Definition
The term hypertrophy is composed of the ancient Greek words “hyper” (excessive) and “trophein” (to feed). In medicine, hypertrophy refers to the enlargement of an organ because the individual cells of the organ increase in size. Thus, in hypertrophy, the individual cells of the organ are enlarged, but the number of cells remains the same.
Hypertrophy can occur as a normal, desired change or as a pathological reaction of an organ. Hypertrophy is caused by hormonal stimulation of the hypertrophic organ or as a reaction to increased demands to which an organ must respond. For example, the heart of athletes is enlarged by hypertrophy when it is stressed by regular training, which increases the physical performance of the athlete.
However, hypertrophy does not have to be positive. In the case of a heart valve defect, the heart reacts to the increased demand with a pathological hypertrophy. Hypertrophy is often confused with the term hyperplasia. In this case, however, an enlargement of an organ occurs because the cells divide to a greater extent. The size of the individual cell remains approximately unchanged in hyperplasia.
Hypertrophy of muscle cells
A muscle consists of long muscle fibers, each muscle fiber is formed by the fusion of many mononuclear precursor muscle cells. A muscle cell therefore has several nuclei and corresponds to a muscle fiber, which can be several centimeters long. The nuclei of a muscle cell can no longer divide, so muscle tissue cannot multiply by cell division.
Muscle fibers can therefore only grow by hypertrophy. A muscle grows by each individual muscle cell increasing in size. When muscle cells grow, the required nuclei of muscle precursor cells, which are located at the edge of a muscle fiber, are made available by fusing the muscle precursor cells with the muscle fiber.
This fusion occurs both during growth from children to adults and during growth of muscle through training. Regular exercise is a growth stimulus for the muscle cells. In both endurance and strength sports, the muscles are stimulated to hypertrophy, but targeted strength training is a stronger growth stimulus than endurance sports and therefore leads to more severe hypertrophy.
Growth factors are released and the muscle metabolism is “boosted” so that the muscle cells hypertrophy. Muscle fibers consist to a large extent of proteins, so protein is needed for muscle growth. A protein-rich diet can support but not trigger hypertrophy of the muscles.
Hormonal factors also have an influence on muscle hypertrophy. The male sex hormone testosterone additionally accelerates muscle growth. Since a man’s testosterone level is many times higher than that of a woman, men find it easier to build muscle mass through training.
However, testosterone is not the only substance that promotes male muscle growth. Recent research shows that strength training releases additional chemical messengers in a man that promote hypertrophy of the muscles. Women lack these messenger substances. Despite these differences, the basic muscle build-up is the same for men and women. Prohibited doping substances such as anabolic steroids also stimulate muscle growth and thus facilitate muscle cell hypertrophy.
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