RESUMO
The work induced changes in the serum level of sodium, potassium, calcium and inorganic phosphates, as well as the relation between the magnitude of such post-exercise changes that were observed in these electrolytes, and the level of physical fitness [indicated by the maximal oxygen consumption], were investigated in 15 male athletes. All changes that occured in these electrolytes after vigorous work performance, were found to be, statistically, insignificant. The serum sodium level was increased by 2.74% compared with the average resting value due to loss of water in sweat in excess than the salt loss which led to a rise in the plasma sodium concentration. The serum potassium level was almost not changed after exercise. In fact, it was very slightly decreased [0.47% compared with the average resting level]. This relative stability, in spite of the great loss in sweat is most probably due to mobilistation of potassium ions from its stores in the intracellular compartments. The serum calcium and inorganic phosphate levels were on the other hand, more markedly decreased, in spite of their poverty in sweat. This may be due to their entry into the tissue cells or deposition in bone as a result of physical stress. The serum inorganic phosphate level was more decreased than the serum calcium level [12.6% and 5.27% respectively], most probably due to additional deposition of phosphates in skeletal muscles as phosphocreatine. The study also revealed that almost no relation existed between the magnitude of the post-exercise changes that occurred in the investigated blood electrolytes and the level of physical fitness, judged by the maximal oxygen consumption. This was confirmed statistically by calculation of the correlation factor [R] which was found to be 0.15, 0.11, 0.07 and 0.09 in cases of sodium, potassium calcium and inorganic phosphate, respectively