscle fibers. Types and subtypes of muscle fibers. Muscle fibers — slow-twitch (MS) and fast-twitch (LH). The activity of aerobic, anaerobic enzymes. Similarities and

differences between male and female muscle fibres.

Structural and functional characteristics of motor units of the muscles. Muscle is an extremely heterogeneous tissue, composed mainly of muscle fibers, connective tissue, nervous and vascular elements, which together provide its main function — actively cuts. In the structure of muscle tissue there are two types of muscle fibers — slow-twitch (MS) and fast-twitch (LH). This division simplifies the tissue organization of the muscles, among which there are different kinds of muscles, due primarily to morphological and functional properties of their fibers. However, the selected types of muscle fibers are relatively independent functional units, characterized by morphological, biochemical and contractile properties.

MS-fibers have the following properties: slow shrink, a large number of mitochondria (“energy center” of the cell), high activity of oxidative enzymes (proteins contribute to a rapid upsurge of energy sources), excellent vascularization (a lot of capillaries), high potential for accumulation of glycogen. BS-fibers have a less developed network of capillaries, fewer mitochondria, high glycolytic capacity, high activity deoxidating enzymes and a higher rate of reduction. In the same muscle contains BS – and MS-fiber. BS-fibers contain an active enzyme ATPase, which is powerfully breaks down ATP with the formation of large amounts of energy, which provides a rapid reduction of the fibers. In MS-fibers ATPase activity is low, therefore energosbytovaya in them is slow. Enzymatic cleavage of ATP is considered one of the most important factors determining the inherent speed muscle contractions. Enzymes that break down sugar and fats that are active in the MS-fibers, that helps to explain the very significant differences between different types of fibers. There are two subgroups BS-fibers: BSA and BSB. BSA-fibers are called fast-twitch oxidative-glycolytic fibers. They are highly contractile abilities and at the same time have a high resistance to fatigue. These fibers are well exposed to the endurance training. BSB-fiber — classic type of fast-twitch fibers, which is related to the use of anaerobic energy sources. Each of these types of fibers are quite well identified under the microscope after appropriate staining of the slices. It is established that the composition of muscle fibers and motor units is determined genetically. Inherited genes already in early childhood determine the number and structure of neurons that form motor units and Innervate muscle fibers. After the establishment of innervation differentiate types of muscle fibers. As we age the ratio of muscle fibers changes: reduced the number of BS-fibers, which leads to increase the percentage of MS-fibers. Muscle fibers are combined into motor units (groups of muscle fibers innervated by one motor neuron), each of them is composed of muscle fibers of a particular type. Structure and function of neurons correspond to the structure and functions combine their muscle fibers. The slow-twitch motor neuron motor unit combines a group of 10-180 MS-fibers and has a small cell body. The fast-twitch motor neuron motor unit innervates from 300 to 800 BS-fibers and features a large cell body and a large number of nerve processes.

In recent decades, in connection with the progress of biochemistry and morphology, it is possible to further explore the structure and function of muscle fibers and motor units of the muscles to expand representations about the features of their adaptation to training and competitive loads. The time required for the maximum voltage BS-fibers, typically less than 0.3-0.5, while the MS-fibers are able to develop a maximum voltage of only 0,8-1,1 C. the Activity of anaerobic enzymes BS-fibers can two times or more greater than the activity of these enzymes in the MS-mode fibers. At the same time, the activity of aerobic enzymes in the MS-mode fibers is about two times higher than BS-fibers. Speaking about the proportions of different muscle fibers in humans, it should be noted that in both men and women have slightly more MS-fibers (according to various authors, from 52 to 55 %). This is quite clearly illustrated by the results of studies in which there were 45 girls and 70 boys aged 16 years. Among BS-fibres predominate fiber type BSA (30-35 %). BSB-fibers is considerably less than 12-15 %. You will need to indicate that muscle women seldom observed a significant prevalence of any type of fibers, which occurs in muscles in men. When considering the adaptation of human muscle during training should take into account the distribution of muscle fibers of different types in the same muscle in different muscles. Special studies have shown that in one muscle changes in the contents of different types of fibers are absent or insignificant. Small differences (5-10 %) can be observed when comparing the results of samples belonging to the Central and peripheral parts of the muscle: the Central part of the muscle may contain more MS-fibers. One person there is a relative homogeneity of the structure of the various muscles. However, along with the structural similarity of the individual muscles of a specific individual can be observed and substantial differences due to the function that is usually performed by the muscle, and the requirement dictated by the function to the muscle fibers of a particular type. For example, the quadriceps and calf muscles of the lower limbs, deltoid and biceps brachii have roughly the same ratio of BS – and MS-fibers. At the same time, the soleus muscle contains 25-40 % more MS-fibers compared with other leg muscles, and triceps brachii contains 10-30% more MS-fibers compared with other muscles of the girdle of the upper limb. Special training leads to thickening of all types of fibers, especially BSB, normally inactive and is very heavily involved in the activities.

D. SC.N. Smooth V. A.; Ph..N. Smooth O. A.

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