Systematic and programmed physical exercise, called training, play a significant role in human health and ability improvement. A moderate physical exercise is considered as a very efficient method of increasing general physical ability and reaching the top results in sport, and simultaneously contributes to health quality of persons having sedentary professions. In active sportspersons, ability of cardiovascular, respiratory and bone-muscle systems are determined by training quality itself. Sportspersons show characteristically better adaptability of neurohumoral system to effort, as well as a higher activity of intracellular enzyme systems. Well-dosed physical exercise has an exceptional influence on human health, above all by regulating cholesterol blood level and electrolyte level of serum, whose minimal change can directly affect human health. This study was aimed to establish quantity and quality of organism response to physical exercise, in regard to level of daily training, by determining lipid fractions level in serum and electrolyte composition of serum. The study involved 50 healthy men in age between 20 and 25, divided into two groups. The first group was composed by physically untrained men, chosen by the random sample method. The other group of subjects was composed by 35 active sportsmen, chosen by direct selection for the best-trained ones among them. In order to reach a submaximal exertion, we used Astrand's test of submaximal exertion on the bicycle-ergometer. Blood samples were taken immediately before and after testing. The following parameters were determined in blood serum: high-density lipoproteins (HDL), low-density lipoproteins (LDL), triglyceride + + 2+ 2+ - content, as well as concentration of sodium (Na ), potassium (K ), calcium (Ca ), magnesium (Mg ) and chlorine (Cl) ions. On the base of our research we concluded that physical exercise of submaximal intensity did not lead to any quantitative and qualitative change of lipid fractions in blood serum of untrained persons. Physically inactive persons had higher serum concentrations of triglycerides and total cholesterol in regard to the investigated sportsmen. At the same time, sportsmen showed a higher HDL content of serum. Physical exertion in sportsmen led to a significant rise of triglycerides and highdensity lipoproteins content of serum, and the levels of total cholesterol and low-density lipoproteins did not changed + ++ significantly. Physical exertion of submaximal intensity in both studied groups caused a significant increase of Na , Ca and ++ + - Mg ion concentration, while concentration of K and Cl ions did not changed significantly. Numerous clinical studies showed that moderate aerobe exercise amplifies endothelial function and reduces cardiovascular risk

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