Nitrogen metabolism in man under hypokinesia and physical exercise

Experimental studies of hypokinetic physiology are generally based on the assumption that diminished muscular activity (progressive reduction of number of steps per day) is hostile to animal and human organisms, since the entire animal kingdom has been formed in a high motor activity environment, which left its imprint on the evolution, structure, function and behavior of living organisms. It has been suggested that physical exercise may be used to prevent changes in man's nitrogen metabolism under hypokinesia. Thus, the aim of this study was to evaluate the effect of physical exercise in attenuating nitrogen metabolic changes under hypokinesia of 90 days in twelve healthy men aged 19 to 23 years. They were divided into two groups with six men in each. The control group was subjected to pure hypokinesia, that is, without the use of any preventive measures, and the experimental group was submitted to combined hypokinesia and physical exercise with energy expenditure of about 500 kcal. For the simulation of the hypokinetic effect the men were kept under an average of 500 steps/day. The caloric value of their diet was about 2400 kcal/day and 2600 kcal/day for the control and experimental groups, respectively. Total nitrogen, urea nitrogen, nitrogen ammonium salts, nitrogen of free amino acids, creatine, creatinine, as well as vitamins C, B1 and 4-pyridoxic acid excretion were measured in urine. Hypokinesia induced a negative nitrogen balance, which was most pronounced in the control group. The excretion of the other nitrogeneous compounds, vitamins, creatine, and creatinine was also increased. Physical exercise had only a limited effect on nitrogen metabolism. We concluded that diminished muscular activity induced a marked increased excretion of nitrogen; at the same time it was revealed that physical exercise cannot be used to counteract effectively the development of adverse reactions of nitrogen metabolism under hypokinetic conditions.